SystemD Overview
SystemD#
All about systemD and more importantly how to use and create services that automatically start on system startup
SystemD is the main adopted system and service manager for Linux
Common Commands#
Show system status
systemctl status
List failed units
systemctl --failed
List installed unit files
systemctl list-unit-files
List all running services
systemctl
Start a service
systemctl start <service_name>
Stop a service
systemctl stop <service_name>
Restart a service:
systemctl restart <service_name>
Show status of a service:
systemctl status <service_name>
Enable a service on startup:
systemctl enable <service_name>
Disable a service during startup:
systemctl disable example1
Creating or altering services#
Units are defined by individual configuration files, called unit files
Unit files provided by debian are found in: /lib/systemd/system
An identically named unit file in /etc/systemd/system, takes precedence over those in /lib/systemd/system
System admins should put unit files in: /etc/systemd/system
Example#
Create this file
[Unit]
Description= kong service
After=syslog.target network.target postgresql.service
[Service]
User=root
Group=root
Type=forking
ExecStart=/usr/local/bin/kong start
ExecReload=/usr/local/bin/kong reload
ExecStop=/usr/local/bin/kong stop
[Install]
WantedBy=multi-user.target
Then run
systemctl start kong
systemctl stop kong
systemctl enable kong
Forking vs Simple#
According to this post on the SystemD Forking vs Simple if a service does not return anything and can only be closed with ctrl+c you should use simple.
If it does daemonise itself, then you should use forking
If a service just does one thing, then oneshot is the right choice.
Using a Python Virtualenv#
The virtualenv is “baked into the Python interpreter in the virtualenv”
For example an elastalert systemd service (Remember ExecStart needs an absolute path):
[Unit]
Description=elastalert
After=elasticsearch.service
[Service]
Type=simple
WorkingDirectory=/home/cent/elastalert/
User=cent
Group=cent
Restart=on-failure
ExecStart=env/bin/python -m elastalert.elastalert --config config.yaml --verbose
[Install]
WantedBy=multi-user.target
Enable and start it:
systemctl daemon-reload
systemctl enable elastalert.service
systemctl start elastalert.service
systemctl status elastalert.service