How to use the command 'systemd-cat' (with examples)

The systemd-cat command is a utility in systemd that allows you to connect a pipeline or program’s output streams with the systemd journal. It is a useful tool for logging and monitoring system output.

Use case 1: Write the output of the specified command to the journal

Code:

systemd-cat command

Motivation: The motivation for using this use case is to capture the output of a specific command and write it to the systemd journal. This can be useful for monitoring the output of a specific command in real-time and analyzing it later using journalctl.

Explanation: The systemd-cat command is used to connect the output streams of a command to the systemd journal. By specifying a command after systemd-cat, the output of that command will be captured and written to the journal. Both stdout and stderr streams are captured.

Example output: Let’s say we want to capture the output of the command ls -l and write it to the journal. We would use the following command:

systemd-cat ls -l

The output of this command will be written to the systemd journal and can be viewed using journalctl.

Use case 2: Write the output of a pipeline to the journal

Code:

command | systemd-cat

Motivation: The motivation for using this use case is to capture the output of a pipeline and write it to the systemd journal. This can be useful for logging the output of complex command pipelines and analyzing them later using journalctl.

Explanation: In this use case, the systemd-cat command is used as a pipe to connect the output of a command pipeline to the systemd journal. The stdout stream of the pipeline is captured and written to the journal, while the stderr stream remains connected to the terminal.

Example output: Let’s say we have a command pipeline that searches for a specific pattern in a log file:

grep "error" logfile.log | systemd-cat

The output of this command pipeline, which contains all the lines in logfile.log that match the pattern “error”, will be written to the systemd journal.

Conclusion:

The systemd-cat command is a useful utility in systemd for connecting a pipeline or program’s output streams with the systemd journal. It provides a convenient way to capture and log output in real-time, which can be useful for monitoring and analyzing system logs.