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89 lines
2.9 KiB
Text
89 lines
2.9 KiB
Text
[id='using-the-command-line-to-view-log-files]
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= Using the command line to view log files
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The `journalctl` command can be used to view messages in the system journal on the command line.
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For plain text log files, generic tools may be used:
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* `cat`, `more`, `less`, `tail`, or `head`.
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* the `grep` command to search for specific information.
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* any text editor of your choosing (nano/pico/vim/emacs)
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Please note that you may require `sudo` access to view these files.
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[id='using-journalctl-to-view-system-information']
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== Using journalctl to view system information
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* To view all collected journal entries, simply use:
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----
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$ journalctl
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----
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* To view a logs related to a specific file, you can provide the `journalctl` command with a filepath.
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The example shown below shows all logs of the kernel device node `/dev/sda`:
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----
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$ journalctl /dev/sda
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----
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* To view log for the current boot use the `-b` option :
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----
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$ journalctl -b
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----
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* To view kernel logs for the current boot, you can add the `-k` option:
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----
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$ journalctl -k -b -1
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----
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[id='using-journalctl-to-view-log-information-for-a-specific-service']
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== Using journalctl to view log information for a specific service
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* To filter logs to only see ones matching the "foo" systemd service:
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----
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$ journalctl -b _SYSTEMD_UNIT=foo
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----
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* Matches can be combined.
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For example, to view logs for systemd-units that match `foo`, and the PID `number`:
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----
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$ journalctl -b _SYSTEMD_UNIT=foo _PID=number
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----
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* If the separator "+" is used, two expressions may be combined in a logical OR.
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For example, to view all messages from the `foo` service process with the `PID` plus all messages from the `foo1` service (from any of its processes):
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----
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$ journalctl -b _SYSTEMD_UNIT=foo _PID=number + _SYSTEMD_UNIT=foo1
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----
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* If two matches refer to the same field, all entries matching either expression are shown.
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For example, this command will show logs matching a systemd-unit `foo` or a systemd-unit `foo1`:
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----
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$ journalctl -b _SYSTEMD_UNIT=foo _SYSTEMD_UNIT=foo1
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----
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NOTE: The files for service modification are stored in a directory within `*/etc/systemd/system*`, to know more about systemd, please refer to <<understanding-and-administering-systemd.adoc#Understanding Systemd Services>>
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[id='Using-journalctl-to-view-older-logs']
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== Using journalctl to view older logs
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* To view older logs use the `--list-boots` option :
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This will show a tabular list of boot numbers, their IDs, and the timestamps of the first and last message pertaining to the boot:
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$ journalctl --list-boots
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-8 42cdeac65d494e938b9cb92f315b08a4 Mon 2018-11-12 10:36:42 CET—Mon 2018-11-12 20:08:24 CET
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-7 c110d2b8705345b786fe310de628bfc7 Tue 2018-11-13 10:29:27 CET—Tue 2018-11-13 10:04:00 CET
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----
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with this ID you can use `journalctl` as usual :
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----
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$ journalctl --boot=ID _SYSTEMD_UNIT=foo
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----
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* To know more about `journalctl`, read the man page:
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----
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$ man journalctl
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----
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