Tag Info

Hot answers tagged

713

Quoting Wikipedia: On Unix-like operating systems (including BSD, GNU/Linux and Mac OS X), tilde often indicates the current user's home directory: for example, if the current user's home directory is /home/bloggsj, then cd, cd ~, cd /home/bloggsj or cd $HOME are equivalent. This practice derives from the Lear-Siegler ADM-3A terminal in common ...


122

That depends on what you mean by “Unix”, and by “Linux”. UNIX is a registered trade mark of The Open Group. The trade mark has had an eventful history, and it's not completely clear that it's not genericized due to the widespread usage of “Unix” refering to Unix-like systems (see below). Currently the Open Group grants use of the trade mark to any system ...


102

The Home key was also used for the tilde character on old terminals. See here for more details.


96

The forward slash / is the delimiting character which separates directories in paths in Unix-like operating systems. This character seems to have been chosen sometime in the 1970's, and according to anecdotal sources, the reasons might be related to that the predecessor to Unix, the Multics operating system, used the > character as path separator, but the ...


94

As is often the case with obscure terms, the Jargon File has an answer: [Unix: from runcom files on the CTSS system 1962-63, via the startup script /etc/rc] Script file containing startup instructions for an application program (or an entire operating system), usually a text file containing commands of the sort that might have been invoked manually once ...


94

Here is all you never thought you would ever not want to know about it: Summary To get the pathname of an executable in a Bourne-like shell script (there are a few caveats; see below): ls=$(command -v ls) To find out if a given command exists: if command -v given-command > /dev/null 2>&1; then echo given-command is available else echo ...


85

Apt started its life around 1997 and entered Debian officially around 1999. During its early days, Jason Gunthorpe was its main maintainer/developer. Well, apparently Jason liked cows. I don't know if he still does. :-) Anyway, I think the apt-get moo thing was added by him as a joke. The corresponding aptitude easter eggs (see below) were added later by ...


79

For distributing archives over the Internet, the following things are generally a priority: Compression ratio (i.e., how small the compressor makes the data); Decompression time (CPU requirements); Decompression memory requirements; and Compatibility (how wide-spread the decompression program is) Compression memory & CPU requirements aren't very ...


60

It appears that you are confusing two very different parts of the OS. It's understandable, because they are often referred to interchangably, but it's technically incorrect, so your question is based on a faulty premise. In order to fully explore and hopefully answer the question that you likely want to ask, a short history lesson is needed. First, there ...


57

The Jargon File has an answer which seems to agree with JanC. wheel: n. [from slang ‘big wheel’ for a powerful person] A person who has an active wheel bit...The traditional name of security group zero in BSD (to which the major system-internal users like root belong) is ‘wheel’... A wheel bit is also helpfully defined: A privilege bit that ...


49

This is a highly simplified history of Unix and its derivatives. Windows does not figure in it because its history is essentially separate. Once upon a time operating systems were complex and unwieldy. One day in the late 1960s, Ken Thompson, Dennis Ritchie and a few of their colleagues at AT&T Bell Labs decided to write a simpler version of Multics to ...


48

Most of these answers are far too late to the game, as the * usage was used on Usenet and elsewhere to refer to the multiplicity of Unixoid systems. This was significantly before "the suits" even knew what was happening in cyberspace and didn't understand it if they did. I found a reference in the comp.risks archive dated May 1987 where the title ...


47

The first hierarchical file system as we know it today was designed for Multics. The design is described in “A General-Purpose File System For Secondary Storage” by R.C. Daley and P.G. Neumann. A salient characteristic of this filesystem is that a directory is a file which can be contained in a directory like any other file. The file structure forms a tree, ...


44

This dates all the way back to the very first edition of Unix, where all the standard file names were only at most 6 characters long (think passwd), even though this version supported a whooping 8 characters in a file name. Most commands had an associated source file ending in .c (e.g. umount.c), which left only 6 characters for the base name. A 6-character ...


42

Yup there were reasons. They are pronounced user and temp. passwd is similar, as is resolv.conf. Unix is an expert friendly, user antagonistic operating system. I was a student when 300 Baud modems were the norm. I was the envy of my fellow students, since I had a Silent 700 terminal from Control Data where I was working. You could see the delay from typing ...


40

I think it stands for "diagnostic messages", as per the older man page (referenced here too). dmesg - system diagnostic messages Dmesg looks in a system buffer for recent kernel diagnostic messages and reproduces them on the standard output One of the oldest references appears to be a man page revision by Kirk McKusick dating back from 1985.


39

I always assumed that this feature derived from cowsay & cowthink. See the Wikipedia article on Cowsay. I've been using these for years on Fedora (I believe they predate 1999) and were used as a way to display fortunes in a more interesting way. $ fortune | cowsay ________________________________________ / It doesn't matter what you do, it only \ | ...


35

It's a Unix system call that creates a file: At a Unix shell prompt, type man 2 creat to learn more.


34

I'd guess lack of features - no command history, no fancy redirection, no command line editing. BSD introduced csh the C shell for those reasons. Another factor is that the Genuine Bourne Shell was only recently available in open source form. Unless you licensed it, you couldn't distribute it. That put it out of reach for free-of-cost distros, and made it ...


33

In The Art of Unix Programming Eric Steven Raymond describes how this practice evolved: In the original Unix tradition, command-line options are single letters preceded by a single hyphen... The original Unix style evolved on slow ASR-33 teletypes that made terseness a virtue; thus the single-letter options. Holding down the shift key required actual ...


31

It seems that the original bzip was pulled circa 1998 due to patent issues with the arithmetic compression used in. A bit of digging (really only reading Wikipedia) turns up an archived link to the bzip2 website from around this time. Here is the relevant section detail this and other differences: How does it relate to your previous offering (bzip-0.21) ...


29

Another expansion - run control On Tue, 4 Nov 2003, goldwyn rodrigues wrote: Does anyone know what RC (in bashrc/mailrc/... ) means or how it originated? I mean, is it an acronym? If yes, what does it stand for? 'rc' stands for 'run control' and is a a convention adopted from older Unix systems. For more info see this: ...


29

chown initially couldn't set the group. Later, some implementations added it as chown user.group, some as chown user:group until it was eventually standardised (emphasis mine): The 4.3 BSD method of specifying both owner and group was included in this volume of POSIX.1-2008 because: There are cases where the desired end condition could not be ...


29

Hit CTRL-U (kill line - this saves the line in the shell's kill-ring), do what you need to do, then at the new prompt, hit CTRL-Y (yank from kill-ring) to get back the original command. Alternatively, and this is particularly useful if you are in a nested command, such as a while or for loop, hit CTRL-C, which adds the command to history without executing ...


28

GNU Info was designed to offer documentation that was comprehensive, hyperlinked, and possible to output to multiple formats. Man pages were available, and they were great at providing printed output. However, they were designed such that each man page had a reasonably small set of content. A man page might have the discussion on a single C function such ...


27

We can distinguish UNIX the trademark from Unix the code-base. AT&T Unix was initially developed at Bell Labs, owned by AT&T. This Unix team became AT&T's Unix System Laboratories (USL) and produced Unix System V (Roman numeral for five) or SysV for short. The University of California at Berkeley (UCB) also licenced Unix for academic use, their ...


27

The bcd command formats the output as a punch card, like this one: From the BSD games man page: bcd ppt morse - reformat input as punch cards, paper tape or morse code The ] stands for where the holes would be. At first glance, it seems to do nothing because it's waiting for input from stdin. Try piping something into it (i.e. command | bcd) to ...


26

Copy-paste is older than the mouse. The first unix editor, ed, had the t command to copy a bunch of lines to a different location. In vi, there are various commands to cut, yank and paste text. To copy text between files, you would save the text to copy in a temporary file and import that temporary file in the target document, e.g. with w and r in ed (:w and ...


25

To trace the real story, try running man cal yourself: The Gregorian Reformation is assumed to have occurred in 1752 on the 3rd of September. By this time, most countries had recognized the reforma- tion (although a few did not recognize it until the early 1900’s.) Ten days following that date were eliminated by the reformation, so the cal- endar for ...


24

For all intents and purposes, a typical modern Linux distribution (Ubuntu, Debian, Red Hat, Fedora, Slackware, etc) is a Unix, but strictly speaking, no system can claim to be Unix without being certified, so instead people say they are Unix-like. They are inspired by Unix, and carry on its culture. This also applies to BSD systems. Mac OS X is certified ...



Only top voted, non community-wiki answers of a minimum length are eligible