Unix Operating System

The diff command uses certain special symbols and instructions to indicate the changes that are required to make two files identical.

 nyy command is used to copy n number of lines to buffer , so 3yy copies three lines to buffer.

%PATH% is an environment variable of DOS not of unix. $PATH is an environment variable of unix.

All the above are invalid funtions of the set command.

Hash (#) because it is the interpreter line file and moves either forward or backward with the help of internal command. So, it is a not command separator.

The x command is used to delete single character in command mode in vi editor.

The cp command copies only files, it does not take any backup of files.

Wc -l is used to print the line count. 

All of the above are the three distinct phases in creation of a process and use three important system calls - fork, exec and wait .

concatenateconcatenate corresponding lines of two files into vertical columns, separated by tab. concatenate means joining

The crontab command is used to schedule jobs. You must have permission to run this command from unix administrator.

All the above mentioned processes are interprocess communication methods.

This is the corrcet answer, i.e. all three- fork, wait and execl are to be used to simulate the command system.

The getc() function is functionally similar to fgetc(),except that it is implemented as a macro.
It runs faster than fgetc(), but it takes more space per invocation and it's name cannot be passed as an argument to a function call. The getc is not a system call.

In bin and passwd file,  names can be found in more than one directory.

The date command displays the date and time. System clock is set by the super-user with the help of date command. With no options the date command will display the current date and time. For e.g., :$date will print fri jul 16:12:06 EDT 2007. The date command is not a filter program.

The tee is a program, which enables you to save a copy of the data being transmitted within a pipeline. It has only one option-a, which appends the output to the specified file, rather than replacing the contents of the file each time. So, redirection in pipes can be achieved by tee.

The date command displays the date and time. System clock is set by the super-user with the help of date command. With no options, the date command will display the current date and time. For e.g: $date will print  fri jul 16:12:06 EDT 2007. For display purpose it will interact, so it is interactive

Both fclose() and fwrite() are library functions which do not return a pointer to the structure FILE.

It is used to set the file-position indicator for the stream pointed to by the stream. The new position is measured in bytes from the begning of the file and obtained by adding offset to the position specified by whence, whose values are defined in <stdio.h>. fseek() function is used to randomly access a file. For example: int fseek(FILE *stream, long offset, int whence);

Init is the program on UNIX operating systems that creates all other processes. Its primary role is to create processes from a script stored in  the file /etc/inittab. Its process ID is 1.SYNOPSIS for init is: /sbin/init [-a ] [ -s ] [ -b ] [ -z xxx ] [ 0123456Ss ]

The getc and getchar commands are implemented as macros rather than the functions.

The exec overlays the calling process with the named file, then transfer to the entry point of the core image of the file. It does not return from a successfull exec call, the calling core image is lost. Because, exec family calls overlays the address space of the process that executed it. So, no chance of getting back to it.

UNIX Administration involves management of user accounts,the file system, hardware configuration, security, device drivers and more. To provide help, UNIX contains directory as the strorage place for all administrative files and inforamtion. etc directory contains init.

Sync keeps all the information in the core memory that should be on disk to be written out. This contains modified i-nodes, modified super blocks and delayed input output block.This should be used by programs which examine the file system. It is mandatory before a boot Synopsis:sync()