Re: [hylafax-users] Hylafax messing with ssh session

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

Niksa Baldun wrote:
> I have the strangest of problems. I am using hylafax with a pool of
> iaxmodems. Sometimes when I connect to the system using ssh, I keep
> getting "ATZ" on the screen and I can't input any commands. Apparently
> hylafax thinks that the ssh pseudo console is actually a modem and it
> tries to communicate with it.
>
> When I restart the system, the problem goes away, but I can't find out
> what triggers it. How would I go about finding the cause of this? I
> tried browsing the system log, but I don't really know what to look for.

iaxmodem uses pseudo-ttys, but the way that Linux works, iaxmodem cannot 
request any particular device name for the pseudo-tty.  So we end up 
with something like /dev/pts/24, but it will vary depending on many 
things and will not be consistent.  For example, ssh also uses 
pseudo-ttys, and often the tty numbers are allocated based on a 
first-come-first-serve basis.

In order to achieve a consistent device name iaxmodem creates a symlink 
to the pseudo-tty, and HylaFAX uses the symlink.

If iaxmodem crashes and is not restarted then HylaFAX will be trying to 
operate on a broken symlink.  And then maybe you log in with ssh and are 
given the pty that iaxmodem was just using.  Now you'll start to get 
faxgetty talking to your pty that ssh is using.

You can make HylaFAX restart iaxmodems when they "wedge" by putting this 
in /var/spool/hylafax/etc/resetmodem :

-----------------------------------------
#!/bin/sh

set -x
exec 2> /tmp/resetmodem.$$


PTY=`ls -l $1 | sed 's/.*-> //g'`

IAXPID=`/usr/bin/sudo /usr/sbin/lsof "$PTY" | grep iaxmodem | sed 
's/^iaxmodem *\([0-9]*\) .*/\1/g'`

/usr/bin/sudo /bin/kill -HUP $IAXPID

exit
-----------------------------------------

Make sure to mark resetmodem as executable (chmod a+x 
/var/spool/hylafax/etc/resetmodem).

You'll also need something like this in your /etc/sudoers file:

uucp  ALL = NOPASSWD: /bin/kill
uucp  ALL = NOPASSWD: /usr/sbin/lsof

Thanks,

Lee.


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