apache - PHP exec() not working properly

Question

I am having difficulty with the PHP exec() function. It seems to not be calling certain functions. For instance, the code echo exec('ls'); produces no output whatsoever (it should, there are files in the directory). That main reason this is a problem for me is that I'm trying execute a .jar from a PHP exec() call.

As far as I know I'm calling the java program properly, but I'm not getting any of the output. The .jar can be executed from the command line on the server. (For the record, it's an apache server).

My php for the .jar execute looks like this:

$output = array();
exec('java -jar testJava.jar', $output);
print_r($output);

All I get for output from this exec() call is Array().

I have had success with exec() executing 'whoami' and 'pwd'. I can't figure out why some functions are working and some aren't. I'm not the most experienced person with PHP either, so I'm not too sure how to diagnose the issue. Any and all help would be appreciated.

Answer 1

The reason why you are not able to execute ls is because of permissions.

If you are running the web server as user A , then you can only ls only those directories which have permissions for user A.

You can either change the permission of the directory or you can change the user under which the server is running by changing the httpd.conf file(i am assuming that you are using apache).

If you are changing the permissions of the directory, then make sure that you change permissions of parent directories also.

To change the web server user, follow following steps:

Open the following file:

vi /etc/httpd/conf/httpd.conf

Search for

User apache
Group apache

Change the user and group name. After changing the user and group, restart the server using following command.

/sbin/service httpd restart

Then you will be able to execute all commands which can be run by that user.

EDIT:

The 'User' should be a non-root user in httpd.conf. Apache by default doesnot serve pages when run as root. You have to set user as a non-root user or else you will get error. If you want to force apache to run as root, then you have to set a environment variable as below:

env CFLAGS=-DBIG_SECURITY_HOLE

Then you have to rebuild apache before you can run it as root.