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Re: [rdiff-backup-users] Symlink backup error message; symlink creation

From: Andrew Ferguson
Subject: Re: [rdiff-backup-users] Symlink backup error message; symlink creation times reset upon restore
Date: Wed, 20 Jun 2007 11:37:00 -0400
User-agent: Thunderbird (Macintosh/20070509)

Eric Jensen wrote:
> Hi all,
> I'm working with the new 1.1.11 release, and I was pleased to find that
> I'm now able to perform a simple test backup from Linux to an
> SMB-mounted filesystem, which doesn't allow symlinks - thanks!.  I
> backed up a single directory, with both a real file and a symlinked
> file.  It gave me an error:
> SpecialFileError symlink_file [Errno 1] Operation not permitted
> while backing up, but did properly store the file's metadata, and it
> restored it as a symlink when I did a restore. 
> Two questions:
> 1.  Should this error occur?  It appears to be backing up the data OK.
>     Maybe just a warning at the beginning that the target filesystem
>     doesn't support symlinks.  (At the default verbosity level, I get a
>     warning about hardlinks, but not about symlinks.)  If I back up a
>     larger directory, I get one of these errors for every symlink in the
>     source tree.

Correct. rdiff-backup currently assumes that the target filesystem
supports symlinks without checking. It fails, gracefully, with the
warning message you saw above, and saves the symlink in the metadata
file so it can be recreated upon restore.

Given that backing-up to an SMB system seems to be working, maybe a
symlink test like the hardlink test would be good.

> 2.  After restoring, I noted that the modification time on the symlink
>     was different from the target:

Yup. symlinks don't have access and mod times in POSIX systems. From the
stat(2) manpage:

"Unlike other filesystem objects, symbolic links do not have an owner,
group, access mode, times, etc.  Instead, these attributes are taken
from the directory that contains the link."

Many Unix systems go beyond POSIX and support owner/group for symlinks
via lchown(2). Also, on Mac OS X, symlink permissions are affected by
the umask. rdiff-backup preserves both of those extra symlink attributes.

Great to hear of success with SMB!


Andrew Ferguson - address@hidden

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