Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs.

learn more… | top users | synonyms

15
votes
3answers
18k views

what is the max length of password on unix/linux system?

what is the max permissible length of password on unix/linux system?
15
votes
4answers
9k views

How to replace part of a text file between markers with another text file?

Say I have a text file like this: # custom content section a b ### BEGIN GENERATED CONTENT c d ### END GENERATED CONTENT I'd like to replace the portion between the GENERATED CONTENT tags with the ...
15
votes
4answers
14k views

removing write permission does not prevent root from writing to the file

I just noticed on my Ubuntu machine (ext3 filesystem) that removing write permissions from a file does not keep root from writing to it. Is this a general rule of UNIX file permissions? Or specific ...
15
votes
2answers
6k views

Linux-like top/netstat/etc. on Mac OS X?

Unix utilities on Mac OS X are quite painful to use. port install coreutils +with_default_names and a few other such replacements fix most of them, but it leaves some in broken Mac OS X defaults - ...
15
votes
2answers
15k views

Why do we use cp to copy files and not dd? (in unix-derivatives)

For normal file copying in *nix, I've only ever seen people use cp (eg. cp /mnt/mydevice/myfile ~/myfile), but I eventually ran into dd, which appears to do the exact same thing (dd if=/mnt/mydevice/...
15
votes
1answer
739 views

Make Firefox use the favicon as window icon under Linux

Is there a Firefox feature, setting, or add-on that arranges it so that the favicon of the currently open web page becomes the icon of the browser window in Linux/X11? In particular, it ought to show ...
14
votes
7answers
1k views

Is there a way to go to any directory from any other directory directly?

Is there a way to go to any directory from any other directory directly? For example, lets say that I'm at root and I wanted to go directly to currentProject without doing: cd dropbox/dev/...
14
votes
7answers
17k views

Is it better to always copy and delete, rather than move?

Generally speaking, I find myself panicking when I realise that if I cancel a file move, it could cause the target or source to be incomplete. This question applies to Windows and Unix-based platforms....
14
votes
7answers
11k views

Advantages of cat'ing file and piping to grep

Are there any additional advantages of cat'ing a file and piping it to grep, besides convenience? The convenience being that, when I retrieve commands such as those below from my history, the cursor ...
14
votes
7answers
24k views

How to make a statement that checks if something is divisible by something else without a remainder (BASH)

#!/bin/bash Echo “Enter a number” Read $number If [$number ] ; then Echo “Your number is divisible by 5” Else Echo “Your number is not divisible by 5” fi the if [$number] statement is what ...
14
votes
3answers
32k views

How to display Unix time in the timestamp format?

I'm looking for a way to display my time in Debian Linux as a timestamp, e.g. 1279628325 I can't find any options to do that with the date command. Any ideas?
14
votes
2answers
15k views

Compress files from OS X terminal?

In the Finder, there is this wonderful ability to right click on a file or directory, select compress from the drop-down, and end up with a zipped file. Is it possible to do the same thing from the ...
14
votes
3answers
15k views

UNIX - mount: only root can do that

I need to allow a non-root user to mount/unmount a device. I am a total noob when it comes to UNIX, so please dumb it down for me. I've been looking all over teh interwebz to find an answer and it ...
14
votes
2answers
11k views

How to make files created in a directory owned by directory group?

Is there a way, on Linux, to cause all new files created in a directory to be owned by the directory's group instead of the creating user's group?
14
votes
1answer
23k views

Console commands to change virtual ttys in Linux and OpenBSD

In Linux one presses Alt-F1, Alt-F2 etc to change virtual ttys. In OpenBSD one shall use Ctrl-Alt-F1 etc instead. Are there are console commands for these two operating systems that can be issued to ...
14
votes
2answers
11k views

what does the @ symbol mean in ls -l directory listing? [duplicate]

Possible Duplicate: ls -la symbolics… what does that last symbol mean? When I run ls -l on my mac I see two .yml files: -rw-r--r-- 1 aa staff 6 Apr 15 05:50 s1.yml -rw-r--r--@ 1 ...
14
votes
7answers
2k views

Is there any functional-like unix shell?

I'm (really) newbie to functional programming (in fact only had contact with it using python) but seems to be a good approach for some list-intensive tasks in a shell environment. I'd love to do ...
14
votes
1answer
20k views

What do the “ALL”s in the line “ %admin ALL=(ALL) ALL ” in Ubuntu's /etc/sudoers file stand for?

What does each ALL mean? I understand that the whole line indicates that the admin group members get admininstartive privileges, but would like to know more info about the position of the ALLS and if ...
14
votes
2answers
14k views

Unix: Is there a way to “copy” file or directory permissions?

I have two files in a directory. One has correct permissions and the other has not. Is there a way I can "copy" the set of permissions from one file to another?
14
votes
2answers
5k views

Linux - alternative places where to store pid file instead of /var/run

As written in the title, where should I let the init script write the pid file? are there any standard paths I should choose instead of the /var/run ? Could /tmp be a good place where to store it or ...
14
votes
6answers
14k views

Start a systemd service inside chroot

With init scripts (or with openrc) I alway could run services from a different installation root. but when I run chroot /somepath/to_root /usr/bin/systemctl start someservice I got: Running in chroot,...
14
votes
3answers
43k views

How to find which files and folders were deleted recently in Linux?

I am having one particular folder (/home/sam/officedocuments) which is having hundreds of folders and files. I think I deleted some files and folders by mistake but I'm not sure. How to find which ...
13
votes
4answers
19k views

Do symbolic link files survive SVN?

Let's say I create a symbolic link file inside an SVN managed path, commit the path to SVN and later checkout the path. 1) Will the symbolic link file survive? 2) If the symbolic link file is made ...
13
votes
3answers
21k views

What does kill -3 mean?

I know kill -9 mean, but anyone can explain what does kill -3 mean? Any special signal it sends out?
13
votes
8answers
2k views

Is there a command for going back a number of steps in a directory, without using cd?

I'm constantly going 'cd ../../../../'. Is there a command/alias that could let me go 'cmd 4' and I'd be taken back 4 directories?
13
votes
5answers
2k views

How to jump back to the first character in *nix command line?

When writing a long command in the *nix command line and having to go back to the first character, in order to add something at the beginning (for instance a nohup, when you realize the process will ...
13
votes
2answers
18k views

How to keep program running after SSH disconnection? [duplicate]

Possible Duplicates: Keep a program running after closing a console, after the program has started How can I use ssh to run a command on a remote Unix machine and exit before the command completes?...
13
votes
7answers
20k views

How can I sort all files by size in a directory?

How can I display the files in a unix directory sorted by their human readable size, going from largest to smallest? I tried du -h | sort -V -k 1 but it does not seem to work.
13
votes
5answers
391 views
13
votes
7answers
8k views

Sorting human readable file sizes

How can I sort a list using a human-readable file-size sort, numerical sort that takes size identifier (G,M,K) into account? Can I sort "du -sh" output for example? Problem: Consider the problem of ...
13
votes
4answers
8k views

How can I recursively grep particular files in a directory?

I'm new to linux and grep, and trying to find my way around. By using find -name *.java I am able to find the names of all of the java files in a particular directory. Suppose I want to count the ...
13
votes
1answer
28k views

In UNIX, what are the Ss, Sl, and Ssl proccess types I see with ps aux?

When doing a ps aux command, I see some process listed as Ss, Ssl and Sl. What do these mean? root 24653 0.0 0.0 2256 8 ? Ss Apr12 0:00 /bin/bash -c /usr/bin/python /var/...
13
votes
9answers
8k views

“Detach” and “Reattach” xterms across X sessions?

Is there a way to save/detach an xterm (or another window), and reopen/load/reattach it on a different X session on the same machine ? What I'm trying to achieve is "move" running xterms between two ...
13
votes
3answers
3k views

Why are there short and long alternatives for command line options?

Most unixoid commands feature short and long alternatives for command line options, like ls -a and ls --all, or ls -A and ls --almost-all. Why do those two ways exist? One is shorter to type, the ...
13
votes
3answers
7k views

Using `find` for multiple file extensions

I am using the following command for counting the lines of text in JAVA files: find . -name '*.java' | xargs wc -l How can I modify the find command parameters to match more than one file extension?...
13
votes
4answers
11k views

Vim highlighting for specific file types (where to put syntax files, vim events, line to put into vimrc)

I have defined a file time jak.vim to offer custom highlighting when I take notes, however it is being applied to some files that do not have the .jak extension. Specifically a file named progress....
12
votes
5answers
3k views

How do we pronounce “/etc” folder? [closed]

Can't find similar question in SU. Anyone knows? Is it only 3 letter e,t and c? I can't find similar things in google. It would be good if someone provide this answer
12
votes
5answers
3k views

Map “untar” to tar xvfz?

How can I map 'untar' as a command to 'tar -xvfz' ? Sorry, but I almost always forget the arguments necessary to 'tar' for this operation.
12
votes
3answers
22k views

Delete files with regular expression

I Tried to delete files that starts with A and ends with 2 numbers but It doesn't do a thing. What I tried: rm ^A*[0..9]2$ Where am I wrong?
12
votes
7answers
9k views

Best practices to alias the rm command and make it safer

Some time ago I erroneously deleted my home folder because I ran a rm -rf * on the wrong terminal, whose working directory was the home folder! I wish I had an alias for the rm command, but it was ...
12
votes
4answers
4k views

What is the reason for rmdir(1) and rm(1) to co-exist?

I use BSD and Linux every day, I have never had a circumstance which I must use rmdir(1) rather than rm(1). What's the purpose of rmdir's existence?
12
votes
8answers
38k views

Tell `ls` to print only the base filename

This is the default behaviour of ls ls /net/nas/data/languages/pypm/sites/rex/free/2.6/*/pool/v/vi/virtual*1.4.4*pypm /net/nas/data/languages/pypm/sites/rex/free/2.6/linux-x86/pool/v/vi/virtualenv-1....
12
votes
4answers
2k views

Who deals with the star * in echo *

Who deals (interprets) the * in echo * Does the echo see the star or the shell take care about it and return a list of filename .. What about cp temp temp*
12
votes
6answers
13k views

How to delete all but one file in Unix? [duplicate]

Possible Duplicate: How to delete all files in a directory except some? How to delete all but one(or some) file in Unix? Something like rm -rf -ignore myfile.txt *
12
votes
3answers
10k views

How Many Unix Groups Can A User Be A Member Of?

We've recently run into a situation at a group-happy site where some group memberships are not being picked up. I seem to remember that there is an upper limit to the number of groups that a user can ...
12
votes
2answers
1k views

Why does redirecting the output of a file to itself produce a blank file?

Why does redirecting the output of a file to itself produce a blank file? Stated in Bash, why do less foo.txt > foo.txt and fold foo.txt > foo.txt produce an empty foo.txt? Since an ...
12
votes
4answers
10k views

Terminal Vs. Shell [duplicate]

Possible Duplicate: What are the differences between shell , console & terminal? This probably sounds like a stupid question but I'm having a lot of trouble clearly differentiating between ...
12
votes
1answer
11k views

What's a good way to install “build essentials” (all common useful commands) on a blank EC2 Linux server?

I want to get some "build essentials" (like gcc, make, etc.) on an empty micro Linux box. Seems inefficient to spend my time trying to try installing one thing, then realize I need gcc, then realize ...
12
votes
2answers
3k views

Unix: Slash after directory names or not

What is the difference between the following commands? mv foo bar mv foo/ bar/ mv foo/ bar mv foo bar/ Or is there no difference? Or does it depend on the command being used? Think for example I ...
12
votes
1answer
3k views

ZSH tab completion of git commands is very slow. How can I turn it off?

If I type: rm <TAB> I'll see possible completions almost instantly. However, if I type: git rm <TAB> It'll hang for several seconds if it's in a git repo, or fail to show any ...