Questions tagged [unix]

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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1475
votes
10answers
1.2m views

How can I sort the output of 'ls' by last modified date?

How can I sort the output of ls by last modified date?
482
votes
38answers
377k 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 ...
469
votes
14answers
461k views

How to copy with cp to include hidden files and hidden directories and their contents?

How can I make cp -r copy absolutely all of the files and directories in a directory Requirements: Include hidden files and hidden directories. Be one single command with an flag to include the ...
466
votes
7answers
589k 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 ...
331
votes
9answers
620k views

How to get the summarized sizes of directories and their subdirectories?

Let's say I want to get the size of each directory of a Linux file system. When I use ls -la I don't really get the summarized size of the folders. If I use df I get the size of each mounted file ...
331
votes
7answers
865k 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:...
314
votes
11answers
190k views

How can I search the bash history and rerun a command?

Can I search history in bash and run the result?
298
votes
5answers
100k views

less command with multiple files: How to navigate to next/previous

I just found out I can use less with multiple files. less status line tells me (END) - Next: file2.txt But how do I navigate previous/next from less?
293
votes
10answers
605k views

If I know the PID number of a process, how can I get its name?

If I have the PID number for a process (on a UNIX machine), how can I find out the name of its associated process? What do I have to do?
258
votes
4answers
291k views

How can I find files that are bigger/smaller than x bytes?

In a terminal, how can I find files that are bigger or smaller than x bytes? I suppose I can do something like find . -exec ls -l {} \; and then pipe the result to awk to filter by file size. But ...
256
votes
3answers
480k views

What is the Windows equivalent of the Unix command cat?

I want to do exactly what unix "cat" does, but on my PC. Is there a simple equivalent command for the Windows command line? Specifically I want to create a file from all the files of a given type in ...
230
votes
8answers
19k 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.
220
votes
6answers
97k views

Choosing between .bashrc, .profile, .bash_profile, etc [duplicate]

This is embarrassing, but after many years of using POSIX systems full time, I still have a hard time figuring out if a shell customization should go in .bashrc, .profile, or somewhere else. Not to ...
217
votes
12answers
56k 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 ...
209
votes
18answers
38k views

What is the advantage of using 'tar' today?

I know that tar was made for tape archives back in the day, but today we have archive file formats that both aggregate files and perform compression within the same logical file format. Questions: ...
200
votes
9answers
18k views

How far will you get with an 'rm -rf /' command?

I've often wondered how far the system will actually get if you run rm -rf /. I doubt the OS would be able to erase itself (?) Bonus Question: After the command has been executed, will rm have ...
197
votes
6answers
277k views

What's different between Ctrl+Z and Ctrl+C in Unix command line?

I'm using Mac OS X Terminal. And I use Ctrl+Z or Ctrl+C to stop some programs. But I realized that I don't know what they're exactly doing. What are they and what's the difference between them? ...
190
votes
5answers
227k views

How to find files with certain text in the Terminal

I'd like to find all files that contain a certain string of text. How would you do that in the Terminal?
184
votes
3answers
82k views

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

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 ...
171
votes
23answers
168k 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?
170
votes
18answers
212k 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): ...
166
votes
10answers
569k views

ls-command: how to display the file size in megabytes?

In Unix (Tru64), how do I make the ls command show the file size in megabytes? Currently I am able to show it in bytes using the following: ls -la
158
votes
10answers
145k 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?
148
votes
10answers
220k views

List the current folder folder's sizes with the terminal?

I want a list of the folders from the current directory or one that I specify with their size. I have tried with du but I only get the size of the directories I specify (du . ./f1), and ls doesn't ...
146
votes
5answers
17k views

How does Linux know that the new password is similar to the previous one?

A few times I tried to change a user password on various Linux machines and when the new password was similar to the old one, the OS complained that they were too similar. I always wondered, how does ...
145
votes
16answers
144k views

Is there a way to see any tar progress per file?

I have a couple of big files that I would like to compress. I can do this with for example tar cvfj big-files.tar.bz2 folder-with-big-files The problem is that I can't see any progress, so I don't ...
133
votes
7answers
147k views

Unix zip directory but excluded specific subdirectories (and everything within them)

I'm trying to zip a directory (on Unix via SSH) but I need to exclude a couple of subdirectories (and all files and directories within them). So far I have this: zip -r myarchive.zip dir1 -x dir1/...
130
votes
4answers
77k 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 ...
122
votes
4answers
38k views

which/whereis differences

What's the difference between which and whereis ?
121
votes
8answers
100k views

How do I configure SSH so it doesn'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 ...
120
votes
18answers
16k views

What's the quickest way to count the number of each character in a file?

I want to count the A's T's C's G's N's and "-" characters in a file, or every letter if needed, is there a quick Unix command to do this?
120
votes
4answers
207k views

What is the “wheel” user in OS X?

I recently reinstalled iTunes and I noticed something peculiar. The "original" version of iTunes has a user in the permissions known as "wheel" that is set to "Read Only". I dragged this version of ...
111
votes
5answers
34k 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 ...
109
votes
2answers
50k 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/...
109
votes
3answers
350k 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?
102
votes
3answers
76k views

How to run Unix commands from within Vim?

How can I run Unix commands while I'm inside vim?
98
votes
3answers
109k views

How do file permissions apply to symlinks?

Let's say you have this structure: + directory -- file1 -- file2 -- file3 -> /tmp/file3 file3 is a link to another file3 somewhere else on the system. Now let's say I chmod 777 the directory and ...
97
votes
12answers
91k views

How to sort first directories then files etc… when using “ls” in Unix

I would like to use the ls command to first show directories and then files. I tried: ls -la | sort -k 1 But I got a wrong order.
97
votes
4answers
153k views

How to copy a file in unix without altering its last modified time?

If I copy some file from some place to another using cp, the timestamp on the copied file is set to the time of the copy. Is there some way to avoid this? I need to copy files without altering their ...
96
votes
3answers
83k views

Unix: How to unsplit in screen

I'm trying to learn how to use screen, in unix so that I don't have to open up several ssh connections and terminal windows just because I want to do more than one thing at the same time on a machine. ...
93
votes
3answers
76k views

How does one switch between windows on VIM?

I'm using both Vim and MacVim (or well, trying to). I installed the Tagbar plugin but find it impossible to switch to the actual Tagbar window to make my selection. I've been reading loads about ...
93
votes
4answers
168k 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 ...
90
votes
15answers
76k 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 ...
90
votes
3answers
153k views

How do I gunzip to a different destination directory?

How do I gunzip to a destination directory other than the current one? This did not work: gunzip *.gz /putthemhere/
89
votes
2answers
51k 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?
88
votes
6answers
34k 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 ...
87
votes
4answers
146k 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 ...
86
votes
4answers
43k views

PowerShell equivalent to the Unix `which` command?

Does PowerShell have an equivalent to the which command found in most (if not all) Unix shells? There are a number of times I'd like to know the location of something I'm running from the command ...
85
votes
3answers
21k 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 ...
84
votes
3answers
121k views

How to close a tmux session

I am using tmux to manage multiple terminal windows. Currently I have 2 windows open with multiple panes. I know that I have to use the prefix (for me it is ctrl+a) to enter commands. How can I ...

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