Describe the functionality of each of the following system c

Describe the functionality of each of the following system calls:

a. kill(456, 0);

b. waitpid(-1,&status, 0);

c. raise(SIGUSR1);

Solution

a. kill(456,0): This is used to send any signal to any process group or process.
Here pid=456 and sig=0
Pid is positive. But sig is 0. So no signal will be sent to the process with pid 456.
But error checking is still performed; this can be used to check for the existence
of a process ID 456.

b. waitpid(-1,&status,0);
here pid=-1, status sig=status, options=0
if pid==-1, then it waits for any child process.
The waitpid() system call suspends execution of the calling process until a child process has changed state (waiting for termination).

c. raise(SIGUSR1);
The raise() function sends the signal sig to the running program.
Then the signal handler in the program will be executed.