Systemd

 

Documentation

• Useful systemd commands
• http://www.freedesktop.org/wiki/Software/systemd/
• https://wiki.ubuntu.com/systemd
• Creating systemd service
• https://wiki.ubuntu.com/SystemdForUpstartUsers
• How To Use Systemctl to Manage Systemd Services and Units
• How to switch from NetworkManager to systemd-networkd on Linux
• https://fedoraproject.org/wiki/SysVinit_to_Systemd_Cheatsheet
• Predictable Network Interface Names
• [https://blog.darknedgy.net/technology/2020/05/02/0/index.html#tech-critique
• Systemd service tutorial
• https://www.freedesktop.org/wiki/Software/systemd/dbus/ Systemd and dbus
• Single user/emergency

Locations

/etc/systemd
/usr/lib/systemd/
/lib/systemd

 

HOWTO

systemctl verbose

SYSTEMD_LOG_LEVEL=debug systemctl start yourservice

Services

List enabled services

See https://www.baeldung.com/linux/systemctl-list-enabled-services

systemctl list-unit-files --state=enabled

Edit systemd service file

systemctl edit --full my.service

Timers

• https://opensource.com/article/20/7/systemd-timers
• https://wiki.archlinux.org/title/Systemd/Timers
• https://linuxhint.com/cron_systemd_timer/ also about random time

man systemd.timer

List active timers

systemctl list-timers

List all timers

systemctl list-timers --all

Enable timer

systemctl enable fstrim.timer

Auto restart crashed services

systemctl edit elasticsearch.service 

add:

[Service]
Restart=always

then

systemctl daemon-reload
systemctl restart elasticsearch.service

And to get an email when service gets restarted: https://dev.to/setevoy/linux-systemd-unit-files-edit-restart-on-failure-and-email-notifications-5h3k

Logs

View systemd logs

journalctl -u postfix

FAQ

Analyze boot processes

systemd-analyze blame

gateway4 has been deprecated

Using routes:

routes:
- to: default
  via: 192.168.1.1

Systemd and DNS

resolvectl status

Change nameserversers resolvectl uses

On Ubuntu

Edit the netplan file

netplan generate
netplan apply

Failed to get global data: Unit dbus-org.freedesktop.resolve1.service not found.

Means systemd-resolved is not running

Restart:

systemctl restart systemd-resolved
      
      

 

Add nameserver

Sacrifice a chicken

 

Flush caches

1. thing from the past

systemd-resolve --flush-caches

now use

resolvectl flush-caches

All status

systemctl status -a

syslog spam

https://psyq123.wordpress.com/2015/06/29/if-you-get-a-lot-of-logspam-from-systemd-in-your-varlogsyslog-this-might-help/

list available services

systemctl list-unit-files

or

systemctl list-units

 

normal interface names

net.ifnames=0

Show failed services

systemctl --failed

 

systemd: Started Session

Change loglevel to notice in /etc/systemd/system.conf

systemctl daemon-reexec

Status

Active: inactive (dead)

parameter ActiveState would return inactive

SubState returns dead