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Posted by Ross Becker on 06/10/30 11:10
There is no output to stderr or stdout from the script being executed.
All I care about are the side-effects of running this remote program. If
something fails, a numeric error-code will be returned.
I have tried this using: system(), shell_exec() - same as backtick
operator, and popen(). I have tried this using an external shell script
which calls the ssh executable. All methods get the same results.
The program on the remote host is successfully executed, but PHP never
comes back if it is operating under the web server. Also note that I
became the same user that the web server runs as to execute the script
under the PHP CLI.
I actually located a bug filed for this in early 2003 reguarding this
happening on SuSE 8.1 with PHP 4.3.1, but the developers dropped it
because there was no feedback from the user.
My worry is that there's also another bug reguarding executing SSH that
the developers closed as bogus claiming it was an SSH problem, and
pointing to an FAQ on the openssh site saying that SSH can hang due to
not knowing if there's further output coming from the program. I'm
hoping that this isn't their answer to my problem, because I can
demonstrate that it all works when PHP runs in CLI mode.
--Ross
Jamie Alessio wrote:
>> I'm attempting to execute some things on remote servers using ssh,
>> using a strictly limited account created for this express purpose. I
>> set up passwordless key authentication from the user the web server
>> runs as to the limited account on the remote server. I wrote some PHP
>> code which calls:
>> system("ssh user@host mycommand", $result)
>>
>> If I become the web-server user and run this via php from the
>> command-line, everything works. The commands are executed remotely,
>> and the expected HTML comes to standard-out.
>>
>> If I run this through apache, I can verify that the authentication
>> happens successfully, and the commands are run, but output to the
>> browser hangs. No errors, nothing. I have attempted using shell_exec,
>> and popen as well- both exhibit the same problems. I can run commands
>> other than ssh without difficulty.
>>
>> This is happening on suse linux 9.1, PHP 4.3.4. Any clues as to what
>> may be happening?
>
> >
> Ross,
> A couple of ideas:
>
> - Here's your code: "system("ssh user@host mycommand", $result)"
> You do realize that $result only contains the return code of the system
> call and not the actual output from the program called via system(), right?
>
> - Do you have any sort of output buffering in the script?
>
> - Have you tried using passthru() or backticks[1] instead of system()?
> Same results?
>
> - Is it possible the ssh command on the remote host is sending the
> output to STDERR instead of STDOUT? I'm not sure that this makes sense
> since you say it is working via PHP CLI, but perhaps you are seeing the
> STDERR output along with the output of your script? This idea a longshot
> at best.
>
> --
> Jamie
>
> 1. http://us4.php.net/language.operators.execution
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