Working with the Unix OS

Processes I
! Signals, Process Groups and Control Terminals
Process structure
p-pid:
p-pgrp:
assigned by kernel
set by setpgrp()
fd0:
fd1:
fd2:
fdi:
control
tty:
tty structure
t_pgrp:
…
socket structure
. so_pgrp:
. set by fcnt1
. socket structure
(F_SETOWN)
so_pgrp:
process group for delivery
of SIGIO, SIGURG signals
process group for delivery of SIGINT,
SIGQUIT, SIGHUP, SIGIO, SIGTSTP,
SIGCONT, SIGWINCH signals
! Disassociate from Control Terminal
if (fork () ! = 0)
exit(0); /* parent process */
/* first child process */
setpgrp(); /* change process group and lose control tty */
! Don’t Reaquire a Control Terminal
signal(SIGHUP, SIG_IGN);
if (fork() != 0)
exit(); /* first child process */
/* second child process continues as daemon */
! System V inittab File
id:run-level:action:command-line
tty01:2:respawn:getty #terminal line 1
! Daemon Termination
Both System V and BSD 4.3 use the SIGTERM signal to notify all processes that the system is going from
multiuser to single-user. If it doesn’t terminate after 20 secs, SIGKILL is sent to the the process.
! Handle SIGCLD Signals
Tells kernel not to generate zombies form children.
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