[Bug 1928259] Re: Package upgrade won't restart services

[Launchpad Bug Tracker]

This bug was fixed in the package nfs-utils - 1:1.3.4-2.5ubuntu6.1

---------------
nfs-utils (1:1.3.4-2.5ubuntu6.1) groovy; urgency=medium

  * d/nfs-common.postinst: always start nfs-utils.service, so the restart in
    the #DEBHELPER# section can do its job if needed (LP: #1928259)

 -- Andreas Hasenack <andreas at canonical.com>  Mon, 24 May 2021 17:55:01
-0300

** Changed in: nfs-utils (Ubuntu Groovy)
       Status: Fix Committed => Fix Released

-- 
You received this bug notification because you are a member of Ubuntu
Foundations Bugs, which is subscribed to nfs-utils in Ubuntu.
https://bugs.launchpad.net/bugs/1928259

Title:
  Package upgrade won't restart services

Status in nfs-utils package in Ubuntu:
  Fix Released
Status in nfs-utils source package in Bionic:
  Fix Committed
Status in nfs-utils source package in Focal:
  Fix Committed
Status in nfs-utils source package in Groovy:
  Fix Released
Status in nfs-utils source package in Hirsute:
  Fix Released
Status in nfs-utils package in Debian:
  New
Status in nfs-utils package in Fedora:
  Confirmed

Bug description:
  [Impact]
  In order to get the fixes provided by a package update, the affected services shipped in it need to be restarted. When that restart does not happen, the system remains running the old binaries with the bug(s).

  This bug was found while testing the fix for #1927745, which affected
  rpc.gssd, one of the services shipped in nfs-common. Without the
  restart, systems that installed the update are still affected by the
  bug.

  [Test Plan]
  To make the test simple, we are not going to mount an NFSv4 share using kerberos. We are just going to have a minimal configuration that gets rpc.gssd running to demonstrate the before and after of this bug.

  For a more thorough testing, which includes actually mounting an NFSv4
  export with kerberos, follow the test instructions of bug #1927745,
  and you will see that the manual restart included because of this bug
  here, after the package is updated, is no longer needed.

  TEST (A)
  # create a VM for the affected ubuntu release under test, login and run:
  sudo touch /etc/krb5.keytab
  sudo chmod 0600 /etc/krb5.keytab

  # install nfs-common
  sudo apt install nfs-common -y

  # note message about nfs-utils.service being disabled/static:
  nfs-utils.service is a disabled or a static unit, not starting it.

  # Manually start rpc-gssd. It will start, but since we have an empty
  # krb5.keytab file, it won't work. That's ok, we are not actually going to
  # mount nfsv4
  sudo systemctl start rpc-gssd.service

  # Check it's running, and make note of its pid:
  pidof rpc.gssd
  2994

  # reinstall nfs-common
  sudo apt install --reinstall nfs-common

  # note rpc-gssd wasn't restarted
  pidof rpc.gssd
  2994

  # install the fixed nfs-common package. Notice the message about starting a disabled or static unit no longer appears:
  sudo apt install nfs-common

  # this time, rpc.gssd is restarted
  pidof rpc.gssd
  5000

  TEST (B)
  This test is to confirm no new services are started after the fixed package is installed for the first time.

  # create a VM for the affected ubuntu release under test, login and run:
  sudo touch /etc/krb5.keytab
  sudo chmod 0600 /etc/krb5.keytab

  # install nfs-common that has the bug
  sudo apt install nfs-common -y

  # take a snapshot of running processes
  pstree > pstree.old

  # purge the nfs-common package
  sudo apt purge nfs-common -y

  # install the new nfs-common package
  sudo apt install nfs-common -y

  # take a new pstree snapshot and compare with the old one
  pstree > pstree.new
  diff -u pstree.old pstree.new

  Should be no difference.

  [Where problems could occur]
  Also known as "I'm doing an unconditional start in postinst, what could go wrong":
  - start services that were not started with the previous package on first install
  - systemd behavior change or bug and suddenly PartOf units also react to "start", instead of just "restart" and "stop" as documented
  - starting services that are not configured, and start fails, breaking postinst (but we have the proverbial || true to avoid that)

  [Other Info]
  This fix is a bit awkward, but I think it's in line with the SRU spirit of doing the least unpredictable change, and one that is simple and can be better understood.

  See the linked MP for an explanation of this fix, why it works, and other tests I did:
  https://code.launchpad.net/~ahasenack/ubuntu/+source/nfs-utils/+git/nfs-utils/+merge/403288

  [Original Description]

  Upgrading the nfs-common debian package will not restart its services.

  Specifically, the package tries to restart "nfs-utils.service", which is a "fake" service meant to coordinate all the other daemons that make up a modern NFS server. This service, however, as it is, cannot be enabled:
  $ sudo systemctl enable nfs-utils.service
  The unit files have no installation config (WantedBy, RequiredBy, Also, Alias
  settings in the [Install] section, and DefaultInstance for template units).
  This means they are not meant to be enabled using systemctl.
  Possible reasons for having this kind of units are:
  1) A unit may be statically enabled by being symlinked from another unit's
     .wants/ or .requires/ directory.
  2) A unit's purpose may be to act as a helper for some other unit which has
     a requirement dependency on it.
  3) A unit may be started when needed via activation (socket, path, timer,
     D-Bus, udev, scripted systemctl call, ...).
  4) In case of template units, the unit is meant to be enabled with some
     instance name specified

  Granted, d/rules of the nfs-utils package doesn't even try:
      dh_systemd_enable -p nfs-common nfs-client.target
      dh_systemd_enable -p nfs-kernel-server nfs-server.service
      dh_installinit -pnfs-common -R
      dh_systemd_start -p nfs-common --restart-after-upgrade nfs-utils.service
      dh_systemd_start -p nfs-kernel-server --restart-after-upgrade nfs-server.service

  We can see it tries to start and restart it, but that won't work on disabled or non-started services: deb-systemd-invoke won't do it:
  # If the job is disabled and is not currently running, the job is not started or restarted.
  # However, if the job is disabled but has been forced into the running state, we *do* stop
  # and restart it since this is expected behaviour for the admin who forced the start.
  # We don't autostart static units either.

  The above can be seen while attempting a fresh install (or even upgrade) of nfs-common:
  (...)
  Setting up nfs-common (1:1.3.4-2.5ubuntu6) ...

  Creating config file /etc/idmapd.conf with new version
  Adding system user `statd' (UID 113) ...
  Adding new user `statd' (UID 113) with group `nogroup' ...
  Not creating home directory `/var/lib/nfs'.
  Created symlink /etc/systemd/system/multi-user.target.wants/nfs-client.target → /lib/systemd/system/nfs-client.target.
  Created symlink /etc/systemd/system/remote-fs.target.wants/nfs-client.target → /lib/systemd/system/nfs-client.target.
  nfs-utils.service is a disabled or a static unit, not starting it.
  ^^^^^^^^^^^^^^^^^

  $ systemctl status nfs-utils.service
  ● nfs-utils.service - NFS server and client services
       Loaded: loaded (/lib/systemd/system/nfs-utils.service; static)
       Active: inactive (dead)

  This was found while testing the fix for bug #1927745. In that bug,
  the affected service is rpc.gssd and it's critical that it be
  restarted, but it's not happening. It will only be restarted if nfs-
  utils.service is already "started".

  I'm marking this bug as "high" because it prevents valid fixes from
  being deployed after just upgrading a package.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/nfs-utils/+bug/1928259/+subscriptions