I did some more investigation, and did not find an explanation, but I am writing it here to maybe save somebody else some effort.
Postfix uses normal(?) `getservbyname(service, protocol)` in the file src/smtp/smtp_connect.c line 363: if ((sp = getservbyname(service, protocol)) == 0) msg_fatal("unknown service: %s/%s", service, protocol); and I see this message in the log. On the other hand, a simple program that performs `chroot("/var/spool/postfix")` and calls `getservbyname()` _works correctly_ on hirsute (C code in attachment): crosser@pccross:~/src$ sudo ./getsrvname [sudo] password for crosser: s_name="smtp", s_port=25, s_proto="tcp" Note though that in such form the the program does not try to use NSS, it just opens `/etc/services` directly. While postfix's `smtp` goes through nsswitch, as can be seen in the strace log from my previous attachment. ** Attachment added: "getsrvname.c" https://bugs.launchpad.net/ubuntu/+source/postfix/+bug/1916541/+attachment/5466343/+files/getsrvname.c -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1916541 Title: smtp "fatal: unknown service: smtp/tcp", probably after libc upgrade To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/postfix/+bug/1916541/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs