openssh unix dev - Apr 2010 - prototype of simple NX client with auto-resuming ssh session

Dear All:

---
Summary, especially for openssh list (to test/reproduce):
THANK YOU for all your help.
Please extract into /home/username/nx on both host and client. cp ssh to a file
named mxssh in that directory. Run
(with an _n_ below)

Start server on the remote host by typing ./server &

Now do:
./nxssh hostname

If you killall client on the remote end, it reconnects "seamlessly" (I
am using this to simulate ServerAliveInterval).

However, if I do this from _within_ the nxclient program it _detects_ my
disconnect even though the thread is still running (I believe).

Any ideas?

Thank you
Misha

p.s. Also right now I have functionality to spawn the server directly from the
client, but somehow the signal(SIGHUP,SIG_HUP) command causes _both_ the server
and client to ignore SIGHUP, even though it is called _only_ in the client. Any
ideas? Thank you!

---

Thank you so much for your help.

I have put my current prototype on the Web at:
people.hnl.bcm.edu/misha/tmp/nx.zip

Includes source code, and binary executables for amd64.

Right now, expects to live in the /home/username/nx folder on the remote machine
(machine being connected to). Expects nx certificates in right places (/usr/NX).

The nxssh requires an ssh executable to be in the same directory called mxssh
(say original nxssh from NoMachine or even plain old ssh for command line
testing).

Currently, I
(1) get a _seamless_ connection from the command line
however
(2) nxclient somehow detects intermediate disconnects

Note the NX part works until a disconnect (I just do killall cient).

Thank you!
Misha

Keisial wrote:
> Misha Koshelev wrote:
>> p.s. Also right now I have functionality to spawn the server directly
from the client, but somehow the signal(SIGHUP,SIG_HUP) command causes _both_
the server and client to ignore SIGHUP, even though it is called _only_ in the
client. Any ideas? Thank you!
>>   
> (I assume you mean SIG_IGN, not SIG_HUP)
> 
> The server inherits the ignoring of SIGHUP. From signal(7)
>>         A  child  created  via  fork(2)  inherits  a  copy  of  its
>> parent's signal dispositions.  During an
>>        execve(2), the dispositions of handled signals are reset to the
>> default; the dispositions of ignored
>>        signals are left unchanged.
> 
> Perform signal(SIGHUP, SIG_DFL); after the fork but before the execv (or
> simply set SIGHUP to whatever you want in the server).
> 
I am sorry. Not sure what I was on when writing my email this morning ;)

What I meant is the following. I have machine A from which I am connecting,
machine B _to_ which I am connecting.

Two scenarios:
i) I start server on machine B. Then, from machine A, I do ssh B nx/client. Now,
on machine B, I do killall client. SIGHUP is sent, client dies, ssh session from
machine A ends.
ii) I ssh B nx/client; the _client_ spawns the server. Now, on machine B, when I
do killall client, the client dies but SSH DOES NOT DISCONNECT!

Why would this be?

Thank you
Misha Koshelev

p.s. The other problem is as follows: in the "nxssh" executable, I
have a while (1) loop where I _fork_ to start a child process, and then execl
ssh. The parent simply has a wait(NULL) call.

Now, from the command line, this creates the illusion of a seamless SSH session
after disconnects. However, nxclient somehow detects this. Any ideas?

Keisial wrote:
> Misha Koshelev wrote:
>> p.s. Also right now I have functionality to spawn the server directly
from the client, but somehow the signal(SIGHUP,SIG_HUP) command causes _both_
the server and client to ignore SIGHUP, even though it is called _only_ in the
client. Any ideas? Thank you!
>>   
> (I assume you mean SIG_IGN, not SIG_HUP)
> 
> The server inherits the ignoring of SIGHUP. From signal(7)
>>         A  child  created  via  fork(2)  inherits  a  copy  of  its
>> parent's signal dispositions.  During an
>>        execve(2), the dispositions of handled signals are reset to the
>> default; the dispositions of ignored
>>        signals are left unchanged.
> 
> Perform signal(SIGHUP, SIG_DFL); after the fork but before the execv (or
> simply set SIGHUP to whatever you want in the server).
In other words - this does not actually happen.

In fact, I do _nothing_ to signals at all in the client, but when I spawn the
server _from_ the client ssh will not disconnect even if the client dies...

Any ideas?

Maybe its not a signal issue at all.

Thank you!
Misha