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.

           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