Truncating a file while it's being used (Linux)

linux unix file logging truncate
Hobo picture Hobo · Jun 11, 2009 · Viewed 69.7k times · Source

I have a process that's writing a lot of data to stdout, which I'm redirecting to a log file. I'd like to limit the size of the file by occasionally copying the current file to a new name and truncating it.

My usual techniques of truncating a file, like

cp /dev/null file

don't work, presumably because the process is using it.

Is there some way I can truncate the file? Or delete it and somehow associate the process' stdout with a new file?

FWIW, it's a third party product that I can't modify to change its logging model.

EDIT redirecting over the file seems to have the same issue as the copy above - the file returns to its previous size next time it's written to:

ls -l sample.log ; echo > sample.log ; ls -l sample.log ; sleep 10 ; ls -l sample.log
-rw-rw-r-- 1 user group 1291999 Jun 11  2009 sample.log
-rw-rw-r-- 1 user group 1 Jun 11  2009 sample.log
-rw-rw-r-- 1 user group 1292311 Jun 11  2009 sample.log

Answer

Peter Eisentraut picture Peter Eisentraut · Jul 16, 2010

As of coreutils 7.0, there is a truncate command.

Related questions

How to get full path of a file?

Is there an easy way I can print the full path of file.txt ? file.txt = /nfs/an/disks/jj/home/dir/file.txt The <command> dir> <command> file.txt should print /nfs/an/disks/…

Read More
Fastest way to tell if two field have the same contents in Unix/Linux?

I have a shell script in which I need to check whether two fields contain the same data or not. I do this a for a lot of files, and in my script the diff command seems to be the …

Read More
How can I convert a file pointer ( FILE* fp ) to a file descriptor (int fd)?

I have a FILE *, returned by a call to fopen(). I need to get a file descriptor from it, to make calls like fsync(fd) on it. What's the function to get a file descriptor from a file pointer?

Read More