21.
What is the output of this program?
#include<stdio.h>
#include<pthread.h>
#include<semaphore.h>
 
void *fun_t(void *arg);
void *fun_t(void *arg)
{
    sem_post(&st);
    pthread_exit("Bye");
}
int main()
{
    pthread_t pt;
    sem_t st;
    void *res_t;        
    if(pthread_create(&pt,NULL,fun_t,NULL) == -1)
        perror("pthread_create");
    if(sem_init(&st,0,0) != 0)
        perror("sem_init");
    if(sem_wait(&st) != 0)
        perror("sem_wait");
    printf("Example\n");
    if(pthread_join(pt,&res_t) == -1)
        perror("pthread_join");
    if(sem_destroy(&st) != 0)
        perror("sem_destroy");
    return 0;
}

25.
What is the output of this program?
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/types.h>
#include<sys/ipc.h>
#include<sys/msg.h>

struct data_st{
    long int id;
    char buff[11];
};
int main()
{
    int m_id,ret;
    struct data_st data1, data2;
    m_id = msgget((key_t)181,0666|IPC_CREAT);
    if(m_id == -1)
        perror("msgget");
    data1.id = 1;
    strcpy(data1.buff,"Example");
    ret = msgsnd(m_id,&data1,11,0);
    printf("%d\n",ret);
    if(msgrcv(m_id,&data2,11,1,0) == -1)
        perror("msgrcv");
    if(msgctl(m_id,IPC_RMID,0) != 0)
        perror("msgctl");
    return 0;
}

26.
What is the output of this program?
#include<stdio.h>
#include<pthread.h>
 
void *fun_t(void *arg);
void *fun_t(void *arg)
{
    sleep(1);
}
int main()
{
    pthread_t pt;
    void *res_t;
    if(pthread_create(&pt,NULL,fun_t,NULL) != 0)
        perror("pthread_create");
    if(pthread_join(pt,&res_t) != 0)
        perror("pthread_join");
    printf("%s\n",res_t);
     return 0;
}

27.
If user tries to remove (rm) a readonly file (444 permission), what will happen?

29.
On Linux, initrd is a file

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