Over the last year or so Mac users have run into problems that appear related to a background service named triald. Some report it stealing huge amounts of CPU, others associate it with various glitches, and a few have noticed gigabytes of disk space apparently being taken up by its folder at ~/Library/Trial, and in their Time Machine backups. This article explains as much as I know about this mysterious new service, and ponders what’s going on.

Trial, as I’ll refer to it, was introduced to macOS in Big Sur, when it appeared in three new private frameworks named Trial, TrialProto and TrialServer. At that time it was version 1.0, with a build number of 174.4 in macOS 11.0.1, and the latter has since risen to 292.18 in Monterey 12.3. In addition to those private frameworks, there are three essential components:

• the background service /usr/libexec/triald
• an XPC service TrialArchivingService.xpc contained in TrialServer.framework
• a launch agent /System/Library/LaunchAgents/com.apple.triald.plist.

Note that all these are on the SSV, therefore can’t be tampered with in any way. The high build number of the version first shipped in Big Sur suggests that Trial may have already been included in iOS, and it’s listed on some iOS sites as being present, with the suggestion that it has something to do with “Apple A/B testing”.

Storage

After a user Home folder has been created, Trial normally creates its own root directory at ~/Library/Trial, which contains folders of NamespaceDescriptors, Treatments, and an SQLite database in the folder v6 named trialdb.db. None of these appears specially protected, although each folder is a warren of sub-folders which makes extracting information from them very difficult. The Trial root directory can readily occupy substantial amounts of disk space: on my production Mac, it appears to contain 1.47 GB in 148,618 items, which is a hefty chunk in backups. Even on a lightly used Mac, it may amount to more than 1 GB and over 300,000 items. However, most of those may be symbolic links, and its real size may thus be considerably less.

This Trial root directory isn’t included in the standard Time Machine exclusions, so unless explicitly added to the user’s exclusion list, it will normally be backed up automatically with the rest of the contents of the Home folder.

Activation and activity

It has been suggested that Trial is only activated on Macs which have been enrolled in Apple’s beta programmes. I don’t think that’s correct, as my production Mac has never been so enrolled, nor has my M1 Pro MBP, but both are active Trial participants. I’m not aware of any control over or opt-out from Trial, although it could be covered in Apple’s general request to share data including panic logs, if you can remember where to control that.

I first noticed Trial when studying Visual Look Up in the log. At the start of each Look Up, the subsystem com.apple.trial enters the following into the log:
Initializing TRIClient. Trial version: TrialXP-292.18
_PASEntitlement: Entitlement "com.apple.private.security.storage.triald" is not