clr-service-restart

A program that restarts systemd services that are using software
components that have been updated.

How it works

The Linux kernel maintains information about running processes in the
procfs filesystem. This information can be used to identify processes
that are using resources that are no longer physically present on
the file system, such as when a binary or system library is updated.

Any software update causes the kernel to see that a reference to a
binary or a reference to a library is no longer corresponding with the
actual current version of the library or binary on the filesystem. If
this happens, the kernel will mark the procfs entries for those
references as (deleted). Specifically the exe symlink will get
marked in this way if the binary is updated, and the maps file will
get updated in this way if a library component is updated.

Using these references, we now know which programs are currently being
executed that are holding references to outdated libraries or binaries,
and therefore should be restarted.

However, we do not want to restart programs that are not part of a
system unit, or in some other way are not part of the system domain. In
order to avoid considering all processes running for the purpose of
restarting them, we restrict consideration to only those processes
that are listed as active tasks in the systemd system.slice
hierarchy maintained under /sys/fs/cgroup/systemd/. This hierarchy
only contains units (and therefore tasks) in the system domain and
excludes user units or user programs.

Configuration

It’s extremely risky to restart all units unconditionally since some
units may require specific ordering, interaction or other factors
to be considered. By default, this program will not restart any
service automatically, and will only consider units that have been
explicitly marked as allowed by either the local administrator
or the distribution. This is done through maintaining symlinks in
/usr/share/clr-service-restart and /etc/clr-service-restart. If a
valid symlink is found in these folders, the unit will be considered
for restarting. If a symlink is found in /etc/clr-service-restart
with the name of a unit pointing to /dev/null it will be
omitted for consideration and not be restarted. Links in the
/etc/clr-service-restart location take precedence over those in
/usr/share/clr-service-restart. Links to /dev/null in the
/usr/share/clr-service-restart location are invalid.

Commands

These symlinks can be manipulated by the local administrator with the
clr-service-restart program, which understands the following 3
commands:

• allow "foo.service":

  Mark “foo.service” as restartable.

• disallow "bar.service":

  Mark “bar.service” as not restartable.

• default "baz.service":

  Remove local preferences and revert to the distribution default
  for “baz.service”.

If clr-service-restart is executed without any commands, it will
restart all services that are marked allow for restart.

Options

The following options are understood. These options may not be used
together with the allow, disallow and default commands.

• -n:

  Don’t actually perform any restarts, just show what would happen
  if the program would execute normally. This makes the program
  more verbose.

• -a:

  Consider all system units. With this option, all system units that
  are running will be considered for restarting. This should normally
  only be done interactively, and never in an automated fashion.

Bugs

Please report bugs to: dev@lists.clearlinux.org

License

Copyright © 2018 Intel Corporation

Author: Auke-jan H. Kok <auke-jan.h.kok@intel.com>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published
by the Free Software Foundation, either version 3 of the License,
or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see https://www.gnu.org/licenses.