What are unix and linux systems

Unix / Linux — Getting Started

What is Unix ?

The Unix operating system is a set of programs that act as a link between the computer and the user.

The computer programs that allocate the system resources and coordinate all the details of the computer’s internals is called the operating system or the kernel.

Users communicate with the kernel through a program known as the shell. The shell is a command line interpreter; it translates commands entered by the user and converts them into a language that is understood by the kernel.

Unix was originally developed in 1969 by a group of AT&T employees Ken Thompson, Dennis Ritchie, Douglas McIlroy, and Joe Ossanna at Bell Labs.

There are various Unix variants available in the market. Solaris Unix, AIX, HP Unix and BSD are a few examples. Linux is also a flavor of Unix which is freely available.

Several people can use a Unix computer at the same time; hence Unix is called a multiuser system.

A user can also run multiple programs at the same time; hence Unix is a multitasking environment.

Unix Architecture

Here is a basic block diagram of a Unix system −

The main concept that unites all the versions of Unix is the following four basics −

Kernel − The kernel is the heart of the operating system. It interacts with the hardware and most of the tasks like memory management, task scheduling and file management.

Shell − The shell is the utility that processes your requests. When you type in a command at your terminal, the shell interprets the command and calls the program that you want. The shell uses standard syntax for all commands. C Shell, Bourne Shell and Korn Shell are the most famous shells which are available with most of the Unix variants.

Commands and Utilities − There are various commands and utilities which you can make use of in your day to day activities. cp, mv, cat and grep, etc. are few examples of commands and utilities. There are over 250 standard commands plus numerous others provided through 3 rd party software. All the commands come along with various options.

Files and Directories − All the data of Unix is organized into files. All files are then organized into directories. These directories are further organized into a tree-like structure called the filesystem.

System Bootup

If you have a computer which has the Unix operating system installed in it, then you simply need to turn on the system to make it live.

As soon as you turn on the system, it starts booting up and finally it prompts you to log into the system, which is an activity to log into the system and use it for your day-to-day activities.

Login Unix

When you first connect to a Unix system, you usually see a prompt such as the following −

To log in

Have your userid (user identification) and password ready. Contact your system administrator if you don’t have these yet.

Type your userid at the login prompt, then press ENTER. Your userid is case-sensitive, so be sure you type it exactly as your system administrator has instructed.

Type your password at the password prompt, then press ENTER. Your password is also case-sensitive.

If you provide the correct userid and password, then you will be allowed to enter into the system. Read the information and messages that comes up on the screen, which is as follows.

You will be provided with a command prompt (sometime called the $ prompt ) where you type all your commands. For example, to check calendar, you need to type the cal command as follows −

Change Password

All Unix systems require passwords to help ensure that your files and data remain your own and that the system itself is secure from hackers and crackers. Following are the steps to change your password −

Step 1 − To start, type password at the command prompt as shown below.

Step 2 − Enter your old password, the one you’re currently using.

Step 3 − Type in your new password. Always keep your password complex enough so that nobody can guess it. But make sure, you remember it.

Step 4 − You must verify the password by typing it again.

Note − We have added asterisk (*) here just to show the location where you need to enter the current and new passwords otherwise at your system. It does not show you any character when you type.

Listing Directories and Files

All data in Unix is organized into files. All files are organized into directories. These directories are organized into a tree-like structure called the filesystem.

You can use the ls command to list out all the files or directories available in a directory. Following is the example of using ls command with -l option.

Here entries starting with d. represent directories. For example, uml, univ and urlspedia are directories and rest of the entries are files.

Who Are You?

While you’re logged into the system, you might be willing to know : Who am I?

The easiest way to find out «who you are» is to enter the whoami command −

Try it on your system. This command lists the account name associated with the current login. You can try who am i command as well to get information about yourself.

Who is Logged in?

Sometime you might be interested to know who is logged in to the computer at the same time.

There are three commands available to get you this information, based on how much you wish to know about the other users: users, who, and w.

Try the w command on your system to check the output. This lists down information associated with the users logged in the system.

Logging Out

When you finish your session, you need to log out of the system. This is to ensure that nobody else accesses your files.

Just type the logout command at the command prompt, and the system will clean up everything and break the connection.

System Shutdown

The most consistent way to shut down a Unix system properly via the command line is to use one of the following commands −

Brings the system down immediately

Powers off the system using predefined scripts to synchronize and clean up the system prior to shutting down

Reboots the system by shutting it down completely and then restarting it

Shuts down the system by powering off

Reboots the system

Shuts down the system

You typically need to be the super user or root (the most privileged account on a Unix system) to shut down the system. However, on some standalone or personally-owned Unix boxes, an administrative user and sometimes regular users can do so.

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Unix vs Linux: What Is The Difference?

If you’ve just started reading and learning about Linux, you might have encountered the term “Unix”. The word itself looks similar to Linux, but what does it mean? Perhaps you’re wondering: what is the difference between Unix and Linux?

Generally, it depends on how you interpret each of these two terms, because both can have different (yet related) meanings. In this article we bring you a simplified story of Linux and Unix to help you understand their relationship. As always, you’re welcome to ask questions and add more information in the comments.

The (Hi)story of Unix and Linux

The story of Unix began in the late 1960s and early 1970s, in the computing research department of AT&T Bell Labs in the United States. Together with MIT and General Electric, the Bell Labs were developing a new operating system. Some of their researchers were unhappy with the progress of the project, and withdrew to create their own OS. In 1970 the new product was given the name Unix, and two years later its code was entirely rewritten in the C programming language. This made it much easier for developers to port Unix to different computing platforms.

As the development of Unix continued, AT&T started selling licenses for its usage to universities, and later to commercial vendors. This meant that not everyone could freely modify and distribute the source code, essentially making Unix a proprietary operating system. Soon, derivatives and variants of Unix for different purposes and with different licenses started popping up, with BSD (Berkeley Software Distribution) as probably the best-known among them.

Linux is based on Unix in spirit and functionality, but not in code. As an operating system, it grew out of two projects: the GNU Project, started by Richard Stallman in 1983, and the Linux kernel, written by Linus Torvalds in 1991. The goal of the GNU Project was to create an operating system similar to Unix, but separate from it; in other words, containing no code from Unix so that it could be further modified and distributed without limitations as free software. Since their own kernel was incomplete, the GNU Project accepted the Linux kernel, and so the operating system GNU/Linux was born.

The design of the Linux kernel was influenced by MINIX, a variant of Unix, but the entire code was written from scratch, not borrowed from it. Unlike Unix, which was used on servers, large mainframes and expensive computers at various institutions, Linux was developed for personal computers, a much simpler type of hardware. However, today it runs on more platforms than any other OS, including servers, embedded systems and mobile phones.

What is Unix?

The term “Unix” can refer to the following:

• the original operating system developed by AT&T Bell Labs from which other operating systems derive.

• the trademark – written in all caps, UNIX – held by The Open Group, which also developed a set of standards for operating systems called Single Unix Specification. Only those operating systems which comply with the standards can legally bear the name “Unix”. The certification is not free, and requires the developers of an operating system to pay trademark royalties for the name.

• all operating systems which are registered with the “Unix” name because they comply with the aforementioned standards. They are AIX, A/UX, HP-UX, Inspur K-UX, Reliant UNIX, Solaris, IRIX, Tru64, UnixWare, z/OS and OS X – yes, the one that runs on Mac computers. (Interestingly enough, OS X celebrated its 14th birthday this week: on March 24. Congratulations!).

What is Linux?

Strictly speaking, the term “Linux” refers only to the kernel. The operating system is not complete without a desktop environment and applications. Since the majority of applications were and still are provided by the GNU Project, the full name of the operating system is GNU/Linux.

However, nowadays many people use “Linux” to refer to any and all Linux distributions, and use the term as a generic name for all operating systems based on the Linux kernel. The version 4.0 of the Linux kernel is currently in development, as Linus Torvalds recently decided to switch to a new numbering system for kernel releases.

Linux is a Unix-like system, which means that it behaves like Unix, but doesn’t contain its code.

Unix-like systems are often described as Un*x, *NIX, or *N?X, or called “Unixoids” in some languages. Linux doesn’t have UNIX certification, and GNU is said to stand for “GNU’s Not Unix”, so in this respect, OS X is “more Unix” than Linux. However, on the level of functionality, the Linux kernel and the GNU/Linux operating system(s) are very similar to Unix and follow most of the principles of Unix philosophy, like having human-readable code, storing system configuration in plain text files, relying on simple, small command-line tools, having a shell, a login and a session manager…

It’s important to note that it’s possible for a Unix-like system to obtain UNIX certification. In some contexts, all operating systems derived from or based on Unix are referred to as Unix-likes, regardless of whether they have the UNIX certificate or not. Also, they can be commercial or free (and open-source) operating systems.

Key Differences

• Linux is free and open-source, the original Unix is not (but some of its derivatives are);

• Linux is a “clone” of the original Unix, but it doesn’t contain its code;

• Linux is just the kernel, while Unix was/is a complete operating system;

• Linux was developed for personal computers, while Unix was primarily for large workstations and servers. Today, Linux supports more platforms than Unix;

• Linux also supports more filesystem types than Unix.

As you’ve seen, the confusion usually stems from the fact that both “Unix” and “Linux” can mean different things. Whichever meaning is being used, the fact remains that Unix was there first, and Linux came later. Linux was born out of a desire for software freedom and portability, and inspired by the Unix approach to computing. It’s safe to say we’re all indebted to the free software movement because, technology-wise, the world would be a much darker place without it.

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Difference Between Linux and UNIX

W hat is the difference between Linux and UNIX operating systems?

UNIX is a copyrighted name, and only big companies are allowed to use the UNIX copyright and name. For example, Apple macOS, IBM AIX, and Sun/Oracle Solaris and HP-UX all are UNIX operating systems. The Open Group holds the UNIX trademark in trust for the industry and manages the UNIX trademark licensing program. Let us see difference between Linux and UNIX OS in this quick tutorial.

Sr.No.	Command & Description
1

Tutorial details
Difficulty level	Easy
Root privileges	No
Requirements	None
Est. reading time	6 minutes

Difference Between Linux and UNIX

Most UNIX systems are commercial in nature. You need to pay for support, software, training, and more. On the other hand, the Linux kernel is free to download and install on your systems free of cost.

Linux is a UNIX Clone

But if you consider Portable Operating System Interface (POSIX) standards, then Linux can be considered as UNIX. To quote from Official Linux kernel README file:

Linux is a Unix clone written from scratch by Linus Torvalds with assistance from a loosely-knit team of hackers across the Net. It aims towards POSIX compliance.

However, “Open Group” does not approve of the construction “Unix-like” and considers it a misuse of their UNIX trademark.

Linux is just a kernel

Linux is just a kernel. All Linux distributions includes GUI system + GNU utilities (such as cp, mv, ls,date, bash and more) + installation management tools + GNU c/c++ compilers + Editors (vi/ed/nano) + and various applications (such as OpenOffice, Firefox). However, most UNIX operating systems are considered as a complete operating system as everything come from a single source or vendor.

As I said earlier, Linux is just a kernel, and Linux distribution makes it complete usable operating systems by adding various applications. Most UNIX operating systems come with A-Z programs such as editor, compilers, and more. For example, HP-UX or Solaris comes with A-Z programs.

BSD family of operating systems

No discussion related to Unix is ever completed without discussing a free version of Unix. Typically all *BSD family of operating systems are available free of cost and try to as close as possible to original Unix concepts. BSD family of operating systems based on BSD, the version of UNIX developed at the University of California, Berkeley. We have several operating systems that are based on BSD, including FreeBSD, OpenBSD, NetBSD, MidnightBSD, Darwin, and DragonFly BSD. Like Unix operating systems, the BSD family of an operating system typically comes with all required applications from a single project. An additional app/software can be installed using ports or binary package system.

License and cost

Linux is Free (as in beer [freedom]). You can download it from the Internet or redistribute it under GNU licenses. You will see the best community support for Linux. Most certified UNIX like operating systems are not free (but this is changing fast, for example, OpenSolaris UNIX). However, some Linux distributions such as Redhat (RHEL) / Novell (SUSE) provides additional Linux support, consultancy, bug fixing, and training for additional fees.

User-Friendly

Linux is considered as most user friendly UNIX-like operating systems. It makes it easy to install sound card, flash players, and other desktop goodies. However, macOS (Apple OS X) is most popular UNIX operating system for desktop and laptop users.

Security Firewall Software

Linux comes with open source netfilter/iptables/nftables based firewall tool to protect your server and desktop from the crackers and hackers. UNIX operating systems comes with its own firewall product (for example Solaris UNIX comes with ipfilter based firewall) or you need to purchase a 3rd party software such as Checkpoint UNIX firewall.

Backup and Recovery Software

UNIX and Linux comes with different set of tools for backing up data to tape and other backup media. However, both of them share some common tools such as tar, dump/restore, cpio and more.

File Systems

• Linux by default supports and use ext3 or ext4 file systems.
• UNIX comes with various file systems such as jfs, gpfs (AIX), jfs, gpfs (HP-UX), jfs, gpfs (Solaris), zfs and more.

System Administration Tools

1. UNIX comes with its own tools such as SAM on HP-UX or smitty on IBM AIX.
2. SUSE Linux comes with Yast/Yast2
3. Red hat Linux comes with its own gui tools called redhat-config-*.

However, editing text config file and typing commands are most popular options for sysadmin work under Linux and Unix-like systems.

System Startup Scripts

Almost every version of UNIX and Linux comes with system initialization script but they are located in different directories:

1. HP-UX – /sbin/init.d
2. AIX – /etc/rc.d/init.d
3. Linux – /etc/init.d. However, newer system uses systemd instead of /etc/init.d/ based script.

End User Perspective

The differences are not that big for the average end-user. They will use the same shell (e.g., BASH or KSH), text editors such as vim, and other development tools such as Perl, PHP, Python 3.x or Eclipse development tool.

System Administrator Perspective

Again, the differences are not that big for the system administrator. However, you may notice various differences while performing the following operations:

1. Software installation procedure
2. Hardware device names
3. Various admin commands or utilities
4. Software RAID devices and mirroring
5. Logical volume management
6. Package management
7. Patch management

UNIX Operating System Names

A few popular names:

1. HP-UX
2. IBM AIX
3. Sun Solaris (now Oracle Solaris)
4. Apple Mac OS X (now macOS)
5. IRIX

Linux Distribution (Operating System) Names

A few popular names:

1. Red hat Enterprise Linux
2. Fedora Linux
3. Debian Linux
4. Suse Enterprise Linux
5. Ubuntu Linux
6. Arch Linux
7. Gentoo Linux

Common Things Between Linux and UNIX

Both share many common applications such as:

1. GUI, file, and windows managers (KDE, Gnome)
2. Shells (ksh, csh/tcsh, bash)
3. Various office applications such as OpenOffice.org/libreoffice.org, and more
4. Development tools (perl, php, python, ruby, GNU c/c++ compilers)
5. Posix interface

A Sample UNIX Desktop Screenshot

Fig.01: UNIX Desktop — IRIX 6.5 Desktop

A Sample Linux Desktop Screenshot

Fig.02: Linux KDE desktop environment

UNIX and Linux Hardware

Commercial UNIX hardware has more advanced initial boot options such as:

• Decide how to boot
• Check system health
• Set hardware parameters
• Hard disk encrption and security

The BIOS that is standard in PCs which is used by Linux has few, of these features. UNIX hardware or servers are pretty expensive as compare to Linux server systems.

Unix Vs. Linux: What’s the Difference?

Cost	Free	Different versions of Unix have varying costs/pricing, according to vendors.
Licensing model	GPL (open source)	Proprietary
Viruses/Malware	Limited amount of virus/malware exists	Again, a limited amount of virus/malware exists.
Architectures support	ARM, x86/x64, Power, Sparc and 100+ architectures	ARM, x86/x64, Sparc, Power, and others.
File systems support	ext<2,3,4>, zfs, xfs, btrfs, FAT32, NTFS and more	UFS, zfs, APFS, JFS and more.
Source code	Available to anyone to download, edit, and redistribute source code under GPL and other approved open source licenses.	Proprietary and closed source code, and you cannot redistribute it.
Sysadmin tools	Yast (SUSE), redhat-config-* and editing config files	SAM on HP-UX, smitty on IBM AIX and other GUI based tools
GUI/desktop examples	GTK-based (GNOME, Xfce and others), QT-based (KDE Plasma, Lumina, LXQt and others)	Motif-based (CDE, VUE and others), Aqua (macOS)
Default shell	bash	ksh, csh or zsh
OS Examples	CentOS, RHEL, Fedora, Arch, OpenSUSE, SUSE, Chrome OS, Android, and 100+ other distros	macOS, Solaris, HP-UX, IBM AIX, SunOS and others

Conclusion

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• UNIX System Management and Security: Differences between Linux, Solaris, AIX and HP-UX
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(Image credit IRIX and KDE wikipedia articles)

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