How to change user's UID&GID and what comes out of that

Solution 1:

I've made some research and noticed two things one should take into account when changing UIDs&GIDs:

1. Numeric UID and GID do not always match: in my case id -u mysql=120 and id -g mysql=127
2. Not all files are owned by user 'mysql' and group 'mysql' simultaneously: these files should be searched for separately.

Therefore, we first change UID and GID:

user=mysql new_uid=600 old_uid=$(id -u $user)
group=mysql new_gid=600 old_gid=$(id -g $user)
sudo usermod -u $new_uid $user
sudo groupmod -g $new_gid $group

Then we find for files owned by the late user and group separately: 'user=mysql' goes to one file, 'group=mysql' goes to another file. Also we exclude some directories from find traversing tree:

chownlist=$(tempfile) chgrplist=$(tempfile) sudo find / \
\( \( -path "/proc" -or -path "/sys" -or -path "/dev" \) -prune \) -or \
\( \( -user $old_uid -fprint0 "$chownlist" \) , \
\( -group $old_gid -fprint0 "$chgrplist" \) \)

And only now it's okay to change owners and groups for these files found:

cat "$chownlist" | xargs -0 sudo chown $user
cat "$chgrplist" | xargs -0 sudo chown :$group
sudo rm "$chownlist" "$chgrplist"

Finally, we check if everything went okay: find files owned by unknown UIDs of GIDs:

sudo find / \( \( -path "/proc" -or -path "/sys" -or -path "/dev" \) -prune \) -or \( -nouser -or -nogroup -print \)

Hope this helps someone.

Solution 2:

Yeah, that's pretty much all you need to do. The only files which should need changing are the logs and data files.

You might want to use find | xargs rather than a loop though.