car@trux.UUCP (Chris Rende) (07/06/90)
I need to run a program via CRON(1M). However, the program aborts (presumably)
because it cannot open it's control tty (/dev/tty). Running it in background
(with &) works, and so does "nohup fussy &".
I'd like to write a program which establishes a control tty and then spawns
the fussy program.
However, I can't figure/find out how to set the control tty. I read in
TERMIO(7) something like "The first terminal file that gets opened becomes
the control terminal". When I wrote a program that disassociates itself from
the control terminal and then does a "fd=open("/dev/ttyi00",O_RDWR);"
it didn't work. I.e, a "ps -ef" shows "?" for the control tty.
Any help would be appreciated.
Thanks,
car.
--
Christopher A. Rende Central Cartage (Nixdorf/Pyramid/SysVR2/BSD4.3)
uunet!edsews!rphroy!trux!car Multics,DTSS,Unix,Shortwave,Scanners,StarTrek
trux!car@uunet.uu.net Minix 1.2,PC/XT,Mac+,TRS-80 Model I,1802 ELF
"I don't ever remember forgetting anything." - Chris Rendecpcahil@virtech.uucp (Conor P. Cahill) (07/06/90)
In article <483@trux.UUCP> car@trux.UUCP (Chris Rende) writes: >However, I can't figure/find out how to set the control tty. I read in >TERMIO(7) something like "The first terminal file that gets opened becomes >the control terminal". When I wrote a program that disassociates itself from >the control terminal and then does a "fd=open("/dev/ttyi00",O_RDWR);" >it didn't work. I.e, a "ps -ef" shows "?" for the control tty. The other requirement is that no other proces has that terminal as its controlling terminal. I would guess that your test is failing because the tty is the controlling terminal for another process. -- Conor P. Cahill (703)430-9247 Virtual Technologies, Inc., uunet!virtech!cpcahil 46030 Manekin Plaza, Suite 160 Sterling, VA 22170
bob@wyse.wyse.com (Bob McGowen x4312 dept208) (07/06/90)
In article <1990Jul06.015108.14622@virtech.uucp> cpcahil@virtech.UUCP (Conor P. Cahill) writes: >In article <483@trux.UUCP> car@trux.UUCP (Chris Rende) writes: >>However, I can't figure/find out how to set the control tty. I read in ----- >>it didn't work. I.e, a "ps -ef" shows "?" for the control tty. > >The other requirement is that no other proces has that terminal as its >controlling terminal. I would guess that your test is failing because >the tty is the controlling terminal for another process. ----- Another possibility is that the open blocked waiting for some line condition, such as carrier detect. In my experience the "?" in the tty column of ps output either means a process with no controlling terminal (which is what I believe you are assuming) OR a line on which an open has begun but NOT completed. In the latter case there is no information available for ps to tell which line is involved. Check the open() man page for details on the O_NDELAY flag. When it is set and the open is on a communications line the open will return without waiting for carrier. Good luck. Bob McGowan (standard disclaimer, these are my own ...) Product Support, Wyse Technology, San Jose, CA ..!uunet!wyse!bob bob@wyse.com
walter@mecky.UUCP (Walter Mecky) (07/11/90)
In article <1990Jul06.015108.14622@virtech.uucp> cpcahil@virtech.UUCP (Conor P. Cahill) writes: < In article <483@trux.UUCP> car@trux.UUCP (Chris Rende) writes: < >However, I can't figure/find out how to set the control tty. I read in < >TERMIO(7) something like "The first terminal file that gets opened becomes < >the control terminal". When I wrote a program that disassociates itself from < >the control terminal and then does a "fd=open("/dev/ttyi00",O_RDWR);" < >it didn't work. I.e, a "ps -ef" shows "?" for the control tty. < < The other requirement is that no other proces has that terminal as its < controlling terminal. I would guess that your test is failing because < the tty is the controlling terminal for another process. The third requirement is that the proces is a process group leader. According to my manual from SCO UNIX 3.2: The very first terminal file opened by the process group leader of a terminal file not already associated with a process group becomes the for that process group. The control terminal plays a special role in handling quit and interrupt signals, as discussed below. The control terminal is inherited by a child process during a fork(S). A process can break this association by changing its process group using setpgrp(S). -- Walter Mecky [ walter@mecky or ...uunet!unido!mecky!walter ]