[Bug 982] New: cu -l /dev/ttyS0 got a signal hangup in 2.5 kernel

[Bug 982] New: cu -l /dev/ttyS0 got a signal hangup in 2.5 kernel

[Martin J. Bligh]

http://bugme.osdl.org/show_bug.cgi?id=982

           Summary: cu -l /dev/ttyS0 got a signal hangup in 2.5 kernel
    Kernel Version: 2.5.75
            Status: NEW
          Severity: normal
             Owner: rmk@arm.linux.org.uk
         Submitter: hien1@us.ibm.com
                CC: sglass@us.ibm.com


Distribution: SuSE SLES8 
Hardware Environment:NetVista 6579-A4U Pentium III - 866 MHz 256MB RAM 
Software Environment:2.5.75 kernel 
Problem Description: cu session fails to log into the other machine which is connected with a 
null modem serial cable between serial ports. 
It works fine in 2.4.19 4GB kernel 
 
Steps to reproduce: 
  1. connecting two systems with a null modem serial cable between serial ports. 
  2. On one machine, do : cu -l /dev/ttyS0 
      On other system, have /sbin/agetty -L 9600 ttyS0 vt100  running. 
      and ttyS0 has been defined in /etc/securetty 
  3. cu session connected and showed you the login prompt. 
  4. Got a hangup signal and disconnected after typing "root" or any user ID. 
      It supposes to prompt you "password:" to let you type the password of the other machine 
      to login to that system.

Re: [Bug 982] New: cu -l /dev/ttyS0 got a signal hangup in 2.5 kernel

[Russell King]

On Sun, Jul 27, 2003 at 10:13:54PM -0700, Martin J. Bligh wrote:
> Distribution: SuSE SLES8 
> Hardware Environment:NetVista 6579-A4U Pentium III - 866 MHz 256MB RAM 
> Software Environment:2.5.75 kernel 
> Problem Description: cu session fails to log into the other machine which is connected with a 
> null modem serial cable between serial ports. 
> It works fine in 2.4.19 4GB kernel 
>  
> Steps to reproduce: 
>   1. connecting two systems with a null modem serial cable between serial ports. 
>   2. On one machine, do : cu -l /dev/ttyS0 
>       On other system, have /sbin/agetty -L 9600 ttyS0 vt100  running. 
>       and ttyS0 has been defined in /etc/securetty 
>   3. cu session connected and showed you the login prompt. 
>   4. Got a hangup signal and disconnected after typing "root" or any user ID. 
>       It supposes to prompt you "password:" to let you type the password of the other machine 
>       to login to that system.

If I remember to update bugzilla...

What seems to be happening is that cu is clearing the "clocal" termios bit.
This means that when the CD line is dropped on ttyS0, cu receives a hangup
signal, as per the POSIX spec.  This seems reasonable.

There is a change of behaviour between 2.4 and 2.5 kernels though
(please confirm) - if you use the "callout" devices in 2.4, you don't
receive this hangup signal, even if the clocal bit is cleared.  Callout
devices no longer exist in 2.5.

The real question is this - why is the CD line being dropped between the
two machines between typing in the user name and asking for the password.

Maybe someone with this problem can give some details about the system
they're trying to log into rather than the local system.

-- 
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html