[Bug 1916541] Re: smtp "fatal: unknown service: smtp/tcp", probably after libc upgrade

[Eugene Crosser]

Thanks Paride,
I am glad that you could reproduce it, and it's not like either I or my system is crazy :)

I noticed something that may or may not be relevant. I have another
machine with hirsute, that was purchased a year+ ago and has undergone
less package upgrades: mail delivery _worked_ there. I did _not_
reconfigure it as "satellite" and I don't remember how it was configured
at the start, probably as all default.

The difference that I noticed is that the contents of
/var/spool/postfix/usr/lib (as filled by posttix's startup procedure) is
significantly different. One wild speculation would be that some shared
lib there is opportunistically loaded that refers to an earlier glibc
version, and that subsequently somehow results in impossibility to load
nss libraries.

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https://bugs.launchpad.net/bugs/1916541

Title:
  smtp "fatal: unknown service: smtp/tcp", probably after libc upgrade

Status in glibc package in Ubuntu:
  New
Status in postfix package in Ubuntu:
  Confirmed

Bug description:
  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 there was no subsequent
  `open()`, 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)

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