set cron job from php - php

Question

I try To set cron job from php but every time i try the code blow it's not work.
tell me what is the problem with this code
$cron = $this->generator();
file_put_contents("cron.txt", $cron);
shell_exec('crontab cron.txt');
generator function make cron job string like below
12 1 * * * /usr/bin/sample >/dev/null 2>&1
the cron.txt file is fine. it contain the string but shell_exec some how not working

Answer 1

Running your scrip with the hardcoded $corn locally works fine for me, i've included a couple of lines to clear the crontab in the beginning and couple of line to confirm the entry. see bellow.
$cron = '12 1 * * * /usr/bin/sample >/dev/null 2>&1';
file_put_contents('cron.txt', $cron);
shell_exec('crontab -r');
shell_exec('crontab cron.txt');
// To check the result
$output = [];
exec('crontab -l',$output);
print_r($output);
Output:
Array
(
[0] => 12 1 * * * /usr/bin/sample >/dev/null 2>&1
)
And here is a way to check the result of the crontab cron.txt execution:
$output = $return = [];
exec('crontab cron.txt',$output, $return);
var_dump($output, $return);
There will be no output nor return in case of success:
array(0) {
}
int(0)

Answer 2

after many search in Dr Google i found out the answer
i have to change the use to Apache user which is www-data
so the command change to crontab -u www-data cron.txt

Answer 3

The issue is that the apache server will run as a separate limited resource account that rightfully should not create cron jobs. This is a pretty easy way to get the host server compromised. Especially if this is running in a publicly accessible ip address space.
However, if the environment is secure and your server administrator allows, you can have the apache process either run as a higher privileged account (yours for example) or to use the suexec feature to run as a designated account with limited but appropriate permissions.