Python script to connect via ssh, run process and disconnect without waiting

Question

I have a problem with running non finishing process via ssh from python script. What I need to do:

Connect to remote server via ssh
Run mongod on this server
Finish script execution without killing mongod process

For now, I'm using subprocess.Popen in this way:

subprocess.Popen(['ssh', 'user@' + host, 'mongod', '-f', '/temp-mongo.conf', '&'])

Problem is that script ends before I'm asked about user password, so it finishes with Too many authentication failures for root.

I tried to use p = subprocess.Popen(...).communicate() and it'a almost ok, but then script waits for mongod command to be finished, what obviously won't happen.

What is proper way to do this? Can I do something to pass password automatically?

start it via systemctl or if you must have a hacky way, nohup xxx & — Dima Tisnek
– Dima Tisnek, Commented Jan 13, 2017 at 9:53

hansaplast · Accepted Answer · 2017-01-13 08:53:49Z

2

I agree with e4c5 that you should use a tool like Fabric for that. If you want to stay with the dirty way something like this should work:

subprocess.call('ssh user@%s "mongod -f /temp-mongo.conf &>/dev/null  &"' % host, 
                shell=True)

Note that you need to do:

quotes around the remote call
add &>/dev/null which routes all output of mongod to /dev/null (without this it will block, not 100% sure why. Probably since the stdout of the shell is attached to the command)
use shell=True so the shell builds up the command for you (so you don't need to put a ", " instead of each space)

This also works with auth over public key (instead of writing the password by hand)

edited Jan 13, 2017 at 8:53

answered Jan 13, 2017 at 8:40

hansaplast

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6 Comments

rzysia Over a year ago

It worked, thanks! I choose "dirty" solution, because I have limited possibilities to install new modules on remote

hansaplast Over a year ago

Fabric doesn't need any remote modules to be installed. But it is an additional learning curve (although it is quite easy to start with). My advice is that whenever you add more jobs like that to your script (and end up in a big if/else battle) or if you have jobs depending on each other, want to run jobs in parallel etc then a switch to fabric is very much worth the effort

rzysia Over a year ago

so fabric is standard library?

hansaplast Over a year ago

no, you need to install the fabric library. But only on your client host where you start the commands, not on the servers where the commands are executed

rzysia Over a year ago

I wrote it wrong in first comment - I'm running this script also on remote machine (from where it connect to another remote machine), so that was shorthand - best way is to not need any module.

|

Nils Werner · Accepted Answer · 2017-01-13 08:29:46Z

0

The proper way for SSH without having to enter passwords is to use public key authentication.

I would also look at Fabric for running commands via SSH.

And you aren't running the command in a shell environment on the server. If you run

ssh host ls &

the & will actually put ssh in the background, not ls on the host. Instead try doing

ssh host sh -c 'ls &'

edited Jan 13, 2017 at 8:29

answered Jan 13, 2017 at 8:25

Nils Werner

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2 Comments

Eli Korvigo Over a year ago

This is a comment, not an answer.

Nils Werner Over a year ago

The question was how do you enter a password for the SSH connection. This is an answer. Also, I have amended more answers to all the other questions and problems OP has.

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