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1621
votes
3answers
315k 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 ...
1216
votes
10answers
320k 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?
1041
votes
16answers
2.4m 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 ...
898
votes
11answers
2.1m 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 ...
805
votes
2answers
158k 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?
743
votes
7answers
1.5m 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 ...
714
votes
2answers
404k 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 "...
653
votes
4answers
2.5m 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 ...
636
votes
3answers
286k 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?
603
votes
13answers
1.4m 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 ...
575
votes
8answers
1.7m 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?
569
votes
3answers
231k views

Difference between nohup, disown and &

What are the differences between $ nohup foo and $ foo & and $ foo & $ disown
546
votes
4answers
223k 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 ...
531
votes
9answers
2.0m views

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

How can I create and extract zip archives from the command line?
524
votes
37answers
549k 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 ...
519
votes
20answers
174k 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 ...
473
votes
25answers
480k 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 ...
473
votes
4answers
1.4m 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.
471
votes
10answers
2.0m 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?
465
votes
8answers
120k 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 ...
464
votes
14answers
534k 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.
457
votes
6answers
720k 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?
451
votes
4answers
158k 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?
449
votes
26answers
690k 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....
448
votes
9answers
181k 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....
440
votes
5answers
105k 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 ...
435
votes
3answers
599k 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 ...
434
votes
4answers
283k 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 ...
427
votes
7answers
588k 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?
422
votes
4answers
958k 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?
413
votes
3answers
293k 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 ...
402
votes
7answers
1.0m 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?
400
votes
24answers
553k 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.
400
votes
9answers
161k 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 ...
395
votes
6answers
240k 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 ...
392
votes
13answers
199k 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 (...
384
votes
5answers
764k 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 ...
374
votes
7answers
42k 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 ...
371
votes
15answers
302k 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.
370
votes
8answers
257k 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 ...
362
votes
8answers
620k 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 ...
362
votes
9answers
541k 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?
360
votes
8answers
332k 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 ...
360
votes
3answers
203k 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 ...
359
votes
4answers
300k 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 ...
353
votes
14answers
58k 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 ...
341
votes
10answers
138k 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 ...
341
votes
4answers
230k 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 ...
334
votes
10answers
823k 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 ...
331
votes
11answers
612k views

How do I remove a user from a group?

Which command should I use to remove a user from a group in Debian? When adding a user to a group, it can be done with: usermod -a -G group user However, I could not find a similar command (...

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