linux

Systemd

→ Systemd-run

Run with the current user environment, with cgroup quota :

systemd-run --user  --scope sh -c 'echo hello ; sleep 10 ; echo $(pwd)'
systemd-run --user -pCPUQuota=200%  --scope sh -c 'echo hello ; sleep 10 ; echo $(pwd)'

→ calendar syntax

# verify syntax https://stackoverflow.com/a/75625764/3865083
systemd-analyze calendar 'Mon..Fri *-*-01' 'Mon *-*-02..03' --iterations 10

→ Journalctl

→ Filter

It centralizes all the systemd logs. You can filter by many criteria. It has a handy command completion:

journalctl _COMM=prometheus --since '2021-11-01 11:00' --until '2021-11-01 12:00'

→ Relative time filter

journalctl _COMM=prometheus --since -1h

→ Follow

This allows to see incoming logs:

journalctl _COMM=sshd -f

→ Kernel

journalctl -k

→ Boot

journalctl -b

→ Priority

0: Emergency. The system is unusable.
1: Alert. A condition has been flagged that should be corrected immediately.
2: Critical. This covers crashes, coredumps, and significant failures in primary applications.
3: Error. An error has been reported, but it is not considered severe.
4: Warning. Brings a condition to your attention that, if ignored, may become an error.
5: Notice. Used to report events that are unusual, but not errors.
6: Information. Regular operational messages. These do not require action.
7: Debug. Messages put into applications to make it easier for them to debug them.

→ Edit systemd files

The system files are located in /usr/lib/systemd/system and are overwriten when the system get updated.

There is two options to make your own unit:

  1. create a systemd file in /etc/systemd/system: it will overwrite the system's one
  2. run systemctl edit <service-name>: it will add content into /etc/systemd/system/<service>.service.d/override.conf. Note that it does not need daemon-reload and can only append config rows.

→ Cleanup journal

journalctl --disk-usage
journalctl --vacuum-size=2G

→ Get logs from service

journalctl -u matrix-synapse.service -f -n 1000

→ Redirect docker to journal

    logging:
      driver: journald
      options:
        tag: my-docker-app

→ Users

Users units are in both :

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