The history of Unix systems and their main components. Please DO NOT USE this tag for shell-related questions; use "command-history" instead.

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158
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3answers
10k views

Why not use “which”? What to use then?

When looking for the path to an executable or checking what would happen would you enter a command name in a Unix shell, there's a plethora of different utilities (which, type, command, whence, where, ...
139
votes
6answers
47k views

Is Linux a Unix?

So, there are lots of different versions of Unix out there: HP-UX, AIX, BSD, etc. Linux is considered a Unix clone rather than an implementation of Unix. Are all the "real" Unices actual descendants ...
24
votes
2answers
2k views

Why do Unix man pages use double backticks in place of double quotes?

I've noticed that man pages and other documents formatted by Unix utilities often use double backticks `` followed by double single quotes '' to wrap quoted phrases instead of the double quote ...
30
votes
6answers
9k views

Single dashes `-` for single-character options, but double dashes `--` for words?

Where did the convention of using single dashes for letters and doubles dashes for words come from and why is continued to be used? For example if I type in ls --help, you see: -a, --all ...
21
votes
4answers
6k views

Evolution of Operating systems from Unix

Can you explain the evolution hierarchy of operating systems (Linux and Windows) from Unix?
662
votes
2answers
136k views

Why was '~' chosen to represent the home directory?

I have often wondered why the ~ (tilde) represents the home directory of a user. Is there a reason behind this, or is it just some infrequently used character?
117
votes
6answers
41k views

Where did the “wheel” group get its name?

The wheel group on *nix computers typically refers to the group with some sort of root-like access. I've heard that on some *nixes it's the group of users with the right to run su, but on Linux that ...
75
votes
9answers
5k views

On what systems is //foo/bar different from /foo/bar?

Throughout the POSIX specification, there's provision (1, 2, 3...) to allow implementations to treat a path starting with two / specially. A POSIX application (an application written to the POSIX ...
40
votes
4answers
5k views

Is the shell ksh93 dead?

On 10/1/2013 Glenn Fowler posted this to the ast-users mailing list: As has been pointed out several times on the AST and UWIN lists, AT&T gives very little support to OpenSouce software, ...
45
votes
5answers
5k views

Why is there a * When There is Mention of Unix Throughout the Internet?

I've noticed that throughout the Internet, within forums and blog posts, Unix always has a * in the word, whether it is *nix or Un*x, as I noticed at the welcoming banner at the Unix StackExchange ...
42
votes
4answers
9k views

What did Ken Thompson mean when he said, “I'd spell creat with an 'e'.”

Ken Thompson, the creator of Unix, was once asked what he'd do if he had it to do over again. He said, "I'd spell creat with an 'e'." What is Ken referring to? Is there a "creat" command?
159
votes
3answers
30k views

What does “rc” in .bashrc stand for?

Is it "resource configuration", by any chance?
11
votes
2answers
13k views

How can you log every command typed

How can you log every command someone has entered into the shell? I'm asking on both the basis of protecting yourself if you are logged into someone else's server and something breaks, or if someone ...
18
votes
2answers
2k views

What is Unix now?

As I read in Wikipedia, Unix started as a revolutionary operating system written mostly in C allowing it to be ported and used on different hardware. Descendants of Unix is mentioned next, mostly BSD. ...
31
votes
1answer
2k views

Were all Unix commands re-written in Linux?

I would like to know which commands were re-written for Linux and which were retained from Unix? I'm new to Linux.
31
votes
5answers
5k views

Why do /usr and /tmp directories for Linux miss vowels in their spellings?

I have often started to think about this but never found a good answer. Why are these two Unix directories not /user and /temp instead? All the other directories under root seem to be exactly what ...
126
votes
4answers
29k views

Why are tar archive formats switching to xz compression to replace bzip2 and what about gzip?

More and more tar archives use the xz format based on LZMA2 for compression instead of the traditional bzip2(bz2) compression. In fact kernel.org made a late "Good-bye bzip2" announcement, 27th Dec. ...
53
votes
5answers
24k views

What is the purpose of the hash command?

If you run hash it shows the path of all commands run since the hash was last reset (hash -r) [root@c04c ~]# hash hash: hash table empty [root@c04c ~]# whoami root [root@c04c ~]# hash hits ...
37
votes
4answers
4k views

What is GNU Info for?

I understand what GNU Info is and how to use it, but what is it for? Why does it exist in parallel to the man pages? Why not write detailed man pages rather than provide a separate utility?
20
votes
6answers
9k views

What is a socket?

Could someone explain to me what a socket is? I see it in many acronyms in context of SSL, etc. Also, why is it called a socket? Is it purely because it was what a name they invented? Or was it the ...
48
votes
2answers
9k views

Why is 'umount' not spelled 'unmount'?

I am wondering if there is any historical or practical reason why the umount command is not unmount.
45
votes
2answers
4k views

Why is rm allowed to delete a file under ownership of a different user?

From the post Why can rm remove read-only files? I understand that rm just needs write permission on directory to remove the file. But I find it hard to digest the behaviour where we can easily delete ...
27
votes
1answer
5k views

Why was '.' chosen to represent the current directory and '..' for parent directory?

After reading this question Design question: Why was '~' chosen to represent the home directory?, next obvious question on my mind was why '.' and '..' was used to represent current directory ...
5
votes
1answer
272 views

Why does 'find -exec cmd {} +' need to end in '{} +'?

Preface: I understand the difference between -exec {} \; & -exec {} +. I also don't have a problem as such, I am just curious about the semantics of find. When ending the -exec argument with + ...
2
votes
2answers
87 views

Why is $ the default symbol for a user shell and # the default symbol for a root shell?

Operating a standard bash shell on a server, the PS1 prompt defaults to ending in a $ for non-root users, and # for root. IE: ubuntu@server:~$ sudo su root@server:/home/ubuntu# Why is this?
4
votes
2answers
306 views

What are all the items on the cover of the “Linux Administration Handbook”?

As I mentioned in What do all the pictures on the front of the "Unix and Linux System Administration Handbook" represent? I'm fairly new to Linux and Unix. @jasonwryan provided an excellent ...
189
votes
5answers
33k views

What's the story behind Super Cow Powers?

As we know, apt-get has Super Cow Powers and aptitude does not: $ apt-get --help | grep -i cow This APT has Super Cow Powers. $ aptitude --help | grep -i cow ...
86
votes
3answers
15k views

Why is the root directory denoted by a / sign?

I have done some research about this on Google, but the results were cloudy. Why is the / sign used to denote the root directory. Are there any solid reasons behind it?
48
votes
6answers
3k views

Is there any reason to have a shebang pointing at /bin/sh rather than /bin/bash?

In most shell scripts I've seen (besides ones I haven't written myself), I noticed that the shebang is set to #!/bin/sh. This doesn't really surprise me on older scripts, but it's there on fairly new ...
15
votes
2answers
4k views

What are the main differences between BSD- and linux-based operating systems?

I am a long time linux user and have recently become interested in playing about with BSD-based operating systems. What are the differences between linux and BSD-based systems. I am interested in ...
29
votes
1answer
3k views

When and how was the double-dash (--) introduced as an end of options delimiter in Unix/Linux?

I don't think the shell/utilities in historical Unix nor in something as "recent" as 4.4BSD supported using a double-dash(or two consecutive hyphens) as an end of options delimiter. With FreeBSD, you ...
33
votes
2answers
2k views

Oldest binary working on Linux?

In a discussion on backwards-compatibility in Linux kernel and GUI ABIs, Alan Cox notes that "my 3.6rc kernel will still run a Rogue binary built in 1992. X is back compatible to apps far older than ...
23
votes
1answer
1k views

What does Ritchie's 1979 PDP-11 `/usr/games/bcd` do?

I recently tried the simh emulator pdp11. The disk image I used can be found on the internet, and instructions for booting it are here. Presumably it belonged to Dennis Ritchie, as the username is "...
24
votes
3answers
914 views

How did the Linux Kernel project track bugs in the Early Days?

We all know that Linus Torvalds created Git because of issues with Bitkeeper. What is not known (at least to me) is, how were issues/tickets/bugs tracked up until then? I tried but didn't get anything ...
29
votes
5answers
2k views

What is the point of mv -f?

The GNU Coreutils manual for mv says: -f --force Do not prompt the user before removing a destination file. However, this already seems to be the default behaviour for mv, so the -f option appears ...
30
votes
3answers
21k views

Why does Unix time start at 1970-01-01?

Why does Unix time start at 1970-01-01? Why not 1971-01-01 or any other date?
11
votes
1answer
1k views

What do all the pictures on the front of the “Unix and Linux System Administration Handbook” represent? [duplicate]

I'm a newcomer to Unix and Linux, and I've been trying to get up to speed on everything. One of the guides I've used is the "Unix and Linux System Administration Handbook" It's a pretty great book, ...
0
votes
1answer
82 views

What can be considered as operating system? [closed]

I am talking about GNU/Linux but not about GNU or Linux! I know that Kernel is the core component in operating system but I want to know what defines the "operating system" (What can be considered as ...
25
votes
2answers
945 views

Where is “export var=value” not available?

I have picked up -- probably on Usenet in the mid-1990s (!) -- that the construct export var=value is a Bashism, and that the portable expression is var=value export var I have been advocating ...
14
votes
3answers
996 views

/usr/bin/ptx: Can you provide a use case or two?

I was going through the list of files included in coreutils and I was able to come up with an example of how I could personally use all of the commands provided except for ptx. Can you give one or two ...
10
votes
3answers
406 views

History of Bash globbing

Is there a historical reason why Bash "globbing" and regular expressions are not identical? For example, I believe that in Bash [1-2]* matches anything that starts with a 1 or a 2 followed by anything ...
5
votes
1answer
52 views

Why did “argument can be squished against option” prevail over “argument is always separate”?

Inspired by the recent question Why does the specific sequence of options matter for tar command?, in which the asker learned why tar -cfv test.tar *.jpg doesn't work, I'd like to ask a followup: ...
4
votes
2answers
237 views

What does it mean when something says that UNIX device files are static?

I've been reading up on udev. In the "overview" section, Wikipedia states that "unlike traditional Unix systems, where the device nodes in the /dev directory have been a static set of files, the Linux ...
9
votes
3answers
332 views

When was process substitution first introduced?

I'm curios to know how long process substitution has been around. What shell first had it? When did it get added to other shells?
6
votes
1answer
201 views

Where does this convention for quotation marks (`` …'') come from? [closed]

Frequently I get asked the question: ``K., where does this convention for quotation marks come from? You know, the one with the two grave accents introducing a quoted string and two regular ...
3
votes
4answers
451 views

Is the Filesystem Hierarchy Standard a UNIX standard or a GNU/Linux standard?

The Filesystem Hierarchy Standard says where to put stuff in a UNIX distribution. Is the FHS used/designed for use outside of GNU/Linux, or is it mostly limited to GNU/Linux?
2
votes
3answers
160 views

Why are POSIX Find Parameters Different from Other Program styles?

Why is a parameter in the POSIX find command added with a single hyphen for multi-character parameter names, while most other programs use single hyphen to indicate multiple single-character flags, ...
1
vote
0answers
60 views

Where does backtick and single quote come from when denoting commands e.g. `prog'? [duplicate]

When referring to commands in tutorials, man pages, and articles I see authors use the backtick and single quote in this way: `./configure' `make' I believe I have seen gcc denote points of failure ...