All Questions
241,248
questions
1862
votes
3
answers
444k
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 we ...
- 9,832
1650
votes
16
answers
3.6m
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 ...
- 27.1k
1612
votes
10
answers
529k
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?
- 35.6k
1389
votes
12
answers
3.5m
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 ...
- 17.6k
1294
votes
13
answers
5.0m
views
How to copy files from one machine to another using ssh
I am using a Linux (CentOS) machine, and I have already connected to another system using SSH.
Now, my question is: How can I copy files from one system to another system?
Suppose, in my environment, ...
- 16.8k
1206
votes
9
answers
3.7m
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?
- 104k
1027
votes
6
answers
1.9m
views
How to see full log from systemctl status service?
I check service status with systemctl status service-name.
By default, I see few rows only, so I add -n50 to see more.
Sometimes, I want to see full log, from start. It could have 1000s of rows.
Now,...
- 10.6k
967
votes
10
answers
1.8m
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 ...
- 245k
958
votes
3
answers
573k
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 "...
911
votes
15
answers
1.1m
views
How can I reduce a video's size with ffmpeg?
How can I use ffmpeg to reduce the size of a video by lowering the quality (as minimally as possible, naturally, because I need it to run on a mobile device that doesn't have much available space)?
I ...
- 15.3k
906
votes
2
answers
2.3m
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?
- 9,173
862
votes
2
answers
179k
views
Why was '~' chosen to represent the home directory?
I have often wondered why the ~ (tilde) character represents the home directory of a user.
Is there a reason behind this, or is it just because tilde is an infrequently used character?
- 7,039
832
votes
4
answers
611k
views
How to cycle through reverse-i-search in Bash?
In the GNU bash shell, I can type Ctrl + R to search for a matching command previously run. E.g., if I type Ctrl + R and then "grep", it lists my last grep command, and I can hit Enter to ...
- 3,797
830
votes
5
answers
370k
views
What does "--" (double dash / double hyphen) mean?
I have seen -- used in the compgen command.
For example:
compgen -W "foo bar baz" -- b
What is the meaning of the -- in there?
- 30.1k
816
votes
40
answers
975k
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 ...
Owen Fraser-Green
808
votes
13
answers
1.8m
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 ...
- 9,572
795
votes
3
answers
448k
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?
- 14.4k
790
votes
6
answers
415k
views
Difference between nohup, disown and &
What are the differences between
$ nohup foo
and
$ foo &
and
$ foo &
$ disown
- 27.7k
787
votes
6
answers
1.3m
views
Problem running find: missing argument to `-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?
- 32.1k
777
votes
8
answers
1.9m
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 ...
- 8,227
776
votes
6
answers
2.1m
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.
- 11.1k
753
votes
9
answers
222k
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 ...
- 7,657
748
votes
11
answers
3.2m
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?
- 66.5k
736
votes
30
answers
1.3m
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....
- 7,925
728
votes
21
answers
1.0m
views
How to get execution time of a script effectively?
I would like to display the completion time of a script.
What I currently do is -
#!/bin/bash
date ## echo the date at start
# the script contents
date ## echo the date at end
This just show's ...
- 27.9k
718
votes
4
answers
318k
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 ...
- 12.6k
717
votes
24
answers
283k
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 ...
- 16.2k
696
votes
5
answers
235k
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 ...
- 35.6k
685
votes
12
answers
851k
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 ...
- 40.7k
682
votes
9
answers
2.4m
views
How do I zip/unzip on the unix command line?
How can I create and extract zip archives from the command line?
- 7,767
671
votes
11
answers
297k
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....
- 7,091
657
votes
4
answers
502k
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 ...
- 7,489
654
votes
24
answers
729k
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 ...
- 6,689
649
votes
11
answers
1.4m
views
How to append multiple lines to a file
I am writing a bash script to look for a file if it doesn't exist then create it and append this to it:
Host localhost
ForwardAgent yes
So "line then new line 'tab' then text" I think its a ...
- 6,935
641
votes
8
answers
477k
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 ...
- 6,752
637
votes
16
answers
795k
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.
- 66.5k
632
votes
26
answers
682k
views
How to generate a random string?
I would like to generate a random string (e.g. passwords, user names, etc.). It should be possible to specify the needed length (e.g. 13 chars).
What tools can I use?
(For security and privacy ...
- 11.2k
630
votes
16
answers
928k
views
How to clear journalctl
I couldn't find in google any safe way to clear systemd journal. Do anyone know any safe and reliable way to do so?
Let's say I was experimenting with something and my logs got cluttered with various ...
- 6,881
619
votes
4
answers
953k
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 ...
- 45.9k
613
votes
28
answers
935k
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.
- 15.3k
591
votes
10
answers
1.0m
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?
- 5,911
589
votes
11
answers
243k
views
Can less retain colored output?
Can I get less not to monochrome its output?
E.g., the output from git diff is colored, but git diff | less is not.
- 32.1k
588
votes
7
answers
539k
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 ...
- 6,433
586
votes
3
answers
511k
views
What is a bind mount?
What is a “bind mount”? How do I make one? What is it good for?
I've been told to use a bind mount for something, but I don't understand what it is or how to use it.
585
votes
9
answers
702k
views
Can grep output only specified groupings that match?
Say I have a file:
# file: 'test.txt'
foobar bash 1
bash
foobar happy
foobar
I only want to know what words appear after "foobar", so I can use this regex:
"foobar \(\w\+\)"
The parenthesis ...
- 19.1k
582
votes
8
answers
964k
views
How do I 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?
user4069
580
votes
4
answers
1.7m
views
In a bash script, using the conditional "or" in an "if" statement
This question is a sequel of sorts to my earlier question. The users on this site kindly helped me determine how to write a bash for loop that iterates over string values. For example, suppose that ...
- 17.2k
575
votes
12
answers
1.1m
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 ...
- 5,875
575
votes
7
answers
298k
views
What is the difference between the Bash operators [[ vs [ vs ( vs ((?
I am a little bit confused on what do these operators do differently when used in bash (brackets, double brackets, parenthesis and double parenthesis).
[[ , [ , ( , ((
I have seen people use them on ...
- 5,899
572
votes
4
answers
700k
views
recursive mkdir
Is there a linux command that I'm overlooking that makes it possible to do something along the lines of:
(pseudo)
$ mkdir -R foo/bar/zoo/andsoforth
Or is there no alternative but to make the ...
Dr.Dredel