Ubuntu – Why does Debian clean php sessions with a cron job instead of using php’s built-in garbage collector

debiangarbage-collectingPHPUbuntu

Debian and derivatives (Ubuntu) don't use the php session garbage collector

session.gc_probability = 0

instead they use a cron /etc/cron.d/php5

09,39 * * * * root [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) ! -execdir fuser -s {} 2>/dev/null \; -delete

Why Debian has chosen to do this?

Best Answer

Because Debian sets very stringent permissions on /var/lib/php5 (1733, owner root, group root) to prevent PHP session hijacking. Unfortunately, this also prevents the native PHP session garbage collector from working, because it can't see the session files there. The cron job runs as root, which does have sufficient access to see and clean up the session files.

Edit: Supporting documentation: The behavior was established in response to bug #267720. (There used to be comments in the stock php.ini file about this, but I don't see them there now in my wheezy-based PHP install.)

Related Solutions

Mysql – Cron job using MySQL/PHP

You could make it all in php, for example my_cron.php content:

<?php
$pid = '/tmp/my_cron.pid';

if (file_exists($pid)) {
    echo "Already running.";
    exit;
} else {
    exec ("touch $pid"); # create the pid file
    # do what you are supose to do here
}

unlink($pid);
?>

Then at your cronjob have something like this:

23 0-23/2 * * * /usr/bin/php /path/to/my/php/file/my_cron.php

Linux – Why does the cron job create a log with a trailing question mark

Running this command will provide more info:

$ crontab -l | cat -tve

I'm fairly confident you will see extra characters at the end of the output, something like this:

*/5 8-20 * * * php /var/www/user/cron_email.php >> /var/www/log/log.txtM-U$

the dollar sign just signals end of line (-e option to cat). Anything betwee .txt and $ is extra garbage, probably due to reasons listed in other answers.

The easiest way to fix this is to set your $EDITOR to a simple editor and re-edit the crontab. For example:

$ EDITOR=/usr/bin/pico crontab -e

then remove any extraneous characters at the end of the line.

Best Answer

Related Solutions

Mysql – Cron job using MySQL/PHP

Linux – Why does the cron job create a log with a trailing question mark

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