Bug 30139
| Summary: | snapshots mount option not documented in mount(8) | ||
|---|---|---|---|
| Product: | Base System | Reporter: | David O'Brien <obrien> |
| Component: | bin | Assignee: | Tom Rhodes <trhodes> |
| Status: | Closed FIXED | ||
| Severity: | Affects Only Me | ||
| Priority: | Normal | ||
| Version: | 5.0-CURRENT | ||
| Hardware: | Any | ||
| OS: | Any | ||
|
Description
David O'Brien
2001-08-27 21:40:00 UTC
Howdy, Here's a diff to the mount man page including the snapshot support. I shamelessly cut'n'pasted from Kirk's README.snapshot file and made some minor edits. Apologies if I've got some of the manpage formatting wrong - it was a 5 minute crash course on mdoc to do this. Regards, Chris Knight --- src/sbin/mount/mount.8.old Tue May 21 10:50:17 2002 +++ src/sbin/mount/mount.8 Wed Jun 19 21:19:34 2002 @@ -181,6 +181,62 @@ All .Tn I/O to the filesystem should be done synchronously. +.It Cm snapshot +This option allows a snapshot of the specified filesystem to be taken. The +.Fl u +flag is required with this option. Note that snapshot files must be created in +the filesystem that is being snapshotted. You may create up to 20 snapshots per +filesystem. Active snapshots are recorded in the superblock, so they persist +across unmount and remount operations and across system reboots. When you are +done with a snapshot, it can be removed with the +.Xr rm +command. Snapshots may be removed in any order, however you may not get back all +the space contained in the snapshot as another snapshot may claim some of the +blocks that it is releasing. Note that the schg flag is set on snapshots to +ensure that not even the root user can write to them. The unlink command makes +an exception for snapshot files in that it allows them to be removed even though +they have the schg flag set, so it is not necessary to clear the schg flag +before removing a snapshot file. +.Pp +Once you have taken a snapshot, there are three interesting things that you can +do with it: +.Pp +.Bl -enum -compact +.It +Run fsck on the snapshot file. Assuming that the filesystem was clean when it +was mounted, you should always get a clean (and unchanging) result from running +fsck on the snapshot. This is essentially what the background fsck process does. +.Pp +.It +Run dump on the snapshot. You will get a dump that is consistent with the +filesystem as of the timestamp of the snapshot. Note that +.Xr dump +has not yet been changed to set the dumpdates file correctly, so do not use this +feature in production until that fix is made. +.Pp +.It +Mount the snapshot as a frozen image of the filesystem. To mount the snapshot +.Pa /var/snapshot/snap1 : +.Bd -literal +mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4 +mount -r /dev/md4 /mnt +.Ed +.Pp +You can now cruise around your frozen +.Pa /var +filesystem at +.Pa /mnt . +Everything will be in the same state that it was at the time the snapshot was +taken. The one exception is that any earlier snapshots will appear as zero +length files. When you are done with the mounted snapshot: +.Bd -literal +umount /mnt +mdconfig -d -u 4 +.Ed +.Pp +Further details can be found in the file at +.Pa /usr/src/sys/ufs/ffs/README.snapshot . +.El .It Cm suiddir A directory on the mounted filesystem will respond to the SUID bit being set, by setting the owner of any new files to be the same On Wed, Jun 19, 2002 at 09:33:11PM +1000, Chris Knight wrote:
> Here's a diff to the mount man page including the snapshot support.
> I shamelessly cut'n'pasted from Kirk's README.snapshot file and made
> some minor edits.
This is a good patch and having snapshots better documented is a big help
to all.
Could you make one more pass over your patch and change one thing.
All sentances should end at the end of a line.
Maybe comma's too,
I don't remember too much about them.
What I wrote above is an example of what I mean. There are no sentances
like the previous one to this that don't end at the end of a line.
+.It Cm snapshot
+This option allows a snapshot of the specified filesystem to be taken.
+The
+.Fl u
+flag is required with this option.
+Note that snapshot files must be created in the filesystem that is being
+snapshotted.
+You may create up to 20 snapshots per filesystem.
+Active snapshots are recorded in the superblock,
+so they persist across unmount and remount operations and across system
+reboots.
Howdy, OK, here's an updated patch. The rest of the mount manpage suggests that line breaks after commas is not necessary. Thanks for the feedback. Sorry about the e-mail address. I must remember to regen my sendmail.cf file after upgrading. Regards, Chris Knight --- mount.8.orig Tue May 21 10:50:17 2002 +++ mount.8 Sun Jun 23 16:58:22 2002 @@ -181,6 +181,73 @@ All .Tn I/O to the filesystem should be done synchronously. +.It Cm snapshot +This option allows a snapshot of the specified filesystem to be taken. +The +.Fl u +flag is required with this option. +Note that snapshot files must be created in the filesystem that is being +snapshotted. +You may create up to 20 snapshots per filesystem. +Active snapshots are recorded in the superblock, so they persist across unmount +and remount operations and across system reboots. +When you are done with a snapshot, it can be removed with the +.Xr rm +command. +Snapshots may be removed in any order, however you may not get back all the +space contained in the snapshot as another snapshot may claim some of the blocks +that it is releasing. +Note that the schg flag is set on snapshots to ensure that not even the root +user can write to them. +The unlink command makes an exception for snapshot files in that it allows them +to be removed even though they have the schg flag set, so it is not necessary to +clear the schg flag before removing a snapshot file. +.Pp +Once you have taken a snapshot, there are three interesting things that you can +do with it: +.Pp +.Bl -enum -compact +.It +Run fsck on the snapshot file. +Assuming that the filesystem was clean when it was mounted, you should always +get a clean (and unchanging) result from running fsck on the snapshot. +This is essentially what the background fsck process does. +.Pp +.It +Run dump on the snapshot. +You will get a dump that is consistent with the filesystem as of the timestamp +of the snapshot. +Note that +.Xr dump +has not yet been changed to set the dumpdates file correctly, so do not use this +feature in production until that fix is made. +.Pp +.It +Mount the snapshot as a frozen image of the filesystem. +To mount the snapshot +.Pa /var/snapshot/snap1 : +.Bd -literal +mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4 +mount -r /dev/md4 /mnt +.Ed +.Pp +You can now cruise around your frozen +.Pa /var +filesystem at +.Pa /mnt . +Everything will be in the same state that it was at the time the snapshot was +taken. +The one exception is that any earlier snapshots will appear as zero length +files. +When you are done with the mounted snapshot: +.Bd -literal +umount /mnt +mdconfig -d -u 4 +.Ed +.Pp +Further details can be found in the file at +.Pa /usr/src/sys/ufs/ffs/README.snapshot . +.El .It Cm suiddir A directory on the mounted filesystem will respond to the SUID bit being set, by setting the owner of any new files to be the same State Changed From-To: open->patched I have applied this change and will see to the MFC. Thanks for the submission! Responsible Changed From-To: freebsd-bugs->trhodes I have applied this change and will see to the MFC. Thanks for the submission! State Changed From-To: patched->closed Patched and closed. This was not MFC'ed as snapshots are not supported in -STABLE. |
