Hobo Hobo - 6 days ago 5
Linux Question

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

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

Take a look at the utility split(1), part of GNU Coreutils.

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