curt@sdcrdcf.UUCP (Curt Dodds) (09/27/85)
References: I am using setpgrp() (in a shell that I am writing) to change the PROCESS GROUP ID of the child after the first fork(). This allows me to use kill() to send signals to that child and all of its children (because they share the same PROCESS GROUP ID). However, it seems that certain programs which try to open the device "/dev/tty" don't work when setpgrp() has been called. Examples are "su" and a version of "mail" that I have. A symptom: a "ps" shows the TTY of each child to be "?". I can even type "ps -t\?" and get a list of these children. Nowhere in the documentation is it indicated that setpgrp() should have any effect on the controlling terminal for a process. Why is this happening? P.S. By removing the call to setpgrp() this problem disappears completely.
alan@drivax.UUCP (Alan Fargusson) (09/29/85)
> I am using setpgrp() (in a shell that I am writing) to change the PROCESS > GROUP ID of the child after the first fork(). This allows me to use kill() > to send signals to that child and all of its children (because they > share the same PROCESS GROUP ID). > > However, it seems that certain programs which try to open the device > "/dev/tty" don't work when setpgrp() has been called. Examples are > "su" and a version of "mail" that I have. > > A symptom: a "ps" shows the TTY of each child to be "?". > I can even type "ps -t\?" and get a list of these children. > > Nowhere in the documentation is it indicated that setpgrp() should have > any effect on the controlling terminal for a process. > > Why is this happening? > > P.S. > By removing the call to setpgrp() this problem disappears completely. I know that the documetation is not clear on this, but the kernel uses the process group to determine the controlling terminal. The result of this is that changing the process group effectivly disconnects the process from the controlling terminal. Some utilities like lpsched use setpgrp() to prevent the terminal from sending them signals because they use signals to decide when there is work to do. -- Alan Fargusson. { ihnp4, amdahl, mot }!drivax!alan
sean@ukma.UUCP (Sean Casey) (09/29/85)
In article <2366@sdcrdcf.UUCP> curt@sdcrdcf.UUCP (Curt Dodds) writes: > >I am using setpgrp() (in a shell that I am writing) to change the PROCESS >GROUP ID of the child after the first fork(). This allows me to use kill() >to send signals to that child and all of its children (because they >share the same PROCESS GROUP ID). > >However, it seems that certain programs which try to open the device >"/dev/tty" don't work when setpgrp() has been called. Examples are >"su" and a version of "mail" that I have. Hey! Are you on System V? Maybe this has something to do with the problem of /dev/tty sometimes not being openable from the console. -- - Sean Casey UUCP: sean@ukma.UUCP or - Department of Mathematics {cbosgd,anlams,hasmed}!ukma!sean - University of Kentucky ARPA: ukma!sean@ANL-MCS.ARPA