Change file ownership recursively without errors

Question

I am trying to write a script that fixes the ownership of all files owned by a specific user, after changing the user's UID.

Currently, I run:

chown -Rhc --from=${OLD_UID} ${NEW_UID} /
chown -Rhc --from=:${OLD_UID} :${NEW_UID} /

Where OLD_UID and NEW_UID are the old and new UIDs of the user I have just modified.

This has the desired effect, but always exits with a return code of 1, because of errors like this:

chown: cannot access ‘/proc/1103/task/1103/fd/4’: No such file or directory
chown: cannot access ‘/proc/1103/task/1103/fdinfo/4’: No such file or directory
chown: cannot access ‘/proc/1103/fd/4’: No such file or directory
chown: cannot access ‘/proc/1103/fdinfo/4’: No such file or directory

My theory is that the process finding all files picks up its own process, which then does not exist when chown tries to access it.

I could just throw away the return code from the commands, but I would prefer not to in case I end up ignoring real errors.

Can anyone suggest an alternative approach that will not report false errors?

Answer 1

You could use find, and tell it to not descent into other filesystems (which should prevent it from accessing virtual filesystems like proc, sys, etc):

find / -xdev -uid ${OLD_UID} -execdir chown ${NEW_UID} {} +

This may not be as efficient.

Another way to filter out the virtual files would be to remount the root filesystem somewhere else:

mkdir /tmp/chroot
mount -o .. -t .. /dev/... /tmp/chroot

And run chown on /tmp/chroot.