Ans: Special Shell Variables:
1. MAIL the pathname of the file where your mail is placed.
2. PATH the list of directories searched for commands.
3. PS1 primary prompt string.
4. PS2 secondary prompt string.
5. ! The process number of the last process runs in the background.
6. # the number of positional parameters.
7. $ the process number of the current shell.
8. ? the exit status of the last command run (0 if it was successfully, non-zero otherwise)

Ans: Device files are of 2 types --- character device file and block device file

type field in the file's inode structure

b--- block device file

c--- character device file

Ans: When processing a command the searches for the utility for the command in the directories specified in the PATH variable and it in invokes that utility. That utility will execute the command with help of kernel and the output is given to shell. And then the displays output to the user.

Ans: command is used to remove a file is rm.

Ans: This symbol is UNIX administrator.
$-this symbol is user prompt in UNIX

Ans:

A {
wait_for(lock_1) {
do something that takes time
wait_for(lock_2) {
do something
}
}
}

B {
wait_for(lock_2) {
do something that takes time
wait_for(lock_1) {
do something
}
}
}
 

start A
start B


A will be holding lock_1, waiting for lock_2
and B will be holding lock_2, waiting for lock_1

hence, deadlock occurs

Ans: :1,$s/ //g

Ans: ps -ef|grep zombie or who -d depending on the system.

Ans: A parent and child can communicate through any of the normal inter-process communication schemes (pipes, sockets, message queues, shared memory), but also have some special ways to communicate that take advantage of their relationship as a parent and child. One of the most obvious is that the parent can get the exit status of the child.

Ans: #rm -fr <Directory name>