Linux Signal Types

 What is a signal ?

               Signal is a notification, a message sent by either operating system or some application to your program (or one of its threads).
     ex:  SIGINT that I already mentioned, tells your program that someone tries to interrupt it with CTRL-C.

from the command prompt you can list all the signal types like :

                               You’ll see that each signal type has a name (such as SIGINT, or just INT) and a number (2 in this case.) Out of a total of 64 signal types shown by kill -l , you’ll probably only need to deal with half a dozen or so,

Signal name	Signal value	Effect
SIGHUP	1	Hangup
SIGINT	2	Interrupt from keyboard
SIGKILL	9	Kill signal
SIGTERM	15	Termination signal
SIGSTOP	17,19,23	Stop the process

In this Signal Number 1,2,9 and 15 are the most used by the system administrator.

Open terminal and type :

1.Enter sleep command with a delay time (10000) running in the background (&)

Here you can see the result [1]  2486 which is the Job No and the Process ID.
 
2.Enter Kill  command with the process ID .

When you check the active  Process with the command ps -aux | grep sleep.we can see the sleep command is terminated.Here you can see the sigterm command executed default.

if you want to kill the command.then:

we can see that after giving the command :
 #Kill - 9 2549
The sleep command was killed. Signal (-9) is SIGKILL.

Control signals in Bash

Ctrl+C	The interrupt signal, sends SIGINT to the job running in the foreground.
Ctrl+Y	The delayed suspend character. Causes a running process to be stopped when it attempts to read input from the terminal.
Ctrl+Z	The suspend signal, sends a SIGTSTP to a running program, thus stopping it and returning control to the shell.