Process groups, jobs, session-related concepts

Inter-process relationships: synchronous, mutex, and others.

Shell Terminal: You can run a foreground job and any number of background jobs, which is called job control.

Process Group : each process belongs to a process group in addition to a process ID. A process group is a collection of one or more processes.
Typically, they are associated with the same job and can receive various signals from the same terminal.

Note: as long as a process exists in a process group, the process group exists, regardless of whether its leader process terminates

job :shell Job (

Shell job and any number of background jobs, which is called job control.

The difference between a job and a process group: If a process in the job has created a child process, the child process does not belong to the job.

A session is a collection of one or more process groups.

A session can have a control terminal. the first process of establishing a session connected to a control terminal is called the control process.
Multiple process groups in a session can be divided into one foreground process group and one or more background process groups. Therefore , a session should include the control process (session first process), a foreground process group, and any background process group.

The kernel sends a corresponding signal to all processes in the foreground process group.

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BG% 1, or BG 1: Put the front desk work backstage.

FG% 1, or FG 1: Put background jobs in the foreground.

How Bash Works: Identify commands (whether justified), fork sub-processes, child Process Execution code (bash background)

Terminal : Open terminal, set up a session, bash is the foreground, there are very many jobs in the background.

InUnixIn the systemUseThe user logs into the system via the terminal and gets aShellProcess,This terminal becomesShellControl of the processTerminal(controlling Terminal),The control terminal is saved inpcb We know fork will replicate pcb information ,shell The terminal is also the control terminal of other processes initiated by the process.

Note: standard input, standard output, and standard error outputs for each process point to the control terminal when no redirection is in progress

#include <stdio.h> #include <unistd.h>int main () {printf ("pid:%d\n", Getpid ());    printf ("In:%s\n", Ttyname (0));    printf ("Out:%s\n", Ttyname (1)); printf ("Err:%s\n", Ttyname (2));}

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Process groups, jobs, session-related concepts