C program to change to default action inside the signal handler

C program to change to default action inside the signal handler

#include<stdio.h>

#include<signal.h>

#include<unistd.h>

void sig_handler(int signo)

{

    if (signo == SIGSEGV) {

        printf("received SIGSEGV\n");

        signal(signo, SIG_DFL);

/*  The raise() function sends a signal to the calling process or thread.

  In a single-threaded program it is equivalent to

   kill(getpid(), sig);

 */

        raise(signo);

    }

}

int main(void)

{    /* register signal handler */

    if (signal(SIGSEGV, sig_handler) == SIG_ERR) {

        printf("\ncan't catch SIGSEGV\n");

    }

    while(1)

        sleep(1);

    return 0;

}

C program to send signal (SIGTERM) from the signal handler(SIGINT) of one process to another process which is registered with SIGTERM

C program to send signal (SIGTERM) from the signal handler(SIGINT) of one process to another process which is registered with SIGTERM

Neelkanth_98$ cat signal1.c

#include<stdio.h>

#include<signal.h>

#include<unistd.h>

void sig_handler(int signo)

{

    int process_id;

    char process_id_from_file[10];

    FILE *pid_fd;

    char command[100];

    sprintf(command,"pidof %s", "test_process");

    pid_fd = popen(command, "r");

    if (pid_fd == NULL)

    {

        return;

    }

    if (fgets(process_id_from_file, sizeof process_id_from_file , pid_fd) == NULL)

    {

        return;

    }

    pclose(pid_fd);

    process_id = atoi(process_id_from_file);

    if (signo == SIGINT) {

        printf("received SIGINT from another process\n");

        kill(process_id, SIGTERM);

        printf("send SIGTERM to another process\n");

        return;

    }

}

int main(void)

{    /* register signal handler */

    if (signal(SIGINT, sig_handler) == SIG_ERR)

        printf("\ncan't catch SIGINT\n");

    while(1)

        sleep(1);

    return 0;

}

Neelkanth_98$ cat signal2.c

#include<stdio.h>

#include<signal.h>

#include<unistd.h>

void sig_handler(int signo)

{

    if (signo == SIGTERM)

        printf("received SIGTERM from test process\n");

}

int main(void)

{    /* register signal handler */

    if (signal(SIGTERM, sig_handler) == SIG_ERR)

        printf("\ncan't catch SIGTERM\n");

    while(1)

        sleep(1);

    return 0;

}

C program to print userid and group id

C  program to print userid and group id 

#include <stdio.h>

#include <sys/types.h>

#include <pwd.h>

#include <unistd.h>

#include <sys/types.h>

#include <grp.h>

int main()

{

    struct passwd *pwd;

    struct group  *grp;

    int uid, gid;

    pwd = getpwnam("nobody");

    if (pwd == NULL) {

        printf("Failed to get uid");

    }

    uid = pwd->pw_uid;

    grp = getgrnam("root");

    if (grp == NULL) {

        printf("Failed to get gid");

    }

    gid = grp->gr_gid;

    printf("\n %d  %d \n", uid, gid);

    return 0;

}

~

C program to implement error handling

C program to implement error handling

#include <stdio.h>

#include <errno.h>

extern int errno ;

int main ()

{

  FILE * pFile;

  pFile = fopen ("unexist.ent","rb");

  if (pFile == NULL)

  {

    perror ("The following error occurred");

    printf( "Value of errno: %d\n", errno );

  }

  else

    fclose (pFile);

  return 0;

}

If file unexist.ent does not exit then it will produce following result:

The following error occurred: No such file or directory

Value of errno: 29

C program to implement software timer

C program to implement software timer

#include <stdio.h>

#include <time.h>

int main()

{

    time_t start = time(NULL);

   for (;;)

    {

        if (time(NULL) > start + 10) {

         printf("10s timeout!\n");               

         break;

    }

}

    return 0;

}