从CLI调用外部命令时，PHP脚本挂起

Question

I have a PHP script that executes an external bash script to make an SSH connection but even though i am using ssh's move to background (-f) as well as an '&' my PHP script hangs.

Problem line in PHP script

system('/usr/local/bin/startProxy 172.16.0.5 9051');

I have also tried :

system('/usr/local/bin/startProxy 172.16.0.5 9051 &');

And the startProxy script is simply :

#!/bin/bash
#
# startProxy <IP_Address> <Proxy_Port>
#
# Starts an ssh proxy connection using -D <port> to remote system
#
ssh -o ConnectTimeout=5 -f -N -D $2 $1 &

Calling the startProxy script from command line works find and the script returns immediately.

When the system() command is run, the called script does run (I can see ssh running via ps), it just never appears to return to the PHP script. I have run into the same issue when trying to call ssh directly via the system() method as well.

Answer 1

Thanks @Martin,

For future self and others, I had to change the system call to

system('/usr/local/bin/startProxy 172.16.0.5 9051 2>&1 >/dev/null');

and to change the startProxy script to :

ssh -o ConnectTimeout=5 -f -N -D $2 $1 2>&1 >/dev/null

before PHP return to the rest of the script!

Anyone able to explain why PHP stops like this if output is not redirected (I presume PHP isn't scanning the command and seeing the redirection part) and also why PHP hangs is i don't include the redirection in the ssh command within startProxy, dispite the fact that both the PHP system call and the ssh command in startProxy where using background options (-f and '&' )