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

Systemctl stop and disable in one command

systemctl disable --now someservice

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

State: degraded

Find failing service

systemctl | grep failed

and if al fixed remove warning with

systemctl reset-failed [unitname]

Analyze boot processes

systemd-analyze blame

remove nameservers from /run/systemd/resolve/resolv.conf

Edit /etc/systemd/resolved.conf Take out the DNS line and

systemctl restart systemd-resolved

gateway4 has been deprecated

Using routes:

routes:
- to: default
  via: 192.168.1.1

Systemd and DNS, list nameservers used

resolvectl status

Change nameserversers resolvectl uses

On Ubuntu

Edit the netplan file

netplan generate
netplan apply

Without editing netplan

So does NOT update your netplan config!

resolvectl dns eth0 8.8.8.8 8.8.4.4

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

Means systemd-resolved is not running

Restart:

systemctl restart systemd-resolved
      

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

Failed with result 'core-dump'

Location of the dumps: /var/lib/systemd/coredump/

• How to analyze a core dump on Linux

apt install systemd-coredump

coredumpctl list

etc