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I have question why is my cmd for "removing all files in directory except last 20" not working within cron but in command prompt yes.

* * * * *  ls -1tr /home/testusr/test | head -n -20 | xargs -d '\n' rm -f  > /var/opt/check.log 2>&1

Directory contains let say 100x files which are named DATA-20140605xxxx generated minute by minute.

Thank advance for any answer.

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  • possible duplicate of Why is my crontab not working, and how can I troubleshoot it? – user9517 Jun 5 '14 at 9:10
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    Does this work from the command line ? Please also work your way through the document linked above it may help you solve your problem and will almost certainly help you gather information that will help us help you. – user9517 Jun 5 '14 at 9:12
  • I have to update it. In command prompt it is working only if you are within directory which you want to clean. When I am somewhere else for example /root and perform previously mentioned command ls -1tr /home/testusr/test | head -n -20 | xargs -d '\n' rm -f I receive rm: cannot remove `DATA-20140605085900-20140605090000': No such file or directory – George_223907 Jun 5 '14 at 9:31
  • It seems that rm doesn´t know exact location. – George_223907 Jun 5 '14 at 9:41
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The problem you are having is caused because the output of your ls command doesn't contain the path to the file it only contains the filename. When a cron job runs, it runs in the users home directory so when your rm is run, it is looking for files in /home/testuser not /home/testuser/test.

You could fix this with a simple cd command

cd /home/testuser/test && ls -1tr /home/testusr/test ...

This however isn't great as you are parsing the output of ls which is a Bad IdeaTM see the link for extensive discussion.

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  • Yes, you are right. Finally I´ve got it. ls -1tr /home/testuser/test/* | head -n -20 | xargs -d '\n' rm -f – George_223907 Jun 5 '14 at 13:00
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If you run that ls from your root directory, you'll get a file list, but NOT a path. So in effect, you're trying to delete DATAblah from whatever the cwd of cron is.

The solution is either:

  • embed a chdir into cron (or wrap your commands in a script).
  • use something other than 'ls.echo /home/testuser/test/*` will give you path names, for example. (But obviously - no defined sort order).
  • find a way to prefix that path to rm.

Wrapper scripts are generally a good bet for this sort of thing though. Could you instead to a time based deletion? IF they're timestamped minute by minute, could you instead delete all files older than say, 10m old?

In which case: find /home/testuser/test/ -mmin +10 -exec rm {} \; might do the trick.

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