Since I have been using rdiff-backup to backup my Xen domU machines, I get a daily message from cron which informs me that some sockets couldn’t be backed-up because the path is too long:
SpecialFileError var/spool/postfix/public/flush Socket error: AF_UNIX path too long
After some digging I have found that this is related to the length limitation of the AF_UNIX constant in one of the kernel header files, and which only allows 107 characters. Depending on where you want to backup to the length can exceed.
The solution is simple. Why do you want to backup sockets at all? Those are bound to the current system and will be executed when an application gets started. So I don’t see a reason to backup those files. Therefor just use the –exclude-sockets option for rdiff-backup.
Please note that you will have to run rdiff-backup twice before the failure message from above will no longer appear.