System_Software_HandsOnList2/030.c at main · superv13/System_Software_HandsOnList2 · GitHub

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/*
..........................................................................................................................................
Name : 030.c
Author : SHRUTI VERMA
Description : Write a program to create a shared memory.
                a. write some data to the shared memory
                b. attach with O_RDONLY and check whether you are able to overwrite.
                c. detach the shared memory
                d. remove the shared memory
Date : 16 Sep 2025
..........................................................................................................................................
*/


#include<unistd.h>
#include<stdlib.h>
#include<stdio.h>
#include<sys/types.h>
#include<sys/shm.h>
#include<sys/ipc.h>


int main() {
    int key, shmid;
    char* data;
    key = ftok("file.txt",34);
    shmid = shmget(key, 1024, IPC_CREAT | 0744);
    data = shmat(shmid, NULL, 0);
    scanf("%[^\n]", data);
    printf("data from shared memory : %s\n", data);
    shmdt(data);

    data = shmat(shmid, NULL, SHM_RDONLY);
    printf("trying to overwrite\n");
    data[0] = 'X';
    printf("%s", data);
    shmdt(data);
}

/*----------------------------------OUTPUT--------------------------------------------

vumma@vumma-VivoBook-15-ASUS-Laptop-X507UF:~/Desktop/SS/HOL2$ gcc 030.c -o 030.out
vumma@vumma-VivoBook-15-ASUS-Laptop-X507UF:~/Desktop/SS/HOL2$ ./030.out
hello guys, it's shruti here
data from shared memory : hello guys, it's shruti here
trying to overwrite
Segmentation fault (core dumped)
vumma@vumma-VivoBook-15-ASUS-Laptop-X507UF:~/Desktop/SS/HOL2$ ipcs -m

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 0          vumma      606        11657952   2          dest
0x00000000 1          vumma      606        11657952   2          dest
0x00000000 8          vumma      600        524288     2          dest
0x22056ed5 11         vumma      744        1024       0

vumma@vumma-VivoBook-15-ASUS-Laptop-X507UF:~/Desktop/SS/HOL2$ ipcrm -m 11
vumma@vumma-VivoBook-15-ASUS-Laptop-X507UF:~/Desktop/SS/HOL2$ ipcs -m

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 0          vumma      606        11657952   2          dest
0x00000000 1          vumma      606        11657952   2          dest
0x00000000 8          vumma      600        524288     2          dest

*/