App extensions, appexes, have become plentiful and widely used by macOS and third-party software, yet discovering and controlling them is patchy and limited. The most coherent access is in System Settings > General > Login Items & Extensions, where some are gathered in the list of Extensions at the end. Others like Safari extensions are controlled in app settings, while most remain hidden out of sight.

To take stock of all these appexes, I turned to the pluginkit command tool, but the lists it generates are seemingly ordered at random, and so extensive that it would require some serious scripting to make any sense. Instead, it’s easier and more effective to put together a little app to do that. So I present you with AppexIndexer, an exploratory utility that displays key information about all appexes recognised by macOS.

Click on its button to Get Appexes and the window below will fill with well over 400 items, arranged in alphabetical order by the first entry in each line, the SDK or NSExtensionPointIdentifier. Some of those should be fairly obvious: for instance, those appexes listed in Photos Editing settings use the com.apple.photo-editing SDK. In a future article I will explore the relationships between settings categories and SDKs given.

Following that comes the display name of that appex, again ordered alphabetically within that SDK group, which should be the same as that used in System Settings. Next comes the path to that appex, so you can inspect it and its Info.plist for further information.

Many appexes also have a parent, so the last two entries given are the name and path to that parent, when they’re available. One quick way to recognise third-party appexes is to glance down the right side of the list, as they invariably have a familiar parent. Appexes built into macOS are far less likely to have parents (and you can read into that what you like!).

Even in a modest installation, you’re likely to see well over 400 in your Mac’s list, from SpamSieve, an Email Extension with the SDK of com.apple.email.extension, through to QuickLook thumbnail previewers, screensavers and wallpaper. I’ve already explained in general terms what these are and how they work, in this article.

One significant feature missing at this stage is Find/Search, which I’m still working on, for LogUI as well. There’s also additional information given by the pluginkit command tool, and more still that’s available from each appex’s Info.plist file inside its bundle. This initial release lets you save the window’s contents using the Save as RTF button, and you can copy any selected entries and paste them as text. Row selection can be continuous using the Shift key, and discontinuous using Command.

Appexes are not only growing in number, but also becoming increasingly important in macOS. In some cases, they include background processes that could be used maliciously as a method of persistence. Although appexes still need to comply with TCC’s strict rules for accessing protected services and data, they can be an effective way to fly under a user’s radar.

AppexIndexer 1.0 build 5 is now available from here: appindexer105
I’m afraid that it requires macOS Sonoma 14.6 or later, to support the features it uses in SwiftUI.

I hope that you find this information of use. Please let me know what features you’d like the app to support, whether you’d like it to access appex property lists, or other useful data, and how you might want to use a future version. While I’ve got my own ideas, I’m interested in yours, and will try to accommodate them.

In 1907, after over twenty years of lucrative work painting portraits, John Singer Sargent closed his studio in London, and cut himself adrift to travel where and when he wanted.

The American artists Jane de Glehn and her husband Wilfrid (1870-1951) were long-standing friends. Sargent first met Wilfrid around 1895 when he was working on murals in Boston Public Library, and Wilfrid married Jane Emmet (1873-1961), sister of Lydia Field Emmet, in 1904. The Fountain, Villa Torlonia, Frascati, Italy (1907) shows Jane working at a lightweight wooden easel in the grounds of the villa.

The composition in his Dolce Far Niente (1907) is complex, with five of the figures staggered and slightly out of line along the gentle curve of the bank crossing this unusually wide canvas, its aspect ratio being more typical of marine views and panoramas. Against this are steep diagonals in the middle of the painting, formed by the edge of the brown reflection on the water, the male in the left pair of figures, and the closest female. The cropping of the horizon and any background beyond the immediate meadow and stream gives a sense of space and recession, aided by the foreshortening of the closest figure, despite the proximity of the individuals to one another.

The painting consists of a multitude of daubs, strokes, and dabs of colour, those marks composed to provide just enough information for the viewer to assemble them into the whole, which as a result ‘pops’ out in a vivid reality.

It’s thought that all three male figures were modelled by Nicola d’Inverno, the painter’s manservant, and the woman seen asleep appears to be his friend Jane de Glehn. Sargent had purchased the costumes in the Middle East during his travels there, and they were transported in trunks to this site, believed to be the brook at Peuterey in the Val d’Aosta, most probably in the summer of 1907.

This painting was hung in the summer exhibition of the New English Art Club, London, in 1909, and was favourably received by the critics. It was sold within an hour of the opening of the press view, to Augustus Healy, founder of the Brooklyn Museum, where it has hung ever since.

Sargent’s bravura watercolour sketch of Grand Canal, Venice (1907) is composed of a sparse, even minimalist, collection of brushstrokes of watercolour assembled into a detailed view of the motif. He views Venice from the level of a gondola, the bows of which are also shown. His palette for these sketches is generally centred on earth colours for the buildings, with blue for the sky, water, and usually the shadows.

The following year, his Flotsam and Jetsam follows in the same style, with the figures of young boys in the foreground sketched in roughly to suggest movement.

Sargent was an early adopter of cadmium yellow pigment in watercolours such as Olive Trees, Corfu from 1909, where it ensured that his greens remained lightfast.

He wasn’t dependent on sophisticated techniques, though: Rio dei Mendicanti, Venice from about 1909 works its magic almost entirely using a combination of passages using wet on dry and wet on wet. There isn’t even much in the way of a graphite drawing under its thin washes.

Sargent met up with the plein air specialist Ambrogio Raffele again when he returned to the Alps during the summers of 1909 to 1911, and painted this watercolour of him as an Artist in the Simplon at some time in those years. Raffele is painting a view of the Fletschhorn, to the south-west of the Simplon Pass, using an improvised easel formed from two crossed poles.

In the summers of 1909-11, Sargent stayed with various friends in the Bellevue Hotel at the top of the Simplon Pass, enjoying the cool mountain air at a time when much of the rest of Europe would have been stiflingly hot. While his family and friends whiled away their days in leisure, Sargent got them to pose for a unique series of informal portraits. They may have been reclining at leisure, but Sargent took those watercolours very seriously, and deployed an amazing array of techniques. Among the finest is his Simplon Pass: The Tease from the summer of 1911. For any watercolour artist, it is a lexicon of advanced techniques.

One of the most unusual, used here extensively, is wax resist. Before applying paint, Sargent scribbled over areas that were intended to be vegetation, using a soft wax crayon, probably made from beeswax. On a fairly rough paper, the wax is deposited unevenly, and when painted over using watercolour it shows the white paper through. This creates disruptive patterns of near-white in the midst of the greens, and a superb effect.

Most of the paint used is transparent watercolour, applied as a wash in small areas, and in gestural marks elsewhere. In the upper third of this detail, he has applied white gouache (opaque watercolour) sufficiently thickly for it to now have fine cracks. The large pale blue area crossing the middle appears to have been rewetted and some of its colour lifted to reduce its intensity, although most of his applications of paint over existing paint have been made wet on dry.

Complex details such as the faces and hands of the figures have undergone multiple repainting, starting with the palest flesh of the face, and progressively darkening to near-black. In most cases, the clean edges of the marks demonstrate that these were applied wet on dry, with as many as six different layers in the hair.

In the midst of this complex assembly of layers, Sargent still keeps to the lines of his original graphite sketch, which he uses to give the parasol form, and maintains small reserved areas, here forming the spectacle frames in the white of the paper. He could have used wax resist here, but if using pure beeswax it’s hard to keep the soft wax to fine lines.

Sargent is the Chess Grand Master, the strategist whose moves at times might almost seem random or abstract, but in the end they all come together to bring this masterly watercolour to life.

For many years, most types of disk image were inefficient in their use of storage space, as they occupied their full size on disk. Until recently, when you created a 5 GB read-write UDIF disk image, one of the most popular, it invariably took up 5 GB in storage, even when empty. This also applied to the raw disk images used by Virtual Machines: give a VM 100 GB, and that’s just what it took on disk. With the introduction of sparse files in APFS, this has changed, and many disk images now only take the space they need. I’m not sure exactly when this change occurred, as Apple still doesn’t appear to have documented it, but it seems to have changed with macOS Monterey.

This is easiest to see with a plain read-write disk image, created using DropDMG or Disk Utility.

Disk image

Here’s one I made earlier, a whole 350 GB in size. When it’s created, it’s automatically attached and mounted at full size. For the sake of example, I then copied a large IPSW to it, so it wasn’t entirely empty.

Unmount it and Get Info on the disk image and you’ll see it does still take up a full 350 GB on disk. Mount it again, though, and APFS works its magic. You can see this in LogUI, or the custom log extract provided by Mints.

When unmounted again it has shrunk down to take little more than the size of the IPSW file in it, at just over 17 GB. That’s less than 5% of its nominal size, without using any compression.

It’s worth looking through entries in the log made by APFS for the mount process. First, APFS checks whether the data store for the disk image is already sparse:
01.470 container_backingstore_is_sparse:1652: Image url file:///Volumes/LaCie2tb/350gbudif.dmg Image path /Volumes/LaCie2tb/350gbudif.dmg
01.470 container_backingstore_is_sparse:1659: Image /Volumes/LaCie2tb/350gbudif.dmg is a flat file, do not consider as sparse

It then sets it to sparse, ready for sparsification:
01.475 handle_apfs_set_backingstore:6207: disk9s1 Set backing store as sparse
01.475 handle_apfs_set_backingstore:6240: disk9 Backing storage is a raw file

Space Manager performs an initial scan for free blocks without any Trimming:
01.479 spaceman_scan_free_blocks:4136: disk9 scan took 0.004272 s (no trims)
01.479 spaceman_fxc_print_stats:477: disk9 dev 0 smfree 81258479/85398014 table 4/452 blocks 81258479 32766:20314619:79974226 100.00% range 35869:85362145 99.95% scans 1

Space Manager then scans and Trims free storage blocks, taking just over 0.7 second to complete:
02.196 spaceman_scan_free_blocks:4106: disk9 scan took 0.717433 s, trims took 0.715705 s
02.196 spaceman_scan_free_blocks:4110: disk9 81258479 blocks free in 25 extents, avg 3250339.16
02.196 spaceman_scan_free_blocks:4119: disk9 81258479 blocks trimmed in 25 extents (28628 us/trim, 34 trims/s)
02.196 spaceman_scan_free_blocks:4122: disk9 trim distribution 1:0 2+:0 4+:0 16+:0 64+:0 256+:25

VM

What happens with an Apple silicon VM is a bit more complicated, and harder to observe. This time the virtualisation app should create the disk image inside the VM bundle as a sparse file to begin with, then copy into that what’s needed for the VM, so skipping the first mount stage and Trimming during the second mount.

The result is the same, though, with a 350 GB VM taking just 22 GB on disk. Inspect that disk image using my free utility Precize, and you’ll see that economy confirmed, and the Sparse File flag set.

Conclusions

For plain read-write disk images and those inside VMs to be sparse files:

• they must contain a suitable raw disk image, such as UDIF read-write;
• the host file system must be APFS, as HFS+ doesn’t support sparse files;
• for normal disk images, they must be stored on an SSD that supports Trimming;
• there must be sufficient free space in the disk image;
• the guest file system can be APFS, either plain or encrypted, or HFS+J;
• for normal disk images, they must have been mounted at least once since first being created.

Apple has just released an update to XProtect for all supported versions of macOS, bringing it to version 5293. As usual, Apple doesn’t release information about what security issues this update might add or change.

This version adds a single new rule for MACOS.SOMA.J.

You can check whether this update has been installed by opening System Information via About This Mac, and selecting the Installations item under Software.

A full listing of security data file versions is given by SilentKnight, LockRattler and SystHist for El Capitan to Sequoia available from their product page. If your Mac hasn’t yet installed this update, you can force it using SilentKnight, LockRattler, or at the command line.

If you want to install this as a named update in SilentKnight, its label is XProtectPlistConfigData_10_15-5293.

Sequoia systems only

This update has also been released for Sequoia via iCloud. If you want to check that manually, use the Terminal command
sudo xprotect check
then enter your admin password. If that returns version 5293 but your Mac still reports an older version is installed, you can force the update using
sudo xprotect update

I have updated the reference pages here which are accessed directly from LockRattler 4.2 and later using its Check blog button.

John Singer Sargent’s move to London in 1886 had proved a commercial success, and he painted portraits of the rich and famous until he closed his studio there in 1907.

His group portrait of The Ladies Alexandra, Mary, and Theo Acheson, normally simply known as The Acheson Sisters, was exhibited at the Royal Academy in 1902, where it was both very popular and favourably received. And at first sight, it is indeed a delight, as they sit around the front of a huge urn decorated with floral garlands, one of the ladies reaching up to pick oranges from a tree just above the urn. Even the late Queen Victoria would, I am sure, have approved. However, there are hidden references that link back through earlier portraits by Sir Joshua Reynolds to Nicolas Poussin’s previous paintings of bacchanalian orgies.

Meanwhile, the other John Singer Sargent continued his travels across Europe and beyond. A visit to Venice in 1902 brought this stunning watercolour of Rio dell Angelo, where he provides his response to the Impressionists’ question on the colour of shadows.

The same year, Sargent visited New York, where he painted this portrait of his friend and fellow artist William Merritt Chase in his fifties. He’s immaculately dressed with a carnation in his button-hole, and the tools of his art in hand.

The following year, Sargent was back in Venice to paint this watercolour of Scuola di San Rocco assembled from a virtuoso series of marks and gestural strokes of the brush.

When he broke free of his studio for the summer of 1904, Sargent travelled to the Alps for his first season of serious plein air painting there. He stayed in the Italian mountain town of Purtud, to the south-west of Mont Blanc, where there was a group of Italian artists doing the same thing. Among them was Ambrogio Raffele (1845-1928), probably the best and most experienced of the group; Sargent became particularly friendly with him, and in An Artist in His Studio (1904) shows Raffele at work in his room there.

This painting is a paradox, in that Sargent shows an accomplished plein air painter working not in front of his motif, but in his bedroom. It’s plausible that Raffele is painting a larger version of the small sketch seen at the lower left of the large canvas.

When he reached Venice, Sargent’s watercolours became even more gestural, as shown in this view of Unloading Boats in Venice (1904).

The following summer Sargent turned his attention to his fellow travellers as they crossed the Alps on their way south. He sketched his friends during their siesta, in this Group with Parasols painted in oils in about 1905.

Here they are again in watercolour, in Siesta from the same year.

A decade after her dancing career had gone into decline, and fifteen years after his first painting of her, Sargent produced a completely different portrait of La Carmencita (c 1905). Now his virtuoso brushstrokes capture her motion. His inspiration was no longer Manet, but Giovanni Boldini and his ‘swish’.

In further time out of his studio, Sargent travelled to North Africa, where he painted this Bedouin Camp in 1905-6.

This portrait of an Arab Woman from 1905-06 is another fine example of his watercolour sketching.

At times, Sargent’s brushstrokes appear so casual that it’s almost as if he was just doodling with pigment, as in the blue shadows In a Levantine Port (1905-6). But they coalesce into the image that Sargent clearly had in his mind all the way along, and pop out at the viewer.

Open System Settings, then General, and Login Items & Extensions. Scroll to the end of that list and you’ll see a section titled Extensions. All looks tidy there and in order, but you’re looking at the tip of the iceberg. Click on the ⓘ button at the right of any of those entries, and prepare to be thoroughly confused. These aren’t, of course, kernel extensions, nor are they only system extensions (although some may be), they’re app extensions, conveniently shortened to appexes, the subject of this article.

System Settings

That section in System Settings is unusual as its list depends entirely on what you have installed on your Mac. Among those you’re most likely to see are:

• Actions allow access to an app’s functions from within other apps, such as Markup provided by macOS.
• Dock Tiles customise the Dock and normally run in the background (although not listed in Background items above), including several phantom ‘apps’ added by macOS.
• File Providers allow you to see both local and remote-storage files together in the Finder, and normally run in the background (although not listed in Background items above). Note this isn’t confined to ‘file providers’ in the sense of cloud services like iCloud Drive.
• File System Extensions, userland file systems, including ExFAT and MSDOS in macOS 15.4, which are intended to replace kernel extensions.
• Finder provides enhanced search and other functions for files and more. These can also be accessed directly through the Quick Actions item in the Finder’s contextual menu.
• Photos Editing provides enhanced editing in the Photos app. This also includes Markup provided by macOS.
• Quick Look includes custom QuickLook thumbnail and preview extensions, replacing qlgenerators.
• Sharing includes features provided in the Share menu. These include some from macOS that can’t be disabled, such as Mail and Messages, others that are optional, as well as third-party apps.
• Spotlight includes custom mdimporter modules to extract indexable content from custom file types not supported by macOS.

To add to the uncertainty, not all those available in Sequoia 15.4 are listed in the Mac User Guide’s total of 17 classes, or Apple’s list of 25 for developers.

Where are appexes?

Most of these are installed as .appex bundles inside a PlugIns folder inside the bundle of an app, although some can instead be in a Library folder inside the app. The best information about each is in the Info.plist file in their appex bundle. In that, the nested dictionary of NSExtensionAttributes is most informative. That gives the NSExtensionPointIdentifier type, which for a QuickLook appex might be com.apple.quicklook.preview, indicating that it generates custom previews for QuickLook, in the way that qlgenerators used to. That type corresponds to the SDK entry listed by pluginkit, described below.

Not all appexes are exposed in System Settings, though. New-style drivers supplied in .dext bundles, that are listed as extensions, aren’t included despite there being 17 bundled in macOS 15.4. There’s also no mention of nearly 200 appexes provided in /System/Library/ExtensionKit/Extensions.

pluginkit

In addition to their control in System Settings, the command tool for working with appexes is pluginkit. Most of its options are aimed at those developing and debugging their own appexes, but there’s one command that will dump details of all managed appexes to a lengthy text file, with a form like
pluginkit -m -vv > ~/Documents/pluginkitOut.text
which pipes its output to the file at ~/Documents/pluginkitOut.text. You can add another v to the options for greater details.

The output from pluginkit reveals just how many appexes there are, possibly as many as 500 or more installed in your Mac. Most are system components that aren’t exposed in System Settings, and many have SDK names, specifying their type, that fall outside the categories listed by Apple. For instance, there’s a com.apple.CloudDocs.iCloudDriveFileProvider appex buried deep in the CloudDocs private framework that has an SDK type of com.apple.fileprovider-nonui for iCloud Drive.

Anomalies

Extensions settings currently appears to be a work in progress. It’s among the most opaque sections in System Settings, with all of its controls accessed through ⓘ buttons and floating windows, rather than being laid out clearly. It’s riddled with inconsistencies, and some sections don’t appear to work properly, most notably Quick Look.

This screenshot shows that Apparency’s Quick Look appex is currently disabled, but at the right is a QuickLook preview demonstrating Apparency’s customisation. This applies to other custom Quick Look appexes in Sequoia 15.4: when apparently disabled, they continue to work normally.

As system qlgenerators aren’t included in the Quick Look list, it can’t be used to disable those to allow third-party appexes to generate thumbnails and previews instead, which might have been a useful function.

Summary

• Appexes are app extensions, now found in the PlugIns or Library folders within app bundles.
• Although some appexes are also system extensions, or their relatives, most aren’t, and simply extend that app’s features.
• Many appexes are controlled in System Settings > General > Login Items & Extensions, at the end.
• Lists shown there vary according to which types of appex are installed. Click on the ⓘ button to view and control them.
• Some system appexes are listed but can’t be disabled, while others can be.
• They can also be controlled and listed using the pluginkit command tool, although that’s not straightforward.
• In Sequoia 15.4, Quick Look appex controls appear dysfunctional.

References

man pluginkit
Apple’s developer master page with links to documentation
QuickLook and its appexes
Dock tile appexes.

Aeneas has been rowed through the Straits of Messina, avoiding the rock pinnacle that Scylla had been transformed into. From there he heads north-west until he meets a fierce northerly storm that blows him and his crew south to the city of Carthage, on the Libyan coast. Ovid breezes through what takes Virgil almost a whole book in the Aeneid, in a brief summary of the affair between Aeneas and Dido, Queen of Carthage. This ends with him abandoning her to fall upon the sword he had given her, and her body to be consumed on her funeral pyre.

Pierre-Narcisse Guérin’s Aeneas tells Dido the misfortunes of the City of Troy, painted in about 1815, is probably the standard work showing the beginnings of their romance. Unfortunately it doesn’t give any clues to its tragic outcome.

In about 1875, when Paul Cézanne was still experimenting with narrative genres, he first drew a compositional study, then painted Aeneas Meeting Dido at Carthage. The queen is at the left, surrounded by her court. The warrior figure of Aeneas stands to the right of centre, and to the right of him is the shrouded spectre of Aeneas’ wife, Creusa, who had been abandoned by Aeneas as the family fled the burning city of Troy.

Normally titled The Death of Dido, Tiepolo’s painting from 1757-70 shows an odd composite scene in which Aeneas, packed and ready to sail with his ship, watches on as Dido suffers the agony of their separation, lying on the bed of her funeral pyre. A portentous puff of black smoke has just risen to the left, although it’s surely far too early for anyone to think of setting the timbers alight.

Dido’s spectacular death is shown best in what is perhaps Henry Fuseli’s most conventional history painting, known simply as Dido (1781). Dido has just been abandoned by Aeneas, has mounted her funeral pyre, and is on the couch on which she and Aeneas made love. She then falls on the sword Aeneas had given her, and that rests, covered with her blood, beside her, its tip pointing up towards her right breast. Her sister Anna rushes in to embrace her during her dying moments, and Jupiter sends Iris (shown above, wielding a golden sickle) to release Dido’s spirit from her body. Already smoke seems to be rising up from the pyre, confirming visually to Aeneas that she has killed herself, as he sails away from Carthage.

After a close call with the Sirens, Aeneas reaches the land of the Cercopes, who had been transformed into apes by Jupiter because of their treachery. The ship continues to the north-west along the coast of Italy, passing Naples.

This has been shown only by those like Antonio Tempesta who engraved for illustrated editions of the Metamorphoses. Tempesta’s Jupiter Changing the Cercopians into Monkeys from around 1600 shows Jupiter at the right, accompanied as ever by his huge eagle, with the transformed monkeys.

Once past Naples, Aeneas and his crew land at Cumae to visit the Sibyl there in her cave. He needs her assistance to go to the underworld to speak to the ghost of his father Anchises. The Sibyl reassures Aeneas that he will achieve his goals, and to that end she takes him to Proserpine’s sacred glade. Finding a golden bough there, she tells Aeneas to break that from the tree. The two of them travel to the underworld bearing that golden bough, make contact with the ghost of Anchises, and return safely.

During their walk back, Aeneas thanks the Sibyl for her help and guidance, and offers to build a temple to her, assuming she is a goddess. The Sibyl points out that she is no goddess, and explains how she had once been offered immortality if she were to let the god Apollo take her virginity. When Apollo had invited her to wish for anything, she had pointed to a pile of sand, and asked to live as many years as there were grains, but forgot to wish for eternal youth to accompany that.

Apollo offered her eternal youth as well, but she declined and remained a virgin. After seven hundred years, with another three hundred still to go, she is well into old age, infirm, and steadily vanishing as her body wastes away until only her voice will remain. With that, the pair reach Cumae, and Aeneas sets sail.

This is depicted in one of Claude Lorrain’s most wonderful coastal landscapes, his Coast View with Apollo and the Cumaean Sibyl from about 1645-49. Although their figures are small, Apollo on the left is holding his lyre in his left arm, trying to persuade the seated Sibyl, to the right, to let him take her virginity. Around them are the ruins of classical buildings and a stand of tall trees, as the land drops away to an idealised view of the coast of Italy. In the small bay immediately below them are some ships, which may be a forward reference to Aeneas’ future visit, although that would have been seven centuries later according to the Sibyl’s account.

JMW Turner didn’t tackle the first part of this story until 1823, when he painted The Bay of Baiae, with Apollo and the Sibyl. His view appears to have been loosely based on Claude’s, but is set at Baiae, in the Bay of Naples. Apollo is again on the left, with his lyre, but the dark-haired Sibyl has adopted an odd kneeling position. She is holding some sand in the palm of her right hand, asking Apollo to grant her as many years of life as there are grains.

When Claude was painting his coastal view, François Perrier was painting a more conventional figurative account of Aeneas and the Cumaean Sibyl (c 1646). Aeneas, stood to the left of the incense burner, appears to be offering to burn incense in honour of the Sibyl, who stands at the right in front of her cave, and is just about to tell him her life-story. Behind Aeneas is a queue of people, including a king, bearing gifts and waiting to consult with the Sibyl. At the top left corner is a temple, and in the clouds above it the god Apollo, I believe.

JMW Turner’s first version of this later scene is thought to have been his first mythological painting, in about 1798. This second version, Lake Avernus: Aeneas and the Cumaean Sybil, dates from 1814 or 1815, and is both an improvement on the original and in better condition. True to the spirit of Claude’s landscape, this too is a mythological landscape showing the beautiful setting of Lake Avernus, near Pozzuoli, to the west of the city of Naples. In the distance are Baiae and the cliffs of Cape Miseno. The Sibyl, who doesn’t show her years, holds aloft a golden sprig rather than a bough, and Aeneas stands with his back to the viewer, as if he too is enjoying the view.

Turner’s last account is The Golden Bough, exhibited in 1834. It shows well how much his style had changed, although it retains compositional features from his earlier paintings. The Sibyl stands on the left, radiant in white light, and holding aloft a more substantial golden branch, with the golden sickle used to cut that branch, in her right hand. Down towards Lake Avernus are the Fates, dancing around a white glow. A couple of female companions of the Sibyl rest under the tree, but Aeneas is nowhere to be seen, although he might be in the middle of the Fates, perhaps. In the right foreground is a snake, a symbol of the underworld.

I hope that you enjoyed Saturday’s Mac Riddles, episode 302. Here are my solutions to them.

1: Shortened characters into the most common extension, formerly ASCII.

Click for a solution

txt

Shortened characters (text, shortened) into the most common extension (it is), formerly ASCII (it used to be).

2: Medical practitioner at the end of word files until gaining a cross in 2002.

Click for a solution

doc

Medical practitioner (a doc) at the end of word files (the extension for Word native format) until gaining a cross in 2002 (progressively replaced by the newer docx from 2002 onwards).

3: At the end of real estate inventory, most commonly for Info and preferences.

Click for a solution

plist

At the end (a filename extension) of real estate (property) inventory (list), most commonly for Info (Info.plist in bundles) and preferences (also usually property lists).

The common factor

Click for a solution

They are common filename extensions.

I look forward to your putting alternative cases.

APFS has two special file types designed to economise on storage space: clone and sparse files. Clone files are two or more distinct files within the same volume whose data is shared; sparse files save space by skipping empty data and only storing data containing information. This article explores how they behave in use, with particular emphasis on Time Machine backups and iCloud Drive. The latter also involves a third type of special file, dataless files.

Clone files

In contrast to hard-linked files, clone files are two or more distinct files within the same file system (volume) whose file extents are identical, so share the same data, as shown below. They’re created by variants of normal file copying, including duplicating in the Finder (and drag-copying within the same volume), and the cp -c command.

Instead of duplicating everything, only the inode and its attributes (blue and pink) are duplicated, together with their file extent information. You can verify this by inspecting the numbers of those inodes, as they’re different, and information in the attributes such as the file’s name will also be different. There’s a flag in the file’s attributes to indicate that cloning has taken place. At first, the two cloned files share the same data blocks and extended attributes, but as the two files are changed by editing, they start to drift apart and become uncloned.

Clone files are becoming more popular thanks to the Hyperspace app, which deduplicates files within the same volume by replacing copies with clones.

Because they can only exist within the same file system, clone files are fragile. Any copy or move to another file system is invariably accompanied by the copying of their full data, and their economy of storage can only remain as long as they stay within the same volume.

Backups

One notable exception to this same-volume rule is in Time Machine backups. As clone files are preserved in local snapshots, when Time Machine constructs a backup as a snapshot in the backup storage volume, shared file extents are retained, so preserving clones. This is reflected in the size of the backup snapshot, and in the report written to the log. For example, when backing up three distinct files and ten clones of one of those, that report included:
14 Total Items in Backup (l: 16 GB p: 11.02 GB)
3 Files Copied (l: 6 GB p: 1.02 GB)
1 Directories Copied (l: Zero KB p: Zero KB)
10 Files Cloned (l: 10 GB p: 10 GB)

Backups made by other utilities are unlikely to reproduce this behaviour, though, as they can’t synthesise snapshots in the way that Time Machine does. To preserve clone files in their backups, they’d have to identify clones in the source and explicitly perform cloning in their backup store. Although Carbon Copy Cloner claims that “in some cases CCC may clone a file on the destination prior to updating its contents”, it doesn’t appear to attempt to preserve clone files in the backups it makes. I’m not aware of any third-party utility that does.

Unfortunately, Time Machine appears unable to restore directly from backup snapshots in the backup store, and performs Finder copies when restoring. That saves each of those clone files as a completely separate file, without any sharing of data. As a result, the space occupied on disk for a restored volume can be substantially greater than the original or its backup. Extensive use of clone files could thus cause problems when restoring from backups.

Of course, rolling a volume back to a local snapshot, such as one made during Time Machine backups, preserves all clone files within that volume.

iCloud Drive

Clone files created within the same volume as local iCloud Drive storage on the Data volume, or cloned when within a folder in iCloud Drive, remain within the same file system and clones are therefore preserved, and when the file is moved to other folders in the same volume.

However, clone files are treated as simple copies as far as iCloud Drive’s remote storage is concerned. While a pair of cloned 5 GB files only use a total of 5 GB local storage, they require a full 10 GB of your iCloud allocation, indicating that their cloud storage is separate and not common to both. Although the effects of eviction (removing local data) and materialisation (restoring local data from cloud storage) are difficult to observe directly, they appear to lose the benefits of cloning.

When the local copy of a file also stored remotely in the cloud is evicted, its data is removed from local storage, rendering it dataless, as shown below.

When that file is to be used locally again, its data has to be downloaded from the cloud service, and the local dataless file is materialised by adding its data back. As far as I can tell, that doesn’t result in the reconstruction of the shared file extents, so changes cloned files into normal copies with different file extents. You would then need to use Hyperspace to restore them as clone files. Other Macs sharing the same iCloud Drive also see them as full copies rather than clones.

These behaviours could also catch the user by surprise.

Sparse files

Unlike clone files, the structure of sparse files in APFS is conventional, as shown below.

They achieve their economy in storage by only including file extents containing non-null data, and thus aren’t dependent on remaining within the same file system (volume), making them more robust. Their primary requirement is that they’re created and maintained using specific file system operations, and are only copied or moved to other APFS file systems.

Backups

When backed up by Time Machine to another APFS volume, sparse files are preserved reliably, and are also restored as sparse files. That isn’t likely to hold, though, if the file is transferred using a network file system such as SMB, as all network transfers currently appear to explode sparse files to full size prior to transfer. Because of the way in which they have to be created, only the app maintaining that file could restore its sparse format. In the case of disk images, this should normally occur the next time they’re mounted in the Finder and Trimmed by APFS.

iCloud Drive

Assessing what happens with sparse files in iCloud Drive is considerably simpler than with clone files. As long as they remain downloaded to local storage, they are preserved, and can be moved in and out of iCloud Drive storage without exploding in size. However, they too are stored in full when in iCloud storage, requiring their full size in your iCloud allocation, and the eviction-materialisation cycle explodes them to full size, and their sparse file flag is removed.

The only way to return a former sparse file to its original economical format is then to open and save it using the app that creates and maintains it. In the case of disk images, this should occur when they’re next mounted and Trimmed.

Conclusions

Clone files:

• are only preserved when moved within the same file system (volume);
• are preserved and restored from local snapshots;
• are preserved in Time Machine backups, but aren’t restored from them;
• aren’t preserved in other backups;
• could result in a restored volume being substantially larger than its original;
• occupy their full space in your iCloud allocation;
• are only preserved in iCloud Drive when they aren’t evicted from local storage;
• can be regenerated using Hyperspace.

Sparse files:

• are only preserved when copied or moved directly between APFS volumes;
• aren’t preserved when copied or moved over network connections, or using SMB;
• aren’t preserved when copied or moved to different file systems, including HFS+;
• are preserved in and restored from local Time Machine backups;
• should be preserved in and restored from other local backups;
• occupy their full space in your iCloud allocation;
• are only preserved in iCloud Drive when they aren’t evicted from local storage;
• can only be regenerated by the app that creates and maintains them.

Both clone and sparse files can result in substantial savings in storage space. However, because that’s fragile, their greatest value is in minimising erase-write cycles in SSDs, hence slowing their ageing.

References

Apple’s APFS Reference (PDF), last revised 22 June 2020.
Dataless files are explained here.
How sparse files work
Files and clones
Special file types, including dataless files

In the first of these two articles tracing the first century of railways in paintings from the early 1840s, I had reached Claude Monet’s views of the Gare Saint-Lazare in Paris before 1880. By this time few countries in Europe had no railways, and trains frequently conveyed artists from their studios in the cities out to the beaches and mountains, journeys that a few years earlier could have taken days rather than hours.

Although Norway was a greater challenge for the railway engineers, Frits Thaulow seized the opportunity to show the results in The Train is Arriving from 1881. The country’s first public steam-hauled railway was developed by the son of George Stephenson, whose Rocket locomotive had inaugurated the first steam railway in the world. Norway’s line opened in 1854, and during the 1870s progressively made its way to Trondheim.

In 1888, Vincent van Gogh gave us The Blue Train (Viaduct in Arles).

Volodymyr Orlovsky’s undated Steppe shows a river in summer, with water levels at their minimum. Cattle are taking the opportunity to drink and cool off in the water. In the distance is the plume of smoke from a railway train, probably carrying grain and other produce from the Ukrainian countryside to one of the growing coastal cities for export.

The twentieth century brought the beginning of the end of the power of steam, marked in an unexpected twist of history. Between 1898 and 1900, a new railway station, initially known as the Gare d’Orléans, was built on the bank of the Seine at Quai d’Orsay, Paris. The first electrified urban railway terminal in the world, it was a star of the Exposition Universelle in 1900, where many Impressionist paintings were exhibited.

Victor Marec’s painting shows construction work being progressed in 1899, with a steam locomotive hauling construction trucks.

The Gare d’Orsay, as it became, started to suffer physical limitations in 1939, and its upper levels closed from 1973. In 1986 it re-opened as the most extensive collection of Impressionist art in the world, the Musée d’Orsay.

Maximilien Luce was one of the most expressive artists, who wasn’t an official war artist, to show scenes relating to the First World War. In his La Gare de l’Est (1917), a collection of wounded and battle-weary soldiers are shown at the entrance to this large Paris railway station.

The Gare de l’Est in Snow (1917) is even better-known, and a classic painting of falling snow in a large city.

Lesser Ury’s Nollendorfplatz Station at Night from 1925 shows the brilliant electric lighting around this busy railway station to the south of the Tiergarten, in one of Berlin’s shopping districts.

By this time, painting trains was becoming something of a sub-genre, particularly as steam trains were being replaced throughout Europe.

Eric Ravilious is one example of a twentieth century artist who painted motifs deeply embedded in the railway, in his Train Landscape from 1940.

A few narrative artists, including Joaquín Sorolla, set their stories inside railway carriages. My favourite among these is Berthold Woltze’s Der lästige Kavalier (1874), rendered into English as The Annoying Bloke, from 1874.

This is set in a railway carriage where there are two men and a young woman. She is dressed completely in black, and stares towards the viewer with tears in her eyes. Beside her is a carpet-bag, and opposite is a small wooden box and grey drapes.

Leaning over the back of her seat, and leering at her, is a middle-aged dandy with a brash moustache and mutton-chop whiskers, brandishing a lit cigar. He appears to be trying to chat her up, quite inappropriately, and very much against her wishes. Behind him, and almost cropped off the left edge of the canvas, is an older man with a dour, drawn face.

The young woman has apparently suffered a recent bereavement, and may even be travelling back after the funeral. She looks too young to have just buried a husband, so I think it more likely that she has just lost her last parent, and is now living alone, prey to the likes of this annoying and abusive bloke.

Lambing dates remain one of life’s great mysteries. Here in the UK, farmers in the north usually lamb earliest, often only just after Christmas when it’s usually bitter cold and snowy up there. Down here in the balmy south, lambs are born three months or more later, typically in April, when they’re often struggling to keep cool in the sunshine. Last week we saw the first of this year’s lambs, and Apple’s Spring OS fest, including Sequoia 15.4.

Size

That update was large, but that isn’t exactly unusual:

• 7 March 2024, Sonoma 14.4 was 3.6 GB (Apple silicon) with 64 vulnerabilities fixed, “the most substantial update of this cycle so far”;
• 27 March 2023, Ventura 13.3 was 4.5 GB with 49 vulnerabilities fixed, being “substantial, and brings many improvements and fixes”;
• 14 March 2022, Monterey 12.3 was 5.3 GB with 45 vulnerabilities fixed, being “very substantial, introducing major new features like Universal Control and Spatial Audio, changing several bundled apps, and fixing many bugs”;
• 26 April 2021, Big Sur 11.3 was 6.62 GB with over 50 vulnerabilities fixed, “the largest update to macOS since Mojave, and quite possibly the largest ever”.

(Figures and quotations from links here.)

Although the 15.4 update wasn’t quite as large as 11.3, at 6.2 GB for Apple silicon, it has comfortably surpassed it in the number of vulnerabilities fixed, 131 in all, and came close to the size of the 15.0 upgrade at 6.6 GB. What’s most disappointing is that, while the first release of Sequoia merited long and detailed accounts of much of what had changed, for 15.4 there’s precious little information beyond its lengthy security release notes.

A stroll through the version numbers of its bundled apps and /System/Library confirms the extent of changes. There was no point in my trying to compile an article listing them, as it might have been briefer to report what hasn’t changed. What’s more to the point is what’s new in 15.4, what are its Spring lambs?

Novelties

Among the new kernel extensions is the first version of AppleProcessorTrace, and there’s a brace to support hardware in Apple silicon chips including a T6020 and T8103 for PCIe, and a T6032. Those appear to be for M2 Pro, M1 and M3 Ultra chips, respectively. There are two new public frameworks, one named CLLogEntry that is presumably for Core Location log entries, the other tantalisingly named SecurityUI. Neither seems to align to anything in Apple’s developer documentation, so might be preparing the ground for what we’ll hear about in early June at WWDC, when the lambs have grown a bit.

I keep a track of the total number of bundles in several of the folders in /System/Library. Since the release of Sequoia 15.0, that containing Private Frameworks has grown from 4,255 to 4,398. Because of their layout, this total overestimates the real change in numbers, and that probably represents a true growth of around 70 Private Frameworks in Sequoia so far.

These Private Frameworks contain code features used privately by Apple’s apps, but not exposed to third-party developers. Although much is of little or no use or advantage, they also contain much that supports changing features in macOS. Using Private Frameworks is a sure way to madness, and something explicitly forbidden in the App Store, but, like the unaffordable car or boat we like to gloat at, there’s no harm in wondering what they will bring in the future.

The list of new Private Frameworks in Sequoia 15.4 is long, and includes: AUSettings, Bosporus, ComputationalGraph, CoreAudioOrchestration, CryptexKit, CryptexServer, DailyBriefing, DeepVideoProcessingCore, Dyld, ExclaveFDRDecode, FPFS, FindMyPairing, various GameServices, GenerativePlaygroundUI, MCCFoundation, MLIR_ML, MobileAssetExclaveServices, Morpheus, MorpheusExtensions, an OnDeviceStorage group, OpenAPIRuntimeInternal, OpenAPIURLSessionInternal, PIRGeoProtos, RapidResourceDelivery, SecureVoiceTriggerAssets, SecurityUICore, and VideoEffect.

While many of those names can inform speculation about what we’re about to see in macOS 16, three merit a little more decoding.

Cryptexes are secure disk images loaded during boot that currently deliver Safari and its supporting components, and the dynamic libraries for all those frameworks, public and private. Accessing them from user-level code isn’t something you’d expect to happen, so those two Private Frameworks, CryptexKit and CryptexServer, hint at further expansion in their use and support.

Bosporus

The Bosporus Strait in Turkey connects the Black Sea to the Sea of Marmara, thence through the Dardanelles to the eastern Mediterranean. It’s a busy thoroughfare formerly used heavily by ships carrying grain and other bulk cargoes from Ukraine and Russia.

View of Constantinople and the Bosphorus (1856) is one of many views that Ivan Aivazovsky made of this great city, which he visited on many occasions. The artist kept his studio in Crimea, on the opposite (northern) shore of the Black Sea.

Morpheus

Morpheus is the god of dreams, whose name is the source of the word morphine. Although usually distinct from Hypnos, god of sleep, he’s sometimes associated with Nyx, goddess of the night, most famously in reference to a passage from Virgil’s Aeneid, painted below by Evelyn De Morgan.

She pairs Nyx with Morpheus in her Night and Sleep, from 1878. The further figure is a young woman wearing long red robes, her eyes closed, clutching a large brown cloak with her right hand, and most likely Nyx. Her left arm is intertwined with a young man’s right arm. He also has his eyes closed, and is most probably Morpheus. He clutches a large bunch of poppies to his chest with his left arm, while his right scatters them, so they fall to the ground below.

Virgil’s lines in Book 4, line 486 read:
hinc mihi Massylae gentis monstrata sacerdos,
Hesperidum templi custos, epulasque draconi
quae dabat et sacros servabat in arbore ramos,
spargens umida mella soporiferumque papaver.
haec se carminibus promittit solvere mentes
quas velit, ast aliis duras immittere curas…

Translated (at Perseus at Tufts University), this reads:
From thence is come
a witch, a priestess, a Numidian crone,
who guards the shrine of the Hesperides
and feeds the dragon; she protects the fruit
of that enchanting tree, and scatters there
her slumb’rous poppies mixed with honey-dew.
Her spells and magic promise to set free
what hearts she will, or visit cruel woes
on men afar.

Spargens umida mella soporiferumque papaver, one of Virgil’s greatest lines, is conventionally translated as “scattering moist honey and sleep-inducing poppy”, and describes well the effects of the opiate drugs derived from opium poppies, including morphine.

I look forward to watching the lambs grow up through the coming summer, and learning about those lambs that came with Sequoia 15.4 at WWDC.

The nineteenth century brought huge changes in technology and society. Some, like telegraphy, telephones and radio, haven’t featured in many paintings, and even the bicycle has largely escaped the canvas. But the advent of railways, and later motor cars, had greater impact on visual art. In this weekend’s two articles, I trace the first century of railways in paintings from the early 1840s.

JMW Turner was among the first painters to capture this in his Rain, Steam, and Speed – The Great Western Railway in 1844. This pioneering railway connected London with rich farming country across the south of England, down into western counties, eventually reaching Cornwall in 1859, fifteen years after Turner completed this painting, and eight years after his death.

William Powell Frith’s The Railway Station (1862) captures the atmosphere of a major railway station in a capital city, here Paddington Station in London, by coincidence Brunel’s terminus for his Great Western Railway. Stations like this became a focus of activity, emotional partings and arrivals, migration, and a fair bit of crime too, everything the narrative painter might wish for.

Britain may have been the first to build railways, but the mania spread like wildfire across Europe and North America.

As the railroad, it started to cover the far greater distances of the USA and Canada. William Hahn’s Southern Pacific R.R. Station at Sacramento (c 1873-4) shows its rapid growth there.

Smoke, steam and other atmospheric effects brought inspiration to the French artists who were developing painting from where Turner’s death had left it.

France had been an early innovator and adopter, although such post-classical motifs wouldn’t have been appropriate for the Salon, of course. It took Édouard Manet painting his favourite model Victorine Meurent, in Le chemin de fer (The Railway) (1873), to break the ice. Its background is the Gare Saint Lazare in Paris. This painting was completed and sold in 1873 to the singer and avid collector Jean-Baptiste Faure, and astonishingly was the only painting accepted of three submitted to the Salon by Manet the following year, where it provoked outrage and ridicule, and a torrent of sarcastic cartoons in the press.

Near Manet’s painting in the Salon, a couple of works by Giuseppe De Nittis were given a warmer reception. Yet sometime between 1869 and 1880, De Nittis painted The Passing of a Train, his unashamed comment on the coming of the train.

As De Nittis, Monet, Pissarro, and the other Impressionists started painting in even more unacceptable styles around Paris, trains and railways came to appear even more.

Claude Monet’s The Railway Bridge at Argenteuil (1873) is one of his several landscapes centred on the railway from the years immediately after the Franco-Prussian War. At this time, Monet was a regular commuter by train: when he, Camille and his son moved out to Argenteuil at the end of 1871, he travelled the short distance into Paris by train.

Monet liked this bridge so much that he painted it again the following year, in The Railway Bridge at Argenteuil (1874).

By the last quarter of the nineteenth century, steam power had become so essential to modern life it was assimilated into the everyday. Paul Cézanne’s family estate in Aix-en-Provence was connected by rail to Paris by 1856, and express trains to the Mediterranean coast enabled many artists whose studios were in the capital to paint in the remarkable light of the Midi. The prominent light ochre structure sweeping across many of Cézanne’s views of Mont Saint-Victoire is the long viaduct built to accommodate the railway that transported artists between Paris and the coast of the Midi.

In 1877, Claude Monet became the most painterly railway buff of them all. By then, he was becoming detached from Argenteuil, and sought a new radically modern urban theme. Where more appropriate than the steaming hubbub of the Gare Saint Lazare? Caillebotte paid the rent for him on a small studio nearby, and Monet gained approval to paint in the station. By the third Impressionist Exhibition of April 1877, Monet had assembled seven views of the station, including one that even seemed to please the critics. Among the paintings from that campaign is his Arrival of the Normandy Train, Gare Saint-Lazare (1877).

Monet was too smitten to stop in the station, though. In his Train Tracks at the Saint-Lazare Station (1877) he reversed the view and started showing railway signalling.

He went even further in his Saint-Lazare Station, the Western Region Goods Sheds (1877), showing the working parts with the smoky city beyond.

Here are this weekend’s Mac riddles to entertain you through family time, shopping and recreation.

1: Shortened characters into the most common extension, formerly ASCII.

2: Medical practitioner at the end of word files until gaining a cross in 2002.

3: At the end of real estate inventory, most commonly for Info and preferences.

To help you cross-check your solutions, or confuse you further, there’s a common factor between them.

I’ll post my solutions first thing on Monday morning.

Please don’t post your solutions as comments here: it spoils it for others.

Disk images, files that contain the contents of a physical storage medium, go back long before the first Mac. Among other tasks, they were originally used to contain representations of floppy disks for replication in manufacture.

Today disk images are at the heart of macOS, and widely used by third-parties. They’re an essential part of macOS installers, home to Recovery mode, and the basis for cryptexes. They’ve been used to burn and replicate optical disks, to archive disk contents, extensively for network backups, and for the distribution of software.

Classic Mac OS

In Classic Mac OS there were two utilities that worked with different formats: Disk Copy used replicas later in DC42 format, after Disk Copy version 4.2, while compressed formats known as DART were handled by the Disk Archive/Retrieval Tool, hence their name.

Mac OS 9 brought Disk Copy 6.0 with added support for the New Disk Image Format (NDIF), which supported resource forks, and ended with its last release version 6.3.3. This also supported read-only Rdxx formats.

By this time, variants of formats had become complex. Here, Disk Copy is configured to create a read-only compressed .img file containing the contents of a standard 1.4 MB floppy disk. In the upper window, it has completed validating the checksum on a self-mounting .smi disk image that’s part of a DiskSet. These could also be signed, using certificates issued not by Apple but by DigiSign.

Here’s Disk Copy saving an image of a hard disk using a similar read-only compressed format, this time to accommodate 1.5 GB.

Mac OS X

The release of Mac OS X 10.1 Puma in 2001 brought Apple’s new Universal Disk Image Format (UDIF), used in DMG disk images, which only had a single fork as its resource fork was embedded in the data fork. Although pre-release versions of Disk Copy 6.4 and 6.5 were available with UDIF support for Mac OS 9, neither was ever released, leaving Classic Mac OS without access to UDIF images. Its support for compression options in Apple Data Compression (ADC) unified the two disk image types, and extended support for images larger than a floppy disk. This new format enabled disk images to represent whole storage devices, complete with a partition map and disk-based drivers.

Tools provided in Mac OS X for working with disk images include Disk Utility and the command tool hdiutil.

On 21 January 2002, the first version of DropDMG, a third-party substitute for creating disk images, was released by C-Command Software. This quickly enabled developers to create disk images with artwork, licences and other features that weren’t accessible from the tools bundled in Mac OS X. DropDMG has flourished over the last 23 years, and remains popular today.

DropDMG’s options for creating a new disk image far exceed those in Disk Utility. Particularly helpful are the compatible version hints shown on various options, to remind you of which file systems are available in different macOS versions, and which types of disk image container are supported. DropDMG will even convert old NDIF disk images last used in Mac OS 9 to more modern formats. It will also change the password of an encrypted disk image from a menu command.

In Mac OS X 10.2 (2002), UDIF and most other supported formats were served from a kernel extension without requiring a helper process. The following year, 10.3 Panther started using a faceless utility DiskImageMounter to mount disk images. Apple then dropped support for embedded resource forks in disk images in Mac OS X 10.4.7, and newly created disk images became less compatible with older Mac OS versions.

Sparse bundles

Until Mac OS X 10.5 Leopard in 2007, all disk images had used single-file formats, although some could be segmented across file sets. Leopard introduced the sparse bundle with its folder of smaller band files containing data. These enabled the image to grow and shrink in size, and became popular means of storing mountable Mac file systems on servers using different file systems.

This is another third-party tool that improved access to disk images from the GUI, DMG Packager, seen in 2009. Unlike DropDMG, this appears to have vanished without trace.

In 2011, with the release of Mac OS X 10.7 Lion, Apple removed more support for old disk image formats. DiskImageMounter no longer opened NDIF .img, .smi self-mounting, .dc42 and .dart compressed formats, although the hdiutil command tool still retained some access to them.

Disk Utility, seen here in 2011, has provided basic access to many disk image formats, but these are only a small selection of options available in the hdiutil command tool, or in DropDMG.

This shows the complex set of options available when creating a new disk image in Disk Utility in OS X 10.10 Yosemite, before the advent of APFS.

Support for compression was enhanced in OS X 10.11 El Capitan with the addition of lzfse in a new ULFO format, and macOS 10.15 Catalina added lzma in ULMO. In both cases, these new formats aren’t accessible in older versions of macOS.

APFS support

The arrival of a pre-release version of the new APFS file system in macOS 10.12 Sierra brought its support in disk images, although only for experimental purposes, and Apple cautioned users to ensure their contents were well backed up.

In addition to adding the more efficient ULMO compressed format, macOS 10.15 Catalina is the last to support many Classic Mac OS disk image formats, including those from DiskCopy42, DART and NDIF from Disk Copy 6.x. Support for AppleSingle and MacBinary encodings, and dual-fork file support, were also removed in macOS 11.0 Big Sur in 2020.

This ‘warning’ alert from 2020 illustrates one of the longstanding issues with disk images. Although integrity checking of disk images using checksums has been valuable, when an error is found there’s no possibility of repair or recovery as the image can’t be ‘attached’, so its file system can’t be mounted.

macOS 12 Monterey in 2021 brought multiple deprecations of older formats, including UDBZ using bzip2 compression, segmented UDIF images, and embedded resources. It’s also thought to be the first version of macOS in which UDIF read/write images (UDRW) have been stored in APFS sparse file format, although Apple has nowhere mentioned that. This has transformed what had previously been space-inefficient disk images that retained empty storage into a format that can prove almost as efficient as sparse bundles. This results from the Trim on mounting HFS+ and APFS file systems within the image freeing unused space, enabling that to be saved in the sparse file format.

Disk images have never been glamorous, but have remained at the heart of every Mac.

References

man hdiutil
Introduction
Tools
How read-write disk images have gone sparse
Performance
Bands, Compaction and Space Efficiency

Appendix: Disk image formats

Supported

• UDRW – UDIF read/write
• UDRO – UDIF read-only
• UDCO – UDIF ADC-compressed
• UDZO – UDIF zlib-compressed
• ULFO – UDIF lzfse-compressed (OS X 10.11)
• ULMO – UDIF lzma-compressed (macOS 10.15)
• UDTO – DVD/CD-R master for export
• UDSP – sparse image, grows with content
• UDSB – sparse bundle, grows with content, bundle-backed, Mac OS X 10.5
• UFBI – UDIF entire image with MD5 checksum.

Unsupported

• DC42 – Disk Copy 4.2 (Classic)
• DART – compressed, for Disk Archive/Retrieval Tool (Classic)
• Rdxx – read-only Disk Copy 6.0 formats
• NDIF – Disk Copy 6.0, including IMG and self-mounting SMI
• IDME – ‘Internet enabled’, on downloading post-processed to automatically copy visible contents into a folder, then move the image to the Trash. Now deemed highly insecure.
• UDBZ – UDIF bzip2-compressed image (deprecated).

Originally known as a toilet table, or simply a toilet, dressing tables or vanities featured near the beds of ladies from the late seventeenth century. They are a fusion of storage boxes used for cosmetics and jewellery, a small flat surface on which to place their contents, and the inevitable mirror to check that she looked right. By the eighteenth century they were made popular by royal mistresses including the Marquise de Pompadour, and became integrated into the morning reception phase of the lady’s day.

William Hogarth even titles the fourth painting in his moralising narrative series Marriage A-la-Mode, The Toilette (c 1743). The Countess Squander is being entertained while completing her dressing and preparations for the day. To the right of the Countess, Silvertongue rests at ease, his feet uncouthly laid on the sofa, clearly intimate with her. He is offering her a ticket to a masquerade ball, where no doubt he will meet her. His left hand gestures towards a painted screen showing such a masquerade.

At the left an Italian castrato (by his wig and jewellery) sings to a flute accompaniment. The rest of the room are disinterested, apart from a woman in white, who is swooning at the singer. The Countess’s bedchamber is behind the pale red drapes at the rear left, and to the right of centre is a typical dressing table with a mirror.

Herman Frederik Carel ten Kate’s Chaperone (1858) recreates an interior from a similar period. A suitor clutching his tricorn hat and walking stick is chatting up a young woman with her companion and moral guard. Behind her chair is a dressing table with a similar layout to Hogarth’s.

Over the next century, dressing tables were modernised and adopted by even the middle classes.

Edgar Degas’ Woman Drying Herself after the Bath is one his first works showing a woman bathing, dating from 1876-77. It’s also one of the few in this series setting the woman in a broader context, here a plain and simple bedroom with a single bed. The woman, wearing only bright red ‘mule’ slippers, stands just behind the shallow metal tub, watching herself in the mirror of her dressing table, as she dries her body with a towel. On its shelf is a small range of cosmetics, with the mandatory mirror behind.

Félix Vallotton affords us a glimpse into the private life of one of the most influential patrons and muses of the day, in his Misia at Her Dressing Table from 1898. Her first marriage was to her cousin Thadée Natanson, who had socialist ideals and lived in artistic circles. The Natansons entertained Marcel Proust, Stéphane Mallarmé, André Gide, and Claude Debussy, but they were closest to their painter friends: Claude Monet, Pierre-Auguste Renoir, Odilon Redon, Paul Signac, and Henri de Toulouse-Lautrec.

For Frederick Carl Frieseke a Nude Seated at Her Dressing Table (1909) is an opportunity for mirror-play. This vanity is more decorative than functional, with curves, a glass top and a painted porcelain figure.

Pierre Bonnard’s domestic interiors are rich with dressing tables, and inventive mirror-play. I show here just two examples.

In Bonnard’s El Tocador, which means The Dressing Table (1908), his partner Marthe’s headless torso is seen only in reflection. The direct view is of the large bowl and pitcher she used to wash herself.

In 1914, Bonnard moved back for a wider view in The Bathroom Mirror. Marthe’s reflection is now but a small image within the image, showing her sat on the side of the bed, with a bedspread matching the red floral pattern of the drapes around her dressing table. Bonnard has worked his usual vanishing trick for himself, and a vertical mirror at the right adds a curiously dark reflection of the room.

Henry Tonks’ The Toilet from the same year separates his nude from her dressing table, and shuns mirror-play altogether.

Félix Vallotton’s Coquèterie (Sauciness) from 1911 shows a young woman still undressed in her white chemise, her unmade bed behind. She looks at herself in the mirror of a small dressing table with that mirror mounted in its lift-up lid, thinking what clothing she should wear from those scattered around.

Have you been able to update an existing lightweight macOS Virtual Machine on Apple silicon to Sequoia 15.4? So far, I’ve had three failures ending in kernel panics, and no successes. Maybe I’m holding it wrong?

Good news …

I’ve had no problems updating VMs from Sonoma 14.7.4 to 14.7.5, or Ventura 13.7.4 to 13.7.5. Those updates went quickly and without a glitch, but Sequoia has been another matter.

… bad news

I’ve now tried to update from Sequoia 15.x to 15.4 with three different VMs:

• freshly installed 15.2
• freshly installed 15.3.2
• lightly used 15.3.2.

None of them had iCloud enabled, but they were each fairly standard in other respects, and all running in Full Security mode, in my virtualisers Vimy and Viable.

Each has failed early, just a minute or two after the update started to install. That was terminated, and the VM briskly rebooted back into its existing version of Sequoia. Shortly after logging back in, they displayed the panic alert.

One VM was so sick at that stage it couldn’t go any further, so had to be humanely destroyed. However, I managed to capture panic logs for the other two. In both cases, the panicked task was com.apple.Mobile, with com.apple.iokit.AppleVirtIOStorage(1.0) at the top of the kernel extensions in the backtrace. The panic occurred on different cores, and its cause was given as “Kernel data abort”.

And a more innocent bug

In the course of looking at this, I happened to notice that creation dates of files in Shared Folders were all incorrect, giving a standard date of Monday, 1 January 2001 at 00:00. All other creation dates in VM folders, the SSV, and even in iCloud Drive folders, were as expected, but none of those in Shared Folders.

However, when any of those mis-dated files or apps were copied into the VM’s local storage, the expected date of creation returned like magic.

I have checked this in VMs running 15.2, 15.3.2, 15.4, 14.7.5 and 13.7.5, and it’s identical in every one. I suspect this may have been going on for some time. Am I holding this one wrong too?

Over to you

• Have you been able to update a Sequoia VM to 15.4?
• Are file creation dates wrong in your VM’s Shared Folders?

Postscript

Thank you all for your responses. I’ve now confirmed that failure to update to 15.4 appears confined to M4 models, and doesn’t afflict my MBP M3 Pro at all. However, the shared folder creation date bug seems just the same there.

By 1880, just two years after he had completed his training under Carolus-Duran in Paris, John Singer Sargent was in the ascendant. His skills were in growing demand for the portraits of the rich and famous, and he also took time to travel and paint abroad, mainly in Spain and Italy.

When he was in Spain in around 1880-81, he painted this Spanish Dancer.

During a visit to Italy in the period 1880-82, he painted these Venetian Glass Workers.

In early 1883, Sargent made overtures to one of the best-known young socialites in Paris, Virginie Amélie Avegno Gautreau, a French creole immigrant from New Orleans, who had married the French banker Pierre Gautreau. Her beauty was the talk of the town, and numerous artists had asked to paint her portrait as a means of promoting their own careers. The first request that she accepted was Sargent’s, in February 1883. She proved a reluctant sitter, and it wasn’t until June of the following year that Sargent was able to pin her down in her estate in Brittany to start preparatory studies. He didn’t complete the finished work until well into the autumn.

We can’t see his original version of Madame X, as its reception drove him to make alterations to tone down its overt eroticism. Her pose was considered sexually suggestive, and one strap of her gown had fallen down her shoulder adding to the image’s sexuality. It caused a scandal when exhibited at the Salon, and was lampooned mercilessly in the press.

Sargent sought temporary solace flirting with the fashion for Impressionism.

He had first met Claude Monet in 1876, but it’s thought that this painting of Claude Monet Painting by the Edge of a Wood was made in 1885, when they were painting together at Monet’s house in Giverny. At the right is Alice, Monet’s wife.

That year Sargent decided to move his portraiture studio away from the scandal in Paris, to London.

By 1886, Sargent had fully settled into his London studio, and the following year had established his reputation, which was reinforced when he exhibited Carnation, Lily, Lily, Rose at the Royal Academy. This was bought immediately by the Tate Gallery. From then until he closed his studio in 1907, he was the leading portrait painter in London. In spite of his obvious success, he was among those who were unhappy with the Royal Academy, and was a founding member of the New English Art Club in 1886.

His uncommissioned work often took him plein air and with progressively loosening style. He visited France frequently, attended Impressionist exhibitions, and developed his friendship with Monet. His informal works were often loose bravura gatherings of marks that appear to have been painted very quickly indeed.

This is shown well in Sargent’s virtuoso Gust of Wind from about 1886-7, which compares with Claude Monet’s La Promenade from 1875.

By the end of the 1880s, his critics in England considered him an Impressionist, but Monet thought he was still under too much influence from Carolus-Duran to be considered Impressionist. His portrait business prospered: in 1887-8 he toured the US and gained over twenty important commissions, including that of Isabella Stewart Gardner, a major patron of the arts in Boston, where twenty-two of his paintings were shown in his first solo exhibition.

Sargent met Dennis Miller Bunker (1861-1890) in November 1887, during that visit to the USA, when Bunker was a rising star of American Impressionism. Like Sargent, Bunker had trained in Paris, and the two became good friends. Bunker stayed with Sargent in England in the summer of 1888, when Sargent painted him at work, in Dennis Miller Bunker Painting at Calcot. Bunker tragically died of meningitis just two years later, at the age of only 29.

Sargent painted this Morning Walk in 1888.

Paul César Helleu (1859–1927) first met Sargent when the former was a precocious student at the École des Beaux-Arts in 1876. Sargent was the first person to buy one of Helleu’s paintings, for which he paid the huge sum of a thousand francs. Helleu and his wife Alice remained close friends with Sargent, and the couple often appear in his paintings. When he painted them in An Out-of-Doors Study in about 1889, they had been married three years.

On the evening of 1 April 1890, when Sargent was back in New York, he, William Merritt Chase and the famous Spanish dancer Carmencita met in Chase’s Tenth Street studio; she danced for them, and they sketched. On this occasion, Sargent opted for a more static pose in his La Carmencita (1890), with her hands at her hips, driving her bust out and her chin high, in assertive pride.

Demand for Sargent’s portraiture skills remained high during the 1890s.

In 1895, two notable young residents of New York City married. He was Isaac Newton Phelps Stokes (1867-1944), a recent graduate of Harvard who studied architecture for three years at the École des Beaux-Arts in Paris, Sargent’s alma mater. He went on to co-found the architectural firm of Howells & Stokes, and was a pioneer in social housing. She was Edith Minturn (1867-1937), daughter of the shipping magnate Robert Bowne Minturn, Jr., and destined to become a philanthropist, socialite, and artistic muse.

A close friend decided that a good wedding gift would be a portrait of Mrs Stokes painted by the greatest of the age, John Singer Sargent. For various reasons this was delayed, but in 1897 the artist and the couple got together and Sargent started work. His original intention had been to paint Mrs Stokes wearing formal evening dress sitting next to an Empire table. However, he changed his mind and decided to paint her standing in informal walking attire next to a Great Dane. As he was reconceiving this in his mind, he turned to a portrait that had been donated to the Metropolitan Museum of Art by Sargent’s patron Henry Marquand in 1889: that of James Stuart, by van Dyck.

Unfortunately, Sargent was unable to find a suitable dog. Mr Stokes then “offered to assume the role of the Great Dane in the picture”, as he put it in his memoirs. The result puts Mrs Stokes in charge, as an example of ‘The New Woman,’ and her husband as a surrogate dog.

All good log browsers provide tools to narrow down the log entries they display. Without those, it would be easy to waste all day wandering through tens of thousands of entries. One common tool provided by macOS, directly and in the log command tool, is filtering using predicates. Although LogUI provides easy access to simple predicates, to get the best from them, it’s worth digging a little deeper, as I do here.

Instant predicates

LogUI’s instant predicates filter log entries according to any of four basic predicate types:

• subsystem, such as com.apple.sharing, the field shown in yellow in log extracts;
• eventMessage, the text message listed in white/black at the end of each entry;
• processImagePath, such as mediaanalysisd, shown in blue, the name of the process making that entry;
• senderImagePath, such as libxpc.dylib, shown in red, the name of the process sending that entry.

These are quick to enter in the text box to the right of the popup menu in the window’s toolbar, but in many circumstances can prove too broad, and need narrowing down further. In other situations, you want to browse entries from two subsystems, or using a combination of criteria. The best way to do that is to write a short predicate. For single use, you can do that in the one-off predicate editor using the Set button.

When you want to reuse that, you can add it to the predicate popup menu using Settings Predicate (currently a bit kludgy).

Predicates

macOS can use predicates in other situations, most commonly for Spotlight search. If you’re interested in those, see Apple’s Predicate Programming Guide. Here I’ll describe predicates as they’re more commonly used to filter log entries, as they’re usually much simpler.

Each simple predicate consist of three parts:

• the name of one of the fields in a log entry, such as subsystem or eventMessage. This sets where the filter looks in each entry;
• an operator, which might be == for ‘equals’ exactly, or for text is commonly CONTAINS[c] for case-insensitive contains;
• text or a numeric value to look for, such as “error” or 513. Only those entries equalling or containing (or whatever the operator means) this in the specified field will then be returned from the log and displayed.

Here are some basic examples.

eventMessage CONTAINS[c] "error"
entries will only be those with the text error in their message field.

subsystem == "com.apple.duetactivityscheduler"
entries will all have that text, ignoring case, but only that text, as the name of their subsystem.

subsystem CONTAINS[c] "com.apple.xpc"
entries will have any subsystem containing that text, which also includes com.apple.xpc.activity.

Fields

Although you can use any of the fields shown in LogUI (and some that aren’t), the most commonly used are, in order as they are shown in LogUI’s window:

• eventType (red) – matches the type of event, such as logEvent (1024), traceEvent (768), activityCreateEvent (513), or activityTransitionEvent (514). Can be given as characters (case-sensitive) without quotation marks, or using the digits given in parentheses. Use these only with the operators == or !=, as they are treated as numbers rather than text.
• category (green) – this matches the category, and varies according to subsystem. This is given as text in quotation marks, and is normally lower-case.
• messageType (white/black) – matches the type of message for logEvent and traceEvent, and includes default (0), release (0), info (1), debug (2), error (16), and fault (17). Can be given as characters (case-sensitive) without quotation marks, or digits as shown in parentheses. Use these only with the operators == or !=, as they are treated as numbers rather than text.
• senderImagePath (red) – this matches the text pattern in the name of the sender, which might be the name of a library, extension, or executable.
• processImagePath (blue) – this matches the text pattern in the name of the process that originated the event.
• subsystem (yellow) – this matches the subsystem specifier, e.g. com.apple.TimeMachine, given as text in quotation marks. You may find it best to use CONTAINS[c] rather than ==, to allow for differences in case and extended subsystem specifiers.
• eventMessage (white/black) – for this, you specify a text pattern, or text, within the message, given as text in quotation marks.

Operators

The following comparisons and other operators are available:

• == (two equals signs) for equality
• != or <> for inequality
• >= or => for greater than or equal to
• <= or =< for less than or equal to
• > for greater than
• < for less than
• AND or && for logical and
• OR or || for logical or
• NOT or ! for logical not
• BEGINSWITH, CONTAINS, ENDSWITH, LIKE, MATCHES for string comparisons, using regex expressions when desired; strings can be compared with case insensitivity and diacritic insensitivity by appending [cd] to the operator, e.g. CONTAINS[c] means case-insensitive comparison
• FALSE, TRUE, NULL have their expected literal meanings.

There are others as well, but you’ll seldom use them to filter log entries.

Building complex predicates

To see the scheduling and dispatch of background activities by DAS-CTS, you need to look at log extracts showing both their entries. Use the predicate
subsystem == "com.apple.duetactivityscheduler" OR subsystem CONTAINS "com.apple.xpc"
to do that. The first part of it includes those entries from DAS, and the second includes those for XPC and its relatives that run CTS. Using an OR between the two parts combines both sets of entries in the one extract.

To see the reports posted by XProtect Remediator, you need to look at those entries made by its subsystem that have the right category, using the predicate
subsystem == "com.apple.XProtectFramework.PluginAPI" AND category == "XPEvent.structured"
Using the AND operator ensures that the only entries shown come from that one subsystem, and they are given just that category.

Time Machine involves a combination of different subsystems and messages. To get a good overview of relevant entries, you can use
subsystem == "com.apple.TimeMachine" OR
(subsystem == "com.apple.duetactivityscheduler" AND eventMessage CONTAINS[c] "Rescoring all") OR
(subsystem == "com.apple.xpc.activity" AND eventMessage CONTAINS[c] "com.apple.backupd-auto") OR
eventMessage CONTAINS[c] "backup" OR
eventMessage CONTAINS[c] "Time Machine" OR eventMessage CONTAINS[c] "TimeMachine"
I’ve broken this down into separate lines, but you shouldn’t do that in the predicate. Taking it line by line it becomes simpler to understand. Use parentheses () to group each part of the predicate carefully as shown.

You can see other examples in the Help book for my free utility Mints: the Further Information pages towards the end give each of the predicates that Mints uses for its log extracts.

Quick summary

• [field name] [operator] [text or numeric value]
• common field names: senderImagePath, processImagePath, subsystem, eventMessage
• common operators: ==, CONTAINS[c]
• filter info: “text”
• combine filters using AND, OR.

In the late nineteenth and early twentieth centuries, there were three dominant painters who flirted with Impressionism but retained conventional styles: Anders Zorn from Sweden, Joaquín Sorolla from Spain, and John Singer Sargent, an American expatriate who worked from studios in Paris and London. All three died in the 1920s, and this year we commemorate the centenary of Sargent’s death on 14 April 1925. This is the first in a series of six articles outlining his career with but a small and personal selection of his paintings.

Sargent was born to American expatriate parents in Florence, Italy, in 1856. He was educated at home and showed early skill in drawing. Already competent in watercolour at the age of 14, he saw many of the works of the great Masters during travels around Europe with his family. In 1874 he succeeded in gaining admission to the École des Beaux-Arts in Paris, where he was taught mainly by Carolus-Duran, and less by Léon Bonnat.

Although his initial enthusiasm was for landscapes, Carolus-Duran encouraged him towards portraiture, and his first significant portrait was accepted by the Salon in 1877. His talent was recognised by the critics, and he made friends with Julian Alden Weir and Paul César Helleu, who in turn introduced him to other leading artists of the day, including Degas, Rodin, Monet, and Whistler.

Sargent’s early style was realist, particularly in portraiture, and leaned towards Impressionism as seen in this painting of Fishing for Oysters at Cançale from 1878, but was quite distinct from the work of the leading Impressionists at that time. In the summer of 1878, John Singer Sargent had just completed his studies with Carolus-Duran, and went off on a working holiday to Capri, staying in the village of Anacapri, as was popular with other artists at the time.

Capri was still quite a select holiday destination then, and unspoilt. But getting a local model was tricky, because of the warnings that women were given by priests. History has proved those priests only too right in their advice. One young local woman, Rosina Ferrara, seemed happy to pose for him, though. She was only 17, and Sargent a mere 22 and just developing his skills in portraiture. Over the course of that summer, Sargent painted at least a dozen works featuring young Rosina, who seems to have become almost an obsession with him.

One, Dans les Oliviers, à Capri, above, he exhibited at the Salon the following year. A near-identical copy A Capriote, below, he sent back for the annual exhibition of the Society of American Artists in New York, in March 1879. The latter is now in the Museum of Fine Arts in Boston.

He also painted a pair of views of what was probably the roof of his hotel. In View of Capri, above, made on cardboard, Rosina stands looking away, her hands at her hips. In the other, Capri Girl on a Rooftop, below, she dances a tarantella to the beat of a friend’s tambourine. The latter painting Sargent dedicated “to my friend Fanny”, presumably Fanny Watts, who modelled for the first portrait that Sargent had exhibited at the Salon the previous year.

Rosina appears to have danced for Sargent again, for him to paint her in Portrait of Rosina Ferrara, above, as a precursor to his later paintings of Spanish dancers. But of all Sargent’s paintings of Rosina, the finest portrait, possibly one of the finest of all his ‘quick’ portraits from early in his career, is another painted in oils on cardboard: Rosina Ferrara, Head of a Capri Girl, below.

This he dedicated to “Hyde” (the artist Frank Hyde), and signed in 1878, while he was still on Capri. There are another couple of portraits he painted of a young woman during that summer on Capri. Although she’s in more serious mood, possibly even a little surly with ennui, I wonder if they also show Rosina Ferrara.

Sargent left Capri, eventually returning to Paris and his inexorable rise to greatness, fortune and success. But that wasn’t the end of Rosina’s modelling career, not by a long way. Frank Hyde, to whom Sargent had dedicated a portrait of her, painted his own version a couple of years later.

Sargent’s famous Portrait of Carolus-Duran (1879) is not only his personal tribute to his teacher, but when it was shown at the Salon proved the foundation of Sargent’s own career as a portraitist.

He continued to travel in Italy and Spain, where in 1880 he painted Smoke of Ambergris, demonstrating what was to come beyond mere portraits.

I’ve long been critical of some of the best-selling utilities for the Mac, that set out to perform deduplication of files by detecting which appear to be identical, and removing ‘spare’ copies. This is because APFS introduced clone files, and in the right circumstances those take up no space in storage, as their data is common and not duplicated at all. As it’s practically difficult to tell whether two files are clones, any utility or command tool that claims to save space by removing duplicates can’t tell you the truth, and in most cases won’t save as much space as it claims.

Claims made by those utilities are often exaggerated. This is because they calculate how much space they think they’ve saved by adding the sizes of the potential duplicates they have deleted. That’s not correct when a clone file is deleted, as that doesn’t actually free any space at all, even though the clone file has exactly the same nominal size as the original.

Benefitting from clone files

I’m delighted to see the eminent John Siracusa turn this on its head and finally make better use of clone files in his app Hyperspace, available from the App Store. Instead of deleting clones, his app can replace duplicate copies with clones, and so achieve real space savings. This comes down to simple arithmetic:

• if you have two copies (not clones) of a file in the same APFS volume, the total size they take on disk is twice the size of one of them;
• if you have two clones (not copies) of a file in the same APFS volume, the total size they take on disk is only the size of one of them, as its clone takes no additional space at all.

Hyperspace thus checks all the files in a selected folder, identifies which are identical copies, and (where suitable) will replace those copies (except an original) with clones, so saving real storage space.

I also think it has the most user-friendly payment scheme: download Hyperspace free of charge and check your Mac with it. If it doesn’t find sufficient savings, and you decide not to use it to replace any duplicates with clones, then it costs you nothing. If you want to reclaim that space, then you can opt to pay according to the amount of space it saves, by subscription, or with a one-time payment. On that basis, I unhesitatingly recommend everyone to download it from the App Store, and at least check their Home folder to see if it’s worth paying to reclaim space. You have absolutely nothing to lose.

In my case, perhaps because I tend to clone files using the Finder’s Duplicate command, the savings that it offered were of little benefit, but your Home folder could be different and release 100 GB or more.

Sparse files

The other space-saving special file type in APFS is the sparse file. Although it can bring great savings in storage space, that’s largely up to the app(s) that create and maintain the file, rather than the user. Devising an app that could go round converting plain to sparse files is harder, and risks incompatibility with those apps that access those files.

Fitting 285 GB into 16.5 GB

As a demonstration of how effective APFS special files are in saving disk space, I built myself a 100 GB partition (APFS Container) on an SSD and tried to fill it with clone and sparse files until I got bored.

At this stage, the 100 GB partition contains:

• One 16.5 GB IPSW image file, with nine clones of it, created using the Duplicate command.
• Eleven 10 GB sparse files and one clone, created using my app Sparsity.

Add those file sizes together and they come to 285 GB, yet the 100 GB partition only has 16.5 GB stored on it, and still has over 83 GB free. No compression is involved here, of course.

As the saying goes, there ain’t such as thing as a free lunch, and that free space could vanish quickly depending on what happens to those files. The worst case is for an app not to recognise sparse files, and write one to disk in plain format, so swallowing 10 GB at once. Editing the cloned files would be a more gradual way of their growing in size. Only changed data would then need to be saved, so free disk space would steadily fall as more changes were made to the clone.

Clone and sparse files are by no means unique to APFS, but they can be impressive, and above all they’re effective at reducing excess erase-write cycles that age SSDs, whatever you do with the storage they free.

I’m very grateful to Duncan for drawing my attention to Hyperspace, and to John Siracusa for an outstanding app.

Apple has just released an update to XProtect for all supported versions of macOS, bringing it to version 5292. As usual, Apple doesn’t release information about what security issues this update might add or change.

This version removes the macos_toydrop_b rule for MACOS.ADLOAD, and amends the rules for MACOS.ADLOAD.I, MACOS.BUNDLORE.MDPLST and MACOS.ADLOAD.IN.

You can check whether this update has been installed by opening System Information via About This Mac, and selecting the Installations item under Software.

A full listing of security data file versions is given by SilentKnight, LockRattler and SystHist for El Capitan to Sequoia available from their product page. If your Mac hasn’t yet installed this update, you can force it using SilentKnight, LockRattler, or at the command line.

If you want to install this as a named update in SilentKnight, its label is XProtectPlistConfigData_10_15-5292.

Sequoia systems only

This update has now been released for Sequoia via iCloud. If you want to check that manually, use the Terminal command
sudo xprotect check
then enter your admin password. If that returns version 5292 but your Mac still reports an older version is installed, you can force the update using
sudo xprotect update

I have updated the reference pages here which are accessed directly from LockRattler 4.2 and later using its Check blog button.

As today is the first day of April, it’s a double danger: as the first of the month you should say rabbit or white rabbit when you first wake up, and it’s All Fools’ Day as well. I have no hoaxes for you this year, I promise, but I do have rabbits, some of them white, and a few hares as well. Rabbits and hares are relatively infrequent in paintings, and where they do occur they seldom have any deeper reading.

Because they’re so familiar, they appear in animal gatherings.

In the left panel of Hieronymus Bosch’s Garden of Earthly Delights (c 1495-1505) is a curious mixture of real and imaginary creatures. There’s an elephant and a giraffe, both early depictions of those species, together with monkeys, brown bears, rabbits, and more, even a white unicorn drinking at the lake on the left.

Among the many superb animal paintings of Paulus Potter, Orpheus and Animals from 1650 is one of his most unusual, showing a wide range of different animal species, some of which weren’t well-known at that time, and one of which (the unicorn) didn’t even exist. Those seen include a Bactrian camel (two humps), donkey, cattle, ox, wild pig, sheep, dog, goat, rabbit, lions, dromedary (one hump), horse, elephant, snake, deer, unicorn, lizard, wolf, and monkey.

In Tintoretto’s Creation of the Animals, the first of his Old Testament cycle for the Scuola della Trinità in Venice, God flies along as he creates pairs of different species of bird, fish, and animal, from cormorants to rabbits.

Among their leading roles is in Elihu Vedder’s delightful painting of the unfortunate Marsyas.

Late in 1877, Carrie Vedder, the artist’s wife, recorded in a letter that her husband had been thinking about Marsyas, and considered that, before the contest with Apollo, Marsyas must have proved his skill with the aulos. He therefore came up with the idea that this must have at least been charming hares with the instrument. He started this painting early in 1878, setting it in the New England winter. This was shipped to Paris for show at the Exposition Universelle later that year, but Vedder was disappointed that it didn’t do well there.

The hare is known from fable for its speed, although not so much when racing against a tortoise.

At some time during the first half of the seventeenth century, Frans Snyders painted the still popular Fable of the Hare and the Tortoise. The tortoise and the hare disputed which of the two was the faster, so agreed to run a race against one another. Although the hare was much faster when running, he laid down beside the path and slept. The tortoise, being aware of his relative slowness, ran as fast as he could, past the sleeping hare, until he won. Snyders shows the hare at full pelt, and the tortoise crawling away in the distance, giving little clue as to the surprising outcome or its cause.

JMW Turner alludes to this fable in his Rain, Steam and Speed – The Great Western Railway from 1844.

Running ahead of this very early steam locomotive as it crosses the River Thames at Maidenhead is a hare, barely visible at the lower right.

Perhaps the most famous painted hare appears in one of Albrecht Dürer’s watercolour masterpieces, dated to 1502.

Following this tradition, one of Bruno Liljefors’ favourite species was the elusive hare. This page of Hare Studies from 1885 shows a tiny part of the image library he assembled, as well as their spring antics.

Unlike the common rabbit, some hares become white for the winter. This is one of the many paintings that Liljefors made of a Winter Hare, here from 1910.

Both hares and rabbits have been traditional meats, and there are several still life and hunting paintings depicting them dead and being prepared for a meal.

Several of Chardin’s small output of about 200 paintings included hanging game, here an undated Rabbit and Copper Pot, elsewhere hares and others.

The rise of the sciences during the nineteenth century didn’t spare rabbits from being used in physiological experiments.

Following the death of the physiologist Claude Bernard, the Sorbonne (where he had taught) commissioned Léon Lhermitte to paint his portrait in 1886. Sadly I’ve been unable to trace an image of the original, but Claude Bernard and His Pupils is a faithful copy of the painting that Lhermitte exhibited at the Salon in 1889. This shows Bernard in the midst of performing an experiment on a rabbit, his students discussing its results, and one writing the experimental observations in the laboratory daybook.

Rabbits have been favourites with children, and kept as domestic pets. From there they appear in some of the most surprising places.

Johann Eleazar Zeissig shows A Family Making Chinese Shadows in his painting from the late 1700s. A family are entertaining themselves late in the evening with the aid of a lamp as a point source of light. An older boy is tracing the silhouette of his mother on a sheet of paper which he holds on the wall behind her. At the upper right are examples of his ‘shadowgraph’ drawings. Three younger children are holding up their hands to form the silhouettes of a rabbit and a cat, clichés of childhood.

August Macke’s Little Walter’s Toys from 1912 includes two of the favourite family pets, a rabbit and guinea pig.

My last guest appearance of a white rabbit is the most curious of all.

JMW Turner painted this narrative landscape of The Bay of Baiae, with Apollo and the Sibyl in 1823. Apollo is on the left, with his lyre, and the dark-haired Sibyl has adopted an odd kneeling position. She’s holding some sand in the palm of her right hand, asking Apollo to grant her as many years of life as there are grains. Opposite the couple, on the other side of the path, under the trees, is a white rabbit.

Maybe it was just the first day of the month.

By anyone’s standards, the macOS log contains a great many entries, and being able to filter out the noise is essential. This is accomplished by applying predicates to determine which entries are extracted and shown in a log browser like LogUI. However, using predicates requires knowledge about the log and its entries, and forms the greatest barrier for most users. This new version of LogUI improves features to help you use predicates to make the log more accessible.

This all happens in the toolbar of its browser window.

The section at the left of the lower row of tools now provides two methods to apply your own predicates: a one-off predicate editor, and an editor for custom entries in its popup menu.

One-off predicates

Click on the Set button to open the one-off predicate editor.

Here you can compose and paste in your own custom predicates that will extract only the log entries that you’re interested in. In this example, only entries whose subsystem is com.apple.duetactivityscheduler, or contains com.apple.xpc, will be gathered and displayed. Those tell you what’s going on with DAS and CTS scheduling and dispatch of background activities.

LogUI keeps that one-off predicate, even after a restart, as it’s automatically written to its preference file.

Once you’ve clicked Save, selecting the [ … ] item in the predicate menu will apply that predicate to each log extract you obtain.

There’s also an additional standard predicate using the senderImagePath.

Custom menu predicates

Predicates listed in that menu below blowhole are custom predicates saved to LogUI’s preferences using its new Predicate tab in its Settings. This editor is very basic at the moment, and its use a little awkward. This is because SwiftUI much prefers menu contents to be static, so adding items to the predicate menu doesn’t go down too well. This editor allows you to add one predicate at a time, in plain text format.

Click on the Append button here and there’ll be a new predicate named XProtect Remediator with the predicate shown. You can only add one new predicate, then need to quit the app before adding another. I’m sorry that’s so laborious, but once you have set up your custom predicates you can return to using LogUI fully.

The Settings General pane now contains a button to Reset Predicates back to their defaults.

Predicates

A basic predicate is composed of a log field name, like subsystem, followed by an operator such as == (equals) or CONTAINS[c] (case-insensitive contains), and a filter term, usually a string like "com.apple.xpc". So the predicate
subsystem CONTAINS[c] "com.apple.xpc"
will return all log entries with their subsystem containing the text com.apple.xpc. You can combine those basic elements into a more selective predicate using combinators such as AND and OR, so
subsystem == "com.apple.duetactivityscheduler" OR subsystem CONTAINS|c] "com.apple.xpc"
returns entries with a subsystem of precisely com.apple.duetactivityscheduler together with those whose subsystem contains the text com.apple.xpc.

Some years ago I wrote a primer here, and you’ll find some useful predicates in the Further Information section in the Help book for Mints. I’ll be writing more here to help you get the best out of LogUI.

There are a couple of oddities with predicates. SwiftUI tends to like using typographic double-quotation marks, but the macOS predicate builder doesn’t accept them as a substitute for straight marks. So LogUI changes all styled marks to straight ones automatically for you, to ensure those shouldn’t cause a problem. However, when it encounters errors it can behave erratically; while I’m trying to make this more robust, I apologise in advance if using a broken predicate upsets LogUI. It’s worth being careful to check your predicates before trying to use them.

LogUI version 1.0 build 37 is now available from here: logui137

My next task is to improve editing and saving predicates to its preferences, to make them accessible as menu customisations.

Apple has just released the update to macOS Sequoia to bring it to version 15.4, and security updates for 14.7.5 and 13.7.5.

The Sequoia update for Apple silicon Macs is about 6.2 GB in size, and 3.9 GB for Intel models, making it one of the largest intermediate updates for some years. For Apple silicon Macs, the update to 14.7.5 is about 3.7 GB, and to 13.7.5 about 3.3 GB.

Among the changes listed by Apple for 15.4 are:

• Adds Memory movies in Photos using AI.
• Adds a Sketch Style option in Image Playground, in AI.
• Adds Mail Categorisation.
• Apple silicon Macs with an internal SD card reader now support SDUC cards larger than 2TB.
• This should resolve problems with some M4 Macs being unable to launch Virtual Machines.
• Content filter extensions correctly receive non-TCP/UDP network protocol traffic.
• Finder no longer fails to copy some dataless files from SMB file shares.

Enterprise release notes are here.

Software Update settings will be automatically changed to enable future macOS updates to be downloaded and installed automatically: if you don’t want that, you’ll need to change that setting once your Mac boots in 15.4.

Security release notes are available for Sequoia, Sonoma and Ventura updates. There are a total of 131 vulnerabilities fixed in 15.4, which must be a record. None is reported as being suspected of exploitation in the wild, and the security updates for Sonoma and Ventura are almost as numerous.

Firmware updates include iBoot (Apple silicon) to version 11881.101.1, and T2 Macs to 2075.101.2.0.0 (iBridge 22.16.14248.0.0,0). The macOS build number is 24E248.

The new version of Safari in 15.4 is 18.4 (20621.1.15.11.10). APFS is updated to version 2332.101.1.

As so much has changed, I won’t be posting a separate article listing significant changes: it looks like pretty well everything has!

Just for reference, the Sequoia 15.0 major version upgrade from Sonoma was 6.6 GB for Apple silicon, and 4.9 GB for Intel – those aren’t that much larger than this ‘minor version update’.

Those intending to update Apple silicon Virtual Machines currently running 15.3.2 should be prepared for the 15.4 update to fail. I’ve tried with two VMs now, one with a fresh copy of 15.3.2, and both have failed early during installation with a kernel panic. However, 15.4 does install correctly from the latest IPSW image file. Older VMs with 14.7.4 and 13.7.4 do update correctly to 14.7.5 and 13.7.5 respectively.

[Last updated 1715 GMT 1 April 2025.]

By the end of Book 13 of Ovid’s Metamorphoses, Aeneas is on the island of Sicily. Scylla has been combing Galatea’s hair, listening to her tell the tragic story of the death of her lover Acis. Ovid resumes the narration for the tale of Scylla, which doesn’t conclude until the start of the next book.

Scylla is walking naked along the beach when the figure of Glaucus suddenly breaks the surface of the water. He’s immediately enchanted by her, and tries to engage her in conversation to stop her from running away. But Scylla runs away in terror, and climbs a nearby cliff. There, she gets her breath back, and tries to work out whether he’s a god or monster with long hair and fishy scales below the waist.

Glaucus assures her that he’s a sea-god. He had once been an ordinary mortal, and fished with nets, and rod and line. One day, the fish that he had caught started to move when he had laid them out on the grass, and one by one they escaped back into the water. He couldn’t understand how that had happened, so chewed stems of the plants they had rested on. He was then transformed and swam off in the sea to visit the gods Tethys and Oceanus for removal of the last remains of his mortal form.

Scylla runs away, leaving Glaucus angry, so he makes his way to the sorceress Circe.

Bartholomeus Spranger painted his version of Glaucus and Scylla in 1580-82. Although the artist hasn’t followed Ovid’s distinctive colour scheme for his body, Glaucus is clearly pleading his case before the beautiful young woman. In the next book, Ovid will describe how Scylla was turned into a rock, and Spranger provides that link forward in the story in his background.

In the middle of the seventeenth century, Salvator Rosa makes Glaucus more of a beast, roughly mauling Scylla’s fair body and giving her good cause for her flight to the cliff.

A little later, probably in the late seventeenth century, Nicola Vaccaro is more sympathetic in his Glaucus fleeing from Scylla. Glaucus may be a bit rough, but arouses more pity. Scylla is accompanied by three Cupids as she flees not to the top of a cliff, but to the goddess Diana above.

The most interesting and unusual depiction of this story is surely JMW Turner’s from 1841, just a decade before his death.

Turner’s Glaucus and Scylla (1841) would perhaps have looked more at home among paintings made fifty or even eighty years later.

The naked Scylla is on the beach at the right, with a couple of cupids flying about. The inchoate form of Glaucus is emerging to the left of centre, holding his arms out towards Scylla. She will have none of it, though, and has already turned to run, and looks back over her shoulder towards him.

We look directly into the setting sun colouring the world a rich gold. In the right background the low coastal land rises to sheer cliffs with a temple on top. A tower atop a nearer pinnacle, or more distant lower red rocks, may be a reference to Scylla’s fate.

In the foreground are clues of the beach setting, with a crab, and several seashells. Turner has applied his paint in innovative and gestural ways, resulting in richly varied textures.

Turner had made an earlier and more traditional study in about 1810-15, but revised it almost completely by the time that he painted this in 1841. Its light appears influenced by the harbour landscapes of Claude, and its general lack of form anticipates Impressionism, perhaps even Abstract Expressionism in passages.

Rejected by the scared Scylla, Glaucus travels from Sicily to visit the sorceress Circe, whom he implores to use her dark arts to force Scylla to return his love. But Circe refuses, telling Glaucus to woo another: as she is in love with him, he could spurn Scylla and love Circe instead.

Glaucus rejects her, saying that nothing will change his love for Scylla. That annoys Circe, who cannot harm Glaucus because of her love for him, so turns her anger on Scylla instead. The sorceress prepares a magical potion from herbs, weaving her spells into it. Dressed in a deep blue robe, she then goes to a small bay where Scylla likes to bathe, and pours her potion into the water.

When Scylla wades into the water the lower half of her body is transformed into a pack of dogs. As Ulysses’ ship passes her, those dogs take some of its crew, but they allow Aeneas to pass safely. Scylla is finally transformed into a rock and becomes a famous hazard to navigation.

John William Waterhouse chose to portray the figure of Circe the sorceress in his Circe Invidiosa (1892). Despite its narrative limitations, this offers a marvellous insight into the character of Circe, as she pours her brilliant emerald green potion into the water, ready for Scylla to come and bathe.

John Melhuish Strudwick also chooses a moment early in Ovid’s story, which makes his painting of Circë and Scylla (1886) narratively rather thin. Circe, dressed in brown rather than blue, is sprinkling her potion into the water from within a small cave, as Scylla, at the left, walks down to bathe.

By far the most complete visual account is Eglon van der Neer’s Circe Punishes Glaucus by Turning Scylla into a Monster (1695). Circe takes the limelight, as she casts her potion from a flaming silver salver held in her right hand. Dripping onto that is the wax from a large candle, held in her left hand. In the water below, Scylla has already been transformed into a gorgonesque figure, with snakes for hair, and the grotesque Glaucus watches from behind. Above and to the right of Circe is a small dragon perched on a rock ledge.

Ary Renan’s Charybdis and Scylla (1894) shows Charybdis the whirlpool with its mountainous standing waves at the left, and the rocks of Scylla at the right.

This fragment of fresco by Alessandro Allori shows Odysseus’ ship passing Charybdis, depicted as a huge head vomiting forth the rough waters of the whirlpool at the right, and the dogs’ heads of Scylla, which have captured three of Odysseus’ crew.

Henry Fuseli’s Odysseus in front of Scylla and Charybdis (1794-96) is another vivid depiction of Odysseus passing the twin dangers. He stands on the fo’c’s’le of his ship, holding his shield up in defence as the oarsmen down below him struggle to propel the craft through the Straits of Messina.

I hope that you enjoyed Saturday’s Mac Riddles, episode 301. Here are my solutions to them.

1: Roll pasted on the interior background.

Click for a solution

Wallpaper

Roll pasted on the interior (what wallpaper is) background (it sets the Desktop, and replaced Desktop & Screen Saver).

2: Secure partition for the idle display.

Click for a solution

Lock Screen

Secure (to lock) partition (a screen) for the idle display (it sets what is shown on the display when it’s idle).

3: Pastime bull’s-eye for the player.

Click for a solution

Game Center

Pastime (a game) bull’s-eye (a centre) for the player (it enables access to game features).

The common factor

Click for a solution

They were all introduced in macOS Ventura’s System Settings, but weren’t in System Preferences.

I look forward to your putting alternative cases.

Most modern Macs start up from their internal SSD, and have a single bootable system installed. Although its structure has changed considerably over recent years, and differs between Intel and Apple silicon Macs, they are generally reliable, and knowledge of their structure and function is seldom required.

Those who need to start their Mac up from two or more versions of macOS, or who do so from an external disk, may be able to get by without deeper understanding, but the moment there’s a problem can become confused, and end up having to install macOS from scratch.

Intel T2 and Apple silicon

Both types of Mac are designed to support Secure Boot, but because of the reliance of Intel Macs on UEFI firmware, they can only boot securely from their internal SSD. Enabling an Intel T2 Mac to start up from an external disk thus requires its boot security to be reduced by changing that in Startup Security Utility, in Recovery mode. Booting from an external system is then straightforward, and doesn’t require additional security measures as used in Apple silicon.

Apple silicon Macs have been designed from the outset to support Secure Boot when starting up from both internal and external disks, and don’t require any reduction in their boot security to be able to start up from multiple systems on external SSDs. It’s a common misunderstanding that trying to change Boot Security in Startup Security Utility can help solve Apple silicon boot problems, but if anything it only complicates them. Almost the only good reason for reducing boot security of an Apple silicon bootable system is when third-party kernel extensions are required. Otherwise don’t tamper with Startup Security Utility, as it will only confuse, as we’ll see later.

For an Apple silicon Mac to boot from a macOS system, that must have a LocalPolicy created and saved to the internal SSD. LocalPolicy is normally created during macOS installation, or when intending to start up from a suitably installed system. Problems with LocalPolicy have been common when using external disks, and are covered in these articles:

• Checking bootable systems using bputil on Apple silicon
• Booting macOS on Apple silicon: LocalPolicy
• Booting macOS on Apple silicon: Multiple boot disks
• Apple’s Platform Security Guide here and here.

Boot disk architecture

Another significant difference between Intel and Apple silicon Macs is the architecture of their internal SSDs: Apple silicon has two additional partitions (APFS containers), and lacks the traditional EFI partition. However, there are no such differences in the structure of their bootable external disks, and its relevance here is limited, and mainly affects Big Sur as I explain below.

macOS 10.13-10.15

Bootable disks in versions of macOS between High Sierra and Mojave (above) are based on their single boot volume, supplemented by hidden Preboot, Recovery and VM volumes. macOS 10.15 Catalina (below) divided that boot volume into a Boot Volume Group, consisting of paired System and Data volumes, in addition to the same three hidden volumes.

Basic support for volume roles was introduced in the first release version of APFS in macOS 10.13, and was extended to cover further roles in 10.15. Thus versions of APFS prior to 1412.x.x don’t understand volume roles used by subsequent systems. From Catalina onwards you can use the command
diskutil apfs listVolumeGroups
to see paired System and Data volumes, for example
+-- Container disk5 5BA1AAC8-3AD4-4594-AF01-7C0AA75CABAD
| |
| +-> Volume Group 68627CBB-D774-444E-97C6-F9511B5030F3
| =================================================
| APFS Volume Disk (Role): disk5s1 (Data)
| Name: Macintosh HD - Data
| Volume UUID: 68627CBB-D774-444E-97C6-F9511B5030F3
| Capacity Consumed: 580769214464 B (580.8 GB)
| -------------------------------------------------
| APFS Volume Disk (Role): disk5s5 (System)
| Name: Macintosh HD
| Volume UUID: 8B9FF440-75C8-4F7F-B09E-9222D44A2276
| Capacity Consumed: 11239186432 B (11.2 GB)

Note that each volume group has its own UUID, which is normally the same as that of the Data volume in the pair. Identification of volumes, containers and other structures in APFS is dependent on these UUIDs, which are an essential part of the GUID Partition Table scheme used to partition disks.

Catalina’s System volume is mounted read-only, but macOS is booted from that volume rather than the Signed System Volume snapshot introduced in Big Sur.

macOS 11

Although the structure of Big Sur internal SSDs in Apple silicon Macs has two additional partitions (APFS containers), Apple_APFS_ISC containing three volumes, and Apple_APFS_Recovery containing two volumes, bootable external disks have the same structure as the internal SSD in Intel Macs.

One important functional difference, which remains relevant to Big Sur boot disks, is that Apple silicon Macs don’t use the paired Recovery volume as their primary Recovery system: booting an Apple silicon Mac running Big Sur into Recovery should instead use the Recovery system installed in their internal SSD, in the Apple_APFS_Recovery partition. In subsequent versions of macOS, that’s used instead for secondary or Fallback Recovery. Thus Big Sur can be a problem when it comes to Recovery, and for this reason is best avoided on Apple silicon Macs. If it’s essential to install a copy of Big Sur, then be prepared for problems with Recovery mode.

macOS 11 also established the architecture for dual-boot partitions, with two or more Boot Volume Groups.

Although the Boot Volume Group has only ever referred to paired System and Data volumes, within each partition/container the group also requires three or four additional volumes, for Preboot, Recovery, VM and (apparently in Big Sur only) Update. How those work with multiple Boot Volume Groups is explained below. Once way to avoid the inevitable complexities is to install each Boot Volume Group into a separate partition/container, which provides each with its own suite of Preboot, Recovery and VM volumes.

As the Signed System Volume (SSV) was introduced in macOS 11, versions of APFS prior to 1677.x.x shouldn’t be expected to understand SSVs.

macOS 12-15

The next significant architectural changes in Apple silicon Macs were the introduction of paired Recovery volumes in macOS 12 Monterey, and of cryptexes in macOS 13 Ventura.

In macOS 11 and 12, Safari, its supporting components, and some other parts of macOS are installed to the Data volume for ease of maintenance. Apple replaced that with separate secure disk images termed cryptexes, loaded from the Preboot volume during the boot process and grafted into the root file system. As a single Preboot volume can be shared by more than one Boot Volume Group, bundled cryptexes must be provided to the correct group, and I suspect that’s accomplished by associating them with their Volume Group UUID. If that becomes confused in any way, cryptexes could be incorrectly associated or missing altogether, something that’s almost certainly fatal to the boot process.

Above is the current layout of a partition/container containing a single bootable system for a Mac running Sequoia. Device names given are illustrative, although their numbering is typical of that seen for external bootable volumes. In this instance, the base name for the Boot Volume Group is External, and the External System volume is unmounted as usual.

Below is a typical partition/container containing two bootable systems named ExternalA and ExternalB. This has two Boot Volume Groups, each consisting of a System volume with its SSV, and a Data volume, to which are added their three common volumes, Preboot, Recovery and VM.

Management

Creation

The most reliable tools for creating and working with Boot Volume Groups and other system components are those in macOS installer apps, and even they can have their moments and bugs. It’s usually possible to ‘clone’ groups using the asr command tool, a feature that’s offered in some third-party utilities including Carbon Copy Cloner and SuperDuper. However, Apple has made it clear that given a choice between supporting asr and addressing boot security, it gives the latter absolute priority. asr has suffered some serious bugs since the SSV was introduced in Big Sur, and shouldn’t be relied on.

asr is careful to ensure that, when cloning Boot Volume Groups, UUIDs are changed so that it doesn’t end up with volumes or groups with the same UUID. That may not be the case when using some other tools such as dd for duplication. If you prefer a simple and stress-free life, it’s better to put your trust in a macOS installer rather than try crafting your own Boot Volume Groups.

Apple’s own tools such as Disk Utility now try to steer the user away from making mistakes, such as deleting just one of a Boot Volume Group, leaving the other orphaned with its firmlinks broken.

Firmware

Firmware is another source of confusion. That installed in the Mac, using its internal storage, should always reflect the firmware that has been included in the most recent version of macOS installed or updated on that Mac, whether that was installed to the internal SSD or to an external disk. The only exception to this is when installing or updating macOS in a Virtual Machine, which can’t affect the host’s firmware.

What may appear more puzzling are the versions reported in System Information: that given as System Firmware should be the iBoot version for the main Mac, and the most recent. The OS Loader, though, varies with the Boot Volume Group, and in older macOS is likely to be earlier than the iBoot version of the main Mac.

Recovery

Recovery system versions are even more complex. When everything works as it should, the version installed in any paired Recovery volume should be the newest of the Boot Volume Groups that it’s paired with, in the same partition/container. If a Mac running 15.3 from its internal SSD has a bootable external disk with a single container with two Boot Volume Groups for 13.7 and 14.7, then the Recovery system for the internal SSD should be 15.3, while that shared by the two systems on the external disk should be 14.7. It’s likely that Fallback Recovery on the internal SSD will be from an earlier version of macOS 15, but that’s less predictable, and there’s no separate Fallback Recovery in external systems.

Switching between systems and their Boot Volume Groups is normally performed using Startup Disk in General settings, or its equivalent in System Preferences. Those record the chosen Boot Volume Group in NVRAM, from where it’s used during the next boot.

That setting is used to determine which Recovery system is used if the next boot is performed with the Power button pressed to enter Recovery mode. That in turn determines what can be performed in Recovery. This is most critical for determining how Startup Security Utility works, as that can only change boot security settings for the chosen Boot Volume Group saved in NVRAM.

For example, in the dual-boot container shown above, selecting ExternalB as the Startup Disk, shutting down, then starting up into Recovery mode should enable Startup Security Utility to control boot security for ExternalB but not ExternalA, nor the system installed on the internal SSD. This can be used to discover which Recovery system is running: open Startup Security Utility and the only boot system that can be changed there is the current default boot system.

APFS

Although APFS should be backward compatible, making it relatively safe to make changes to an older version of APFS from a newer system, forward compatibility is more limited. Using older versions of Disk Utility or tools like fsck on newer versions of APFS risks errors, failure and at worst damage. The Appendix at the end of this article summarises version numbering in APFS and major changes to beware of. Although not easy to discover the version of APFS used to create or modify any given volume, one way is to use
fsck_apfs -n -S [device]
giving the volume’s device name. The report should then be prefaced by a statement such as
The volume [volume name] was formatted by diskmanagementd (1412.141.1) and last modified by apfs_kext (945.250.134).
telling you that volume was created by macOS 10.15, and was last changed by macOS 10.14.

Troubleshooting

The first and fundamental step in trying to diagnose the cause of problems with multiple Boot Volume Groups or bootable external disks is to examine their container and volume structure using two diskutil commands:
diskutil apfs list
lists all APFS volumes by container and gives key information about each, including role and UUID, and
diskutil apfs listVolumeGroups
lists all recognised Boot Volume Groups, which you can tally against the first. Pipe these to text files so you can study and refer back to them.

Those should enable you to verify that the structure is as intended, and to establish the relationships between systems and paired Recovery volumes. From there you should be able to focus on the Boot Volume Group that’s misbehaving, ensuring that its Data volume has been backed up. If necessary, that can be used as a migration source if that group needs to be deleted and reinstalled.

Tips & tricks

• The host Mac must be capable of running that version of macOS.
• macOS installers are the most reliable means of creating and installing Boot Volume Groups.
• During macOS installation, an external disk must be connected to a port other than the DFU port, as listed here and in Mactracker.
• When installing an older major version of macOS, perform this from an external bootable HFS+ volume as detailed by Apple.
• Use an HFS+J partition on an external SSD rather than a USB ‘thumb’ drive.
• Boot from an installer volume through Recovery mode.
• When using a laptop Mac, run it from mains power throughout macOS installation.
• Apple silicon Macs boot from external disks in Full Security, and reducing that doesn’t solve any problems.
• Each container with one or more Boot Volume Groups contains one set of Preboot, Recovery and VM volumes shared between them.
• If you’re unsure which Recovery system you’re using, open Startup Security Utility, as the only group it can change settings for is the one it’s booted into.
• Big Sur doesn’t support paired Recovery on Apple silicon, and that can cause problems.
• The version of Recovery installed in any paired Recovery volume should be that of the newest of the Boot Volume Groups that it’s paired with.
• Use fsck_apfs -n -S [device] to discover the APFS version.
• Use diskutil apfs list and diskutil apfs listVolumeGroups to discover volume structure.
• Try using a Virtual Machine instead, if you don’t need to be able to run software from the App Store.

Appendix: APFS version numbers

APFS major version numbers change with major version of macOS:

• macOS 10.12 has APFS version 0.3 or 249.x.x, which shouldn’t be used at all.
• 10.13 has 748.x.x, which doesn’t support Fusion Drives, but has basic support for volume roles.
• 10.14 has 945.x.x, the first version to support Fusion Drives.
• 10.15 has 1412.x.x, the first version to support the multi-volume boot group, and introduces extended support for volume roles, including Data, Backup and Prelogin.
• 11 has 1677.x.x, the first version to support the SSV, and Apple silicon. On M1 Macs, it doesn’t support the paired Recovery volume.
• 12 has 1933.x.x until 12.2, thereafter 1934.x.x, which support the paired Recovery volume on Apple silicon.
• 13 has 2142.x.x, and is probably the first to support trimming of UDRW disk images and their storage as sparse files.
• 14 has 2235.x.x, until 14.3, thereafter 2236.x.x.
• 15 has 2313.x.x until 15.2, thereafter 2317.x.x until 15.4, thereafter 2332.x.x.

Following a series of disastrous defeats of the French Army, on 19 September 1870, Prussian forces had taken control of the country around Paris, and put the capital under siege. With the surrender of the French Emperor Napoleon III, a provisional republican government had been established, and ushered in the Third Republic as successor to the Second Empire, in the most difficult of circumstances.

The new French government wasn’t yet ready to admit defeat. They called for guerilla warfare against the occupying Prussian forces to deprive them of supplies, and the formation of large armies from the unoccupied provinces to the west and south. Prussian opinion favoured the bombardment of Paris to try to bring the war to a more rapid conclusion, but thankfully Prussian High Command wouldn’t accept that on moral grounds.

As the Prussians sent small armies out to the provinces to disrupt French attempts at re-organisation, conditions in Paris steadily deteriorated.

Anton von Werner shows the contrasting life In the Troops’ Quarters Outside Paris (1894), here in the luxurious Château de Brunoy, which had been abandoned to or requisitioned by those occupying forces. Prussian soldiers were blamed for the almost complete destruction of Pissarro’s work prior to the war, when they occupied his house in 1870.

Édouard Detaille’s painting of action at Champigny, December 1870 (1879) took place only 12.5 km (under eight miles) from the centre of Paris.

There were French counter-attacks. On 29 October 1870, General Carey de Bellemare attacked the Prussian Guard at Le Bourget, despite having no orders to do so, and forced them to cede the town to his troops. Despite these positions being of little value to either side, the Prussians re-took them in the Battle of Le Bourget on 30 October. Although incorrectly dated, de Neuville shows French soldiers sheltering in a Bivouac after the Battle of Bourget, 21 December 1870 (1873). This was a major blow to the beleaguered citizens still in Paris.

As the winter grew colder, Parisians were starting to starve. A city which had long been proud of its restaurants and food was reduced to scavenging meals based on horse, dog, cat, and even the city’s rats.

Jean-Louis-Ernest Meissonier’s romanticised view of The Siege of Paris from 1870 combines almost every symbol relevant to the city’s distress, dressing Marianne in a lionskin against a battle-worn flag. Meissonier had originally been attached to the staff of Napoleon III, and accompanied him in early phases of the war in Italy. During the siege of Paris, though, he was a Colonel commanding an improvised infantry unit, and knew well the realities of combat.

Another artist who was trapped inside Paris was the great illustrator and painter Gustave Doré, who made several works showing scenes such as this Sister of Charity Saving a Child. An Episode of the Siege of Paris (1870-71).

The greatest memorial to those who lost their lives in the siege, and those who survived it, is Louis-Ernest Barrias’ bronze The Defence of Paris of 1883. This has so dominated the part of the city where it’s situated that the area is known as La Défense.

Military action continued into 1871, although it was already clear that France was utterly defeated. Secret discussions about an armistice started on 23 January, but the French government feared that their capitulation could precipitate rebellion, even revolution.

Édouard Detaille’s depiction of The Armistice of 28th January 1871 (1873) shows the moment the symbolic white flag was raised over a bleak plain.

To the nearly 400,000 French dead from the war, the Prussians were determined to add profound insult: as shown in Anton von Werner’s painting of the Crowning of Wilhelm I as Emperor of Germany, in Versailles (1882). Prussia had celebrated victory in this ceremony held at the most famous of French royal palaces, on 18 January 1871.

Neither were participants afraid to spread ‘false news’: Emil Hünten’s undated Welcome of Empress Eugénie by Prussian Soldiers shows an event that never occurred. When the Empress was told of her husband’s surrender to the Prussians at the Battle of Sedan, she’s reported to have said:
“No! An Emperor does not capitulate! He is dead!… They are trying to hide it from me. Why didn’t he kill himself! Doesn’t he know he has dishonored himself?!”

With hostile crowds forming outside her Tuileries Palace, she slipped out to find sanctuary in the company of her American dentist, then fled to England by yacht on 7 September 1870. She was later joined by the former emperor, and the couple lived at Chislehurst in Kent. She never fraternised with Prussian soldiers.

Gustave Doré had a deeply personal involvement, as he had been born in Strasbourg, a French city the Prussians had taken early in the war. He volunteered to serve in the National Guard, and produced several moving paintings of the suffering of Paris.

His The Enigma (souvenirs de 1870) and two other works were painted using grisaille, greys normally used to model tones in traditional layered technique. This shows the shattered and still-burning remains of the city in the background, bodies of some of the Prussian artillery in the foreground, and two mythical beasts silhouetted in an embrace. The winged creature is female, and probably represents France, who clasps the head of a sphinx, who personifies the forces that determine victory or defeat. The enigmatic question would then relate to the Franco-Prussian War, and the reasons for France’s defeat.

Over the next seventy-five years, France and Germany were to fight one another twice more, before the Treaty of London of 5 May 1949 created the Council of Europe, which West Germany joined in 1951, and became ancestor of the European Union.

One of the magic tricks that characterised the Mac was its association between documents and their apps. No longer did a user have to type in both the name of the app and the document they wanted it to edit. All they needed to do was double-click the document, and it magically opened in the right app.

In Classic Mac OS, that was accomplished by hidden Desktop databases and type and creator codes. For example, a text document might have the type TEXT and a creator code of ttxt. When you double-clicked on that, the Finder looked up which app had the creator code ttxt, which turned out to be the SimpleText editor, and opened that document using that app.

Although those ancient type and creator codes still live on today in modern macOS, they no longer fulfil that role. Instead, each file has what used to be a Uniform Type Indicator (UTI), now wrapped into a UTType, such as public.plain-text, normally determined by the extension to its name, .txt or .text. When you double-click on a file, LaunchServices looks up that UTType in its registry, discovers which app is set as the default to open documents of that type, then launches that app with an AppleEvent to open the document you picked.

Recognising that we often want to open a document using a different app rather than the default, the Finder’s contextual menu offers a list of suitable apps in its Open With command. That list is built and maintained by LaunchServices, and has changed in recent versions of macOS. Whereas those lists used to consist of apps installed in the traditional Application folders, LaunchServices now scours every accessible volume and folder using Spotlight’s indexes to build the biggest lists possible. If you happen to have an old copy of an app tucked away in a dusty corner, LaunchServices will find it and proudly display it alongside those in everyday use, like a game dog triumphantly presenting not one dead pheasant but every one from miles around.

For those with lean systems, this gives them the flexibility to open a large text document using BBEdit rather than TextEdit, or to select which image editor to use for a JPEG. But for those of us with lots of apps lurking in storage, the result is absurd and almost unusable. It’s bad enough working through the 33 apps that LaunchServices lists as PNG editors, but being offered 70 text editors is beyond a joke.

Unfortunately, there’s no lasting way to block unwanted apps from being added to the list LaunchServices builds for this Open With feature. You can gain temporary relief by excluding them from Spotlight search, but should you ever open the folder they’re in using the Finder, those are all added back. This also afflicts apps in folders shared with a Virtual Machine, where the list includes App Store apps that can’t even be run from within that VM.

There are, of course, alternatives. I could drag and drop the document from its Finder window towards the top of my 27-inch display to the app’s icon in the Dock at the foot, which is marginally less awkward than negotiating my way through that list of 70 apps.

But there are better solutions: why not empower me to determine which of those 70 apps should be offered in the Open With list? This is such a radical idea that it used to be possible with the lsregister command that has become progressively impotent, as LaunchServices has cast its net further in quest of more apps to flood me with. Or maybe use a little machine learning to include only those text editors I use most frequently to open documents? Apple could even brand that LaunchServices Intelligence, although that’s a little overstated.

I can’t help but think of what those magicians from forty years ago would have done, but I’m certain they wouldn’t have offered me that list of 70 apps to choose from.