1

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?

2

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.

  • In the case of the second solution, isn't there still /tmp/chroot/dev? Also, is it really safe to mount the same filesystem in two places? – Barmar Dec 12 '14 at 22:38
  • @Barmar indeed, but none of the device files would be owned by a normal user, right? Some systems don't allow it, but some do. So, I don't know. – muru Dec 12 '14 at 22:40
  • Of course, but the objective is to keep it from drilling into the device directory in the first place. – Barmar Dec 12 '14 at 22:43
  • @Barmar One of the objectives is. If it really is important, bind-mounting an empty folder over /tmp/chroot/dev should solve that problem. – muru Dec 12 '14 at 22:44
  • That seems to be the primary objective -- he just wants to prevent the errors when it tries to recurse into subdirectories that disappear while the command is running. – Barmar Dec 12 '14 at 22:46

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