http - PHP won't execute code in cmd -

when execute

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

via cmd in putty works perfectly, when attempt execute via php :

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

nothing happens. have idea of why not working? have modify setting in php.ini or doing wrong?

i'll second recommendation @ apache log file, i'll wager permissions issue (i've had problem...). apache (httpd?) have read/write access /html/file.png , s3://bucket/files/file.png? s3cmd require special permissions? need use gksudo?