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

[Niksa Baldun <niksa.baldun@xxxxxxxxx>]

Lee,

Many thanks for detailed explanation.

I am unclear on the resetmodem script, however. You are using lsof on
the pseudo-tty, but if iaxmodem already crashed, that tty will not
exist. Or am I wrong?

Thanks,

Niksa


On 03/22/2010 06:05 AM, Lee Howard wrote:
> 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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