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

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116
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10answers
82k views

How do I set up SSH so I don't have to type my password?

How do I set up SSH so I don't have to type my password when connecting to a host?
23
votes
0answers
24k views

ls -la symbolics… what does that last symbol mean?

Possible Duplicate: what does the @ mean on the output of ls on os x terminal? when I type ls -la I get this familiar output... drwxr-xr-x+ 38 kent staff 1292 Nov 6 11:09 . drwxr-xr-...
185
votes
8answers
13k views

What do the parentheses and number after a Unix command or C function mean?

I keep seeing parentheses and a number after a command in Unix or Linux or C function. For example: man(8), ftok(2), mount(8), etc. What do these mean? I see them in man too.
238
votes
27answers
136k views

How to execute a command whenever a file changes?

I want a quick and simple way to execute a command whenever a file changes. I want something very simple, something I will leave running on a terminal and close it whenever I'm finished working with ...
56
votes
12answers
31k views

How can I trigger a notification when a job/process ends?

The place I work at has commands that take a long time to execute. Is there a command/utility that I can use to notify me when the command execution is over? It could be a popup window or maybe a ...
32
votes
8answers
35k views

How Unix is Mac OS X? [closed]

From my limited knowledge: The Unix OS coder assumes the user knows what they're doing etc. versus the Apple's you can only do it the way you are allowed to do it, etc. Compared to other variations ...
11
votes
3answers
20k views

How can I use ssh to run a command on a remote Unix machine and exit before the command completes?

How can I use ssh to run a command on a Unix machine and exit before the command completes? For instance, if I type ssh localhost 'sleep 60 &' ssh hangs on my terminal until sleep completes, ...
30
votes
2answers
67k views

Allow specific user permission to read/write my folder

I have a folder /home/samantha/folder that I want to share with the user tom. He can read/write the folder. How do I do that? chown wouldn't do it because I still want to be able to be the owner of ...
37
votes
12answers
38k views

What commands can I use to reset and clear my terminal?

I have been using the command: reset to clear my terminal. Although I am pretty sure this is not what I should be doing. Reset, as the name suggests resets your entire terminal (changes lots of ...
27
votes
1answer
4k views

Is there a way to make bash more TAB friendly?

I use bash on both my Mac and as my cygwin shell. Overall, I'm quite pleased with it. My one complaint however is that its TAB completion isn't as good as Windows Command Line TAB completion. For ...
16
votes
2answers
5k views

Unix: Files starting with a dash, -

Ok, I have a bunch of files starting with a dash, -. Which is not so good... and I want to rename them. In my particular case I would just like to put a character in front of them. I found the ...
9
votes
2answers
29k views

How to change user in WinSCP?

I'm using WinSCP to access Unix computers. How can I change user after I have logged into a Unix server using WinSCP? E.g. I have personal account in Unix computer A. I can log into this computer ...
197
votes
12answers
41k views

How can I change to the previous directory instead of going up?

I currently spend a lot of my working hours moving back and forth between two paths which are very far down the tree and divert from each other at root. It strikes me that my life would be a lot ...
70
votes
4answers
242k views

What is the .bashrc file?

Unix shells when starting read the .bashrc file and execute commands written in it. What is this file and what does it execute?
70
votes
13answers
100k views

Unix/Linux find and sort by date modified

How can I do a simple find which would order the results by most recently modified? Here is the current find I am using (I am doing a shell escape in PHP, so that is the reasoning for the variables): ...
60
votes
3answers
12k views

What does the 'rc' in `.bashrc`, etc. mean?

Well, this is embarrassing. I feel like I just realised I don't know a loyal colleague's name after working with them for 10 years. "Hey, er... *cough!*, thanks for that great job you did on setting ...
74
votes
2answers
38k views

Why does Windows use backslashes for paths and Unix forward slashes?

It annoys me having used Unix in college and now working on the Windows side. What's the history behind this decision? Anyone know why it worked out this way?
21
votes
3answers
7k views

Use GNU screen as login “shell”

What's the best way to have screen automatically run when you open a new shell, whether by login, xterm, or anything else? I see the most common recommendation is to put exec screen in your regular ...
9
votes
3answers
44k views

How do I reset the $PATH variable on Mac OS X?

I've messed up my path variable, and now some apps that I run raise errors saying Command Not Found (error 127) for commands like date and sleep. These commands work fine when executed directly in the ...
22
votes
5answers
30k views

tar – extract discarding directory structure

unzip has a nifty option -j, whereby the directory structure of the archive is discarded, and all files are extracted into the same directory. Is there a way of making tar work in the same way? ...
8
votes
4answers
5k views

Keep a program running after closing a console, after the program has started [duplicate]

Possible Duplicate: How do I detach a process from Terminal, entirely? I've a program running in a Unix console on a remote Unix computer. I (stupidly) didn't run it using nohup &, and now ...
9
votes
4answers
1k views

Unix tools: what if a file is named minus something?

I'm always wondering: most GNU/Unix tools take options in the form "minus something", sometimes followed by an argument. What if you got a file named minus something? $ ls -f $ rm -f $ ls -f $ mv -f ...
237
votes
8answers
250k views

What is the “You have new mail” message in Linux/UNIX?

Sometimes, when I log into a box and 'su' to root, I get a cute little message saying I have mail (thank GOD it's not AOL). Where is this mail? What does it contain? Who/What sent it? How important ...
68
votes
4answers
109k views

How to make new file permission inherit from the parent directory?

I have a directory called data. Then I am running a script under the user id 'robot'. robot writes to the data directory and update files inside. The idea is data is open for both me and robot to ...
123
votes
5answers
290k views

How can I make chown work recursively?

I've got a directory called pdfs that contains a bunch of sub- and sub-sub-directories. I want to change ownership on all PDF files in all of the subfolders. I just tried this: chown -R someuser:...
48
votes
11answers
21k views

What is the relationship between Unix, Linux, Ubuntu, Debian and Android?

What is the relationship between Unix, Linux, Ubuntu, and Debian? I suspect they are all Operating Systems that are based upon one another - similar to how Windows is based on DOS. Is my suspicion ...
37
votes
4answers
69k views

How do I make sudo preserve my environment variables?

Using sudo 1.7.4p4 on Solaris 5.10 and sudo 1.6.7p5 on RHEL4 u6 I can't see how to preserve my environment variables, for instance $PYTHONPATH. I've added this line to sudoers, but it doesn't make any ...
45
votes
3answers
14k views

How do I reload .inputrc?

Background I have heard that the readline module is reading ~/.inputrc and that is how it changes the behaviour of keystrokes under programs such as bash. Question How can I reload this after ...
56
votes
4answers
45k views

What does load average mean in unix/linux?

If I run uptime, I get something like this: 10:50:30 up 366 days, 23:27, 1 user, load average: 1.27, 2.06, 1.54 What do those numbers on the end mean? The man page tells me it's "the load ...
51
votes
2answers
10k views

'less' command clearing screen upon exit - how to switch it off?

How to force the less program to not clear the screen upon exit? I'd like it to behave like git log command: it leaves the recently seen page on screen upon exiting it does not exit the less even ...
29
votes
4answers
15k views

How are PID's generated?

On *nix, PIDs are unique identifiers for running processes. How are PID's generated? Is it just an integer which gets incremented or a more complex structure such as a list? How do they get recycled? ...
17
votes
2answers
10k views

What does the @ in ls -al mean? [duplicate]

Possible Duplicate: ls -la symbolics… what does that last symbol mean? What does the @ in the below execution of ls -al mean? atom:Lib fak$ ls -al total 1056 drwxr-xr-x 5 fak staff ...
28
votes
6answers
5k views

What is the general consensus on “Useless use of cat”?

When I pipe multiple unix commands such as grep, sed, tr etc. I tend to specify the input file that is being processed using cat. So something like cat file | grep ... | awk ... | sed ... . But ...
2
votes
7answers
9k views

Automatically restart a Unix job if it goes down?

I have a job that I would like to "daemonize" on Unix: I want it to come up when the computer boots, and I want it to restart if it goes down. A simple way to do this is to setup a cronjob that runs ...
11
votes
3answers
2k views

Calling a script with ./bla.sh vs. . bla.sh

Can anybody explain to me what the shell does in the two examples A) and B) below? It obviously behaves differently, but I can't find out why the output is different. Example: Let's have a script in ...
1
vote
3answers
3k views

Modification of files with 777 permissions but not with 755 permissions?

I can modify the files with 777 permissions, but not with 755. I do it by sourcing some sed commands. I find it odd because I can modify the files with even 700 permissions in Vim. Why is it not ...
6
votes
3answers
2k views

Difference between df -k and du -sh

df -k /dev/sda6 25396228 21249088 2836240 89% /export 21G used versus du -sh /export 3.4G /export The 3.4G is correct because we have removed all non essential file but free ...
23
votes
6answers
2k views

Learning the basics of Linux/Unix [closed]

I would like to learn the basics of Linux; In contrast to tutorials that teach how to do common tasks with Ubuntu or something. I'm looking for a structured introduction, not a reference. Also I would ...
50
votes
14answers
47k views

Is there a way to display a countdown or stopwatch timer in a terminal?

How can I display a real-time countdown timer on the Linux terminal? Is there an existing app or, even better, a one liner to do this?
57
votes
4answers
24k views

Bash: Spaces in alias name

I am trying to create an aliases in bash. What I want to do is map ls -la to ls -la | more In my .bashrc file this is what I attempted: alias 'ls -la'='ls -la | more' However it does not work ...
66
votes
12answers
6k views

What command do I need to use to remove a file called `-rf`?

I did something crazy at some point that created a file called -rf on my filesystem. Now I can't figure out how to delete it... I've tried: rm "-rf" rm \-rf These just exit immediately, arrgh! ...
26
votes
3answers
83k views

Command: sudo su -

I understand what su - does logs you into root with the root environment (as opposed to su which logs you into root with your environment) And I understand what sudo does you are root for one ...
28
votes
5answers
13k views

Mac OS X: at command not working

I am going to schedule a job by using at command. Here I tried the following command: $ at now + 1 minute echo 'Test at command' <EOD> I saw the job is scheduled by using at -l. However, I ...
17
votes
3answers
43k views

Copy list of files

I have a list of files separated by spaces in a file list.txt. I'd like to copy them to a new folder. I tried to do: cp `cat list.txt` new_folder but it did not work. How would you do this ? ...
47
votes
4answers
72k views

What is effect of CTRL + Z on a unix\Linux application

I was curious and confused that what exactly is the behaviour of CTRl+Z. I know, If a process in running in foreground, and we press ctrl+z, it goes to background. But what exactly happens. Does it ...
45
votes
4answers
17k views

What is the origin of the UNIX $ (dollar) prompt?

The UNIX prompt uses a $ symbol to indicate that your input is expected. I was wondering why this symbol was chosen—if there is a reason. Dollar just seems a little unexpected. A > symbol would ...
22
votes
2answers
32k views

Understanding top command in unix

When I run top -c command on my UNIX box I get the output below: top - 03:09:34 up 5 days, 6:14, 1 user, load average: 0.00, 0.00, 0.00 Tasks: 175 total, 1 running, 174 sleeping, 0 stopped, ...
58
votes
2answers
20k views

How to start vim without executing /etc/vimrc?

On my Linux server at work, the admins did not install cscope, and I installed it from source in my home directory and added it to the $PATH. The trouble is, the /etc/vimrc has a reference to /usr/...
45
votes
5answers
26k views

How do I configure SSH so it dosen't try all the identity files automatically?

I have been putting my ssh identity files inside my ~/.ssh/ folder. I have probably about 30 files in there. When I connect to servers, i will specify the identity file to use, with something like ...
34
votes
8answers
21k views

Rename a group of files with one command

If I have a group of files with a .htm extention, how can I rename them all to .html? mv *.htm *.html does not work.