Comment 0 for bug 1916541

On hirsute, on Jan 20, postfix stopped sending outgoing mails with the error

Feb 22 23:35:18 pccross postfix/smtp[9582]: fatal: unknown service: smtp/tcp

There were no changes in the system other than daily upgrades.

Strace shows that `smtp` process (while chrooted), after successful open of the file in the queue, tried to use NSS, ran `fstat()` against `/etc/nsswitch.conf`, that succeeded (presumably using the copy in the /var/spool/postfix/etc/ directory), but did there was no subsequent read, and the next syscall is `sendto()` of the error message to syslog.

There was a big upgrade between the last successful and the first unsuccessful email delivery, and among other things libc was updated from 2.32-0ubuntu6 to 2.33-0ubuntu2. I suspect that there was some change in the NSS in libc that resulted in the failure of `getservbyname()`.

Is anybody else observing this problem?

ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: postfix 3.5.6-1
ProcVersionSignature: Ubuntu 5.10.0-14.15-generic 5.10.11
Uname: Linux 5.10.0-14-generic x86_64
ApportVersion: 2.20.11-0ubuntu59
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: X-Cinnamon
Date: Tue Feb 23 00:02:13 2021
EtcMailname: pccross.average.org
Hostname: pccross
PostconfMydomain: localdomain
PostconfMyhostname: pccross.localdomain
PostconfMyorigin: /etc/mailname
ResolvConf:
 # Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
 # DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

 nameserver 127.0.0.1
 search average.org
SourcePackage: postfix
UpgradeStatus: No upgrade log present (probably fresh install)