tldr/pages/linux/journalctl.md

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# journalctl
> Query the systemd journal.
> More information: <https://manned.org/journalctl>.
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- Show all messages with priority level 3 (errors) from this [b]oot:
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`journalctl -b --priority={{3}}`
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- Delete journal logs which are older than 2 days:
`journalctl --vacuum-time={{2d}}`
- Show only the last N li[n]es and [f]ollow new messages (like `tail -f` for traditional syslog):
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`journalctl --lines {{N}} --follow`
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- Show all messages by a specific [u]nit:
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`journalctl -u {{unit}}`
- Show logs for a given unit since the last time it started:
`journalctl _SYSTEMD_INVOCATION_ID=$(systemctl show --value --property=InvocationID {{unit}})`
- Filter messages within a time range (either timestamp or placeholders like "yesterday"):
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`journalctl --since {{now|today|yesterday|tomorrow}} --until {{YYYY-MM-DD HH:MM:SS}}`
- Show all messages by a specific process:
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`journalctl _PID={{pid}}`
- Show all messages by a specific executable:
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`journalctl {{path/to/executable}}`