[SOLVED] Executing on remote server terminates while loop

pgb205 · 04-07-2017, 05:42 PM

Bash script looks like

#!/bin/bash
local_command1
while read line; do
local_command2;
ssh remotesrv "somecommand";
done< /tmp/file

/tmp/file has multiple lines but if I run as above the script stops after reading only first line. Commenting out ssh remotesrv "somecommand"; makes while loop read entire file as intended. I suspect it's something with having to connect to remote shell that breaks the loop but am not sure.

Please let me know what I am doing incorrectly.

michaelk · 04-07-2017, 08:04 PM

Does the script stop and you are back and the command line prompt or does your script just hang?

Can you connect to the remote server using ssh from the command line?

Are you using ssh keys?

pgb205 · 04-07-2017, 09:52 PM

Quote:

Originally Posted by michaelk

Does the script stop and you are back and the command line prompt or does your script just hang?

Can you connect to the remote server using ssh from the command line?

Are you using ssh keys?

I'm back at the command prompt on the server where the above script was run from. Yes I can connect to the remote server via ssh using keys.

ntubski · 04-07-2017, 10:45 PM

(Please use [code][/code] tags.)

The reason your script stops is because the ssh command reads from stdin, which means it reads all the rest of your /tmp/file on the first run. You can solve this by redirecting or using the -n option.

Code:

ssh remotesrv "somecommand" < /dev/null
# or
ssh -n remotesrv "somecommand"

ssh(1)

Code:

     -n      Redirects stdin from /dev/null (actually, prevents reading from
             stdin).  This must be used when ssh is run in the background.  A
             common trick is to use this to run X11 programs on a remote
             machine.  For example, ssh -n shadows.cs.hut.fi emacs & will start
             an emacs on shadows.cs.hut.fi, and the X11 connection will be
             automatically forwarded over an encrypted channel.  The ssh program
             will be put in the background.  (This does not work if ssh needs to
             ask for a password or passphrase; see also the -f option.)

pgb205 · 04-07-2017, 11:01 PM

ntubski . thank YOU! I think this helped.