Classic Shell Scripting

Changing File Ownership

At first blush, changing file ownership is pretty easy. Given the list of usernames and new UID numbers, we ought to be able to write a loop like this (to be run as root):

while read user old new
do
        cd /home/$user                 Change to user's directory
        chown -R $new .                Recursively change ownership, see chown(1)
done < old-new-list

The idea is to change to the user's home directory and recursively chown everything to the new UID number. However, this isn't enough. It's possible for users to have files in places outside their home directory. For example, consider two users, ben and jhancock, working on a joint project in /home/ben/declaration:

$ cd /home/ben/declaration
$ ls -l draft*
-rw-r--r--    1 ben       fathers    2102 Jul  3 16:00 draft10
-rw-r--r--    1 jhancock  fathers    2191 Jul  3 17:09 draft.final

If we just did the recursive chown, both files would end up belonging to ben, and jhancock wouldn't be too happy upon returning to work the day after the Great Filesystem Reorganization.

Even worse, though, is the case in which users have files that live outside their home directory. /tmp is an obvious example, but consider a source code management system, such as CVS. CVS stores the master files for a project in a repository that is typically not in any home directory, but in a system directory somewhere. Source files in the repository belong to multiple users. The ownership of these files should also be changed over.

Thus, the only way to be sure that all files are changed correctly everywhere ...