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ygoe
Asked: 2016-12-04 08:15:29 +0800 CST

Delete certain files in cron

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How can I regularly delete certain files in cron?

I'm trying to delete empty files older than 15 minutes in the PHP sessions directory. I've tried several methods, all failed with different error messages.

4-59/10 *   * * *     root   [ -d /var/lib/php/sessions ] && find /var/lib/php/sessions/ -type f -cmin +15 -size 0c -print0 | xargs -n 200 -r -0 rm

xargs doesn't find 'rm'. It also won't find '/bin/rm'.

4-59/10 *   * * *     root   [ -d /var/lib/php/sessions ] && find /var/lib/php/sessions/ -type f -cmin +15 -size 0c -exec rm '{}'

Missing argument for -exec option.

4-59/10 *   * * *     root   [ -d /var/lib/php/sessions ] && find /var/lib/php/sessions/ -type f -cmin +15 -size 0c -delete

-delete option is unknown, find must be old.

Can Ubuntu 16.04 still do that? The first version mentioned worked fine on 14.04. Maybe I have to create a separate shell script file and simply write its name into the cron config if that's what cron can do. All the above commands work fine in an interactive bash shell (maybe except the last). Just not in cron.

cron

1 Answers

  1. To avoid dealing with cron's command line syntax, don't put the command in the crontab. Write a simple bash wrapper around the command, and call the script from the crontab. This wrapper will let you set up the environment ($PATH), I/O redirection, error handling, ...

    Also, I note that you are using the crontab format used in root's special (/etc/crontab, /etc/cron.d/, /etc/cron.daily/, /etc/cron.hourly/, /etc/cron.monthly/, /etc/cron.weekly/) setup. Is this your intent? Or are you using sudo crontab? I disrecommend that.

    You have: 

    [ -d /var/lib/php/sessions ] && find /var/lib/php/sessions/ -type f -cmin +15 -size 0c -print0 | xargs -n 200 -r -0 rm

    You need: 

    [ -d /var/lib/php/sessions ] && /usr/bin/find /var/lib/php/sessions/ -type f -cmin +15 -size 0c -print0 | /usr/bin/xargs -n 200 -r -0 /bin/rm

    You have: 

    [ -d /var/lib/php/sessions ] && find /var/lib/php/sessions/ -type f -cmin +15 -size 0c -exec rm '{}'

    You need an escaped semicolon ("\;") to terminate the -exec: 

    [ -d /var/lib/php/sessions ] && /usr/bin/find /var/lib/php/sessions/ -type f -cmin +15 -size 0c -exec rm '{}' \;

    "find must be old"? Does find --version look like: 

     $ find --version
find (GNU findutils) 4.7.0-git
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Eric B. Decker, James Youngman, and Kevin Dalley.
Features enabled: D_TYPE O_NOFOLLOW(enabled) LEAF_OPTIMISATION FTS(FTS_CWDFD) CBO(level=2)

    What version of Ubuntu are you running? find ... -delete has been around for a long time. Are you BusyBox?

    Here is a script that I use to illustrate some cron issues:

    (My environment uses $HOME/bin and $HOME/var/log):

    In $HOME/bin/recordenv: 

    #!/bin/bash
# Record the environment that a job enjoys
# $1 is the "type" (cron, at, batch, gui, text) are suggested values.
# $1 is NOT validated. Output goes to ${HOME}/var/log/{env,set,alias}.$1
if [[ "$1" ]] ; then
    ext="$1"
    env | sort >${HOME}/var/log/env.$ext
    set        >${HOME}/var/log/set.$ext
    alias      >${HOME}/var/log/alias.$ext
    /bin/ls -l ${HOME}/var/log/env.$ext ${HOME}/var/log/set.$ext ${HOME}/var/log/alias.$ext
else
    echo "User error."
    exit 1
fi

    To use it, call $HOME/bin/recordenv cron from crontab.

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