rsyslog

The rocket-fast system for log processing

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imjournal: Systemd Journal Input Module

Module Name: imjournal
Author: Milan Bartos <mbartos@redhat.com> (This module is not project-supported)
Available since: 7.3.11

Purpose

Provides the ability to import structured log messages from systemd journal to syslog.

Note that this module reads the journal database, what is considered a relativly performance-intense operation. As such, the performance of a configuration utilizing this module may be notably slower than when using imuxsock. The journal provides imuxsock with a copy of all “classical” syslog messages, however, it does not provide structured data. Only if that structured data is needed, imjournal must be used. Otherwise, imjournal may simply be replaced by imuxsock, and we highly suggest doing so.

We suggest to check out our short presentation on rsyslog journal integration to learn more details of anticipated use cases.

Warning: Some versions of systemd journal have problems with database corruption, which leads to the journal to return the same data endlessly in a tight loop. This results in massive message duplication inside rsyslog probably resulting in a denial-of-service when the system ressouces get exhausted. This can be somewhat mitigated by using proper rate-limiters, but even then there are spikes of old data which are endlessly repeated. By default, ratelimiting is activated and permits to process 20,000 messages within 10 minutes, what should be well enough for most use cases. If insufficient, use the parameters described below to adjust the permitted volume. It is strongly recommended to use this plugin only if there is hard need to do so.

Notable Features

Configuration Parameters

Note

Parameter names are case-insensitive.

Module Parameters

PersistStateInterval

type default mandatory obsolete legacy directive
integer 10 no $imjournalPersistStateInterval

This is a global setting. It specifies how often should the journal state be persisted. The persists happens after each number-of-messages. This option is useful for rsyslog to start reading from the last journal message it read.

StateFile

type default mandatory obsolete legacy directive
word none no $imjournalStateFile

This is a global setting. It specifies where the state file for persisting journal state is located. If a full path name is given (starting with “/”), that path is used. Otherwise the given name is created inside the working directory.

Ratelimit.Interval

type default mandatory obsolete legacy directive
integer 600 no $imjournalRatelimitInterval

Specifies the interval in seconds onto which rate-limiting is to be applied. If more than ratelimit.burst messages are read during that interval, further messages up to the end of the interval are discarded. The number of messages discarded is emitted at the end of the interval (if there were any discards). Setting this to value zero turns off ratelimiting. Note that it is not recommended to turn of ratelimiting, except that you know for sure journal database entries will never be corrupted. Without ratelimiting, a corrupted systemd journal database may cause a kind of denial of service (we are stressing this point as multiple users have reported us such problems with the journal database - information current as of June 2013).

Ratelimit.Burst

type default mandatory obsolete legacy directive
integer 20000 no $imjournalRatelimitBurst

Specifies the maximum number of messages that can be emitted within the ratelimit.interval interval. For futher information, see description there.

IgnorePreviousMessages

type default mandatory obsolete legacy directive
binary off no $ImjournalIgnorePreviousMessages

This option specifies whether imjournal should ignore messages currently in journal and read only new messages. This option is only used when there is no StateFile to avoid message loss.

DefaultSeverity

type default mandatory obsolete legacy directive
severity 5 no $ImjournalDefaultSeverity

Some messages comming from journald don’t have the SYSLOG_PRIORITY field. These are typically the messages logged through journald’s native API. This option specifies the default severity for these messages. Can be given either as a name or a number. Defaults to ‘notice’.

DefaultFacility

type default mandatory obsolete legacy directive
facility LOG_USER no $ImjournalDefaultFacility

Some messages comming from journald don’t have the SYSLOG_FACILITY field. These are typically the messages logged through journald’s native API. This option specifies the default facility for these messages. Can be given either as a name or a number. Defaults to ‘user’.

UsePidFromSystem

type default mandatory obsolete legacy directive
binary 0 no none

Retrieves the trusted systemd parameter, _PID, instead of the user systemd parameter, SYSLOG_PID, which is the default. This option override the “usepid” option. This is now deprecated. It is better to use usepid=”syslog” instead.

UsePid

type default mandatory obsolete legacy directive
string both no none

Sets the PID source from journal.

syslog
imjournal retrieves SYSLOG_PID from journal as PID number.
system
imjournal retrieves _PID from journal as PID number.
both
imjournal trying to retrieve SYSLOG_PID first. When it is not available, it is also trying to retrive _PID. When none of them is available, message is parsed without PID number.

IgnoreNonValidStatefile

type default mandatory obsolete legacy directive
binary on no none

When a corrupted statefile is read imjournal ignores the statefile and continues with logging from the beginning of the journal (from its end if IgnorePreviousMessages is on). After PersistStateInterval or when rsyslog is stopped invalid statefile is overwritten with a new valid cursor.

WorkAroundJournalBug

type default mandatory obsolete legacy directive
binary off no none

New in version 8.37.0.

When journald instance rotates its files it is possible that duplicate records appear in rsyslog. If you turn on this option imjournal will keep track of cursor with each message to work around this problem. Be aware that in some cases this might result in imjournal performance hit.

Statistic Counter

This plugin maintains statistics for each listener and for each worker thread. The listener statistic is named “imjournal”.

The following properties are maintained for each listener:

  • read - total number of message read from journal since startup.
  • submitted - total number of messages submitted to main queue after reading from journal for processing since startup. All records may not be submitted due to rate-limiting.
  • discarded - total number of messages that were read but not submitted to main queue due to rate-limiting.
  • failed - total number of failures to read messges from journal.
  • poll_failed - total number of journal poll failures.
  • rotations - total number of journal file rotations.
  • recovery_attempts - total number of recovery attempts by imjournal after unknown errors by closing and re-opening journal.
  • ratelimit_discarded_in_interval - number of messages discarded due to rate-limiting within configured rate-limiting interval.
  • disk_usage_bytes - total size of journal obtained from sd_journal_get_usage().

Here is an example output of corresponding imjournal impstat message, which is produced by loading imjournal with default rate-limit interval and burst and running a docker container with log-driver as journald that spews lots of logs to stdout:

Jun 13 15:02:48 app1-1.example.com rsyslogd-pstats: imjournal: origin=imjournal submitted=20000 read=216557
discarded=196557 failed=0 poll_failed=0 rotations=6 recovery_attempts=0 ratelimit_discarded_in_interval=196557
disk_usage_bytes=106610688

Although these counters provide insight into imjournal end message submissions to main queue as well as losses due to rate-limiting or other problems to extract messages from journal, they don’t offer full visibility into journal end issues. While these counters measure journal rotations and disk usage, they do not offer visibility into message loss due to journal rate-limiting. sd_journal_* API does not provide any visibility into messages that are discarded by the journal due to rate-limiting. Journald does emit a syslog message when log messages cannot make it into the journal due to rate-limiting:

Jun 13 15:50:32 app1-1.example.com systemd-journal[333]: Suppressed 102 messages from /system.slice/docker.service

Such messages can be processed after they are read through imjournal to get a signal for message loss due to journal end rate-limiting using a dynamic statistics counter for such log lines with a rule like this:

dyn_stats(name="journal" resettable="off")
if $programname == 'journal' and $msg contains 'Suppressed' and $msg contains 'messages from' then {
        set $.inc = dyn_inc("journal", "suppressed_count");
}

Caveats/Known Bugs:

  • As stated above, a corrupted systemd journal database can cause major problems, depending on what the corruption results in. This is beyond the control of the rsyslog team.
  • imjournal does not check if messages received actually originated from rsyslog itself (via omjournal or other means). Depending on configuration, this can also lead to a loop. With imuxsock, this problem does not exist.

Build Requirements:

Development headers for systemd, version >= 197.

Example

The following example shows pulling structured imjournal messages and saving them into /var/log/ceelog.

module(load="imjournal" PersistStateInterval="100"
       StateFile="/path/to/file") #load imjournal module
module(load="mmjsonparse") #load mmjsonparse module for structured logs

template(name="CEETemplate" type="string" string="%TIMESTAMP% %HOSTNAME% %syslogtag% @cee: %$!all-json%\n" ) #template for messages

action(type="mmjsonparse")
action(type="omfile" file="/var/log/ceelog" template="CEETemplate")

See also

Help with configuring/using Rsyslog:

  • Mailing list - best route for general questions
  • GitHub: rsyslog source project - detailed questions, reporting issues that are believed to be bugs with Rsyslog
  • Stack Exchange (View, Ask) - experimental support from rsyslog community

See also

Contributing to Rsyslog:

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