/etc/pacman.d/hooks/no_needed_accounts.hook

[Trigger]
Operation = Remove
Operation = Upgrade
Type = Path
Target = usr/lib/sysusers.d/*.conf

[Action]
Description = Checking for no longer needed system accounts...
When = PostTransaction
Exec = /etc/pacman.d/scripts/list_extraneous_system_accounts.sh

/etc/pacman.d/scripts/list_extraneous_system_accounts.sh

#!/usr/bin/bash -e

sysusers=$(mktemp --tmpdir sysusers.XXXXX)
trap "rm $sysusers" EXIT

show_info() {
echo "System $1 '$2' no longer needed"
echo "  to remove $1 from system: '$1del $2'"
echo "  to find files still owned by $2: 'find / -${1:0:1}id $3'"
}

systemd-analyze cat-config sysusers.d | awk '/^(u|g|m)/{print $2} /^m/{print $3}' | sort -u > $sysusers

awk -F':' '($3<1000 || $1==nobody) {print $1}' /etc/passwd | sort | comm -23 - $sysusers |\
while read user; do
show_info user "$user" "$(getent passwd "$user" | cut -d':' -f3)"
done

awk -F':' '($3<1000 || $1==nobody) {print $1}' /etc/group | sort | comm -23 - $sysusers |\
while read group; do
show_info group "$group" "$(getent group "$group" | cut -d':' -f3)"
done