Background Services and Crons

Source: https://abarrak.gitbook.io/linux-sysops-handbook/

To list the available categories of daemons, run:

$ systemctl -t help

There are 3 types of daemons: 1. services, 2. sockets, 3. paths. Use the following to see the system's processes in each:

$ systemctl
$ systemctl list-units --type=service
$ systemctl list-units --type=socket --state=LOAD
$ systemctl list-units --type=path --all
$ systemctl list-unit-files

To view the status of a daemon use the status command or its state shortcuts:

$ systemctl status kubelet
$ systemctl is-active dockerd
$ systemctl is-enabled sshd.service

Additionally, use the following to list a daemon dependencies:

$ systemctl list-dependencies nginx.service

The cron daemon crond is responsible for managing the user's and system's scheduled jobs. Use the command crontab to manage jobs and their files in the user account or in the system wide /etc/crontab, /etc/cron.d/ locations.

$ sudo crontab -l
$ sudo crontab -e
$ vim /etc/cron.d/my-backup

The syntax of crontab entries is captured by the diagram below. Use the https://crontab.guru/

An example of a cron entry that runs backup command, every day at 5:00 AM:

0 5 * * * /usr/bin/daily-backup