[SOLVED] Kernel does not store logs

Sentih · 05-08-2019, 07:11 AM

No logs are to be found /var/log. I am building custom OS and something keeps going wrong. I should be able to fix problem myself, but I need to know what caused the problem. I have about second to read error messages. Then system is down. Any ideas?

syg00 · 05-08-2019, 07:19 AM

Start by reading this - zero info means zero assistance. Simple as that.

Sentih · 05-08-2019, 07:58 AM

Quote:

Originally Posted by syg00

Start by reading this - zero info means zero assistance. Simple as that.

All right. Is there a way to capture output of kernel and/or runit (process #1) during boot? Runit fails and shuts system down. Information I need is being printed on screen for fraction of second and I would like to save it to file.

EDIT:
More detalied description. I decided to create OS using Linux-libre kernel for educational purposes.

I compiled the kernel and modules
I compiled glibc and installed it
I compiled and installed coreutils
I compiled and installed runit
I installed some basic programs from util-linux
I chose dash as my shell

As stated above runit doesn't work and I don't expect you to fix it. I must have made a mistake and I want to fix it. I please you to help me to read error messages. They appear on my screen for really short time so I can't read them. I need to freeze screen or log output of kernel and/or runit. How do I achieve this? Directory /var/log is empty.

pan64 · 05-08-2019, 12:45 PM

did you try to mount that root filesystem from another os and check /var/log?
Did you try to look for boot.log on the net?

hazel · 05-08-2019, 03:58 PM

The kernel doesn't write logs. syslogd and klogd do. Check your /etc/syslog.conf file. It determines where logged data goes. The one I have on LFS says:

Code:

# Begin /etc/syslog.conf

auth,authpriv.* -/var/log/auth.log
*.*;auth,authpriv.none -/var/log/sys.log
daemon.* -/var/log/daemon.log
kern.* -/var/log/kern.log
mail.* -/var/log/mail.log
user.* -/var/log/user.log
*.emerg *

# End /etc/syslog.conf

syg00 · 05-08-2019, 06:43 PM

If runit is failing, none of the userland daemons will be invoked. Attach a serial console.

Sentih · 05-09-2019, 01:34 PM

Quote:

Originally Posted by pan64

did you try to mount that root filesystem from another os and check /var/log?

Yes, exactly.

Quote:

Originally Posted by hazel

The kernel doesn't write logs.

Definitely not a good news.

Quote:

Originally Posted by syg00

If runit is failing, none of the userland daemons will be invoked. Attach a serial console.

I don't have one. I don't have any suitable device at all.

I think I have an idea. I may edit runit's code so it will pause before shutdown. But I don't have time today. Yesterday is a day, too.

hazel · 05-09-2019, 01:49 PM

The kernel only writes to its internal message ring. These are the messages you read with the dmesg command. The logs in /var/log are written by the twin daemons installed from the sysklogd package. klogd takes the output off the message ring and stores it in files, while syslogd does the same with output from daemons. If you haven't installed these packages, you won't have any messages except the boot messages at the system console.

If you think about it, the kernel can't write messages to disk because it has to be able to run before any discs are mounted.

Sentih · 05-10-2019, 02:36 PM

Solved. Runit can't find some scripts even they do exist. I'm going to keep modified version as I may encounter further problems.

I'm thankful you taught me something new.