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Systemd Tutorial / Guide

Service Management

sudo systemctl start nginx start service
sudo systemctl stop nginx stop service
sudo systemctl restart nginx restart service
sudo systemctl reload nginx reload service config
sudo systemctl reload-or-restart nginx reload if possible or restart
sudo systemctl enable nginx enable
sudo systemctl enable –now unit enable and start
sudo systemctl disable nginx disable service
sudo systemctl reenable unit disable and re-enable
sudo systemctl mask nginx link to dev null
sudo systemctl unmask nginx set link back

Listing units:

systemctl all active
systemctl list-units all active
systemctl list-units –all all in mem active/inactive
systemctl list-unit-files all unit files ( including not in mem )
systemctl list-units –all –state=inactive  
systemctl list-units –type=service  

Status and info:

systemctl status nginx
systemctl cat nginx
systemctl list-dependencies nginx
systemctl list-dependencies –all nginx
systemctl show nginx

Checks:

systemctl is-active nginx
systemctl is-enabled nginx
systemctl is-failed nginx

More:

systemctl status pid  
systemd-analyze blame how long it took for each component to boot

Service commands ( for systemd and sysv init ):

sudo service nginx start
sudo service nginx stop
sudo service nginx status

Systemd Files and Directories

/lib/systemd/system

/run/systemd/system

/etc/systemd/system

/usr/lib/systemd/system/

Override or add parts of a unit file:

/etc/systemd/system/example.service.d
nginx.conf

Edit Services

sudo systemctl edit nginx.service  
sudo systemctl edit –full nginx.service full, not just snippet
sudo systemctl daemon-reload  
systemctl revert unit revert to vendor version

An example service:

/etc/systemd/system/myservice1.service
[Unit] Description=My useful service [Service] Type=simple ExecStart=/bin/bash /usr/bin/myservice1.sh [Install] WantedBy=multi-user.target

Another example service:

/etc/systemd/system/server1.service
[Unit] Description=My good server After=network.target [Service] type=Simple User=user1 Restart=on-failure RestartSec=1 StartLimitBurst=5 StartLimitIntervalSec=10 StartLimitAction=reboot ExecStart=/bin/python /opt/server1/scripts/server1.py [Install] WantedBy=multi-user.target </code>

Targets ( Runlevels )

systemctl list-units –type=target active targets
systemctl list-unit-files –type=target show all targets
systemctl get-default show default target
sudo systemctl set-default multi-user.target change default target
sudo systemctl set-default graphical.target change default target
systemctl list-dependencies multi-user.target show target units
sudo systemctl isolate multi-user.target switch to different target (temp)

Reboot / Poweroff

sudo systemctl poweroff  
sudo systemctl halt  
sudo systemctl reboot  
sudo systemctl rescue rescue / single user mode
systemctl hibernate  
systemctl suspend  
systemctl hybrid-sleep  

User Level Units

systemd –user user instance started by PAM ( on Arch )
/usr/lib/systemd/user/ from installed packages
~/.local/share/systemd/user/ for packages installed in home dir
/etc/systemd/user/ system wide, placed by admin
~/.config/systemd/user/ user controlled

Command:

systemctl –user enable unit

User env vars:

~/.config/environment.d/*.conf user env vars

See HERE for more info on user env vars.

Logs

Key info:

/etc/systemd/journald.conf The config file
/var/log/journal binary logs go here

Basic log commands:

journalctl show all log entries
journalctl -b only since boot
journalctl -k kernel messages, since boot (dmesg)
journalctl -k -b -5 kernel messages, 5 boots ago
journalctl -u nginx logs for this service
journalctl –utc UTC Timestamps

Time related info which is useful when working with logs:

timedatectl list-timezones
sudo timedatectl set-timezone zone
timedatectl status

To make sure persistent logging is enabled, first make sure this directory exists:


sudo mkdir -p /var/log/journal

And that this setting is in place:

sudo nano /etc/systemd/journald.conf
[Journal] Storage=persistent

More time sepecification:

journalctl –list-boots show boots that journald knows about
journalctl -b -1 journal from previous boot
journalctl -b caf0524a1d394ce0bdbcff75b94444fe specific boot
journalctl –since “2015-01-10 17:15:00”  
journalctl –since “2015-01-10” –until “2015-01-11 03:00”  
journalctl –since yesterday  
journalctl –since 09:00 –until “1 hour ago”  

Even more time specification:

journalctl -u nginx –since today
journalctl -u nginx -u php-fpm –since today

By PID, UID, GID:

journalctl _PID=8088 by PID
journalctl _UID=33 by user ID
journalctl -F _GID by group ID

Check the docs for fields:

man systemd.journal-fields

Priority:

journalctl -p err by priority

Severity levels

0 emerg
1 alert
2 crit
3 err
4 warning
5 notice
6 info
7 debug

Output control:

journalctl –no-full truncate long lines
journalctl -a all info, including unprintable chars
journalctl –no-pager output directly, good for piping

Json and pretty json output:

journalctl -o json
journalctl -o json-pretty

Available formats:

cat just show the message field
export binary, good for backups
json Standard - one entry per line
json-pretty JSON but pretty
json-sse server-sent event compatible JSON
short default syslog style
short-iso default format with ISO 8601 wallclock timestamps
short-monotonic default with monotonic timestamps
short-precise default with microsecond precision
verbose all fields including hidden

Tail equivalent for journald:

journalctl -n most recent 10
journalctl -n 20 most recent 20
journalctl -f follow

Disk usage and log clearing:

journalctl –disk-usage show disk usage
sudo journalctl –vacuum-size=1G remove old entries until the log is this size
sudo journalctl –vacuum-time=1years remove entries older than a year

/etc/systemd/journald.conf Settings:

SystemMaxUse max disk space to use (persistent storage)
SystemKeepFree amount of disk space to keep free (persistent storage)
SystemMaxFileSize max file size before logs are rotated (persistent storage)
RuntimeMaxUse max disk space to use (volatile storage)
RuntimeKeepFree amount of disk space to keep free (volatile storage)
RuntimeMaxFileSize max file size before logs are rotated (volatile storage)

Network

Boot

Learn more HERE

Other - Extra Info

Systemd init scripts:

/etc/init.d/

KDE GUI tool:


sudo apt install kde-config-systemd  
kcmshell5 kcm_systemd

Jobs / Timers

References