50 Fun Facts About Unix

In which 1990s blockbuster does a child recognise a Unix system and steer a real three-dimensional file browser?

Jurassic Park put genuine software on screen: fsn, a 3D file navigator from Silicon Graphics, running on one of the company's own Unix workstations.

Which software company licensed Unix in the late 1970s and sold its own version under the name Xenix?

Microsoft published Xenix from 1980, years before Windows existed, and by the late 1980s it was probably the most commonly installed Unix of all.

Which desktop operating system first won official UNIX certification with a release in 2007?

macOS earned its UNIX 03 registration from The Open Group, the industry consortium that has held the Unix trademark since the 1990s.

Which free software project, launched by Richard Stallman in 1983, has a recursive name declaring that it is not Unix?

GNU was designed to work like Unix while containing none of its code, so that anyone could copy, study and change the whole system freely.

Which Unix-like kernel did a University of Helsinki student release in 1991 after taking a course on Unix?

Linux was first released on 17 September 1991 by Linus Torvalds, and a modified version of the same kernel now sits inside every Android phone.

Which programming language did Dennis Ritchie create at Bell Labs, in which the Unix kernel was rewritten in 1973?

C grew out of an earlier Bell Labs language called B, and rewriting Unix in it made the system far easier to move to new kinds of computer.

Bell Labs, where Unix was written in 1969, was the research arm of which American telephone giant?

AT&T was barred by a 1956 antitrust settlement from any business but communications, so Unix could not be sold and went out for the cost of media and shipping.

Which username conventionally belongs to the Unix superuser, the all-powerful account whose user ID number is zero?

root may read, change or delete anything on the system, and BSD systems often add a backup account called toor, the same name spelled backwards.

Which text encoding was first sketched on a placemat in a New Jersey diner in 1992 by two Unix veterans?

UTF-8 was up and running within days of that sketch, and since 2008 it has been the most common text encoding on the World Wide Web.

Which nickname describes a Unix process that has finished running but still holds an entry in the process table?

Zombie processes linger only until the parent program reads their exit status, at which point the dead entry is said to be reaped.

Which Unix command prints the names of the files in a directory, and adds sizes, owners and dates when given -l?

ls is short for list, and a command of that name has been part of Unix since the very first version of the system.

Which Unix command changes the working directory, and returns to the user's home directory when typed with no arguments?

cd is usually built into the shell itself, because a separate program could change only its own directory and never the shell's.

Which three-letter Unix command, built into many shells, reports the directory in which a user is working?

pwd is short for print working directory, and it has been part of Unix since the fifth version of the system.

Which Unix command, named after a word meaning to chain together, writes one or more files to standard output?

cat is short for catenate, a variant of concatenate, and given several file names it writes them out end to end as a single stream.

Which Unix command displays the reference page for another command, taken from eight numbered sections?

man is short for manual, and its pages still follow a format set out in 1971 for the first Unix Programmer's Manual.

Which Unix command, run with the options -r and -f, nearly erased Pixar's Toy Story 2 during production in 1998?

rm destroyed about 90 per cent of two years' work, and the film survived only because a technical director kept a backup on her home computer.

Which Unix search command, by one account, was written to help analyse who wrote the Federalist Papers?

grep is named after g/re/p, the ed editor instruction that searches globally for a regular expression and prints every matching line.

Which Unix command sets who may read, write or run a file, accepting octal modes such as 755?

chmod is short for change mode, and each octal digit is a sum in which read counts 4, write counts 2 and execute counts 1.

Which Unix command sends its arguments back to the terminal, the usual way a shell script shows a message?

echo joined Unix in its second version, after Doug McIlroy programmed it as what he called a finger exercise and it proved useful.

Which two-letter Unix command both renames a file and carries it to a different directory?

mv merely relabels a file when both names sit on the same file system, so even an enormous file moves without its data being touched.

Which Unix command sends a signal to a running process, by default the termination request known as SIGTERM?

kill is something of a misnomer, because it can deliver any signal at all, and a program may catch the default one and tidy up before exiting.

Which Unix command shows the closing lines of a file, and with the option -f keeps watching a growing log?

tail prints the final ten lines unless told otherwise, and its follow option then adds each new line as another program writes it.

Which two-letter Unix command reports how many lines, words and bytes a file contains?

wc stands for word count, and given the option -l it prints only the number of lines, a favourite way to count the results of another command.

Which Unix filter collapses adjacent identical lines into one, so its input is usually run through sort first?

uniq compares only neighbouring lines, and its counting option prefixes each surviving line with the number of times it occurred.

Which Unix command, first developed for writing to magnetic tape drives, bundles many files into one archive file?

tar is short for tape archive, and the single bundled files it produces are popularly known as tarballs.

Which Unix pager, written by Mark Nudelman in the 1980s, was named as a joke on the older pager called more?

less added the one thing its predecessor lacked, scrolling backwards through a file, and it opens huge files at once because it never reads the whole file first.

Which Unix command prints September 1752 with eleven days missing, as Britain left the Julian system?

cal follows British history, so its page for September 1752 jumps straight from the 2nd to the 14th.

Which screen editor did Bill Joy write in the 1970s, a program every certified UNIX system must still include?

vi takes its name from the visual mode of an older line editor called ex, and the two have always been one and the same program.

Which Unix text tool, developed at Bell Labs by Lee McMahon, is best known for its s command that substitutes text?

sed is short for stream editor, and it began as a wish for a substitution tool to sit beside Unix's pattern-searching command.

Which Unix scheduler, named after the Greek word for time, runs commands at moments set out in five fields?

cron takes its orders from tables called crontabs, in which a row of five asterisks means run the job every single minute.

Which single character names the top-level directory of a Unix file system, the one that contains every other file?

Slash marks the trunk of the tree from which every other directory branches, and strictly speaking that topmost directory has no name at all.

Which top-level Unix directory stores system-wide configuration files, and no longer any binaries?

/etc was called the etcetera directory in early Bell Labs documents, because it once held everything that did not belong anywhere else.

Which special Unix file throws away everything written to it, earning the nicknames bit bucket and black hole?

/dev/null is a running joke among system administrators, who like to warn newcomers that it is already 98 per cent full.

Which Unix data structure stores a file's owner, permissions and disk block locations, but never the name of the file?

inode probably stands for index node, though Dennis Ritchie admitted in 2002 that he no longer knew for certain what the letter i had meant.

Which kind of Unix file, created with ln -s, merely points to another file and breaks if that target is deleted?

Symbolic links are independent files, so deleting one leaves its target untouched, while one whose target has vanished is said to be dangling.

Which character does a Unix shell expand to the user's home directory, a habit traced to the ADM-3A terminal's keyboard?

Tilde shared a key with the word Home on the Lear Siegler ADM-3A, a terminal in common use when the convention took hold in the 1970s.

Unix file names beginning with which character are left out of an ordinary directory listing, making them hidden files?

Dot files began by accident, in Rob Pike's telling: early Unix skipped such names simply to hide each directory's entries for itself and its parent.

Which Unix feature, championed by Doug McIlroy and typed as a vertical bar, feeds one command's output into the next?

Pipe support was added to Unix in a single night in 1973, and the whole lab spent the following day gleefully chaining commands together.

What is the usual name for the characters #! that open a Unix script and tell the system which interpreter to run?

Shebang lines work as a magic number: the program loader spots those two bytes and hands the file to the interpreter named after them, such as /bin/sh.

Which Unix environment variable holds the colon-separated list of directories that the shell searches for a command?

PATH grew out of a search path added by Version 3 Unix, when the single program directory /bin had grown too crowded and /usr/bin was added beside it.

Which Bell Labs programmer wrote the original Unix in 1969 and, decades later at Google, co-designed the Go language?

Ken Thompson also invented the B language and co-built Belle, a hardware chess machine that became a world champion among chess computers.

Which 1960s time-sharing project, abandoned by Bell Labs in 1969, does the name Unix deliberately pun upon?

Multics was the multiplexed giant, so the small newcomer was first dubbed Unics, and no one can remember who later changed the spelling.

Which Californian university's Unix releases, begun in 1978, added virtual memory and internet networking?

Berkeley gave its initial to BSD, a family of Unix systems whose freely licensed networking code later found its way even into Windows.

Which Bell Labs scientist, the K in the AWK language, claims credit for giving Unix its name in 1970?

Brian Kernighan also gave programming its most famous first exercise: the hello, world program first appeared in a tutorial he wrote in 1972.

Which prize did the two creators of Unix share in 1983 for their work on the operating system?

Turing Award night produced a classic of its own, when one of the pair used his acceptance speech to describe a back door hidden inside a compiler.

Which IEEE standards family, named at Richard Stallman's suggestion, defines what a Unix-like system must offer?

POSIX replaced the working title IEEE-IX, which the standards committee found far harder to pronounce and to remember.

Which keyword closes an if block in a Unix sh script, a habit its author borrowed from ALGOL 68?

fi is simply the opening keyword reversed, and case blocks likewise end in esac, yet loops close with done where the older language wrote od.

Which word, borrowed at MIT from an imaginary being in physics, describes a Unix program running in the background?

Daemon programs are customarily given names ending in the letter d, which is why the one that answers incoming SSH connections is called sshd.

Which Unix permission flag, invented and patented by Dennis Ritchie, lets a program run with its owner's privileges?

Setuid bit protection won Bell Labs a patent in 1979, which the company handed to the public domain that same year for anyone to use.

Which Bell Labs successor to Unix takes its name from a 1950s science-fiction film directed by Ed Wood?

Plan 9 stretched the Unix idea that everything is a file across whole networks, and its mascot is a bunny called Glenda.