Advanced Programming in the UNIX® Environment

ptg10805159

302 Process Relationships Chapter 9

background

process group(s)

foreground

process group

login shell

login

exec

gettyor

telnetd

exec,aftersetsid,then

establishing controlling terminal

init,inetd,orlaunchd

user at a

terminal

terminal

driver

terminal-generated signals(SIGINT

,SIGQUIT

,SIGTSTP

)

delivered to process group

terminal input/output

read from terminal

generates

SIGTTIN

write to terminal may

generate

SIGTTOU

tcsetpgrp

to set process group

for controlling terminal

change in statusof children

change in status

setpgidof children

setpgid

session

Figure 9.9Summary of job control features with foreground and background jobs, and terminal driver

group to the actual terminal. The dashed line corresponding to theSIGTTOUsignal

means that whether the output from a process in the background process group appears

on the terminal is an option.

Is job control necessary or desirable? Job control was originally designed and

implemented beforewindowing terminals werewidespread. Some people claim that a

well-designed windowing system removes any need for job control. Some complain

that the implementation of job control — requiring support from the kernel, the terminal