Revision as of 13:01, 6 March 2025

Documentation

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

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

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

@@ Line 1: / Line 1: @@
-=Documentation=
-*[https://www.dynacont.net/documentation/linux/Useful_SystemD_commands/ Useful systemd commands]
-*http://www.freedesktop.org/wiki/Software/systemd/
-*https://wiki.ubuntu.com/systemd
-*https://wiki.ubuntu.com/SystemdForUpstartUsers
-*[https://www.digitalocean.com/community/tutorials/how-to-use-systemctl-to-manage-systemd-services-and-units How To Use Systemctl to Manage Systemd Services and Units]
-*[http://xmodulo.com/switch-from-networkmanager-to-systemd-networkd.html How to switch from NetworkManager to systemd-networkd on Linux]
-*https://fedoraproject.org/wiki/SysVinit_to_Systemd_Cheatsheet
-*[https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/ Predictable Network Interface Names]
-*[https://blog.darknedgy.net/technology/2020/05/02/0/index.html#tech-critique
-=Locations=
+&nbsp;
+= Documentation =
+*[https://www.dynacont.net/documentation/linux/Useful_SystemD_commands/ Useful systemd commands]
+*[http://www.freedesktop.org/wiki/Software/systemd/ http://www.freedesktop.org/wiki/Software/systemd/]
+*[https://wiki.ubuntu.com/systemd https://wiki.ubuntu.com/systemd]
+*[https://wiki.archlinux.org/index.php/Systemd Creating systemd service]
+*[https://wiki.ubuntu.com/SystemdForUpstartUsers https://wiki.ubuntu.com/SystemdForUpstartUsers]
+*[https://www.digitalocean.com/community/tutorials/how-to-use-systemctl-to-manage-systemd-services-and-units How To Use Systemctl to Manage Systemd Services and Units]
+*[http://xmodulo.com/switch-from-networkmanager-to-systemd-networkd.html How to switch from NetworkManager to systemd-networkd on Linux]
+*[https://fedoraproject.org/wiki/SysVinit_to_Systemd_Cheatsheet https://fedoraproject.org/wiki/SysVinit_to_Systemd_Cheatsheet]
+*[https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/ Predictable Network Interface Names]
+*[[https://blog.darknedgy.net/technology/2020/05/02/0/index.html#tech-critique https://blog.darknedgy.net/technology/2020/05/02/0/index.html#tech-critique]
+*[https://mohsensy.github.io/sysadmin/2018/08/19/systemd-service-tutorial.html Systemd service tutorial]
+*[https://www.freedesktop.org/wiki/Software/systemd/dbus/ https://www.freedesktop.org/wiki/Software/systemd/dbus/ Systemd and dbus]
+*[https://www.thegeekdiary.com/how-to-boot-into-rescue-mode-or-emergency-mode-through-systemd-in-centos-rhel-7-and-8/ Single user/emergency]
+= Locations =
   /etc/systemd
   /usr/lib/systemd/
   /lib/systemd
-=FAQ=
+&nbsp;
+= 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://opensource.com/article/20/7/systemd-timers]
+*[https://wiki.archlinux.org/title/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
+== 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 ===
+# thing from the past
+ systemd-resolve --flush-caches
+now use
+ resolvectl flush-caches
+== All status ==
-==All status==
   systemctl status -a
-==syslog spam==
+== syslog spam ==
-https://psyq123.wordpress.com/2015/06/29/if-you-get-a-lot-of-logspam-from-systemd-in-your-varlogsyslog-this-might-help/
+[https://psyq123.wordpress.com/2015/06/29/if-you-get-a-lot-of-logspam-from-systemd-in-your-varlogsyslog-this-might-help/ 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 ==
-==list available services==
   systemctl list-unit-files
 or
   systemctl list-units
+&nbsp;
+== normal interface names ==
-==normal interface names==
   net.ifnames=0
-==Show failed services==
+== Show failed services ==
   systemctl --failed
+&nbsp;
+== systemd: Started Session ==
-==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

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