Task 1
======

man man
man -k wait
man -s 2 wait
apropos = man -k
whatis  = man -f

Task 2
======

who | sort

Extra example using pipes:

Show 25 most common given names of users who have user account in cs-computer.

Solution:

cat /etc/passwd | awk -F: '{print $5}' | awk '{print $1}' | sort | uniq -c | sort -n | tail -25r

Task 3
======

Using dup
---------

#include <stdio.h>

main()

    int putki[2];
    int pid,pid2;

    /* create a pipe */   
    if (pipe(putki) != 0) {perror("pipe"); exit(1);}

    /* Parent creates 1st child */
    pid = fork();
    if (pid == -1) {perror("fork"); exit(1);}
    if (pid == 0) {
      /* This is the 1st child */
      /* Close standard out (writing) and redirect putki[1] to it */
      close(1); dup(putki[1]);
      /* close putki[0] and putki[1] of child */
      close(putki[0]); close(putki[1]);
      /* exec who, which writes to standard output */
      execlp("who","who",NULL);
    } else
      /* Parent process*/
      {
       /* Parent creates 2nd child */
        pid2 = fork();
        if (pid2 == -1) {perror("fork"); exit(1);}
        if (pid2 == 0) {
           /* This in the 2nd child*/
           /* Sort reads here from standard input */
           /* Close standard in (reading) and redirect putki[0] to it */
           close(0); dup(putki[0]);
           /* close putki[0] and putki[1] of child */
           close(putki[0]); close(putki[1]);
           /* sort gets input from standard in */
           execlp("sort","sort",NULL);
           }
        printf("Childs completed\n");
        exit(0);
    }
}


Using dup2
----------

#include <stdio.h>

main()

    int putki[2];
    int pid,pid2;

    /* create a pipe */   
    if (pipe(putki) != 0) {perror("pipe"); exit(1);}

    /* Parent creates 1st child */
    pid = vfork();
    if (pid == -1) {perror("fork"); exit(1);}
    if (pid == 0) {
      /* This is the 1st child */
      dup2(stdout,putki[1]);
      /* close putki[0] and putki[1] of child */
      close(putki[0]); close(putki[1]);
      /* exec who, which writes to standard output */
      execlp("who","who",NULL);
    } else
      /* Parent process*/
   {
        /* Parent creates 2nd child */
        pid2 = vfork();
        if (pid2 == -1) {perror("fork"); exit(1);}
        if (pid2 == 0) {
           /* This in the 2nd child*/
           /* Sort reads here from standard input */
           /* Close standard in (reading) and redirect putki[0] to it */
           dup2(stdin,putki[0]);
           /* close putki[0] and putki[1] of child */
           close(putki[0]); close(putki[1]);
           /* sort gets input from standard in */
           execlp("sort","sort",NULL);
           }
        printf("Childs completed\n");
        exit(0);
    }     
}

NOTE: also popen can be used to create a pipe between the
      calling program and the command to be executed.

Task 4
======

man -k scheduler
man sched_setscheduler

or

man sched

more detailed information in
 
/usr/include/sched.h


Three scheduling policies are defined; others may be defined
by the system.  The three standard policies are indicated by
the values of the following symbolic constants:

     SCHED_FIFO
               First in-first out (FIFO) scheduling policy.

     SCHED_RR  Round robin scheduling policy.

     SCHED_OTHER
               Another scheduling policy.