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.)

Related: http://unix.stackexchange.com/questions/196168/does-less-have-a-feature-like-tail-follow-name — Volker Siegel, Apr 14 '15 at 14:26

score 223 · Accepted Answer · edited Oct 15 '14 at 23:33

223

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.

edited Oct 15 '14 at 23:33

answered Oct 16 '11 at 15:43

andcoz

17,130

7

Awesome, yes, I am. (just for the record, this is a GNU tail option - where GNU tail is of course the default on Ubuntu). – maxschlepzig Oct 16 '11 at 15:51
You are right :-/ I did not noticed that Ubuntu in your question was only an example. – andcoz Oct 16 '11 at 17:08
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. – maxschlepzig Oct 16 '11 at 18:22
3

Is tail -F /var/log/kern.log equivalent to tail -f --follow=name --retry /var/log/kern.log? – Basj Sep 15 '17 at 13:03
4

@Basj - according to http://man7.org/linux/man-pages/man1/tail.1.html it's equivalent – andrej Aug 09 '18 at 17:43

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

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