How to do a `tail -f` of log rotated files?

Question

On a long running system I usually have a terminal with

$ tail -f /var/log/kern.log

or something like this open.

But from time to time I have to restart such command because no new messages are displayed anymore.

I assume this is because of the log rotating job that has replaced the log file tail -f was 'watching'.

How can I avoid this restarting issues?

Can I invoke tail such that it notices the rotating process and does the right thing?

(I notice this issue on a Ubuntu 11.04 system that uses rsyslogd by default.)

Solution

Use the -F option instead:

tail -F /var/log/kern.log

The -F option tells tail to track changes to the file by filename, instead of using the inode number which changes during rotation. It will also keep trying to open the file if it's not present.

Comments

[maxschlepzig]

Awesome, yes, I am. (just for the record, this is a GNU tail option - where GNU tail is of course the default on Ubuntu).

[serb]

You are right :-/ I did not noticed that Ubuntu in your question was only an example.

[maxschlepzig]

not a problem at all - I just commented for completeness (sometimes I just want to look what is POSIX and what is not). The question was indeed pretty much about Ubuntu.

[jiffy.of.eternity]

Is tail -F /var/log/kern.log equivalent to tail -f --follow=name --retry /var/log/kern.log?

[andrej]

@Basj - according to man7.org/linux/man-pages/man1/tail.1.html it's equivalent