Redhat made a modification to the useradd program that locks the group file
in the open_files function.  However, the close_files function only unlocks
the group file if a change was made.  This leads to a lock file being left
in /etc/group.lock whenever a user is added and a default group specified
with the -g option.

Having this lock file hanging around doesn't seem to cause any problems --
most of the time!  After a reboot or a long uptime, the PID in the lock
file can be reused by another process and when this happens, the useradd
program cannot lock the group file.  If the new process is a daemon, the
useradd program can NEVER lock the group file.

Suggested change: Always unlock the group file on exit.