Unix

Unix and Linux have a common command structure, similar command shell environments, common set of standard utility programs, games, development tools, functions, manual (help) file format. They do not have a common history.

The Unix System Program was original developed at Bell Laboratories by Dennis Ritchie and Ken Thompson in 1969. It was the property of AT&T (or some branch of it), was free with source to educational institutions and was later offered commercially for DEC PDP computers for 12 to 20 thousand dollars and more depending on the installed computers. Unix and BSD (a free derivative of UNIX) were licensed and ported to various other systems vendors such as DEC (ultrix, osf/1, TRU64. etc), SUN (sunos), Microsoft (xenix), IBM (AIX), HP (HPux), Apple (OSx), and many more. BSD itself had a whole bunch of different free implementations under a BSD license.

There was also a lawsuit between BSD and Novell (which had purchased ownership of UNIX) claiming BSD should not be giving away BSD UNIX for free. It ended with BSD allowed to continue its free licensing after making some changes to its software base.

Linux was a result of an independent project by Linus Torvald with a small group of independent hackers that became very popular. He developed a kernel system program that was compatible with UNIX but was written independently of UNIX, had no UNIX code in it, was not subject to a UNIX licensing issues, and was distributed under a GPL license. The Linux kernel together with some independently written programs, together with many free programs borrowed from BSD constitute a Linux distribution.

lex and yacc are two utility programs used primarily in Unix (but can be used in Windows as well, for example) that create files and code used by parsers and grammar checkers.

You describe what the grammar should be and it creates a shell program that is capable of recognizing the grammar as being legal or not legal. These utilities can provide routines to parse, tokenize, and other tasks that would be too time consuming to do by hand.

Costs for a Unix license vary by vendor and number of users on the system. Most new system hardware comes bundled with at least a 2 user license. It can get very expensive depending on the vendor and the bundled products.

I've seen Unix versions on mainframes that are upwards of 20,000 dollars a year, and some server based versions that are under $1000.

The process is called 'init'

The user needs an account and password and responds appropriately when ftp or telnet asks for the credentials.

Any process can be placed in the background by using the '&' at the end of the command, or by suspending the process and issuing the 'bg' command.

There really is no good way to 'measure' the accuracy of the 'sleep' command because it is not designed to be accurate; it depends on the state of the system and other things going on at the same time. It uses an approximate value to suspend the process but is not designed to be extremely accurate.

The value used in the sleep command is the number of seconds to suspend the process, which is subject to other processes running, possibly at a higher level than the current one. Since the process is probably not running at a real time level you wouldn't be able to check the acccuracy of the suspended time with any reliability.

The current terminal or console.

Depends on where exactly you are seeing the letter "s" - could mean a setuid or setgid program.

It is considered to be in a "zombie" state and will stay in the system until it is rebooted. These processes may not be killed by any signal either.

Shell is a program which allows the user to access the computer system. Shell is an interface between the user and computer system.

Kernel is the only way through which the programs (all programs including shell) can access the hardware. Its a layer between the appliation programs and hardware. It is the core of most of the operating systems and manages everything including the communication between the hardware and software.

KERNEL is the core part of operating system. It contain modules like device modules and other modules etc. Kernel is written in C language. Basically kernel is mediator between hardware and Operating System. But SHELL is an interface between users and operating system. Both are mediator but work is totally different.

Let we have an example of "eject" command in Linux operating system:

User give a command to Shell through input device like keyboard and see that command on video Device like monitor, but in actual concept is user give a command to shell, then this shell transfer that command to kernel.when kernel have module of that command then it transfer to hardware like CDROM. After that hardware behave as the module in kernel and then kernel again transfer the output to Shell. And finally shell transfer that output to user.

Hardware <---> Kernel <---> Shell <---> User

icore inode is work before inode.

icore inode is dynamic information about the file.

incore inode tranlate information or data,in other words incore inode made before inode and any manipulation or information changed in the icore inode.....

inode doesnot change file information & not perform any operation on file............

SunOS is the older version of Unix from Sun Microsystems that existed before Solaris.

It's $ for normal commands, and # for system-administration. You mustn't actually type these when you enter a command.

The answer varies on system and kernel configuration settings, but you can string together a lot of commands. The maximum path on several systems is at least 1024 characters, which can include a lot of commands.

Ultimately, however, it depends on system resources.

Typically, programs store program information in hidden files in your home directory. The 'ssh' program stores cached host keys in the ".ssh" folder.

The immediate predecessor to Unix was MULTICS.

No, scripts are slower than compiled program, and shell scripts are especially slow, for they keep running external commands.

You don't indicate what you mean by "communication". Since there are many different answers your question needs to be more specific.

Currently, The Open Group owns the "Unix" trademark.

No, Unix branded operating systems are proprietary and copyrighted. They are not free or open systems software.

From its start until 1993, Unix distributions included all their source code.

Programmers have made many free and open Unix-like operating systems, including Linux, NetBSD, FreeBSD, OpenBSD, Dragonfly BSD, Mach, OpenSolaris, etc.

sftp works pretty much the same way as regular ftp, except that it utilizes port 22 and uses an encrypted stream for the actual file transfer.

So, if you know how to use ftp you know how to use sftp as well..

Recursively removes all files from the directory and all under it.

root