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If you use OpenBSD and administrate machines, you may be aware that packages can install new dedicated users and groups, and that if you remove a package doing so, the users/groups won't be deleted, instead, `pkg_delete` displays instructions about deletion.
In order to keep my OpenBSD systems clean, I wrote a script looking for users and groups that have been installed (they start by the character `_`), and check if the related package is still installed, if not, it outputs instructions that could be run in a shell to cleanup your system.
#!/bin/sh
SYS_USERS=$(mktemp /tmp/system_users.txt.XXXXXXXXXXXXXXX)
PKG_USERS=$(mktemp /tmp/packages_users.txt.XXXXXXXXXXXXXXX)
awk -F ':' '/^_/ && $3 > 500 { print $1 }' /etc/passwd | sort > "$SYS_USERS"
find /var/db/pkg/ -name '+CONTENTS' -exec grep -h ^@newuser {} + | sed 's/^@newuser //' | awk -F ':' '{ print $1 }' | sort > "$PKG_USERS"
BOGUS=$(comm -1 -3 "$SYS_USERS" "$PKG_USERS")
if [ -n "$BOGUS" ]
then
echo "Bogus users/groups (missing in /etc/passwd, but a package need them)" >/dev/stderr
echo "$BOGUS" >/dev/stderr
fi
EXTRA=$(comm -2 -3 "$SYS_USERS" "$PKG_USERS")
if [ -n "$EXTRA" ]
then
echo "Extra users" >/dev/stderr
for user in $EXTRA
do
echo "userdel $user"
echo "groupdel $user"
done
fi
rm "$SYS_USERS" "$PKG_USERS"
Write the content of the script above in a file, mark it executable, and run it from the shell, it should display a list of `userdel` and `groupdel` commands for all the extra users and groups.
With this script and the package `sysclean`, it's quite easy to keep your OpenBSD system clean, as if it was just a fresh install.
It's not perfect in its current state because if you deleted an user, the according group that is still left won't be reported.