exec dont work for svn

hi, i want to do a svn update (subversion) from php using exec (or system) now, this works: exec("ls; pwd",$out); foreach($out as $line)echo"<br/>$line\n"; and this also works and print me the help from subversion: exec("svn help",$out); foreach($out as $line)echo"<br/>$line\n"; but this doesnt work: exec("svn update",$out); foreach($out as $line)echo"<br/>$line\n"; dont print anything... dont update the files, pwd returns me the correct path... any ideas? im using cpanel... php5 and fedora 4 php runs as nobody...