Ensure all local interactive users have a primary group that exists

# Check for users with non-existent primary groups (UID >= 1000)
bad_users=""
while IFS=: read -r user _ uid gid _ _ _; do
  if [ "$uid" -ge 1000 ] 2>/dev/null; then
    if ! grep -q "^[^:]*:[^:]*:${gid}:" /etc/group 2>/dev/null; then
      bad_users="$bad_users $user(gid=$gid)"
    fi
  fi
done < /etc/passwd
if [ -z "$bad_users" ]; then
  echo "OK: All interactive users have valid primary groups"
  exit 0
fi
echo "FAIL: Users with non-existent primary groups:$bad_users"
exit 1

expected_exit:

0

note:

For each user with a non-existent primary group, either create the missing group with groupadd, or assign the user to an existing group with usermod -g <valid_group> <username>.