背景

有时我们运行某个任务，需要保证任务不占据终端影响其他作业，或者保证当前session退出后，任务依然可以继续运行。

方案

• command &
• nohup command &
• CTRL+Z;bg %n; disown %n
• setsid command

使用方法

command &

该方法可以使任务放在后台执行，从而不影响当前终端其他作业，但是如果当前终端退出，也会导致后台任务接收到SIGHUP信号并退出。

-rwx------. 1 Appmanager devops 69 Jun 19 06:07 findBigFiles.bash
[appmanager@localhost toutiao]$ cat findBigFiles.bash 
#! /bin/bash

sleep 1m
find $HOME -size +10M | xargs ls -l --block-size=M
[appmanager@localhost toutiao]$ ./findBigFiles.bash > output.log &
[1] 2644

## 退出当前终端，新开终端并查看进程
[appmanager@localhost ~]$ ps -fu appmanager
UID          PID    PPID  C STIME TTY          TIME CMD
appmana+    2769    2768  0 06:08 pts/0    00:00:00 -bash
appmana+    2818    2769  0 06:08 pts/0    00:00:00 ps -fu appmanager
 
## 重新后台执行程序
[appmanager@localhost toutiao]$ ps -fu appmanager                 
UID          PID    PPID  C STIME TTY          TIME CMD
appmana+    2769    2768  0 06:08 pts/0    00:00:00 -bash
appmana+    2889    2769  0 06:11 pts/0    00:00:00 /bin/bash ./findBigFiles.bash
appmana+    2890    2889  0 06:11 pts/0    00:00:00 sleep 1m
appmana+    2891    2769  0 06:12 pts/0    00:00:00 ps -fu appmanager

[appmanager@localhost toutiao]$ ps -fu appmanager     
UID          PID    PPID  C STIME TTY          TIME CMD
appmana+    2769    2768  0 06:08 pts/0    00:00:00 -bash
appmana+    2906    2769  0 06:13 pts/0    00:00:00 ps -fu appmanager
[1]+  Done                    ./findBigFiles.bash > output.log
[appmanager@localhost toutiao]$ cat output.log 
-rw-------. 1 appmanager devops 35M May 28 19:06 /home/appmanager/.cache/pip/http/d/6/1/f/e/d61fe4b09676f0692c240e67193e3af065d7b9e72f8577595151e51f
-rw-r--r--. 1 appmanager devops 11M May 16 08:49 /home/appmanager/mnt/ansible/roles/Tomcat/files/Apache-tomcat-8.5.79.tar.gz

nohup command &

nohup可以使shell命令忽略SIGHUP信号，避免父进程退出时，子进程也退出。&使任务后台执行。

[appmanager@localhost toutiao]$ nohup $HOME/tmp/toutiao/findBigFiles.bash > output.log 2>&1 &
## 退出当前终端，新开终端并查看进程
[appmanager@localhost ~]$ psfu 
UID          PID    PPID  C STIME TTY          TIME CMD
appmana+    3045       1  0 06:20 ?        00:00:00 /bin/bash /home/appmanager/tmp/toutiao/findBigFiles.bash
appmana+    3046    3045  0 06:20 ?        00:00:00 sleep 1m
appmana+    3102    3101  1 06:21 pts/0    00:00:00 -bash
appmana+    3134    3102  0 06:21 pts/0    00:00:00 ps -fu appmanager

[appmanager@localhost ~]$ psfu 
UID          PID    PPID  C STIME TTY          TIME CMD
appmana+    3102    3101  0 06:21 pts/0    00:00:00 -bash
appmana+    3154    3102  0 06:22 pts/0    00:00:00 ps -fu appmanager
[appmanager@localhost ~]$ cat tmp/toutiao/output.log 
nohup: ignoring input
-rw-------. 1 appmanager devops 35M May 28 19:06 /home/appmanager/.cache/pip/http/d/6/1/f/e/d61fe4b09676f0692c240e67193e3af065d7b9e72f8577595151e51f
-rw-r--r--. 1 appmanager devops 11M May 16 08:49 /home/appmanager/mnt/ansible/roles/tomcat/files/apache-tomcat-8.5.79.tar.gz

CTRL+Z;bg %n; disown %n

使用disown可以忽略执行jobs id接收到的SIGHUP信号，避免父进程的退出而导致子进程的退出。

## CTRL + 会暂停当前执行的程序
[appmanager@localhost toutiao]$ bash -x ./findBigFiles.bash > output.log 2>&1
^Z
[1]+  Stopped                 bash -x ./findBigFiles.bash > output.log 2>&1
[appmanager@localhost toutiao]$ bg %1
[1]+ bash -x ./findBigFiles.bash > output.log 2>&1 &
[appmanager@localhost toutiao]$ disown %1

## 退出当前终端，新开终端并查看进程
+ sleep 1m
+ xargs ls -l --block-size=M
+ find /home/appmanager -size +10M
-rw-------. 1 appmanager devops 35M May 28 19:06 /home/appmanager/.cache/pip/http/d/6/1/f/e/d61fe4b09676f0692c240e67193e3af065d7b9e72f8577595151e51f
-rw-r--r--. 1 appmanager devops 11M May 16 08:49 /home/appmanager/mnt/ansible/roles/tomcat/files/apache-tomcat-8.5.79.tar.gz

setsid command

setsid指定当前进程的父进程为1，不受当前session的退出的影响，但是前提是需要在命令执行时就设置。

[appmanager@localhost toutiao]$ setsid ./findBigFiles.bash > output.log 2>&1 &
[1] 3823
[appmanager@localhost toutiao]$ psfu 
UID          PID    PPID  C STIME TTY          TIME CMD
appmana+    3729    3728  0 06:43 pts/0    00:00:00 -bash
appmana+    3824       1  0 06:49 ?        00:00:00 /bin/bash ./findBigFiles.bash
appmana+    3825    3824  0 06:49 ?        00:00:00 sleep 1m
appmana+    3826    3729  0 06:49 pts/0    00:00:00 ps -fu appmanager
[1]+  Done                    setsid ./findBigFiles.bash > output.log 2>&1

## 退出当前终端，新开终端并查看进程
[appmanager@localhost toutiao]$ psfu 
UID          PID    PPID  C STIME TTY          TIME CMD
appmana+    3729    3728  0 06:43 pts/0    00:00:00 -bash
appmana+    3824       1  0 06:49 ?        00:00:00 /bin/bash ./findBigFiles.bash
appmana+    3825    3824  0 06:49 ?        00:00:00 sleep 1m
appmana+    3827    3729  0 06:49 pts/0    00:00:00 ps -fu appmanager
[appmanager@localhost toutiao]$ ll
total 4
-rwx------. 1 appmanager devops 74 Jun 19 06:11 findBigFiles.bash
-rw-r--r--. 1 appmanager devops  0 Jun 19 06:49 output.log
[appmanager@localhost toutiao]$ cat /opt/
cat: /opt/: Is a directory
[appmanager@localhost toutiao]$ cat output.log 
-rw-------. 1 appmanager devops 35M May 28 19:06 /home/appmanager/.cache/pip/http/d/6/1/f/e/d61fe4b09676f0692c240e67193e3af065d7b9e72f8577595151e51f
-rw-r--r--. 1 appmanager devops 11M May 16 08:49 /home/appmanager/mnt/ansible/roles/tomcat/files/apache-tomcat-8.5.79.tar.gz