Linux Guard Service-foreground process and background process switch

Put an executing program into the background

[[email protected] 01]# Ctrl+Z

This causes the program to be moved to the background, but cannot continue output (in paused state)

[[email protected] 01]# ./test1-1 1552227155222715522271552227^Z[1]+  已停止                  ./test1-1[[email protected] 01]# [[email protected] 01]# [[email protected] 01]# jobs[1]+  已停止                  ./test1-1

Let the daemon continue to run in the background

[[email protected] 01]# bg %1[1]+ ./test1-1 &1552227[[email protected] 01]# 155222715522271552227^C

List background Programs

[[email protected] 01]# jobs

Show list of programs that have entered the background

[[email protected] 01]# jobs[1]   已停止                  ./test1-1[2]-  已停止                  ./test1-1[3]+  已停止                  man jobs

where + is the countdown to the first background process,-is the second-to-last background process, ahead of the background process sequence number

[[email protected] 01]# jobs[1]-  已停止                  ./test1-1[2]+  已停止                  ./test1-2

Switch a specific daemon to the foreground

[[email protected] 01]# fg %n

where n is the background process ordinal in the jobs list

[[email protected] 01]# fg %1./test1-115522271552227

View Parent Process identity

[[email protected] 01]# ps f   PID TTY      STAT   TIME COMMAND 49561 pts/1    Ss     0:00 -bash 49959 pts/1    T      0:00  \_ ./test1-1 49960 pts/1    T      0:00  \_ ./test1-2 49962 pts/1    R+     0:00  \_ ps f  2496 tty1     Ss+    0:00 -bash

Use PS f to display all processes in a tree to see whether the parent process of test1-1 Test1-2 is-bash

View process identity on new terminal

[[email protected] ~]# ps f   PID TTY      STAT   TIME COMMAND 50060 pts/3    Ss     0:00 -bash 50093 pts/3    R+     0:00  \_ ps f 50010 pts/2    Ss+    0:00 -bash 49561 pts/1    Ss+    0:00 -bash 49959 pts/1    T      0:00  \_ ./test1-1 49960 pts/1    T      0:00  \_ ./test1-2  2496 tty1     Ss+    0:00 -bash

After the new terminal is opened Test1-1 and Test1-2 's parent process is PTS/1-bash is the old terminal, the-bash of the new terminal is PTS/3, this use of jobs has no test1-1 and test1-2

Log out terminal when pressing CTRL+D

[[email protected] 01]# 登出

Show a stopped task, then use PS-EF to view the list, background tasks still exist
Press once again to Ctrl+d, the terminal has been logged out, switch to another terminal to view

Last login: Sun Oct 15 18:26:48 2017 from 192.168.80.1[[email protected] ~]# ps -ef | grep testroot      49959      1  0 18:27 ?        00:00:00 ./test1-1

The process continues to run after adoption by the INIT process, calling the orphan process to place the program directly in the background execution &

[[email protected] 01]# ./test1-1 &

This enables the program to continue running in the background automatically and output

[[email protected] 01]# ./test1-1 &[1] 49856[[email protected] 01]# 15522271552227

Keep daemon in existence after terminal end

Using daemons to keep a process from terminating as a parent process

daemon(0,0);

The state meaning in Ps-ef

D    不可中断     Uninterruptible sleep (usually IO)R    正在运行，或在队列中的进程S    处于休眠状态T    停止或被追踪Z    僵尸进程W    进入内存交换（从内核2.6开始无效）X    死掉的进程<    高优先级N    低优先级L    有些页被锁进内存s    包含子进程+    位于后台的进程组；l    多线程，克隆线程  multi-threaded (using CLONE_THREAD, like NPTL pthreads do)

Linux Guard Service-foreground process and background process switch