The journalctl command

The journalctl command

This is a good linux command for Linux maintenance.
First step is to read the documentation:

[root@localhost mythcat]# man journalctl
JOURNALCTL(1) journalctl JOURNALCTL(1)

NAME
 journalctl - Query the systemd journal

SYNOPSIS
 journalctl [OPTIONS...] [MATCHES...]

DESCRIPTION
 journalctl may be used to query the contents of the systemd(1) journal
 as written by systemd-journald.service(8).

 If called without parameters, it will show the full contents of the
 journal, starting with the oldest entry collected.

 If one or more match arguments are passed, the output is filtered
 accordingly. A match is in the format "FIELD=VALUE", e.g.
 "_SYSTEMD_UNIT=httpd.service", referring to the components of a
 structured journal entry. See systemd.journal-fields(7) for a list of
 well-known fields. If multiple matches are specified matching different
 fields, the log entries are filtered by both, i.e. the resulting output
 will show only entries matching all the specified matches of this kind.
 If two matches apply to the same field, then they are automatically
 matched as alternatives, i.e. the resulting output will show entries
 matching any of the specified matches for the same field. Finally, the
 character "+" may appear as a separate word between other terms on the
 command line. This causes all matches before and after to be combined
 in a disjunction (i.e. logical OR).
 ...

The self maintenance method is to vacuum the logs.
This help you with free space into your Linux OS.
For example: I got 3 Gigabytes of data in just 3 days.

# journalctl --vacuum-time=3d

Vacuuming done, freed 3.7G of archived journals on disk. To clean up this you can use the command into several ways:

• by time

journalctl --vacuum-time=2d

• retain only the past 500 MB

journalctl --vacuum-size=500M

As you know: The is an init system used in Linux distributions to bootstrap the user space and manage all processes subsequently. The journald daemon handles all of the messages produced by the kernel, initrd, services, etc. You can use the journalctl utility, which can be used to access and manipulate the data held within the journal. Lets start with some examples: How to see the configuration file for this process:

[root@localhost mythcat]# cat /etc/systemd/journald.conf

Also you can see the status of this service:

[root@localhost mythcat]# systemctl status systemd-journald
? systemd-journald.service - Journal Service
 Loaded: loaded (/usr/lib/systemd/system/systemd-journald.service; static; vendor preset: disabled)
 Active: active (running) since Tue 2017-03-28 09:12:20 EEST; 1h 8min ago
 Docs: man:systemd-journald.service(8)
 man:journald.conf(5)
 Main PID: 803 (systemd-journal)
 Status: "Processing requests..."
 Tasks: 1 (limit: 4915)
 CGroup: /system.slice/systemd-journald.service
 ??803 /usr/lib/systemd/systemd-journald

Mar 28 09:12:20 localhost.localdomain systemd-journald[803]: Runtime journal (/run/log/journal/) is 8.0M,
max 371.5M, 363.5M free.
Mar 28 09:12:20 localhost.localdomain systemd-journald[803]: Journal started
Mar 28 09:12:22 localhost.localdomain systemd-journald[803]: System journal (/var/log/journal/) is 3.9G,
max 4.0G, 23.8M free.
Mar 28 09:12:23 localhost.localdomain systemd-journald[803]: Time spent on flushing to /var is 915.454ms

I hope this article will help you on Linux maintenance

download file now