systemd-journald RateLimitBurst is sometimes divided by 4

Bug #1732803 reported by David Glasser on 2017-11-17
10
This bug affects 1 person
Affects Status Importance Assigned to Milestone
systemd (Ubuntu)
Medium
Unassigned
Xenial
Medium
Unassigned

Bug Description

[Impact]

systemd-journald allows you to configure a per-service journal rate limit in /etc/systemd/journald.conf via the RateLimitBurst parameter. systemd-journald has
code that effectively increases the rate limit when there is a lot of disk space available.
However, all versions of systemd before v232 had a bug which would shrink the rate limit
when there is between 1 and 16 MB available on disk.

If you designed a service to log at a rate R and configured RateLimitBurst to a little above R, this can lead to loss of logs when free disk is between 1 and 16 MB, as your service will be surprisingly rate limited at lower than your configured rate.

This bug was fixed upstream in https://github.com/systemd/systemd/pull/4218
It is a straightforward one-line change that makes the code match the comments under it.

[Test Case]

Run a systemd service that prints lots of logs (eg `yes`). Fill your disk to have only 1MB full. Use journalctl to see how many log lines are between "Suppressed" lines. Note that it is 1/4 of what you'd expect. (Admittedly this test case is a little hard to achieve since journald itself is writing to disk. I did run into this in production.)

[Regression Potential]

This does mean that journald can write slightly more to disk than it did before when free disk is between 1 and 16MB, but given that the full burst rate is available below 1MB it seems unlikely that any systems are depending on this change in order to not break.

The fix has been in systemd since v232 (shipped in Zesty). I would like to see it in Xenial.

[Other Info]

I am seeing this on:
ubuntu@ip-10-0-2-135[i-0b196ce4b8dc3fc55] 1 ~/systemd-229$ lsb_release -rd
Description: Ubuntu 16.04.3 LTS
Release: 16.04
ubuntu@ip-10-0-2-135[i-0b196ce4b8dc3fc55] 0 ~/systemd-229$ apt-cache policy systemd
systemd:
  Installed: 229-4ubuntu19
  Candidate: 229-4ubuntu21
  Version table:
     229-4ubuntu21 500
        500 http://us-east-1.ec2.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
 *** 229-4ubuntu19 100
        100 /var/lib/dpkg/status
     229-4ubuntu10 500
        500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
     229-4ubuntu4 500
        500 http://us-east-1.ec2.archive.ubuntu.com/ubuntu xenial/main amd64 Packages

This bug seems to date back to the original implementation of rate limiting (https://github.com/systemd/systemd/commit/6e409ce10d).

David Glasser (glasser) wrote :
David Glasser (glasser) wrote :

Correction: I believe this occurs when the amount of remaining space until journald hits its allocated limit is between 1 and 16MB, not when the entire filesystem has that little space left. (This makes it much more likely to occur: any system that is using logs enough for them to be rotated due to space will hit this issue whenever it's near rotation time.)

David Glasser (glasser) wrote :

This is my first attempt at a debdiff and an SRU. I'd love to know if I've filed it properly!

Evan Broder (broder) on 2017-11-22
Changed in systemd (Ubuntu):
status: New → Fix Released
David Glasser (glasser) wrote :

I got some advice on mistakes in my update to changelog. This version should be better.

Changed in systemd (Ubuntu Xenial):
status: New → In Progress
Changed in systemd (Ubuntu):
importance: Undecided → Medium
Changed in systemd (Ubuntu Xenial):
importance: Undecided → Medium

Hello David, or anyone else affected,

Accepted systemd into xenial-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/systemd/229-4ubuntu21.2 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-xenial to verification-done-xenial. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-xenial. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

Changed in systemd (Ubuntu Xenial):
status: In Progress → Fix Committed
tags: added: verification-needed verification-needed-xenial
Dimitri John Ledkov (xnox) wrote :

Journal is still operating correctly. It is hard to trigger the particular edge condition in question, but overall journal operation has not regressed.

tags: added: verification-done verification-done-xenial
removed: verification-needed verification-needed-xenial
Launchpad Janitor (janitor) wrote :

This bug was fixed in the package systemd - 229-4ubuntu21.2

---------------
systemd (229-4ubuntu21.2) xenial; urgency=medium

  [ Dimitri John Ledkov ]
  * udev: Mark ndb devices as inactive until connected. (LP: #696435)
  * networkd: in dhcp, change UseMTU default to true, to accept DHCP provided MTU by default.
    (LP: #1717471)
  * sysctl: apply parameters in-order, instead of randomly. (LP: #1718444)
  * networkd: apply promote_secondaries, to make DHCP lease changes work.
    (LP: #1721223)
  * shutdown: sync filesystems, before going into a killing spree.
    (LP: #1722481)
  * sysctl: do not fail, when cannot apply sysctl changes due to read-only sysfs in containers.
    (LP: #1734409)
  * networkd,wait-online: add RequiredForOnline to mark mandatory/optional links for boot.
    (LP: #1737570)

  [ David Glasser ]
  * journald: don't reduce BurstRateLimit on low disk space (LP: #1732803)

 -- Dimitri John Ledkov <email address hidden> Wed, 21 Feb 2018 13:46:37 +0000

Changed in systemd (Ubuntu Xenial):
status: Fix Committed → Fix Released

The verification of the Stable Release Update for systemd has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

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