Cron Job with PHP
This topic has been teasing me a moment before I went to bed yesterday night. Since it related to my current works, so I had to get it done soon or late. However, thinking about cron daemon will also think about the file permission & some annoyed things connected to it’s correlation flows. I mean, for example what crontab user signed in Linux when a cron job executed from PHP? Does it root, nobody, guest or what? Well, we’ll find it in a minutes.In shorts, I made an HTML page containing a checkbox purposed to enabled or disabled a single cron service. The cron it self will running a simple wall command in every minutes. Here’s below the complete script:
<?
if (isset($_POST['Submit']))
{
if ($_POST['cbcrontab']==1)
{
$cron=1;
echo('Crontab Aktif');
system ("echo \*/1 \* \* \* \* /usr/bin/wall test cron dari PHP coy > /tmp/crontab");
system ("crontab /tmp/crontab");
}
else
{
$cron=0;
echo('Crontab TDK Aktif');
system ("crontab -r");
}
}
?>
<html>
<head>
<title>Cron Job Test</title>
</head>
<body>
<form name="form1" method="post" action="index.php">
<input name="cbcrontab" type="checkbox" id="cbcrontab" value="1" <? if ($cron) echo('checked'); ?>>
<font size="1" face="Verdana, Arial, Helvetica, sans-serif">Aktifkan Crontab</font>
<input type="submit" name="Submit" value="Submit">
</form>
</body>
</html>
When the checkbox checked, it will executing a file writing process to a file containing a line of cron command in temporary folder. In a wide public service such as in hosting services, you may use Linux global variable referring to temporary folder & temporary file since you’ll face a limited permission access to it.
In other condition, if the checkbox is unchecked, it’s action will simply removing the cron service from system by executing crontab –r command. Now, let’s test the script by loading it from client browser, checked the checkbox & hit the submit button. Then, switch back to Linux & find out what happened exactly from terminal.
From the first command – listing cron table from user root by giving command crontab –u root -l, you see that old crontab for root session still persist & there’s no new changes was made into it. The above script just not affected to root system anyway. What about the second command? It’s also work the same, nothing changes for nobody user cron session. So, who’s cron session changed? Take a look at last command, the above script influence apache user. That’s it, the puzzle has been solved! Within apache user, the cron worked great from PHP. According to this, the executable script listed as parameter in cron table line (such as /usr/bin/wall) must be visible to apache user. For custom bash shell script or any executable application, make sure to granted it by changing the attribute to 777 mode in order the script will work & visible to apache user. Good day!
Labels: PHP
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