What is ‘Systemd’?
- It’s an init system
- The init system is the process running on your server(PID 1)
- It manages all services that run in the background
Working with Units
- Units in Systemd are resources that it’s able to manage.
- These includes services, timers, mounts, automounts, and there’s more
Frequent commands
Start/Stop/Service
systemctl status <service-name> to check the status
systemctl start <service-name> to start the service
systemctl stop <service-name> to stop the service
systemctl restart <service-name> to restart the service
Enable/Disable
systemctl enable <service-name> to start the service while booting
systemctl disable <service-name> to not start the service while booting
enabled by default in ubuntu/Debian, disabled by defaults in Fedora/Centos
Where are unit files stored?
service files are text files that contain instructions on how systemd needs to manage the service.
Systemd Unit Directories
- /etc/systemd/system –
- /run/systemd/system – contains runtime systemd units
- /lib/systemd/system – anytime you install a library and it contains systemd service file, that’s stored here
If all three directories conains a same service file name, it takes priority as above order.
when need to override the config of the installed lib service, write a new service file in the higher priority unit directories. Because when updating the library via apt, the service file in lib will be overwritten.