UNIX/LINUX Introduction Copyright © 2017 – Curt Hill

UNIX Developed by Bell Labs around 1972 Simplified MULTICS Software development system Simplified MULTICS An OS and project from which Bell Labs withdrew C was designed so that UNIX could be written in something other than assembly Without question the most influential OS yet Many varieties of UNIX and LINUX Copyright © 2017 – Curt Hill

Features Multi-user and multi-tasking Tree shaped directory Command processor is termed a shell Commands are just executables Commands allow file redirection, file pipes and concurrency Many of these features were first or very early in UNIX Copyright © 2017 – Curt Hill

History Before and after 1972 most OSs were proprietary In Assembly or proprietary languages Source code was often distributed to installation with strong non-disclosure restrictions Usually could only used on one class of machine IBM was dominant with approximately 75% of the market Copyright © 2017 – Curt Hill

MULTICS Joint project of several manufacturers Perhaps MULTICS was the most influential OS, since it strongly influenced UNIX However, it grew too large to be used on anything but a substantial mainframe Bell Labs pulled out, probably because it did not fit their business model More interested in smaller OSs for smaller machines Copyright © 2017 – Curt Hill

The Gang A number of people believed that an OS can be powerful and yet small Ritchie, Kernighan, Plauger among others Dennis Ritchie writes the first C compiler so that they could do the job in C rather than assembly Then it requires half the effort or less The first UNIX is research project Only used at Bell Labs Copyright © 2017 – Curt Hill

Philosophy The gang never thought of themselves as OS maintainers They provided the basic features but allowed nearly anyone to improve their code Everyone could obtain any piece of source code If they could improve the code they did so They then convinced the system administrator to make it the standard Word got out Copyright © 2017 – Curt Hill

GNU A movement starts that provides alternatives to UNIX commands: GNU Good Not UNIX Many of these improved codes are distributed through them as Open Source GNU is part of the Free Software Foundation Copyright © 2017 – Curt Hill

Escape Bell Labs is largely a research center They think of themselves as a private research university without students The corporation wants to see usable prototypes developed, but does pure research There are no plans to market UNIX The researchers start giving it to others Usually universities Later businesses as well Copyright © 2017 – Curt Hill

Variants Each computer manufacturer and some others customize their copy and start distributing it IBM – AIX HP – HPUX Sun – Solaris Berkeley – BSD Copyright © 2017 – Curt Hill

Recapture ATT realizes that others are making money off of their work Some of these are in competition in some markets They assert that everybody should pay them royalties Most business pay up because it is fair They have made money off it ATT is also the largest company on the planet at the time Copyright © 2017 – Curt Hill

Renegades Two groups react negatively University of California at Berkley Linus Torvalds Copyright © 2017 – Curt Hill

Berkeley Berkeley has put a lot of effort into their version They have not made any money on it, nor do they intend to market it Neither have they signed any kind of non-disclosure or non-distribution agreement Much of the fairness argument of ATT just does not fly for their case They file suit Copyright © 2017 – Curt Hill

Conclusion of the Suit Berkeley wins There are now two independent UNIXs System V from ATT BSD from Berkeley Copyright © 2017 – Curt Hill

Linus Torvalds Linus recognizes that the kernel is the only part that could ever be copyrighted Everything above that was written elsewhere or could be replaced , such as by GNU or by others He decides to write a different kernel as a summer project Takes a little longer than that This occurs while ATT and Berkeley are litigating Copyright © 2017 – Curt Hill

LINUX Kernel Linus names his new kernel LINUX After himself This kernel takes the same APIs as original with completely different underlying code Compare with Oracle suit against Google He makes it open source Copyright © 2017 – Curt Hill

The UNIX Family Tree Copyright © 2005 - Curt Hill

Importance of UNIX/LINUX Several things have contributed to the impact It is open source It is very old Many of the original bugs have been removed Most features that are desirable have been added Its original small approach makes it efficient Has not suffered commercial bloat Copyright © 2017 – Curt Hill

Commands The UNIX command-line is always provided by one or another shell Bourne shell (sh) C shell (csh) BASH (from GNU) Korn Shell Among others Similarly, there are multiple GUI interfaces, generically called XWindows Gnome Copyright © 2017 – Curt Hill

Servers Generally some flavor of UNIX/LINUX is the preferred OS for servers Usually free and open source Performs well Large group of people generating usable code for it Most of the networking utilities were first constructed for UNIX Copyright © 2017 – Curt Hill

File System UNIX popularized the tree-shaped directory system Files may be either ordinary or directories Any directory may have other directories or files in it Unlike the MicroSoft OS convention a forward slash delimits directories An initial slash starts at the root directory Copyright © 2017 – Curt Hill

Devices MS copied the basic form of DOS from CPM This includes device latters After DOS 1 they largely copy features from UNIX A mount point is a name that indicates the root of a new device Thus the / is the root of the entire file system Copyright © 2017 – Curt Hill

Relative directories MS copied the UNIX convention for relative directories One dot says this directory Two dots says the previous Copyright © 2017 – Curt Hill

Directory information Each file has several dates: Creation time and date Last change Last access It also indicates an owner and a group It had nine permission bits Read, write and execute One set for owner, group and world Copyright © 2017 – Curt Hill

Home pages UNIX was always a multi-user system Shared and system files were generally near the root in common directories There was also a usr directory which generally housed all the user’s local space Each user received a directory in usr which is named for their login They created directories and files in that Copyright © 2017 – Curt Hill

Finally Learning command line UNIX/LINUX should not be that hard Once we have this background There are a large number of commands that will be considered in another presentation Copyright © 2017 – Curt Hill