8
votes
6answers
1k views

Detect init system using the shell

This may have more to do with detecting operating systems, but I specifically need the init system currently in use on the system. Fedora 15 now uses systemd, Ubuntu uses Upstart, while others use ...
6
votes
4answers
6k views

Why is my variable being localized in one 'while read' loop, but not in another seemingly similar loop [duplicate]

Why do I get different values for $x from the snippets below? #!/bin/bash x=1 echo fred>junk ; while read var ; do x=55 ; done <junk echo x=$x # x=55 .. I'd expect this result x=1 cat ...
27
votes
3answers
3k views

What does size of a directory mean in output of 'ls -l' command?

What does size of a directory mean in output of ls -l command?
9
votes
5answers
1k views

Why do I need to quote variable for if, but not for echo?

I've read that you need double quotes for expanding variables, e.g. if [ -n "$test" ]; then echo '$test ok'; else echo '$test null'; fi will work as expected, while if [ -n $test ]; then echo ...
7
votes
3answers
8k views

How do I know that my CPU supports 64bit operating systems under Linux?

How can I find out that my CPU supports 64bit operating systems under Linux, e.g.: Ubuntu, Fedora?
5
votes
2answers
323 views

Portability of file descriptor links

I've always wondered this but never took the time to find out, so I'll do so now - how portable is the usage shown here of either /proc/$$/fd/$N or /dev/fd/$N? I understand POSIX guarantees /dev/null, ...
10
votes
1answer
2k views

What does *~ mean?

At the end of a makefile I saw rm -f *~ *.class I understand the *.class, but what's *~?
6
votes
3answers
448 views

Access to original contents of mount point

On my headless NAS I have sdf1 (a flash-card) mounted as / while /home is mounted from lv00 (an LVM volume backed by a software RAID). To be able to access the machine when the RAID fails, I have a ...
5
votes
3answers
21k views

Shell Script for logging into a ssh server

I tried writing a shell script which can do automatic login into a ssh server using password which is mentioned in the script. I have written the following code: set timeout 30 /usr/bin/ssh -p 8484 ...
1
vote
2answers
2k views

df says I have 20G more disk space used than du. Why? [duplicate]

I used du to list all folders and sort by size, the results simply doesn't add up to how much disk space is used(using df). There's about 20G in discrepency, why? [root@xxx lib]# du --max-depth=1 -h ...
5
votes
1answer
148 views

How to allow to run su instantly after I added the user to the appropriate group

I have the su executable with the following permissions: bash-4.2# ls -la /bin/su -rws--s--- 1 root wheel 59930 Sep 14 2012 ./su When I am logged in as a user, not in the wheel group and try to ...
5
votes
3answers
355 views

When you type “ls -a”, what is the significance of “.” and “..”?

Whenever you type ls -a into the command prompt, you usually get all of your folders, files, and then you see that the first two entries are . and .. Just curious, but what is the significance of ...
5
votes
1answer
419 views

LoggedFS configuration file syntax

What is the syntax of the LoggedFS configuration file? The official documentation only had usage instructions for the loggedfs command and a configuration file example. Ok, it's XML, but what are ...
4
votes
2answers
714 views

CP: max source files number arguments for copy utility

Consider that there are countless number of files under /src/ cp /src/* /dst/ How many files cp will successfully process?
4
votes
2answers
290 views

`find` with multiple `-name` and `-exec` executes only the last matches of `-name`

When I'm using find . -type f -name "*.htm*" -o -name "*.js*" -o -name "*.txt" it finds all the types of file. But when I add -exec at the end: find . -type f -name "*.htm*" -o -name "*.js*" -o ...
112
votes
4answers
17k views

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

Why are there so many places to put a binary in Linux? There are atleast these five: /bin/ /sbin/ /usr/bin/ /usr/local/bin/ /usr/local/sbin/ And on my office box, I do not have write permissions ...
69
votes
1answer
74k views

How to set default file permissions for all folders/files in a directory?

I want to set a folder such that anything created within it (directories, files) inherit default permissions and group. Lets call the group "media". And also, the folders/files created within the ...
58
votes
9answers
4k views

Tips for putting ~ under source control

I want to put my home directory (~) under source control (git, in this case), as I have many setting files (.gitconfig, .gitignore, .emacs, etc.) in there I would like to carry across machines, and ...
158
votes
22answers
83k views

Repeat a Unix command every x seconds forever

There's a builtin 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 ...
60
votes
17answers
6k views

Where should I put software I compile myself?

I need to compile some software on my Fedora machine. Where's the best place to put it so not to interfere with the packaged software?
31
votes
7answers
5k views

Linux tools to treat files as sets and perform set operations on them

Does anyone know of any linux tool specifically designed to treat files as sets and perform set operations on them? Like difference, intersection, etc?
47
votes
10answers
17k views

how do you sort du output by size?

How do you sort du -sh /dir/* by size? I read one site that said use | sort -n but that's obviously not right. Here's an example that is wrong. [~]# du -sh /var/* | sort -n 0 /var/mail 1.2M ...
20
votes
5answers
14k views

Split pages in pdf

I have a scanned pdf file which has scanned two pages on one virtual page (page in pdf file). The resolution is with good quality. The problem is I have to zoom when reading and drag from left to the ...
22
votes
2answers
13k views

Do the parent directory's permissions matter when accessing a subdirectory?

If I have a root folder with some restrictive permission, let's say 600, and if the child folders/files have 777 permission will everybody be able to read/write/execute the child file even though the ...
59
votes
4answers
16k views

Why hard links not allowed to directories in UNIX/Linux

I read in text books that UNIX/Linux doesn't allows hard links to directories but soft links do. Is it because, when we have cycles and if we create hardlinks, and after some time we delete the ...
34
votes
3answers
12k views

What is the difference between Halt and Shutdown commands?

What is the difference between the halt and shutdown commands?
37
votes
6answers
15k views

Different linux distros sharing the same /home folder?

What is the best way to share the same /home directories between different linux distribution? I mean, I want to have both, say, Fedora and Arch, and I want to find my files at home no matter which ...
35
votes
6answers
3k views

Can I configure my shell to print STDERR and STDOUT in different colors?

I want to set my terminal up so stderr is printed in a different color than stdout; maybe red. This would make it easier to tell the two apart. Is there a way to configure this in .bashrc? If not, is ...
22
votes
4answers
13k views

List packages by installation date

How can I list installed packages by installation date? I installed a lot of stuff to compile a certain piece of code, and I want to get a list of the required packages, which are the ones I installed ...
15
votes
2answers
3k views

Measure pipe throughput in the shell

There is a shell command that allows to measure how fast the data goes through it, so you can measure the speed of output of commands in a pipe. So instead of: $ somecommand | anothercommand you ...
45
votes
3answers
2k views

How do the internals of sudo work?

How does sudo work internally? How is it possible that it can become root without having the root password, unlike su? What syscalls, etc. are involved in the process? And why is however sudo does it ...
43
votes
4answers
36k views

Limit memory usage for a single Linux process

I'm running pdftoppm to convert a user-provided PDF into a 300DPI image. This works great, except if the user provides an PDF with a very large page size. pdftoppm will allocate enough memory to ...
33
votes
4answers
46k views

How to reload udev rules without reboot?

How should one reload udev rules, so that newly created one can function? I'm running Arch Linux, and I don't have a udevstart command here. Also checked /etc/rc.d, no udev service there.
30
votes
3answers
14k views

What does “LC_ALL=C” do?

What does the C value for LC_ALL do in Unix-like systems? I know that it forces the same locale for all aspects but what does C do?
28
votes
7answers
8k views

A tool for automatically applying RandR configuration when external display is plugged in

is there a tool which enables one to: remember current RandR configuration (position, orientation, resolution etc) on per-monitor basis, automatically apply last known good configuration as soon as ...
12
votes
5answers
36k views

How can I read line by line from a variable in bash?

I have a variable which contains multiline output of a command. What's the most effecient way to read the output line by line from the variable? For example: jobs="$(jobs)" if [ "$jobs" ]; then ...
19
votes
5answers
15k views

How to find creation date of file?

I want to find out the creation date of particular file, not modification date or access date. I have tried with ls -ltrh and stat filename.
12
votes
5answers
11k views

Show only stderr on screen but write both stdout and stderr to file

How can I use BASH magic to achieve this? I want to only see stderr output on the screen, but I want both stdout and stderr to be written to a file. Clarification: I want both stdout and stderr to ...
7
votes
5answers
10k views

How to create a DEB file manually?

I want to create a DEB file manually. I would like to just provide a folder which contains data to install, and a script to be executed after installation. Is this possible?
29
votes
7answers
10k views

What is the difference between symbolic and hard links?

When would you use one over the other?
27
votes
5answers
22k views

How to reconnect a logically disconnected USB device?

It is possible for a USB storage device to become logically disconnected: the device is still plugged in, but is invisible from the operating system (e.g. it's not listed under /proc/bus/usb). Maybe ...
20
votes
10answers
5k views

How can I reliably get the operating system's name?

Say I am logged into a remote system, how can I know what it's running? On most modern Linuxes (Linuces?), you have the lsb_release command: $ lsb_release -ic Distributor ID: LinuxMint Codename: ...
11
votes
6answers
8k views

How to make a process invisible to other users?

How could you launch a process and make it invisible to the top command? The process is started by a normal user (not root), and should not be visible to other normal users.
11
votes
2answers
3k views

How to change previous/next word shortcut in bash?

How do I configure Ctrl-Left and Ctrl-Right as previous/next word shortcuts for bash (currently alt-b and alt-f)?
10
votes
2answers
39k views

Can I resize the root partition without uninstalling and reinstalling Linux (or losing data)?

I have started using a machine that has both Debian and Windows 7 installed. However, after installing some programs I started getting a message that there is not enough space. I knew that the system ...
18
votes
1answer
510 views

How do keyboard input and text output work?

Suppose I press the A key in a text editor and this inserts the character a in the document and displays it on the screen. I know the editor application isn't directly communicating with the hardware ...
16
votes
2answers
3k views

How to blacklist a correct bad RAM sector according to MemTest86+ error indication?

MemTest86+ (the version included with Ubuntu 13.04) says Failing address: 002f796c48 - 759.5 MB What should I specify in the memmap kernel parameter to bypass this area? I've tried running ...
27
votes
5answers
5k views

Why do /usr and /tmp directories for Linux miss vowels in their spellings?

I have often started to think about this but never found a good answer. Why are these two Unix directories not /user and /temp instead? All the other directories under root seem to be exactly what ...
18
votes
2answers
2k views

Display stuff below the prompt at a shell prompt?

Lets's say my prompt looks like this (the _ represents my cursor) ~ % _ Is there any way I could make it look like this ~ % _ [some status] The question was originally about zsh, but now has ...
17
votes
8answers
788 views

How to tell what type of filesystem you're on?

Is there a command to tell what type of filesystem you're using?

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