All Questions

1583
votes
3answers
306k views

Why does man print “gimme gimme gimme” at 00:30?

We've noticed that some of our automatic tests fail when they run at 00:30 but work fine the rest of the day. They fail with the message "gimme gimme gimme" in stderr, which wasn't expected. Why are ...
1154
votes
9answers
301k views

What is the exact difference between a 'terminal', a 'shell', a 'tty' and a 'console'?

I think these terms almost refer to the same thing, when used loosely: terminal shell tty console What exactly does each of these terms refer to?
961
votes
16answers
2.2m views

How do I get the size of a directory on the command line?

I tried to obtain the size of a directory (containing directories and sub directories) by using the ls command with option l. It seems to work for files (ls -l file name), but if I try to get the size ...
832
votes
11answers
1.9m views

How to correctly add a path to PATH?

I'm wondering where a new path has to be added to the PATH environment variable. I know this can be accomplished by editing .bashrc (for example), but it's not clear how to do this. This way: export ...
797
votes
2answers
155k 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?
695
votes
7answers
1.4m views

How can I replace a string in a file(s)?

Replacing strings in files based on certain search criteria is a very common task. How can I replace string foo with bar in all files in the current directory? do the same recursively for sub ...
665
votes
2answers
377k views

How to unfreeze after accidentally pressing Ctrl-S in a terminal?

It's a situation that has happened quite often to me: after I press (with a different intention) Ctrl-S in a terminal, the interaction (input or output) with it is frozen. It's probably a kind of "...
612
votes
3answers
271k views

What is the purpose of the lost+found folder in Linux and Unix?

There is a folder at the root of Linux and Unix operating systems called /lost+found/ What is it for? Under what circumstances would I interact with it? How would I interact with it?
597
votes
4answers
2.3m views

How to copy files from one machine to another using ssh [duplicate]

I'm using Linux (centos) machine, I already connected to the other system using ssh. Now my question is how can I copy files from one system to another system? Suppose, in my environment, I have two ...
546
votes
13answers
1.3m views

How do I grep for multiple patterns with pattern having a pipe character?

I want to find all lines in several files that match one of two patterns. I tried to find the patterns I'm looking for by typing grep (foo|bar) *.txt but the shell interprets the | as a pipe and ...
526
votes
4answers
212k views

Why is printf better than echo?

I have heard that printf is better than echo. I can recall only one instance from my experience where I had to use printf because echo didn't work for feeding some text into some program on RHEL 5.8 ...
525
votes
3answers
210k views

Difference between nohup, disown and &

What are the differences between $ nohup foo and $ foo & and $ foo & $ disown
505
votes
8answers
1.4m views

How to install a deb file, by dpkg -i or by apt?

I have a deb package for installation. Shall I install by dpkg -i my.deb, or by apt? Will both handle the software dependency problem well? If by apt, how can I install from the deb by apt?
498
votes
20answers
163k views

Preserve bash history in multiple terminal windows

I consistently have more than one terminal open. Anywhere from two to ten, doing various bits and bobs. Now let's say I restart and open up another set of terminals. Some remember certain things, some ...
497
votes
9answers
1.9m views

How do I zip/unzip on the unix command line?

How can I create and extract zip archives from the command line?
491
votes
36answers
513k views

Tracking down where disk space has gone on Linux?

When administering Linux systems I often find myself struggling to track down the culprit after a partition goes full. I normally use du / | sort -nr but on a large filesystem this takes a long time ...
447
votes
25answers
448k views

Repeat a Unix command every x seconds forever

There's a built-in Unix command repeat whose first argument is the number of times to repeat a command, where the command (with any arguments) is specified by the remaining arguments to repeat. For ...
442
votes
13answers
501k views

What if 'kill -9' does not work?

I have a process I can't kill with kill -9 <pid>. What's the problem in such a case, especially since I am the owner of that process. I thought nothing could evade that kill option.
438
votes
9answers
1.9m views

How to switch between users on one terminal?

I'd like to log in as a different user without logging out of the current one (on the same terminal). How do I do that?
432
votes
4answers
1.3m views

Zip all files in directory?

Is there a way to zip all files in a given directory with the zip command? I've heard of using *.*, but I want it to work for extensionless files, too.
431
votes
8answers
110k views

What do the numbers in a man page mean?

So, for example, when I type man ls I see LS(1). But if I type man apachectl I see APACHECTL(8) and if I type man cd I end up with cd(n). I'm wondering what the significance of the numbers in the ...
420
votes
26answers
628k views

Why am I still getting a password prompt with ssh with public key authentication?

I'm working from the URL I found here: http://web.archive.org/web/20160404025901/http://jaybyjayfresh.com/2009/02/04/logging-in-without-a-password-certificates-ssh/ My ssh client is Ubuntu 64 bit 11....
415
votes
7answers
556k views

Check package version using apt-get/aptitude?

Before I install a package I'd like to know what version I would get. How do I check the version before installing using apt-get or aptitude on debian or ubuntu?
411
votes
9answers
162k views

Why is it better to use “#!/usr/bin/env NAME” instead of “#!/path/to/NAME” as my shebang?

I notice that some scripts which I have acquired from others have the shebang #!/path/to/NAME while others (using the same tool, NAME) have the shebang #!/usr/bin/env NAME. Both seem to work properly....
409
votes
4answers
141k views

What does “--” (double-dash) mean? (also known as “bare double dash”)

I have seen -- used in the compgen command. For example: compgen -W "foo bar baz" -- b What is the meaning of the -- in there?
408
votes
5answers
96k views

/usr/bin vs /usr/local/bin on Linux

Why are there so many places to put a binary in Linux? There are at least these five: /bin/ /sbin/ /usr/bin/ /usr/local/bin/ /usr/local/sbin/ And on my office box, I do not have write permissions to ...
405
votes
6answers
643k views

How to run find -exec?

I'd like to find the files in the current directory that contain the text "chrome". $ find . -exec grep chrome find: missing argument to `-exec' What am I doing wrong?
392
votes
3answers
540k views

Does curl have a --no-check-certificate option like wget?

I am trying to make a curl request to one of our local development servers running a dev site with a self-signed SSL cert. I am using curl from the command line. I saw some blog posts mentioning that ...
390
votes
3answers
253k views

How to cycle through reverse-i-search in BASH?

In the terminal, I can type CTRL-R to search for a matching command previously typed in BASH. E.g., if I type CTRL-R then grep is lists my last grep command, and I can hit enter to use it. This only ...
388
votes
9answers
155k views

When should I not kill -9 a process?

I am always very hesitant to run kill -9, but I see other admins do it almost routinely. I figure there is probably a sensible middle ground, so: When and why should kill -9 be used? When and why ...
374
votes
4answers
821k views

How do I make `ls` show file sizes in megabytes?

What commands do I need for Linux's ls to show the file size in MB?
371
votes
7answers
41k views

How can I find the implementations of Linux kernel system calls?

I am trying to understand how a function, say mkdir, works by looking at the kernel source. This is an attempt to understand the kernel internals and navigate between various functions. I know mkdir ...
369
votes
7answers
975k views

Can I zip an entire folder using gzip?

I'm trying to zip a folder in unix. Can that be done using the gzip command?
368
votes
13answers
185k views

Turn off buffering in pipe

I have a script which calls two commands: long_running_command | print_progress The long_running_command prints a progress but I'm unhappy with it. I'm using print_progress to make it more nice (...
367
votes
6answers
214k views

What is the difference between /opt and /usr/local?

According to the Filesystem Hierarchy Standard, /opt is for "the installation of add-on application software packages". /usr/local is "for use by the system administrator when installing software ...
366
votes
24answers
510k views

How can I resolve a hostname to an IP address in a Bash script?

What's the most concise way to resolve a hostname to an IP address in a Bash script? I'm using Arch Linux.
363
votes
15answers
296k views

What are the pros and cons of Vim and Emacs?

How would you compare these editors? What are the pros and cons of each? [note] This is not meant to be answered by those who "hate one and love another" or those who haven't used both.
363
votes
3answers
254k views

Using “${a:-b}” for variable assignment in scripts

I have been looking at a few scripts other people wrote (specifically Red Hat), and a lot of their variables are assigned using the following notation VARIABLE1="${VARIABLE1:-some_val}" or some expand ...
357
votes
7answers
242k views

Execute vs Read bit. How do directory permissions in Linux work?

In my CMS, I noticed that directories need the executable bit (+x) set for the user to open them. Why is the execute permission required to read a directory, and how do directory permissions in Linux ...
352
votes
5answers
703k views

Finding the PID of the process using a specific port?

I am installing hadoop on my Ubuntu system. When I start it, it reports that port 9000 is busy. I used: netstat -nlp|grep 9000 to see if such a port exists and I got this: tcp 0 0 ...
345
votes
14answers
55k views

In Bash, when to alias, when to script, and when to write a function?

It's taken me almost 10 years of Linux usage to ask this question. It was all trial and error and random late-night internet surfing. But people shouldn't need 10 years for this. If I were just ...
339
votes
3answers
189k views

refresh changed content of file opened in vi(m)

I have a config-file that I keep open in vim, but that sometimes gets changed on disk, without these changes being reflected on the terminal. Can I refresh the content on the screen without closing ...
338
votes
9answers
492k views

How to display `top` results sorted by memory usage in real time?

How can I display the top results in my terminal in real time so that the list is sorted by memory usage?
336
votes
7answers
576k views

How do I copy a folder keeping owners and permissions intact?

So I was going to back up my home folder by copying it to an external drive as follows: sudo cp -r /home/my_home /media/backup/my_home With the result that all folders on the external drives are now ...
325
votes
8answers
292k views

How to force ssh client to use only password auth?

If I use pubkey auth from e.g.: an Ubuntu 11.04 how can I set the ssh client to use only password auth to a server? (just needed because of testing passwords on a server, where I default log in with ...
323
votes
10answers
129k views

How do I delete a file whose name begins with “-” (hyphen a.k.a. dash or minus)?

How do you remove a file whose filename begins with a dash (hyphen or minus) -? I'm ssh'd into a remote OSX server and I have this file in my directory: tohru:~ $ ls -l total 8 -rw-r--r-- 1 me ...
319
votes
4answers
262k views

Scroll inside Screen, or Pause Output

I use screen for my command-line tasks while managing the servers where I work. I usually run small commands (mostly file-system tasks) but sometimes I run more extensive tasks (like DBA). The output ...
317
votes
4answers
212k views

How does reverse SSH tunneling work?

As I understand this, firewalls (assuming default settings) deny all incoming traffic that has no prior corresponding outgoing traffic. Based on Reversing an ssh connection and SSH Tunneling Made ...
312
votes
10answers
752k views

How to forward X over SSH to run graphics applications remotely?

I have a machine running Ubuntu which I SSH to from my Fedora 14 machine. I want to forward X from the Ubuntu machine back to Fedora so I can run graphical programs remotely. Both machines are on a ...
307
votes
5answers
79k views

Why is Kali Linux so hard to set up? Why won't people help me?

I've installed Kali Linux, or I'm trying to install it. Why is it so hard? Why doesn't it recognize my hardware? Why do I need to set up so many things manually? Why can't I install the applications I ...

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