[Bug 1810351] Re: journalctl fails to work inside systemd service

[Edward Gow]

Part of the mystery is solved and part not.

SOLVED:

The problem was that journal entries were not being stored on disk and
journalctl was not showing entries from memory.

The default Ubuntu config has settings  
Storage=auto
SplitMode=uid

Also, the directory /var/log/journal does not exist by default and does
not get created in Storage=auto mode. Creating the /var/log/journal
directory and restarting journald so that entries get stored to disk
fixes the problem.


NOT SOLVED:

It is still unclear why journalctl would display output when run from
the shell but not when run from systemd. It would seem that in a systemd
--user unit it could not access the in-memory logs.


I would suggest that the default Ubuntu install should have the /var/log/journal directory in place so that journalctl will work correctly out-of-the-box.

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https://bugs.launchpad.net/bugs/1810351

Title:
  journalctl fails to work inside systemd service

Status in systemd package in Ubuntu:
  New

Bug description:
  Using

  Ubuntu 16.04.4 LTS

  and

  Package: systemd
  Architecture: amd64
  Version: 229-4ubuntu21.10
  Multi-Arch: foreign
  Priority: required
  Section: admin
  Origin: Ubuntu

  The journalctl(1) command cannot be used in a systemd OnFailure
  service to get error logs. To replicate the issue

  1) Create a service unit

  [Unit]
  Description=%n

  [Service]
  #ExecStart=/bin/sh -xv -c 'systemctl --user status <your unit> -o cat -n 20 | mail -s "Unit failed" <your email address>'
  ExecStart=/bin/sh -c 'journalctl --user-unit=<your unit> -o verbose -q -n 20 | mail -s "Unit failed" <your email address>'

  2) enable the unit

  3) start the unit

  You will get a failure message from journalctl and mail of

  sh[28225]: No journal files were opened due to insufficient permissions.
  sh[28225]: mail: Null message body; hope that's ok

  4) switch the comment # to the journalctl ExecStart and uncomment the
  systemctl ExecStart line

  From systemctl you will get journal output in the email.

  The man page for systemctl states  "In addition, journalctl
  --unit=NAME or journalctl --user-unit=NAME use a similar filter for
  messages and might be more convenient."  and indeed it would if it
  worked properly.

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