Date: Wed, 19 Jun 2002 04:40:04 -0700 (PDT) From: "Chris Knight" <chris@aims.com.au> To: freebsd-bugs@FreeBSD.org Subject: Re: bin/30139: snapshots mount option not documented in mount(8) Message-ID: <200206191140.g5JBe4X76502@freefall.freebsd.org>
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The following reply was made to PR bin/30139; it has been noted by GNATS. From: "Chris Knight" <chris@aims.com.au> To: <freebsd-gnats-submit@FreeBSD.org>, <obrien@FreeBSD.org> Cc: Subject: Re: bin/30139: snapshots mount option not documented in mount(8) Date: Wed, 19 Jun 2002 21:33:11 +1000 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 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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