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Re: [rdiff-backup-users] comments about rdiff-backup


From: Faheem Mitha
Subject: Re: [rdiff-backup-users] comments about rdiff-backup
Date: Tue, 22 Nov 2005 14:33:28 -0500 (EST)



On Tue, 22 Nov 2005, Keith Edmunds wrote:

I see this as down to the system administrator to manage, and much easier too. For example, suppose I have two backup jobs, one backing up user xxx and a second backing up user yyy. Those two backup jobs might writing, respectively, to:

        /backups/home/xxx/...
        /backups/home/yyy...

That won't cause a problem at all. Now suppose on your system you backup the whole of /home. A second invocation is started, so at one point there are two rdiff-backup processes, and they are writing to the directories shown above. How should rdiff-backup decide that the former pair of processes are safe to run, but the latter pair are not? Yes, it can be done by parsing command lines of other processes - but even that may not be possible if each of user xxx and yyy are running the backup process under their own UIDs.

Actually, one could use some kind of locking mechanism, since the directory being written to by rdiff-backup is well-defined by the existence of the rdiff-backup-data directory at the top level.

This is hardly an ideal solution though, since one problem with locking is guaranteeing that it be released correctly.

What I do:

        #!/bin/bash
        # Start of script
        ACTIVE_FLAG=/var/run/backup_in_progress
        [ -e $ACTIVE_FLAG] && exit 1 || touch $ACTIVE_FLAG
        .
        .
        # End of script
        rm $ACTIVE_FLAG

Actually it's a little more sophisticated than that, but you get the idea.

Yes, fair enough. I'm doing something similar in concept, but using mounts of LVM volumes instead. The trouble with what you are doing it that if the script exits unexpectedly, the ACTIVE_FLAG file might still remain, no?

I was just wondering if this issue had been considered, and what the concensus thinking about it was.

Thanks for your comments.
                                                                   Faheem.




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