SNAPSHOT(8) BSD System Manager's Manual SNAPSHOT(8)NAMEsnapshot — UFS/ZFS snapshot management utility
SYNOPSISsnapshot [options] [command] [arguments]
DESCRIPTION
The snapshot command is a convenience frontend to mount(8) and
mdconfig(8) for the management of UFS/ZFS snapshots. It is also the
underlying tool used in the periodic snapshot scheduler
periodic-snapshot(8) and the mounting/unmouning command in the amd(8) map
/etc/amd.map.snap. It provides the making, expiring, visiting, mounting
and unmounting of filesystem snapshots.
The following global options are available:
-v Display verbose messages showing the essential system commands
involved in the operation.
-h Display a short usage help message and exit.
-d subdir
Set the subdirectory on filesystems under which snapshots are
placed. The default is the conventional .snap subdirectory
dump(8) uses, too.
The following commands are available:
snapshot list [fs ...]
List all existing snapshots on all filesystems or just the par‐
ticular filesystems specified by fs. The output shows both
actual disk-space user usage ("User", "User%") and the disk-space
snapshot usage ("Snap", "Snap%").
snapshot make [-g max-generations] fs:tag[.generation]
Makes a new snapshot generation named tag on filesystem fs,
located in the file fs/subdir/tag.generation. If the generation
part is omitted, generation 0 is used. All older generations
(with numbers greater than generation) are rotated and all obso‐
leted generations (with numbers greater or equal to
max-generations) are removed. Keep in mind that a maximum total
number of 20 snapshots can be created on a UFS filesystem only.
A max-generations number of 0 effectively deletes all snapshots
on filesystem fs of name tag only.
snapshot mount [-o mount-option] fs:tag[.generation] dir
Mounts the fs snapshot tag.generation (or tag.0 if generation is
omitted) under dir by attaching the snapshot file to the next
free md(4) device and mounting this device read-only onto the
target directory. If options -o are specified, they are passed-
through to mount(8).
snapshot umount dir
Unmounts a snapshot by umounting the md(4) device from dir, deat‐
taching the snapshot file from the corresponding md(4) device and
deleting the device.
snapshot visit fs:tag[.generation]
This is just a convenience command which mounts the specified
filesystem on /mnt, temporarily changes to /mnt, starts an inter‐
active shell there for inspecting the snapshot content, and upon
exit from the shell immediately unmounts the snapshot again.
EXAMPLE
The following sample session illustrates the making, rotation, mounting,
unmounting and removal of snapshots:
root# snapshot list /var
Filesystem User User% Snap Snap% Snapshot
root# snapshot make -g4 /var:test
root# snapshot list /var
Filesystem User User% Snap Snap% Snapshot
/var 1172MB 14.8% 4MB 0.1% test.0
root# snapshot make -g4 /var:test
root# snapshot list /var
Filesystem User User% Snap Snap% Snapshot
/var 1176MB 14.8% 4MB 0.1% test.0
/var 1176MB 14.8% 4MB 0.1% test.1
root# snapshot make -g4 /var:test
root# snapshot list /var
Filesystem User User% Snap Snap% Snapshot
/var 1181MB 14.9% 4MB 0.1% test.0
/var 1181MB 14.9% 4MB 0.1% test.1
/var 1181MB 14.9% 4MB 0.1% test.2
root# snapshot make -g4 /var:test
root# snapshot list /var
Filesystem User User% Snap Snap% Snapshot
/var 1186MB 15.0% 4MB 0.1% test.0
/var 1186MB 15.0% 4MB 0.1% test.1
/var 1186MB 15.0% 4MB 0.1% test.2
/var 1186MB 15.0% 4MB 0.1% test.3
root# snapshot make -g4 /var:test
root# snapshot list /var
Filesystem User User% Snap Snap% Snapshot
/var 1186MB 15.0% 4MB 0.1% test.0
/var 1186MB 15.0% 4MB 0.1% test.1
/var 1186MB 15.0% 4MB 0.1% test.2
/var 1186MB 15.0% 4MB 0.1% test.3
root# snapshot mount /var:test.2 /mnt
root# ls /mnt
account cron heimdal mail opkg spool
at db lib msgs preserve tmp
backups empty log named run yp
root# snapshot umount /mnt
root# snapshot make -g0 /var:test
root# snapshot list /var
Filesystem User User% Snap Snap% Snapshot
root# _
By using an amd(8) map /usr/local/etc/amd.map.snap containing
/defaults type:=program
* mount:="/usr/local/sbin/snapshot snapshot mount /${key} ${fs}";\
unmount:="/usr/local/sbin/snapshot snapshot umount ${fs}"
and a /etc/rc.conf configuration of
amd_enable="YES"
amd_flags="-a /.am -c 1800 -w 60 -l syslog /snap /usr/local/etc/amd.map.snap"
even non-privileged users can access arbitrary snapshots
fs:tag[generation] by just accessing /snap/fs:tag[generation]. For
instance, if a snapshot hourly.2 exists on filesystem /var one can then
access an old state of file /var/tmp/foo.txt by simply accessing the path
/snap/var:hourly.2/tmp/foo.txt.
SEE ALSOmount(8), mdconfig(8), md(4), periodic-snapshot(8),
http://people.freebsd.org/~rse/snapshot/.
HISTORY
The snapshot utility first appeared in FreeBSD.
AUTHORS
Ralf S. Engelschall ⟨rse@FreeBSD.org⟩
BSD September 3, 2004 BSD
