Ans: The `fork ()' used to create a new process from an existing process. The new process is called the child process, and the existing process is called the parent. We can tell which is which by checking the return value from `fork ()'. The parent gets the child's PID returned to him, but the child gets 0 returned to him.

Ans: Unix identifies each process with a unique integer called ProcessID. The process that executes the request for creation of a process is called the 'parent process' whose PID is 'Parent Process ID'. Every process is associated ...  

Ans: While booting, special process called the 'swapper' or 'scheduler' is created with Process-ID 0. The swapper manages memory allocation for processes and influences CPU allocation. The swapper in turn creates 3 children:
the process dispatcher,
vhand and
dbflush
With IDs 1,2 and 3 respectively.
This is done by executing the file /etc/init. Process dispatcher gives birth to the shell. Unix keeps track of all the processes in an internal data structure called the Process Table (listing command is ps -el).

Ans: A shell is an interactive user interface to operating system services that allows an user to enter commands as character strings or through a graphical user interface. The shell converts them to system calls to the OS or forks off a process to execute the command. System call results and other information from the OS are presented to the user through an interactive interface. Commonly used shells are sh,csh,ks etc.

Ans: The privileged mount system call is used to attach a file system to a directory of another file system; the unmount system call detaches a file system. When you mount another file system on to your directory, you are essentially splicing one directory tree onto a branch in another directory tree. The first argument to mount call is the mount point, that is, a directory in the current file naming system. The second argument is the file system to mount to that point. When you insert a cdrom to your UNIX system's drive, the file system in the cdrom automatically mounts to /dev/cdrom in your system.

Ans: FIFO is otherwise called as 'named pipes'. FIFO (first-in-first-out) is a special file which is said to be data transient. Once data is read from named pipe, it cannot be read again. Also, data can be read only in the order written. It is used in interprocess communication where a process writes to one end of the pipe (producer) and the other reads from the other end (consumer).

Ans: Poll() in UNIX is used for to wait for some event on a file descriptor. When poll() is used, the user must allocate an array of pollfd structures, and pass the number of entries in this array. int poll(struct pollfd *ufds, unsigned int nfds...  

Ans: Zombie is a process state when the child dies before the parent process. In this case the structural information of the process is still in the process table. Since this process is not alive, it cannot react to signals. Zombie state can finish when the parent dies. All resources of the zombie state process are cleared by the kernel

Ans: A fork() system call in UNIX is used to create processes. It returns a process ID. The process created becomes the child process of the caller. After the child process is created both parent and child will execute the next instruction. Depending on the return values child process can be determined.

Ans: A link is a pointer or reference to another file. A directory in UNIX has a list of file names and their corresponding inodes. A directory entry can have an Inode pointing to another file.
This is a hard link. When a hard link is made, then the i-numbers of two different directory file entries point to the same inode.
A symbolic link or a soft link is a special type of file containing links or references to another file or directory in the form of a path. The path may be relative or absolute. To create a symbolic link, following command is used:
Ln –s target link_name
Here, target is the path and link_name is the name of the link. Symbolic links can be created to create a file system based on different views of the user.