Spawn subshell for SSH and continue with program flow

Question

I\'m trying to write a shell script that automates certain startup tasks based on my location (home/campusA/campusB). I go to University and take classes in two different ca

Answer 1

Having a ssh with pseudy tty on background shell

In addition to @shellter's answer, I would like make some precision:

where @shelter said:

The man page on our system gave no hint that such a thing was possible

On my system (Debian 7 GNU/Linux), if I hit:

man -Pcol\ -b ssh| grep -A3 '^ *-t '

I could read:

     -t      Force pseudo-tty allocation.  This can be used to execute arbi‐
             trary screen-based programs on a remote machine, which can be
             very useful, e.g. when implementing menu services.  Multiple -t
             options force tty allocation, even if ssh has no local tty.

Yes: Multiple -t options force tty allocation, even if ssh has no local tty.

This mean: If you remotely run a tool that require access to pseudo terminal ( pty like /dev/pts/0), you could run them by using -t switch.

But this would work only if ssh is run from a shell console (aka having his own pty). If you plan to run them is shell session without console, like background scripts, you may use Multiple -t to enforce pseudo tty allocation from ssh.

Multiple ssh shell on one ssh connection

In addition to answers from @tommy and @geekosaur, I would make some precision:

@tommy point to a very intersting feature of ssh. Not sure this have a lot to do with answer, but speaking around long time connection, this feature has to be clearly understood.

Once a connection is established, ssh could (and know how to) use them to drive a lot of thing in this one connection:

• -L let you drive remote TCP connections to local machines/network. (full syntax is: -L localip:localport:distip:distport) where localip could be specified to permit other hosts from same local domain to access same tcp bind, and distip could by any host from distant network ( not only localhost ) sample: -L192.168.1.31:8443:google.com:443 permit any host from local domain to reach google through your host: http://192.168.1.31:8443

• -R Same remarks in reverse way!

• -M Tell ssh to open a local unix socket for bindind next ssh consoles. Simply open two terminal window. First in both window, hit: ssh somewhere than hit netstat -tan | grep :22 or netstat -tan | grep 192.168.1.31:22 (assuming 192.168.1.31 is your onw host's ip)

  Than compare close all your ssh session and in first terminal, hit: ssh -M somewhere and in second, simply ssh somewhere. you may see in second terminal:

  $ ssh somewhere
  + ssh somewhere
  Last login: Mon Feb  3 08:58:01 2014 from elsewhere
  

  If now you hit netstat -tan | grep 192.168.1.31:22 (on any of two oppened ssh session;) you must see that there is only one tcp connection.

  This kind of features could be used in combination with -L and maybe some sleep 86399...

  To work around a tcp killer router that close every inactive TCP connection from more than 120 seconds, I run:

  ssh -M somewhere 'while :;do uptime;sleep 60;done'
  

  This ensure connection stay up even if I dont hit a key for more than two minutes.