Shell Script Learning Summary 12--system signal

Signal is a process communication mechanism in Linux system. We can use a specific signal to interrupt the process. Each signal is associated with an integer value.

The KILL command can be used to send a signal to a process, while the trap command handles the received signal.

Kill

List all available signals

[email protected] ~]# kill-L1) SIGHUP2) SIGINT3) Sigquit4) Sigill5) SIGTRAP6) SIGABRT7) Sigbus8) SIGFPE9) SIGKILLTen) SIGUSR1 One) SIGSEGV A) SIGUSR2 -) Sigpipe -) SIGALRM the) SIGTERM -) Sigstkflt -) SIGCHLD -) Sigcont +) SIGSTOP -) SIGTSTP +) Sigttin A) Sigttou at) Sigurg -) sigxcpu -) Sigxfsz -) SIGVTALRM -) sigprof -) Sigwinch in) SIGIO -) SIGPWR to) Sigsys the) sigrtmin *) sigrtmin+1     $) sigrtmin+2    Panax Notoginseng) sigrtmin+3 -) sigrtmin+4     the) sigrtmin+5     +) sigrtmin+6     A) sigrtmin+7     the) sigrtmin+8 +) sigrtmin+9     -) sigrtmin+Ten     $) sigrtmin+ One     $) sigrtmin+ A     -) sigrtmin+ - -) sigrtmin+ -     the) sigrtmin+ the     -) sigrtmax- -    Wuyi) sigrtmax- -     the) sigrtmax- A -) sigrtmax- One     Wu) sigrtmax-Ten     -) sigrtmax-9     About) sigrtmax-8     $) sigrtmax-7 -) sigrtmax-6     -) sigrtmax-5     -) sigrtmax-4     A) sigrtmax-3     +) sigrtmax-2 the) sigrtmax-1     -) Sigrtmax

Only a few of them are often used.

SIGHUP 1   --   suspend detection of the control process or end of the terminal.

SIGINT 2   --   Send this signal when CTRL + C

SIGKILL 9  --   strong kill process

SIGTERM 15--  default termination process

SIGTSTP 20--ctrl+z When the signal is sent

Usage, such as strong kill httpd process 19421

19421~]# Kill-919421

Trap

Once the trap assigns a signal to a function, the corresponding function is executed when the script receives the corresponding signal.

Example 1:

[email protected] sbin]# Vim demo_trap.sh #/bin/bashfunction hander () {        is  ' hander ' SIGINT  while true;  Do  1done         

Ps: The function of the dead loop is to keep the process active.

Execute, and press CTRL + C

 is 11756^chey,received signal:sigint

Example 2, the production environment is used as a springboard machine, so that normal operation users can only operate scripts

[email protected] profile.d]# pwd/etc/profile.d[[email protected] profile.d]# vim tiaoban.sh
function trapper () {
Trap ': ' INT EXIT TSTP term HUP
}
If [$UID-ne 0];then
While True;do
Trapper
Clear
echo [1] WEB Server
echo "" Echo [2] APP Server echo""Echo [3] DB Server echo""echo [x] Exit echo""Read-P"Option:"Nu Case$nuinch    1) SSH [email protected]192.168.1.20    ;; 2) SSH [email protected]192.168.1.30    ;; 3) SSH [email protected]192.168.1.40    ;;    x) exit;; *) echo"usage:[123x]"Read-P"Press any key to continue."Esacdonefi

When logged in with a normal user, execute the script directly, and press CTRL + C to enter the command line

Shell Script Learning Summary 12--system signal