recreating just the uid/gid unix permissions from tar

Question

I was restoring a root partition based on a tar backup from system-rescue-cd. It went ok except the uid/gid mappings on the system-rescue-cd disk did not match the ones on this debian system that I was restoring. This broke a number of packages and setuid/setgid permissions. For example, the atjobs in spool was owned by bin instead of daemon, and the man pages weren't owned by the man uid.

How do I detect and recreate just the permissions from the tarball without starting the restore process over?

I found I could detect the uid/gid differences via "(cd / ; tar jdpf /my/backup.tar.bz2)" but now I have to filter out the "Uid differs" and "Gid differs" output and it doesn't include the directories in the output, just the files.

If disk space wasn't an issue, maybe rsync could do this, if I untar to another disk?

I do not want to extract files again as contents have changed on the system. I just want to adjust the permissions.

Answer 1

You can get a list of all the chown commands to issue like this:

tar --numeric-owner -tvjf backup.tar.bz2 | 
perl -e 'while (<STDIN>) { s|/|:|;  @t = split(" ");  print "chown $t[1] \x27$t[5]\x27\n";  }' |
tee /tmp/chown_cmds

Output will be like:

chown 0:119 './var/cache/jockey/driverdb-OpenPrintingDriverDB.cache'
chown 0:119 './var/cache/jockey/check'
chown 0:7 './var/cache/cups/'
chown 7:7 './var/cache/cups/ppds.dat'
...

Have a look at /tmp/chown_cmds, make sure it looks good and run this to restore all the uids/gids from the backup:

$ cd / ; sudo bash /tmp/chown_cmds

You could filter out files owned by root to make the list way shorter.