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How to obtain the current value of _BOOT_ID in systemd-journald?

I can do something ugly such like:

journalctl -o verbose  --since '2016-05-17' | egrep '^[ ]+_BOOT_ID' | tail -n 1| cut -d"=" -f2

Is there a more clever way of do that?

  • If you're in fact interested in seeing the journal, not the boot ID, you could use journalctl -b --since '2016-05-17' which will give you the log for the current boot starting with that date. – Cristian Ciupitu Apr 3 '18 at 1:30
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Alternate method:

cat  /proc/sys/kernel/random/boot_id

This version contains some dashes. The formatting of the boot ID output by journalctl contains no dashes.

The random(4) man page mentions it:

/proc interfaces

  The files in the directory /proc/sys/kernel/random (present since 2.3.16) provide additional information about the /dev/random device:

  uuid and boot_id

  These read-only files contain random strings like 6fd5a44b-35f4-4ad4-a9b9-6b9be13e1fe9. The former is generated afresh for each read, the latter was generated once.

  • 1
    Ok, we can use tr -d '-' < /proc/sys/kernel/random/boot_id in order to delete dashes. – sebelk May 19 '16 at 20:26
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journalctl --list-boots | head -1 | cut -d ' ' -f 3

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