paramiko and nohup ''

Question

OK so I have paramiko v2.2.1 and I am trying to login to a machine and restart a service. Inside the service scripts it basically starts a process via nohup. However if I allow paramiko to disconnect as soon as it is done the process started terminates with a PIPE signal when it writes to stdout.

If I start the service by ssh'ing into the box and manually starting it there is no issue and it runs in the background fine. Also if I add long sleep 10 before disconnecting (close) paramiko it also seems to work just fine.

The service is started via a init.d script via a line like this:

env LD_LIBRARY_PATH=$bin_path nohup $bin_path/ServerLoop.sh \
  "$bin_path/Service service args" "$@" &

Where ServerLoop.sh simply calls the service forever in a loop like this so it will never die:

SERVER=$1
shift
ARGS=$@
logger $ARGS
while [ 1 ]; do
    $SERVER $ARGS
    logger "$SERVER terminated with exit code: $STATUS. Server has been restarted"
    sleep 1
done

I have noticed when I start the service by ssh'ing into the box I get a nohup.out file written to the root. However when I run through paramiko I get no nohup.out written anywhere on the system ... ie this after I manually ssh into the box and start the service:

root@ts4700:/mnt/mc.fw/bin# find / -name "nohup*"
/usr/bin/nohup
/usr/share/man/man1/nohup.1.gz
/nohup.out

And this is after I run through paramiko:

root@ts4700:/mnt/mc.fw/bin# find / -name "nohup*"
/usr/bin/nohup
/usr/share/man/man1/nohup.1.gz

As I understand it nohup will only redirect the output to nohup.out if "If standard output is a terminal" (from the manual), otherwise it thinks it is saving the output to a file so it does not redirect. Hence I tried the following:

In [43]: import paramiko

In [44]: paramiko.__version__
Out[44]: '2.2.1'

In [45]: ssh = paramiko.SSHClient()

In [46]: ssh.set_missing_host_key_policy(AutoAddPolicy())

In [47]: ssh.connect(ip, username='root', password=not_for_so_sorry, look_for_keys=False, allow_agent=False)

In [48]: stdin, stdout, stderr = ssh.exec_command("tty")

In [49]: stdout.read()
Out[49]: 'not a tty
'

So I am thinking that nohup is not redirecting to nohup.out when I run it through paramiko because tty is not returning a terminal. I don't know why adding a sleep(10) would fix this though as the service if run on the command line is quite verbose.

I have also noticed that if the service is started from a manual ssh its tty in the ps ax output is still set to the ssh tty ... however if the process is started by paramiko its tty in the ps ax output is set to "?" .. since both processes are run through nohup I would have expected this to be the same.

If the problem is that nohup is indeed not redirecting the output to nohup.out because of the tty is there a way to force this to happen or a better way to run this sort of command via paramiko?

Thanks all, any help with this would be great :)

paramiko and nohup ''

0 Answers