[systemd-devel] --Reboot-- lines in journal

[Dave Howorth]

On Thu, 14 May 2020 16:12:49 +0300
Mantas Mikulėnas <grawity at gmail.com> wrote:
> On Thu, May 14, 2020 at 3:55 PM Dave Howorth <systemd at howorth.org.uk>
> wrote:
> 
> > What do --Reboot-- lines in the journal mean and how do they get
> > there?
> >
> > I can't find any explanation on
> > https://www.freedesktop.org/software/systemd/man/journalctl.html or
> > related pages I've tried.
> >
> > I should explain why I'm interested. On my openSUSE box, I can see
> > for example:
> >
> > # journalctl --list-boots
> > -1 3c9ab70ade084dfab277efe733e18949 Mon 2020-03-02 23:44:11 GMT—Sun
> > 2020-03-29 08:54:38 BST
> >  0 c56183ea7877444a8252dd89a32b31f3 Sun 2020-03-29 09:15:30 BST—Thu
> > 2020-05-14 13:16:49 BST
> > # journalctl | grep Reboot
> > -- Reboot --
> > #
> >
> > Which looks fairly sane with what I think I should expect. But on
> > two Raspberry pis that I have with persistent logging enabled they
> > both have a huge excess of --Reboot-- lines. For example:
> >
> > $ sudo journalctl --list-boots
> > -3 a9346655ca5d4700ab470bfd1b94d5da Thu 2019-02-14 10:11:59 GMT—Wed
> > 2020-05-13 18:31:22 BST
> > -2 c4f8ab5ec73b40818b1607b3436b90b5 Wed 2020-05-13 18:32:51 BST—Wed
> > 2020-05-13 18:46:29 BST
> > -1 0af9c854355f4a12a64dd00e6d3d98c1 Wed 2020-05-13 19:32:57 BST—Wed
> > 2020-05-13 22:33:24 BST
> >  0 fc5b35dbb3604dfbb4e2cdc99e117a75 Wed 2020-05-13 22:33:24 BST—Thu
> > 2020-05-14 12:46:07 BST
> > $ sudo journalctl | grep Reboot | wc
> >    1667    5047   22095
> > $
> >
> > What do the apparently excess 1664 --Reboot-- messages mean?
> >  
> 
> The "--Reboot--" line is simply shown every time the _BOOT_ID field
> changes between two entries -- even if it changes to a previously
> seen boot ID (which shouldn't happen normally, but *might* be caused
> by lack of a RTC?).
> 
> Meanwhile --list-boots has a bit more complex logic for discovering
> the boots, and it also stops the search completely if it finds a boot
> ID that it has already seen.
> 
> (What do you get from, let's say, `journalctl -o json | jq -r
> "._BOOT_ID" | uniq -c`? Does it show several distinct ranges for each
> boot ID?)

Thanks for the reply. A lot of lines similar to this (from start):

      2 4449e609d5144646b1bf70028bf8f1d0
     59 bc489744282a46ffbc28fd31de4c6aa9
     62 3164d610039145b4a1f7bc964eaaa85b
    450 a9346655ca5d4700ab470bfd1b94d5da
      1 4449e609d5144646b1bf70028bf8f1d0
     27 4e807f1301de45dfb4e13551ae10a287
      1 bc489744282a46ffbc28fd31de4c6aa9
      2 4e807f1301de45dfb4e13551ae10a287
      1 4449e609d5144646b1bf70028bf8f1d0
      2 4e807f1301de45dfb4e13551ae10a287

I've attached the complete list, FWIW

I've never even heard of a _BOOT_ID before, so it seems I'll need to do
some reading to answer my original questions. Where's a good place to
start?

> -- 
> Mantas Mikulėnas
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