Does Safari restore the previous user profile after a failed upgrade?

Direct Answer

No. Safari does not automatically restore the previous user profile after a failed macOS upgrade. Whether the pre‑upgrade profile remains usable depends entirely on whether a data‑migration step had already begun before the failure occurred.

Why the Profile Usually Survives

Safari keeps all user data—bookmarks, history, cookies, tabs, and extensions—in ~/Library/Safari/. A standard macOS upgrade replaces the Safari application bundle in /Applications/Safari.app but leaves ~/Library/Safari/ untouched. If the installer rolls back the bundle (or simply fails before touching it) and no migration script has run, launching Safari afterward will open the existing profile exactly as it was.

When a New Data Store Is Created

A fresh store appears only when a migration has started and then been interrupted. Major Safari version jumps (for example, Safari 16 → 17 on Ventura → Sonoma) include a one‑time schema upgrade for History.db, Bookmarks.plist, and the cookies store. The migration runs the first time the new Safari binary launches. If power loss, a forced reboot, or an installer error occurs after the migration begins but before it finishes, Safari detects an incomplete or incompatible store on next launch and creates a clean one, effectively discarding the pre‑upgrade data.

Conditions That Trigger a New Store

• Upgrade crosses a Safari major version that includes a data‑schema change.
• The new Safari binary launches at least once (even briefly) before the failure.
• Migration logs show entries such as SafariMigration or WebKitDataMigration in ~/Library/Logs/DiagnosticReports/ or /var/log/system.log.

Supported Recovery Options

Apple provides no supported rollback for application data after a failed upgrade. Recovery is manual:

1. Time Machine – Restore ~/Library/Safari/ from a snapshot taken before the upgrade attempt.
2. iCloud Safari sync – If enabled and the last successful sync completed before the migration started, signing in on another device (or after a clean macOS install) may pull the pre‑upgrade data down. This is not guaranteed; a partially migrated local store can overwrite iCloud data on next sync.
3. Manual copy – If you kept a copy of ~/Library/Safari/ (e.g., via a third‑party backup tool), replace the current folder while Safari is quit.

Verification Steps

1. Quit Safari.
2. Open ~/Library/Safari/ in Finder (⌘⇧G → ~/Library/Safari).
3. Check modification dates on Bookmarks.plist, History.db, and Cookies.binarycookies. Dates before the upgrade attempt suggest the profile was not migrated.
4. Launch Safari → About Safari. If the version number matches the pre‑upgrade build, the old bundle (and therefore the old profile) is still in use.
5. Search Console.app for SafariMigration or WebKitDataMigration around the upgrade timestamp.

One Diagnostic Detail Needed

Which macOS version were you upgrading from and to (e.g., Ventura 13.6 → Sonoma 14.0)? The exact version pair determines whether a schema migration exists for that transition, which changes the likelihood of profile loss.