Find all files with an undefined GID (A group without an entry in /etc/group)

On several of our CentOS 5 systems, the /etc/group file was munged by an automated script.

As a result, there are some files on the system which have an undefined GID-- the GID is not defined in /etc/group. For example, the following file is owned by GID 103, when it should be owned by the group 'mysql'.

# ls -ld /var/lib/mysql/mysql/user.frm 
-rw-rw---- 1 mysql 103 10330 Apr  1 02:47 /var/lib/mysql/mysql/user.frm

Is there a way for me to find ALL files on this system which are owned by undefined groups?

I know I can do something like this to find all files owned by GID 103:

find / -gid 103

However, I want to find ALL files which are owned by an undefined group.

From serverfault Stefan Lasiewski

• you may try a quick and dirty solution like:

  find .  -ls | gawk '$6 ~ /^[0-9]+$/ {print}'
  

  it's definitely not a beauty, but should work.

  Alex : I like that better than what I was coming up with :)
  From Daniel

• Doesn't your version of find have the -nogroup option?

  Here is a perl one-liner:

  perl -MFile::Find -e 'find({ wanted => sub { getgrgid((stat(_))[5]) or \
    print ((stat(_))[5], " $File::Find::name\n") }, follow => 1 }, "/")'
  

  Christopher Karel : Despite the other accepted answer, this one really is the -right- one. Using the `-nogroup` flag with find will return all files with which the GID doesn't map to an actual group. Exactly what the poster was looking for.

  Zoredache : Wow, I wonder why I have never noticed this option before.

  Stefan Lasiewski : You win! I had no idea that option existed. I even scanned the manpage and missed this option.
  From embobo

• If you have -gid but not -nogroup you may be able to use this or something like it:

  gids=($(cut -d: -f3 /etc/group | sed 's/.*/! -gid & /'))
  find /dir/to/start ${gids[@]} -ls
  

  From Dennis Williamson