When I execute 

`s3cmd put --acl-public --guess-mime-type /html/file.png s3://bucket/files/file.png`

via cmd in putty it works perfectly, however when I attempt to execute this via PHP : 

`system("s3cmd put --acl-public --guess-mime-type /html/file.png s3://bucket/files/file.png");` 

nothing happens. Does anyone have an idea of why it is not working? Do I have to modify a setting in php.ini or am I doing something wrong?