How to view linux kernel logs live?

Question

I have a kernel module logging input of some sensor while I work with it. I want to see if there is a command that outputs /var/log/messages (for example) but waits for more logs to come. That is, some program like dmesg except that it stays on and keeps printing newly-come logs.

Solution 1

Have you tried tail -F, eg.

tail -F /var/log/messages

Solution 2

You can:

• execute dmesg every second: while true; do dmesg -c; sleep 1; done
• print everything appended to /var/log/messages: tail -f /var/log/messages
• dump the logs on the serial port and read them on another PC. You will need to add to your kernel boot parameters: console=ttyS0,115200 console=tty0 ignore_loglevel and remove quiet

Comments

[Admin]

Thanks that's what I wanted. I read the man page for tail but the part for -f was not at all understandable to me.

[Admin]

@Shahbaz : Be careful if you are looking at a file that is log rotated, i.e. logs are automatically archived, like syslog.0, syslog.1.gz etc.. As soon as the file you watching is rotated, you won't see any new lines. You have to restart tail -f. (At least this is the case on my system)

[Admin]

@Xavier T. Thanks. I was just doing this for a small test however to see if my driver worked

[ar.]

You can of course use the tail -F command which watches for changed/rotated files and continues to watch the file with the given name.