Systemd on Lloyd Rochester's Geek Blog

Timer example in systemd

Sat, 09 Jul 2022 00:00:00 +0000

Timer example in systemd

We can use systemd instead of cron timers in Unix. Using systemd timers is easy and provides numerous benefits over using Cron which are documented below. These timers more are complicated than cron, however, they are much more powerful.

Creating a `systemd` timer

Let us look at the logical hierarchy of a timer on systemd and the files associated before we look at an example.

Logical Requirements

To create a systemd timer the following are required:

Systemd: Timers

Tue, 30 Jun 2020 00:00:00 +0000

Systemd: Timers

In the fourth post on how to create a service in systemd we will create a timer that will run every minute sending messages to our example foo service over a socket. We’re essentially creating a cron job socket client.

Project Creation of an autotools project and start/stop a daemon service.
Journalling/Syslog to enable logging, notify of state changes and accept reloads.
Socket creation of a Unix Domain Socket for other processes to send messages to our service through remote procedure calls.

What the example will do?

We already have a Unix Domain Socket created by systemd that is listening on /var/log/foo.socket. We also have a service called foo.service that is listening to this socket . When messages are received on the socket the service will log them to the journal and syslog.

Systemd: A Service and a Socket

Fri, 26 Jun 2020 00:00:00 +0000

Systemd: A Service and a Socket

This is the third post on how to create a service in systemd. See the first post to create a autotools project and start/stop a daemon service. Or the second post to enable logging, notify of state changes and accept reloads. In this post we’ll create a Unix Domain Socket so that other processes can send messages to our service through remote procedure calls.

The socket we will use in this post is a Unix Socket with domain AF_UNIX of type SOCK_DGRAM. This type of socket is well suited for example purposes and is also ideal for remote procedure call applications. It is limited to communication on the same host, not over the internet. Unix Domain sockets are always reliable and are guaranteed to be delivered in order without duplication. Since this example uses a datagram socket we can receive the full message on each reception. Typically, the size of a datagram socket is under 2048 bytes see socket(7) and look for the SO_SNDBUF option for more details on maximum datagram size.

Status, Reloading and Journalling in Systemd

Tue, 23 Jun 2020 00:00:00 +0000

Status, Reloading and Journalling in Systemd

This is the second post on how to create a service in systemd. In the first post we created an autotools project and were able to start, stop and get basic status on the service. In this post we’ll build on the autotools project to add logging to syslog and journald. We will also give an example on how we could reload the service with a systemctl reload foo. We will also use the sd_notify(3) API to notify the service manager the status of what the service is doing.

Systemd and Autotools

Mon, 22 Jun 2020 00:00:00 +0000

Systemd and Autotools

This post starts a tutorial series on how to create a systemd service in Linux. This first post is likely the hardest part as we create an autotools project with the source code and systemd unit files. Having this setup in autotools saves significant time installing unit files that systemd requires, building our C code, installing, and uninstalling our program. If you can get through this first post the following posts should come easily.

Systemd on Lloyd Rochester's Geek Blog

Timer example in systemd

Timer example in systemd

Creating a systemd timer

Logical Requirements

Systemd: Timers

Systemd: Timers

What the example will do?

Systemd: A Service and a Socket

Systemd: A Service and a Socket

Status, Reloading and Journalling in Systemd

Status, Reloading and Journalling in Systemd

Systemd and Autotools

Systemd and Autotools

Creating a `systemd` timer