Linux Survival Basics

Read Current-Boot Logs for One Service

Old service logs can make a current incident look worse or point you at errors from last week.

Command

journalctl -u nginx -b --no-pager -n 80

What changed

Nothing changes. journalctl prints the last 80 current-boot log entries for the unit.

Danger

safe

When to use it

Use after a reboot or restart when you only care about the current boot session.

When not to use it

Do not use for pre-reboot diagnosis; remove -b or use --since with an exact time range.

Undo or recovery

No undo needed because the command is read-only.

Expected output

Recent current-boot journal lines for nginx.

demo script

Disposable terminal steps

journalctl -u nginx -b --no-pager -n 80
journalctl --disk-usage

Terminal transcript Demo JSON

simulated output

What it looks like

disposable vessel

::fixture-ready::
$ journalctl -u nginx -b --no-pager -n 80
Jun 25 14:12:10 vps nginx[842]: start worker processes
Jun 25 14:12:11 vps nginx[842]: ready for connections
Jun 25 14:18:42 vps nginx[842]: reload complete
::exit-code::0
$ journalctl --disk-usage
Archived and active journals take up 412.8M in the file system.
::exit-code::0

YouTube Short

Read only this boot's service logs.

When a server has rebooted, stale logs can waste your time. Add -b to journalctl and cap the output.

experiments

A/B tests to run

Metric: save_rate

A: Avoid stale logs.

B: Post-reboot diagnosis needs -b.