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Linux Notes

by Stuart D. Gathman
Last updated Oct 21, 2006

Here I record lessons learned for those desperately searching with Google for obscure answers - as I have done on many occasions.
  • SELinux and Backup
  • RPM and Prelink

  • SELinux and Backup

    When upgrading systems remotely, using the install CDs is not an option. Instead, we install locally, then backup the system and transmit the backup to the remote site and install on a spare partition. I just started doing this for CentOS-4.4, and there is a snag with SELinux. It seems that SELinux adds an attribute to files that is not transferred via rsync. I haven't checked, but I suspect tar does not save SELinux attributes either. The result is that SELinux does not work on the restored system, and you have to disable it.

    The only SELinux aware archiver I'm aware of is star. There is a star package for CentOS-4.4. However, you have to have an SELinux kernel to restore the star archive.

    UPDATE: If you don't have any custom security attributes, you can restore the defaults with fixfiles. It will restore defaults for a package to the attributes stored in RPM, or restore files globally according to the ruleset in /etc/selinux.

    RPM and Prelink

    While figuring out the SELinux problem, I got a scare when I happened to check some CentOS programs against the RPMs they were installed with. The program files were about 5K bigger! Had we been owned? Well maybe, but it turns out that there is a prelink package which adds extra info to all programs and shared objects in the system. The extra info is supposed to help dynamically linked programs load faster. RPM runs prelink with the -u (undo) option to get the file with prelinking undone, so it can check the unprelinked file against the RPM database.

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