-----Original Message----- From: listbounce@xxxxxxxxxxxxxxxxx [mailto:listbounce@xxxxxxxxxxxxxxxxx] On Behalf Of Joke de Buhr Sent: Tuesday, August 17, 2010 2:03 PM To: secureshell@xxxxxxxxxxxxxxxxx Subject: Re: Dynamically allocated port on reverse forward On Tuesday 17 August 2010 06:59:33 ADFHAU wrote: > Hi, > > > If I invoke ssh this way: > > ssh -R 0:localhost:22 remote_ssh_server > > > > ssh prints a debug message like: > > Allocated port 40454 for remote forward .... > > > > before it drops to the shell. > > > > Is there a way of querying the allocated port on the remote site to > > make it usable within scripts? For example to execute a command via > > ssh on the origin site in this case. > > If you could determine the ancestry of the script process, back to the > sshd driving it and then look up the pid in lsof or netstat output, > you could probably do it. > > That or if the script had access to logs and the logging level were > high enough. Determine the sshd process can be done via $PPID from thin the login shell: echo "shell pid: $$, sshd pid: $PPID" Unfortunately using lsof -p $PPID (or /proc/$PPID) doesn't work in this case because the login user doesn't have read permissions to query the sshd process (not the sshd daemon). Unless lsof is executed as root this doesn't work. ---- You probably know this, but to dismiss the simplest stuff first: You can specify a port, rather than relying on dynamic allocation. Just use a number instead of 0. If you pick under 1024 you'll have to be logging in as root on the remote side as those numbers are reserved. FAILED IDEA: A nifty trick for local forwards to different machines is to bind them to alternate local interfaces. Example: /etc/hosts 127.0.0.2 local2 127.0.0.3 local3 ssh user@remote -L local2:22:host2:22 -L local3:22:host3:22 ssh user@local2 # goes to host2 tunneled via initial ssh connection ssh user@local3 # goes to host3 tunneled via initial ssh connection Alas, when I tested remote forwards to alternate interfaces on the remote machine, the resolution failed. ssh user@remote -R 0:local2:22 -R 0:local3:22 netstat -tl Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 localhost:55313 *:* LISTEN tcp 0 0 localhost:42267 *:* LISTEN The hope was that you'd be able to see: netstat -tl Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 local3:55313 *:* LISTEN tcp 0 0 local2:42267 *:* LISTEN You could, of course, just alias 10.0.0.0/8 ip addresses to a local interface, but that's probably a bit much work. As a side note, it seems a major disappointment that there's no escape sequence to list these. On my Ubuntu 10.4 test machines ~# failed to list remote forwards. Also, if you dynamically forward multiple ports, how do you tell which dynamically assigned remote port maps to each local port?
