I don't have a strong opinion either, but given that scripts would ignore the warnings and the resulting numeric users are going to face random, seemingly unrelated issues thanks to the interaction with systemd, I think I prefer the failure.
FWIW, I've prepared a test version in a PPA[1] which keeps the rules from Debian[2] but prevents the fully numeric names. This is what it looks like: $ useradd 0 useradd: invalid user name '0' $ echo $? 3 $ sudo useradd 0c0 $ sudo useradd 0 --badnames $ cat /etc/passwd | grep ^0 0c0:x:1001:1001::/home/0c0:/bin/sh 0:x:1002:1002::/home/0:/bin/sh [1] https://launchpad.net/~vtapia/+archive/ubuntu/sf305373 [2] https://salsa.debian.org/debian/shadow/-/blob/master/debian/patches/506_relaxed_usernames -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1927078 Title: Don't allow useradd to use fully numeric names To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/shadow/+bug/1927078/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
