SIGUSR1 not received - linux

Question

This is my first Program....ctrlcsignal.c
enter code here
#include<stdio.h>
#include<unistd.h>
#include<signal.h>
void signal_handler(int sigNo)
{
//if Ctrl+c signal
if(sigNo==SIGINT){
printf("value of SIGINT:-%d\t",SIGINT);
printf("received SIGINT\n");
}
// if some other signal , but this part wont get executed
// as the signal_handler function is registered with SIGINT only
else
{
printf("Some other signal found");
printf("value of other signal:-%d",sigNo);
}
}
int main(void)
{
//registering the signal handler function with a signal
kill(19574,SIGUSR1);
if(signal(SIGINT,signal_handler)==SIG_ERR)
{
printf("\n can't catch SIGINT\n");
}
while(1) //infinite loop
sleep(1); // 1s ,so that the CPU is not busy
return 0;
}
and this my second program....userdefinedsignals.c
enter code here
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
void signal_handler(int sigNo)
{
printf("function entered...");
// check for userdefined Signal SIGUSR1
if (sigNo == SIGUSR1)
{
printf("received SIGUSR1 with value :- %d",SIGUSR1);
}
//checking for KILL Signal
else if (sigNo == SIGKILL)
{
printf("received SIGKILL with value :- %d",SIGKILL);
}
//checking for STOP Signal
else if (sigNo == SIGSTOP)
{
printf("received SIGSTOP with value :- %d",SIGSTOP);
}
// if some other signal , but this part wont get executed
// as the signal_handler function is registered with SIGINT only
else
{
printf("Some other signal found");
printf("value of other signal:-%d",sigNo);
}
}
int main(void)
{
int pid_t;
printf("process id is %d",getpid());
//registering the signal handler function with a signal
if(signal(SIGUSR1,signal_handler) == SIG_ERR)
{
printf("\n can't catch SIGSIGUSR1\n");
}
if(signal(SIGKILL,signal_handler)==SIG_ERR)
{
printf("\n can't catch SIGKILL\n");
}
if(signal(SIGSTOP,signal_handler)==SIG_ERR)
{
printf("\n can't catch SIGSTOP\n");
}
while(1) //infinite loop
sleep(1); // 1s ,so that the CPU is not busy
return 0;
}
I get the pid of the second process ... suppose xxxx
then i use the following command...
enter code here
kill -USR1 xxxx
but it shows nothing ....
also then i tried by calling the following function int the first program...but no use..
enter code herekill(xxxx,SIGUSR1);
HELP ME..!!!!

Answer 1

Works here.
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <stdarg.h> /* vsnprintf() */
#include <signal.h> /* signal */
void myprintf(FILE *fp, char *fmt, ...)
{
char buff[512];
int rc,fd;
va_list argh;
va_start (argh, fmt);
rc = vsnprintf(buff, sizeof buff, fmt, argh);
if (rc < 0 || rc >= sizeof buff) {
rc = sprintf(buff, "Argh!: %d:\n", rc);
}
if (!fp) fp = stderr;
fd = fileno(fp);
if (fd < 0) return;
if (rc > 0) write(fd, buff, rc);
return;
}
void signal_handler(int sigNo)
{
switch (sigNo ) {
case SIGUSR1:
myprintf(NULL, "received SIGUSR1 with value :- %d\n", SIGUSR1);
break;
case SIGKILL:
myprintf(NULL, "received SIGKILL with value :- %d\n", SIGKILL);
break;
case SIGSTOP:
myprintf(NULL, "received SIGSTOP with value :- %d\n", SIGSTOP);
break;
default:
myprintf(NULL, "Some other signal occured: %d\n", sigNo);
break;
}
return;
}
int main(void)
{
pid_t mypid;
mypid = getpid();
printf("process id is %d\n", (int) mypid);
if(signal(SIGUSR1,signal_handler) == SIG_ERR)
{ printf("\n can't catch SIGSIGUSR1\n"); }
if(signal(SIGKILL,signal_handler)==SIG_ERR)
{ printf("\n can't catch SIGKILL\n"); }
if(signal(SIGSTOP,signal_handler)==SIG_ERR)
{ printf("\n can't catch SIGSTOP\n"); }
if(signal(SIGCONT,signal_handler)==SIG_ERR)
{ printf("\n can't catch SIGCONT\n"); }
while(1) {
sleep(1);
}
return 0;
}

Answer 2

You're catching the signal all right, but not seeing the message because you don't terminate lines properly, and the standard output stream on your system is line buffered (assuming your program runs in a terminal).
Standard C defines three levels of buffering for output streams:
unbuffered, where output is transmitted immediately
line buffered, where output is transmitted when a newline character is encountered
fully buffered, where output is transmitted when an internal buffer fills
(This is a simplification - see a C reference or the Standard for details).
Consider:
#include <stdio.h>
#include <unistd.h>
int main(void)
{
printf("Hello");
pause();
}
This produces no output in a terminal. Fix it by terminating the line:
printf("Hello\n");
This will produce the expected output in a terminal.
If stdout is not connected to a terminal - for example, you redirect to a file - then the stream becomes fully buffered. This:
./a.out > foo
Ctrl-C
cat foo
produces no output, even with the newline character added. Here you need an explicit flush to transmit the output before the buffer is full.
#include <stdio.h>
#include <unistd.h>
int main(void)
{
printf("Hello\n");
fflush(stdout);
pause();
}
This produces output even when redirected to a file.