shell_exec缺少一些输出

shell_exec wont show all the output. My code basically run psexec to capture data from other server. The command works just fine on the CMD. but in PHP, ONLY part of the output is missing. i do get the PSEXEC header messages and some of the output

already use the 2>&1 and still i dont get the output i want,, but i do get the process

$cmd = "psexec \\server1 omnistat -previous -since {$before} -until {$now}";
$output = shell_exec($cmd);

i expected the output will be ( running on CMD on the same server )

PsExec v2.2 - Execute processes remotely
Copyright (C) 2001-2016 Mark Russinovich
Sysinternals - www.sysinternals.com


Session ID       Type     Status               User.Group@Host
===============================================================================
2019/08/12-1     Backup   Completed            xxx
2019/08/12-2     Backup   Completed            xxx
2019/08/12-3     Backup   Aborted              xxx
2019/08/13-1     Media    Completed            xxx
--hundreds of lines below

but i only get this ( in web browser view:source)

PsExec v2.2 - Execute processes remotely
Copyright (C) 2001-2016 Mark Russinovich
Sysinternals - www.sysinternals.com


Session ID       Type     Status               User.Group@Host
===============================================================================

even when using 2>&1, i only get messages that the command run successfully