:PROPERTIES:
:ID:       941e0a85-1bb4-45be-a729-1b577c7ee317
:END:
#+title: Command line: journalctl
#+date: "2021-05-20 23:07:39 +08:00"
#+date_modified: "2021-09-01 22:39:16 +08:00"
#+language: en
#+property: header-args  :results none


The logging daemon of systemd (see [[id:d83c099a-fc11-4ccc-b265-4de97c85dcbe][systemd-journald]]).
Not only it can view your logs, you can ask to view specific logs and delete some of them.

For more information, see =journalctl.1= manual page.




* Options

- =-b, --boot [ID][+OFFSET]= shows the logs starting from given boot time (or current boot if empty).
- =-e, --pager-end= to go to the end of the logs.
- =-f, --follow= watches the logs.
- =-k, --dmesg= prints the logs from the kernel.
- =--list-boots= prints a list of boots useful for knowing the boot logs from =-b=.
- =--user-unit= shows logs from a user unit.
- =-u, --unit [UNIT]= shows the logs of a system unit.
- =--vacuum-time [TIMESPAN]= deletes logs older than the specified timespan [fn:: View =systemd.time.5= for more information.].
- =-x, --catalog= prints helpful messages such as the documentation URIs.




* Examples

This tool is already comprehensive.
Needs a comprehensive database of examples to fight against this scope.


** Watch the logs from a specific unit at boot time

#+begin_src
journalctl --user-unit borgbackup.service -fb
#+end_src


** Delete the logs older than a month

#+begin_src
journalctl --vacuum-time=1m
#+end_src


** View the latest logs with helpful messages

#+begin_src
journalctl -xe
#+end_src


** Get the logs of a service unit from 2 boots ago

#+begin_src
journalctl --boot -2 --user-unit borgbackup@personal-drive.service
#+end_src