shell脚本学习总结12--系统信号

信号是Linux系统中一种进程通信机制。我们可以使用特定的信号来中断进程。每一种信号都同一个整数值相关联。

kill命令可用来想进程发送信号，而trap命令用来处理所接收的信号。

kill

列出所有可用的信号

[root@LAMP ~]# kill -l
 ) SIGHUP     ) SIGINT     ) SIGQUIT     ) SIGILL     ) SIGTRAP
 ) SIGABRT     ) SIGBUS     ) SIGFPE     ) SIGKILL    ) SIGUSR1
) SIGSEGV    ) SIGUSR2    ) SIGPIPE    ) SIGALRM    ) SIGTERM
) SIGSTKFLT    ) SIGCHLD    ) SIGCONT    ) SIGSTOP    ) SIGTSTP
) SIGTTIN    ) SIGTTOU    ) SIGURG    ) SIGXCPU    ) SIGXFSZ
) SIGVTALRM    ) SIGPROF    ) SIGWINCH    ) SIGIO    ) SIGPWR
) SIGSYS    ) SIGRTMIN    ) SIGRTMIN+    ) SIGRTMIN+    ) SIGRTMIN+
) SIGRTMIN+    ) SIGRTMIN+    ) SIGRTMIN+    ) SIGRTMIN+    ) SIGRTMIN+
) SIGRTMIN+    ) SIGRTMIN+    ) SIGRTMIN+    ) SIGRTMIN+    ) SIGRTMIN+
) SIGRTMIN+    ) SIGRTMIN+    ) SIGRTMAX-    ) SIGRTMAX-    ) SIGRTMAX-
) SIGRTMAX-    ) SIGRTMAX-    ) SIGRTMAX-    ) SIGRTMAX-    ) SIGRTMAX-
) SIGRTMAX-    ) SIGRTMAX-    ) SIGRTMAX-    ) SIGRTMAX-    ) SIGRTMAX-
) SIGRTMAX-    ) SIGRTMAX    

经常用到的只有几个

SIGHUP 1   ——   对控制进程或终端终结进行挂起检测。

SIGINT 2   ——   Ctrl+C时发送该信号

SIGKILL 9  ——   强杀进程

SIGTERM 15 ——  默认终止进程

SIGTSTP 20 —— Ctrl+Z时发送该信号

用法,例如强杀httpd进程19421

[root@LAMP ~]# kill -s SIGKILL
[root@LAMP ~]# kill - 

trap

一旦trap将某个函数分配一个信号，当脚本运行收到相应的信号，就会执行相应的函数

实例1：

[root@localhost sbin]# vim demo_trap.sh 

#/bin/bash
function hander(){
        echo Hey,received signal : SIGINT
}

echo My process ID is $$
trap 'hander' SIGINT

while true;do
        sleep
done

Ps：死循环的作用是使进程一直处于活动状态。

执行，并按Ctrl+C

[root@localhost sbin]# sh demo_trap.sh
My process ID is
^CHey,received signal : SIGINT

实例2，生产环境用作于跳板机，使普通操作用户连接只能操作脚本

[root@LAMP profile.d]# pwd
/etc/profile.d
[root@LAMP profile.d]# vim tiaoban.sh

function trapper(){
    trap ':' INT EXIT TSTP TERM HUP
}
if [ $UID -ne 0 ];then
while true;do
    trapper
    clear
    echo [1] WEB Server
    echo ""
    echo [] APP Server
    echo ""
    echo [] DB Server
    echo ""
    echo [x] Exit
    echo ""
    read -p "Option: " nu
    case $nu in
    )
      ssh redhat@192.168.1.20
    ;;
    )
      ssh appadmin@192.168.1.30
    ;;
    )
      ssh oracle@192.168.1.40
    ;;
    x)
      exit
    ;;
    *)
     echo "USAGE:[123x]"
     read -p "Press any key to continue."
     esac
done
fi

当用普通用户登陆时，直接执行脚本，并按ctrl+c等命令都无法进入命令行

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