gromox\-snapshot \(em Helper to create snapshots of mailboxes

gromox\-snapshot calls btrfs(8) or cp(1)/\-\-reflink to create snapshots of the

current state of mailboxes as needed. gromox\-snapshot is meant to be

periodically invoked by a systemd timer (or, failing that, a classic cron job).

The default interval of gromox\-snapshot.timer is hourly.

.PP

The program generates snapshots "for this day" / "for this week" / etc., rather

than snapshots which are at least one day / one week / etc. apart. When the

snapshotter is run periodically, this evens out and is not a concern at all.

The program has no command-line options.

/etc/gromox/snapshot.cfg will be read on startup. It is a trivial key=value

file, with one variable per line.

.TP

Make daily snapshots and keep them for \fIn\fP days. Use \fI0\fP to

deactivate daily snapshotting.

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Default: \fI7\fP

.TP

Make hourly snapshots and keep them for \fIn\fP hours. Use \fI0\fP to

deactivate hourly snapshotting.

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Default: \fI0\fP

.TP

Make monthly snapshots and keep them for \fIn\fP months (more precisely,

\fIn\fP*31 days). Use \fI0\fP to deactivate monthly snapshotting.

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Default: \fI0\fP

.TP

Make weekly snapshots and keep them for \fIn\fP weeks. Use \fI0\fP to

deactivate weekly snapshotting.

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Default: \fI4\fP

.TP

When btrfs is used, this directive specifies the root directory of the nearest

btrfs subvolume. (As of Linux 6.2.1, it is not possible to snapshot arbitrary

directories; it has to be the root of a subvolume. Confer with `btrfs sub list`

to see subvolumes.) Otherwise, this must point to the Gromox data directory.

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Default: \fI/var/lib/gromox\fP

.TP

The directory where snapshots (these are subdirectories) will be placed. This

directory needs to be on the same device as the snapshot source

(subvolume_root, see above).

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Default: \fI/var/lib/gromox-snapshots\fP

.PP

Each time "category" (days, weeks, etc.) is independently evaluated and

snapshots are always made from the subvolume_root, never from another snapshot.

A weekly snapshot generated on the first day of the week is not strictly equal

to the daily snapshot generated for the same day, as there is technically a

very small time window between individual btrfs commands.

.IP \(bu 4

Invalid cross-device link: snapshot_archive was not on the same device as

subvolume_root.

.IP \(bu 4

Operation not supported: the filesystem employed on snapshot_archive does not

support reflinks

When a reflink-based snapshot is deleted (which happens via /bin/rm), rm may

modify the directory's timestamp. If that rm call is interrupted without

completing, the next run of gromox-snapshot will erroneously consider the

directory as "too new" and not resume the deletion until it has sufficiently

aged again.

\fBgromox\fP(7)