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~/glossary / Linux & operations

journald

journald (systemd-journald) is the systemd logging service that collects messages from the kernel, services and applications in one structured journal.

daniele@mikweb: ~/glossary — man journald

You read the journal with journalctl. The most useful options are -u for a service, --since for a time range, -p err for errors and -f to follow. -b -1 shows the log of the previous boot, for example after a crash.

On some systems journald only keeps logs in RAM (/run/log/journal), so they are gone after a reboot. Create /var/log/journal or set Storage=persistent in journald.conf to keep them.

Disk usage is capped with SystemMaxUse. If /var is full, journalctl --vacuum-size=500M frees space quickly.

Example

journalctl -u php8.3-fpm --since "1 hour ago" -p warning
daniele@mikweb: ~/glossary — ls

Related terms

systemd unitA systemd unit is a configuration file that systemd uses to manage a service, timer, mount, socket or other system object.logrotatelogrotate is a Linux tool that renames, compresses and deletes log files by time or size so the disk does not fill up.OOM killerThe OOM (out of memory) killer is the Linux kernel function that forcibly terminates a process when memory is exhausted, to keep the system alive.

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