Backup and restore

A whole VM can be turned into a single backup file and put back later: over itself, to undo a mistake or an update gone wrong, or as a new VM.

What goes into a backup#

The VM's whole folder, macos-<number>:

• the macOS disk;
• the boot disk with OpenCore;
• the firmware's settings;
• the VM's identity (serial number, MLB, UUID, ROM and MAC address) and all of its settings.

The installers (the recovery, or the copy of a full installer image) are left out, since an installed VM never uses them again and they can be several GB. To include them, use --with-installers. A VM restored without them cannot reinstall macOS from itself: create a new VM for that. A VM whose macOS is not installed yet always keeps its installers.

Backing up#

In the console, choose Backup & Restore (key 6) › Back up a VM, or run:

osx-reims backup 10

The VM must be shut down while it is copied. If it is running, OSX-REIMS asks whether it may shut it down first — macOS is asked to shut down, as with Shut down. If it has not gone within a minute (a confirmation in the VM window, an app keeping it up, or the setup assistant, which ignores the request), the console offers to wait longer, force the power off or cancel.

The file goes to /opt/osx-reims/backup, named macos-<number>-YYYYMMDD-HHMMSS.osxreims.tar.zst. It is compressed with zstd, but a macOS disk compresses little, because macOS already compresses its own files: expect a file almost the size of the VM's data. As an example, a Ventura VM with 26.7 GB of data made a 21.7 GB file in 32 seconds.

• The file can be read by your user alone, because it carries the VM's identity.
• While it is being written, it has a hidden name ending in .partial, and it gets its final name only once it is complete. A file left by an interrupted backup is removed by the next one.

Restoring#

In the console, choose Backup & Restore › Restore a backup, or run osx-reims restore, which lists the backups, newest first. When the VM the backup came from still exists, OSX-REIMS asks how to restore it:

When the VM it came from no longer exists, the backup comes back under its own number, as it was.

osx-reims restore macos-10-20261017-153000.osxreims.tar.zst --replace
osx-reims restore macos-10-20261017-153000.osxreims.tar.zst --as 12

The VM is unpacked into a hidden folder next to the others and only takes its place once it is complete and checked; when replacing, the old VM is moved away only then. So a restore that fails, a damaged file or a cancelled run leaves every VM as it was.

• A backup made by a newer OSX-REIMS than the installed one is refused.
• A VM that opened with the computer (autostart) is offered to do so again.

Listing and deleting#

osx-reims backup --list
osx-reims backup --delete macos-10-20261017-153000.osxreims.tar.zst

In the console, deleting is Backup & Restore › Delete a backup. osx-reims doctor has a Backups line, with how many there are and the free space in the folder.

Where to keep them#

Backups are kept on the same disk as the VMs, unless /opt/osx-reims/backup is a mount point of another disk. A backup protects a VM from a mistake or an update gone wrong, not from the disk failing: copy the files somewhere else to keep them safe.

The folder is created by setup and kept when the package is removed.

Options#