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How to truncate a log file using Ubuntu Linux

Have you ever wanted to truncate a log file that was being written to by a running process without stopping the process to do so?

If so then all you need is the following to clear out the active log file:
cat /dev/null > some_log_file.log
There are some other great tips over on the Bash Cures Cancer blog.

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Comments

askbill said…
Thanks a bunch. Just what I was looking for.
7:42 pm GMT
Anonymous said…
:> filename

(colon greater-than filename) is a much shorter syntax :)
3:14 pm GMT
nowinter said…
but, if the file is still being appended by a process, it worth nothing in the sence of file size. the file will be updated to its actual size (with NULs) as soon as the appending process flushes..
3:52 pm GMT
Anonymous said…
depending on the log file you might also want to send a HUP to the program that has the file open. Eg. if you truncate /var/log/messages do a 'sudo killall -HUP syslogd'
5:20 am GMT
The Leading Wedge said…
Nice. Came in handy just now. No need to remember anything anymore in the Google age.
12:10 pm BST
A Rocha International said…
Another useful, er, use for cat /dev/null -- I'm copying files verbosely to my external hard drive. I've noticed a directory that had several versions of the same video: mpg, avi, flv, and dv -- the latter with 9 GB :P I didn't need that one, so _while_it was copying the .dv I went
cat /dev/null > /path/unnecessary-long-file.dv
Thanks for the tip!
and hey presto -- the backup moved on to the next file, and I didn't break the cp command (which would be very hard to resume) (yes, I hear that rsync is a better way of doing this, I'll check it for next time)
11:00 am GMT
Anonymous said…
Brilliant, thanks for this
9:51 am GMT
Anonymous said…
> some_log_file.log
7:08 pm BST
Anonymous said…
There is already a command which is the best way to do this:

truncate -s0 some_log_file.log
7:10 pm BST
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