How to see shutdown log
freebsd at edvax.de
Sun Jul 26 20:18:35 UTC 2020
On Sun, 26 Jul 2020 09:41:43 -0400, Ernie Luzar wrote:
> Polytropon wrote:
> > On Fri, 24 Jul 2020 20:58:01 -0400, Ernie Luzar wrote:
> >> When you boot the system a bunch of messages roll across the screen to
> >> fast to read. The dmesg -a command will show these to you to read at
> >> your own pace. When you issue the shutdown or halt command a bunch of
> >> different messages roll across the screen to fast to read.
> >> Is there a way view these messages after the system comes back up later?
> > Yes, those are located to /var/log/messages, as long as
> > file system access is possible; the last kernel messages
> > therefore aren't being logged.
> I checked and what is logged to /var/log/messages on host shutdown is no
> were close to the messages I see fly past on the console terminal.
The problem probably is that at a certain point, messages will
only be written to terminal and to memory buffer, but not to a
file because no file access is possible anymore (kernel still
runs, but disks have been unmounted, so no VFS access can be
Messages in the RAM will not survive a reboot. However, those
created at system startup are copied to the log file as soon
as it becomes accessible.
> This is real easy for people to test so give it a run.
Sure. There is a possibility that might work, even though I
have not tested it: You could "hijack" the kernel printing
routine (the one that emits the messages) and have it copy
characters to a line printer, a virtual one or a real one,
and then you could see those messages.
It would maybe also be possible to read the system console's
file /dev/console and copy everything that is written to it
> Thinking maybe something else is controlling what goes to the message
> file on shutdown. Have any ideas where I should look?
Basically, /var/log/messages contains all messages created
with the system logging mechanism. When programs decide to
emit messages by a simple printf() to whatever is their
controlling terminal, those won't be logged. To get those
messages, checking the console buffer (rather than the
system message buffer) is probably a better way to do.
Again, note that file access is made impossible at a certain
stage during system shutdown that is usually followed by
other stages that also can print messages. If you really
want to get those messages, you need a way to capture them
independently from anything that is a log file unter VFS
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...
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