PHP script running at Apache and Linux doesn't create file

Question

I need some help as my script doesn't create a file. I want to run this script at cronjob. I am using Debian Linux with PHP and Apache.

My script is locate at /var/www/myapplication folder. I want to create / write a file at /var/www/myapplication/testfolder.

The commands I use in the php script is:

echo `whoami`;
exec ('whatever >> testfolder/testing.txt');

Folder rights:

drwxrwxrwx 2 www-data www-data 4096 Jul 27 09:55 testfolder

When I run the script directly from browser (http://127.0.0.1/myscript.php)
- it doesn't create the file (testing.txt)
- echo whoami says: www-data
When I run the script from the server with root rights (su):

php -q /var/www/myapplication/myscript.php >>log3.txt

it creates the file (testing.txt)
echo whoami says: root
log3.txt is created at /var/www/myapplication folder
1. When I run the script from crontab:
  - - - /usr/bin/php -q /var/www/myapplication/myscript.php >>log3.txt
it doesn't create the file (testing.txt)
echo whoami says: root
log3.txt is created at /root folder

Why isn't testing.txt created my I run my script from crontab as a cronjob ?

EM-Creations: Because I want redirect 'whatever' command output to create the necessary file (testing.txt). — Tass Mark
– Tass Mark, Commented Jul 27, 2015 at 8:21
Try shell_exec. Also, make sure the www-data user has correct write permissions for the directory. — EM-Creations
– EM-Creations, Commented Jul 27, 2015 at 8:29
EM-Creations: Thank you. I tried shell_exec, but the result is same: testing file is not created, only the log3.txt. log3.txt contains: root — Tass Mark
– Tass Mark, Commented Jul 27, 2015 at 8:38

Bryan Abrams · Accepted Answer · 2015-07-27 08:39:47Z

You shouldn't be executing operating system commands directly, there are already functions and objects avaliable in PHP for writing and read files. As well, you shouldn't be giving them permission to be writing files to /. Even though you're running it from localhost, if you ever expose the service you're allowing public users to run operating system commands.

You also mention in your comment that you want to redirect the output of 'whatever' to a file, but I still don't see why you couldn't do this with the PHP provided functions.

Regardless, to answer the original question when you run the script via localhost you're accessing it via Apache which means the user www-data is running the PHP script. When you access it via your cronjob you're calling PHP from the commandline and another user is accessing the service.

You can see the error that is being returned from attempting to write to the file by logging in with the user running the cronjob and using echo exec(...).

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