How to execute remote SSH command in background using PHP exec()?

Question

Is there a simple way to execute SSH commands in the background on remote machines from PHP without using ssh2_*? The PHP script is executed by the user from bash (no Apache involved), so it's not an issue of rights. I've tried doing this:

exec("ssh -f -o UnknownHostsFile=/dev/null -o StrictHostKeyChecking=no -i {$keyFile} {$user}@{$ip} {$remoteCommand} 2>&1 >/dev/null </dev/null");

For example:

exec("ssh -f -o UnknownHostsFile=/dev/null -o StrictHostKeyChecking=no -i /home/data/id_rsa [email protected] '/home/user/script.sh ; exit' 2>&1 >/dev/null </dev/null");

All PHP variables have been escaped with escapeshellarg() and $remoteCommand is a bash script on the remote machine that sleeps for a few minutes and then starts executing some commands.

My problem is that if I execute that SSH command from bash, it gives control back to bash immediately. If I execute it from php using exec() it waits until the remote command executes. I've tried adding 2>&1 >/dev/null </dev/null after /home/user/script.sh, but the execution still doesn't return control to the PHP script.

I don't understand the problem with bash. Don't you want it to give control back to bash immediately? Aren't you trying to execute in the background? — davidethell
– davidethell, Commented Dec 13, 2011 at 10:19
If you don't mind elaborating, why don't you want to use ssh2_*? — favoretti
– favoretti, Commented Dec 13, 2011 at 10:20
@favoretti I have used it before and it is something I would like to avoid. — f.ardelian
– f.ardelian, Commented Dec 13, 2011 at 10:22

macjohn · Accepted Answer · 2011-12-13 10:22:09Z

1

I think you are missing an & at the end of your command for sending the execution to the background.

answered Dec 13, 2011 at 10:22

macjohn

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1 Comment

f.ardelian Over a year ago

Yes, I was missing that, but it still didn't help.

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