进程的前后执行和并发执行

1.信号发送kill

1）kill：内部命令，可用来向进程发送控制信号，以实现对进程的管理，每个信号对应一个数字，信号名称以SIG开头，不分大小写。

2）显示当前系统可用信号：

kill -l
trap -l

3）常用信号

范例：发送信号重读配置文件

[root@centos8 ~]# yum -y install httpd
[root@centos8 ~]# systemctl start httpd
[root@centos8 ~]# echo '<h1>weilian<h1>' > /var/www/html/index.html
[root@centos8 ~]# cat /var/www/html/index.html 
<h1>weilian<h1>
[root@centos8 ~]# ss -ntl
State                    Recv-Q                   Send-Q                                     Local Address:Port                                     Peer Address:Port                  Process                   
LISTEN                   0                        128                                              0.0.0.0:111                                           0.0.0.0:*                                               
LISTEN                   0                        32                                         192.168.122.1:53                                            0.0.0.0:*                                               
LISTEN                   0                        128                                              0.0.0.0:22                                            0.0.0.0:*                                               
LISTEN                   0                        5                                              127.0.0.1:631                                           0.0.0.0:*                                               
LISTEN                   0                        128                                            127.0.0.1:6010                                          0.0.0.0:*                                               
LISTEN                   0                        128                                                 [::]:111                                              [::]:*                                               
LISTEN                   0                        128                                                    *:80                                                  *:*                                               
LISTEN                   0                        128                                                 [::]:22                                               [::]:*                                               
LISTEN                   0                        5                                                  [::1]:631                                              [::]:*                                               
LISTEN                   0                        128                                                [::1]:6010                                             [::]:*     
[root@centos8 ~]# mkdir /data/html/
[root@centos8 ~]# echo '<h1>N64<h1>' > /data/html/index.html
[root@centos8 ~]# cat /data/html/index.html
<h1>N64<h1>
[root@centos8 ~]# vim /etc/httpd/conf/httpd.conf 
[root@centos8 ~]# ps aux | grep httpd
[root@centos8 ~]# kill -1 3843
[root@centos8 ~]# ps aux | grep http

4）向进程发送信号

按PID：

kill pid

例：

kill -1 pid

按名称：killall来自于psmisc包

killall [-SINGNAL] comm...

例：

[root@centos8 ~]# pidof bash
3350 2945 868
[root@centos8 ~]# killall bash
[root@centos8 ~]# pidof bash
3350 868

按模式：pkill

例：

[root@centos8 ~]# su - wang
[wang@centos8 ~]$ tail -f /etc/passwd
[root@centos8 ~]# pgrep -u wang -l
34444 bash
34484 tail
[root@centos8 ~]# pkill -u wang
[root@centos8 ~]# pgrep -u wang -l
34444 bash

5）

简单来说，0信号就是检查一个进程是否正常

例：

[root@centos8 ~]# ping 192.168.93.133
[root@centos8 ~]# kill -0 35053
[root@centos8 ~]# echo $?
0

如果为0，表示正常，如果不为零，表示不正常

以后再生产中，会用其进行健康性检查，当然，此方式有局限性，当进程处于停止或僵尸状态，此方式仍认为是健康的

2.作业管理

1）前台作业：通过终端启动，且启动后一直占据终端后台作业，可通过终端启动，但启动后进入后台运行（释放终端）

例：

1 2	`[root@centos8 ~]# ping 192.168.93.133 &` `[root@centos8 ~]# killall -2 ping`

范例：将后台停止进程变为运行用bg或kill -18

[root@centos8 ~]# ping 192.168.93.133
按ctrl+z将其置为后台停止，只对前台起作用
[root@centos8 ~]# jobs #查看作业编号
[root@centos8 ~]# bg 1 #将其恢复为后台运行/kill -18 %1

范例：将后台运行变为后台用kill -19

[root@centos8 ~]# ping 192.168.93.133 &
[root@centos8 ~]# jobs
[root@centos8 ~]# kill -19 %2

范例：将后台恢复为前台fg

[root@centos8 ~]# fg 1
[root@centos8 ~]# fg 2
[root@centos8 ~]# jobs
[root@centos8 ~]#

2）

3.并行

利用后台执行，实现并行功能，即同时运行多个进程，提高效率

1）法一：

cat all.sh
f1.sh&
f2.sh&
f3.sh&

2）法二：

(f1.sh&);(f2.sh&);(f3.sh&)

3）法三：

f1.sh&f2.sh&f3.sh&

后台执行，终端一关就停了

4.断开终端，使程序持续运行

1）screen

[root@centos8 ~]# yum -y install screen
[root@centos8 ~]# screen
[root@centos8 ~]# ping 192.168.93.133
#关闭终端
[root@centos8 ~]# ps aux | grep ping
root        2570  0.0  0.1 388700  1348 tty2     Sl+  20:21   0:00 /usr/libexec/gsd-housekeeping
root       36388  0.0  0.2  32460  2300 pts/2    S+   22:40   0:00 ping 192.168.93.133
root       36400  0.0  0.1  12136  1104 pts/0    R+   22:41   0:00 grep --color=auto ping
[root@centos8 ~]# kill -9 36388
[root@centos8 ~]# ps aux | grep ping
root        2570  0.0  0.1 388700  1348 tty2     Sl+  20:21   0:00 /usr/libexec/gsd-housekeeping
root       36413  0.0  0.1  12136  1140 pts/0    R+   22:41   0:00 grep --color=auto ping
[root@centos8 ~]#

2）nohub

例：

[root@centos8 ~]# nohub ping 192.168.93.133
#他会把执行结果全都放在一个名叫 nohub.out的文件里。所以我们进行修改
[root@centos8 ~]#nohup ping 192.168.93.133 &> /dev/null &
[root@centos8 ~]#ps aux | grep ping
#关闭终端
[root@centos8 ~]#ps aux | grep ping
[root@centos8 ~]#killall ping