do you believe X-application will "kill" the CDE and come back to login dialog Post: 24874

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Top Forums Programming do you believe X-application will "kill" the CDE and come back to login dialog Post 24874 by chenhao_no1 on Friday 19th of July 2002 03:20:09 AM

07-19-2002

Registered User

1 . thanks Perderabo
2 . I do a experiment in Compaq Tru64 Unix.
It (X-applicaton ) "kill" the CDE sometimes .
When the X-Application "kill" the CDE and let me come back to login dialog , it catch all signal SIGHUP (I use sigacton() (its sa_flags = SA_SIGINFO) ). signal SIGHUP , which sent by pid = 0 ,uid = 0 ( in fact it is [kernel idle] )
I add the tcgetsid(STDIN_FILENO) in source code , I find that When I launch the X-applicaion the "session leader" is 2345 (it will change ) , and When I launch the X-application from a menu button , its "session leader" is -1.

I can not understand why the kernel send the SIGHUP . Because :

3. "the signal is sent to the controlling process(session leader) associated with a controlling terminal if a disconnect is detected bye the terminal inferface" . But When I type the command "ps aux ",I found that the TTY of the X-applicaton is ??? , which indicate that it do not have a controlling terminal device (maybe I am wrong) . Since the X-applicaton does not have a controlling terminal , Why does the kernel sent SIGHUP to it

4 "the signal is also generated if the session leader terminato" . But I use tcgetsid(STDIN_FILENO), I find that the session leader is -1 . Since the session leader is dead (because it is -1) , how can it receive SIGHUP . (sometimes when the session leader is -1 ,the X-applicaton work correctly)

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setsid

SETSID(2)						     Linux Programmer's Manual							 SETSID(2)

NAME

       setsid - creates a session and sets the process group ID

SYNOPSIS

       #include <unistd.h>

       pid_t setsid(void);

DESCRIPTION

       setsid() creates a new session if the calling process is not a process group leader.  The calling process is the leader of the new session,
       the process group leader of the new process group, and has no controlling tty.  The process group ID and session ID of the calling  process
       are set to the PID of the calling process.  The calling process will be the only process in this new process group and in this new session.

RETURN VALUE

       The session ID of the calling process.

ERRORS

       On  error,  -1  will be returned.  The only error which can happen is EPERM. It is returned when the process group ID of any process equals
       the PID of the calling process. Thus, in particular, setsid fails if the calling process is already a process group leader.

NOTES

       A process group leader is a process with process group ID equal to its PID. In order to be sure that setsid will succeed,  fork	and  exit,
       and have the child do setsid().

CONFORMING TO

       POSIX, SVr4.

SEE ALSO

       setpgid(2), setpgrp(2)

Linux 1.0.0							    1994-08-27								 SETSID(2)