I tried using system("ssh user@host mycommand > /dev/null 2>&1") and got the same results.
You are correct that I am using "su" to become the same user that the web server runs under, after temporarily changing the password file to give said user a valid shell. I can verify that the shell does not affect whether this problem occurs or not, and I have determined that the SSH process is not left lying around after it executes- The remote command is run, ssh executes, PHP simply never comes back.
Bug link is here: http://bugs.php.net/bug.php?id=22946
At this point I'd love to hear from anyone running a different version of PHP, OS, or Apache who can actually execute this to find out if they experience results which are the same or different.
--Ross
Jamie Alessio wrote:
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.Ross,
Since you don't care about the output from the program can you start the process in the background so that PHP won't wait on it?
system("ssh user@host mycommand &");
and based on the notes at From http://us4.php.net/system you might need something like:
system("ssh user@host mycommand > /dev/null 2>&1 &");
I think this gives up your ability to check on whether the script was command actually ran successfully though which might not be acceptable for your situation.
Some more random ideas...
- Could ssh possibly be relying on some environment variables to behave properly that are available on the command line that aren't available when running system() via the web server? I'm assuming you "become the webserver" by doing something like "sudo apache" or "sudo nobody" in which case you'd have environment variables lying around that won't exist for the apache process. A quick look at "man ssh" lists a bunch of environment variables it uses/sets, but none of them look like obvious culprits.
> 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. > URL to the bug report?
-- Jamie
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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