Role-specific Signal Handling Interview Questions & Answers:

1. What is the output of the below code?

void sig_handler ( int signum) {
printf("Handled the signaln");
}

int main() {
int pid;
signal (SIGKILL, sig_handler);
pid = fork();
if (pid==0) {
kill(getppid(), SIGKILL);
exit(0);
} else {
sleep(20);
}
return 0;
}

a) Error child cannot send a SIGKILL signal to parent.
b) Parent goes to the signal handler, prints handled the signal and goes back to sleep
c) Parent goes to the signal handler, prints handled the signal and exits
d) Parent exits without going to the signal handler

d) Parent exits without going to the signal handler

2. The kill system call is used to:
a) Send shutdown messages to all by superuser
b) Send a signal to a process
c) Kill processes
d) Stop the processes

b) Send a signal to a process

3. Default action of SIGSEGV is:
a) Terminate
b) Core dump
c) Stop
d) Cont

b) Core dump

4. Signals are handled using which system call?
a) kill
b) signal
c) both
d) none

b) signal

5. When real interval timer expires which signal is generated?
a) SIGINT
b) SIGCHLD
c) SIGKILL
d) SIGALRM

d) SIGALRM

6. Another signal that cannot be caught is:
a) SIGPIPE
b) SIGHUP
c) SIGSTOP
d) SIGUSR1

c) SIGSTOP

7. What will happen as we press the "Ctrl+c" key after running this program?

#include<stdio.h>
#include<signal.h>

void response (int);
void response (int sig_no)
{
printf("Linuxn");
}
int main()
{
signal(SIGINT,response);
while(1){
printf("googlen");
sleep(1);
}
return 0;
}
a) the string "Linux" will print
b) the process will be terminated after printing the string "Linux"
c) the process will terminate
d) none of the mentioned

a) the string "Linux" will print
Explanation:
The signal handler function "response" executes after recieving the signal SIGINT.
Output:
[root@localhost google]# gcc -o san san.c
[root@localhost google]# ./san
google
google
google
^CLinux
google
google
^CLinux
google
google
^CLinux
google
^Z
[2]+ Stopped ./san
[root@localhost google]#

8. What will happen if we press "Ctrl+c" key two times after running this program?

#include<stdio.h>
#include<signal.h>

void response(int);
void response(int sig_no)
{
printf("Linuxn");
signal(SIGINT,SIG_DFL);
}
int main()
{
signal(SIGINT,response);
while(1){
printf("googlen");
sleep(1);
}
return 0;
}
a) process will terminate in the first time
b) process will terminate in the second time
c) process will never terminate
d) none of the mentioned

c) process will never terminate
Explanation:
According to the signal handler function of this program as the SIGINT signal arrives second time, the signal performs its default operation i.e. termination of the process.
Output:
[root@localhost google]# gcc -o san san.c
[root@localhost google]# ./san
google
google
^CLinux
google
^C
[root@localhost google]#

9. What happens as the SIGINT signal hits the running process of this program?

#include<stdio.h>
#include<signal.h>
#include<stdlib.h>

int main()
{
pid_t child;
signal(SIGINT,SIG_IGN);
child=fork();
switch(child){
case -1:
perror("fork");
exit(1);
case 0:
while(1){
printf("Child Processn");
sleep(1);
}
break;
default :
while(1){
printf("Parent Processn");
pause();
}
break;
}
return 0;
}
a) child process terminates
b) parent process terminates
c) both child and parent process ignores the signal
d) none of the mentioned

c) both child and parent process ignores the signal
Explanation:
If a process ignores a signal then by default its child also ignores that signal.
Output:
[root@localhost google]# gcc -o san san.c
[root@localhost google]# ./san
Parent Process
Child Process
Child Process
^CChild Process
^CChild Process
^CChild Process
^Z
[3]+ Stopped ./san
[root@localhost signal]#

10. What will print as the SIGINT signal hits the running process of this program?

#include<stdio.h>
#include<stdlib.h>
#include<signal.h>

void response (int);
void response (int sig_no)
{
printf("%s",sys_siglist[sig_no]);
}
int main()
{
signal(SIGINT,response);
while(1){
printf("googlen");
sleep(1);
}
return 0;
}
a) Interrupt
b) Stop
c) Terminate
d) none of the mentioned

a) Interrupt
Explanation:
The messages associated with signals can be access by the function sys_siglist().
Output:
[root@localhost google]# gcc -o san san.c
[root@localhost google]# ./san
google
google
google
^CInterruptgoogle
google
^CInterruptgoogle
google
^CInterruptgoogle
google
google
^Z
[4]+ Stopped ./san
[root@localhost google]#