Questions specifically about Linux, as opposed to Unix-like systems in general, or to questions about a specific distribution or program.

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35
votes
11answers
17k views

How do I find how long ago a Linux system was installed?

How can I find the time since a Linux system was first installed, provided that nobody has tried to hide it?
35
votes
4answers
7k views

How can I mount a block device from one computer to another via the network as a block device?

Is it possible to export a block device such as a DVD or CDROM and make it so that it's mountable on another computer as a block device? NOTE: I'm not interested in doing this using NFS or Samba, I ...
34
votes
2answers
20k views

Why is swappiness set to 60 by default?

I just read some stuff about swappiness on Linux. I don't understand why the default is set to 60. According to me this parameter should be set to 10 in order to reduce swap. Swap is on my hard ...
34
votes
2answers
53k views

timestamp, modification time, and created time of a file

I just know that ls -t and ls -f give different sorting of files and subdirectories under a directory. What are the differences between timestamp, modification time, and created time of a file? How ...
33
votes
4answers
1k views

Does bash open files in O_APPEND when using “>>” on linux?

If we use echo 1234 >> some-file then Documentation says that the output is appended. My guess is that, if some-file does not exist, then O_CREAT will make a new file. If > was used, then ...
33
votes
6answers
48k views

Uploading directories with sftp?

I'm having some trouble uploading directories(which contain other directories a few levels deep) by sftp. I realize I could work around this by gzipping, but I don't see why that's necessary. Anyway, ...
33
votes
5answers
19k views

Difference Between cp -r and cp -R (copy command)

cp- r is meant to copy files recursively, and cp -R for copying directories recursively. But I've checked, and both appear to copy both files and directories, the same thing. So, what's the difference ...
33
votes
12answers
51k views

Efficiently delete large directory containing thousands of files

We have an issue with a folder becoming unwieldy with hundreds of thousands of tiny files. There are so many files that performing rm -rf returns an error and instead what we need to do is something ...
33
votes
2answers
5k views

Why is video tearing such a problem in Linux?

I've used many variants of Linux(mostly Debian derivatives) for over a decade now. One problem that I haven't seen solved satisfactorily is the issue of horizontal tearing, or Vsync not being ...
33
votes
2answers
11k views

What is this new /run filesystem?

I just ran df -h a minute ago and noticed a filesystem has been added that I'm not familiar with. Does anyone know why /run exists? Is this something that's been added by the kernel? By Arch Linux? ...
33
votes
4answers
34k views

Creating a ram disk on Linux

I have a machine with 62GB of RAM, and a trunk that's only 7GB, so I thought I would create a RAM disk and compile there. I am not a Linux expert. I found instructions on the internet to create the ...
33
votes
2answers
30k views

Difference between pts and tty

Possible Duplicate: What is the exact difference between a 'terminal', a 'shell', a 'tty' and a 'console'? I always see pts and tty when I use the who ...
32
votes
9answers
15k views

Why put things other than /home to a separate partition?

So recently a Debian 5.0.5 installer offered me to have separate /usr, /home, /var and /tmp partitions (on one physical disk). What is the practical reason for this? I understand that /home can be ...
32
votes
4answers
30k views

How to display meminfo in megabytes in top?

Sometimes it is not comfortable to see meminfo in kilobytes while you have several gigs of RAM. In Linux it looks like that: And here is how it looks in Mac OS X: Is there a way to display ...
32
votes
11answers
25k 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: ...
32
votes
2answers
123k views

Compress a folder with tar?

I'm trying to compress a folder (/var/www/) to ~/www_backups/$time.tar where $time is the current date. This is what I have: cd /var/www && sudo tar -czf ~/www_backups $time" I am ...
32
votes
11answers
12k 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 ...
32
votes
7answers
22k views

Linux Kernel: Good beginners' tutorial [closed]

I'm interested in modifying the kernel internals, applying patches, handling device drivers and modules, for my own personal fun. Is there a comprehensive resource for kernel hacking, intended for ...
32
votes
1answer
1k views

What happens when Ctrl + Alt + F<Num> is pressed?

I am looking for an explanation of what happens in Linux when this key combination is pressed to change the current terminal. In particular, what software component intercepts this key combination and ...
31
votes
10answers
45k views

List partition labels from the command line

Is there a command that will list all partitions along with their labels? sudo fdisk -l and sudo parted -l don't show labels by default. EDIT: (as per comment below) I'm talking about ext2 labels - ...
31
votes
5answers
32k 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 ...
30
votes
7answers
39k views

Correctly determining memory usage in Linux

I'm a bit confused on some of the results I am seeing from "ps" and "free". On my server, this is the result of "free -m" [root@server ~]# free -m total used free shared ...
30
votes
3answers
2k views

Can a bash script be hooked to a file?

I want a script to sleep unless a certain file is modifed/deleted (or a file created in a certain directory, or ...). Can this be achieved in some elegant way? The simplest thing that comes to my mind ...
30
votes
3answers
12k views

Shell: how to go to the beginning of line when you are inside a screen?

I am inside a screen (screen -Ra). I have a long command, and I am at the end. Instead of keeping the left arrow, how can you go to the beginning of the line? CTRL-A works when I am in a normal ...
29
votes
3answers
3k views

Does grep use a cache to speed up the searches?

I have noticed that subsequent runs of grep on the same query (and also a different query, but on the same file) are much faster than the first run (the effect is easily noticeable when searching ...
29
votes
3answers
4k views

Can TCP provide more than 65535 ports?

Is it possible to setup a Linux system so that it provides more than 65,535 ports? The intent would be to have more than 65k daemons listening on a given system. Clearly there are ports being used ...
29
votes
2answers
5k views

Will Linux start killing my processes without asking me if memory gets short?

I was running a shell script with commands to run several memory-intensive programs (2-5 GB) back-to-back. When I went back to check on the progress of my script I was surprised to discover that some ...
29
votes
5answers
25k views

How can I tell what version of linux I'm using?

Often times I will ssh into a new client's box to make changes to their website configuration without knowing much about the server configuration. I have seen a few ways to get information about the ...
29
votes
1answer
2k views

Oldest binary working on Linux?

In a discussion on backwards-compatibility in Linux kernel and GUI ABIs, Alan Cox notes that "my 3.6rc kernel will still run a Rogue binary built in 1992. X is back compatible to apps far older than ...
28
votes
5answers
36k views

How to easily build your own Linux Distro? [duplicate]

I wanted to have a go at creating my very own Linux Distribution. Could you suggest some nice and easy-to-follow tutorials (preferably text based and not videos). I have heard something about Arch ...
28
votes
7answers
6k views

Block network access of a process?

Is it possible to block the (outgoing) network access of a single process?
28
votes
4answers
1k views

Execution of possibly harmful program on Linux

I'm writing a program that will test programs written by students. I'm afraid that I can't trust them and I need to make sure that it won't end up badly for the computer running it. I was thinking ...
27
votes
2answers
2k views

Why does a software package run just fine even when it is being upgraded?

Say I am running a software, and then I run package manager to upgrade the software, I notice that Linux does not bring down the running process for package upgrade - it is still running fine. How ...
27
votes
4answers
29k views

What's the best way to join files again after splitting them?

If I have a large file and need to split it into 100 megabyte chunks I will do split -b 100m myImage.iso That usually give me something like xaa xab xac xad And to get them back together I have ...
27
votes
5answers
71k views

Can I set up system mail to use an external SMTP server?

Is it possible to set up system mail on a linux box to be sent via a different smtp server - maybe even with authentication? If so, how do I do this? If that's unclear, let give an example. If I'm at ...
27
votes
3answers
5k views

Why do some Linux distributions still have /dev/ttyS0, ttyS1, etc., even though newer computers don't have such a serial port?

Many new laptop and desktop computers do not have 9-pin/25-pin serial ports. Why do many Linux distributions still contain /dev/ttyS0, dev/ttyS1 device files? Since udev can create the device files ...
27
votes
2answers
112k views

How to get the complete and exact list of mounted filesystems in Linux?

I usually use mount to check which filesystems are mounted. I also know there is some connection between mount and /etc/mtab but I'm not sure about the details. After reading How to check if /proc/ is ...
26
votes
9answers
2k views

Uninstalling programs on Linux

I've been using Windows and Mac OS for the past 5 years and now I'm considering to use Linux on a daily basis. I've installed Ubuntu on a virtual machine and trying to understand how I can use Linux ...
26
votes
2answers
74k 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?
26
votes
6answers
4k views

Why isn't there a truly unified package manager for Linux?

Why isn't there a unified package manager that acts as an interface between the end-user and the underlying low-level package manager (apt, yast, pacman, etc.)? Is it hard to do and therefore not ...
26
votes
3answers
12k views

A list of available DBus services

Is there such a thing as list of available DBus services? I've stumbled upon a few (like those provided by NetworkManager, Rhythmbox, Skype, HAL). I wonder if I can find a rather complete list of ...
26
votes
6answers
60k views

How to list all files in the size order

I would like to list all files in the order of big to small in size and the files could be present anywhere in a certain folder.
26
votes
7answers
7k views

Force directory to always be in cache

I've been testing out different methods to improve the time it takes to compile my entire c++ project. Currently it takes ~5 minutes. I experimented with distcc, ccache, and others. Recently, I ...
26
votes
5answers
13k views

What is the difference between kernel drivers and kernel modules?

When I do a lspci -k on my Kubuntu with a 3.2.0-29-generic kernel I can see something like this: 01:00.0 VGA compatible controller: NVIDIA Corporation G86 [Quadro NVS 290] (rev a1) Subsystem: ...
26
votes
12answers
3k views

How can I tweak my Linux desktop to be more responsive?

I have the experience that Linux works fine until the physical memory is exhausted. As soon as swap space is used the performance is severely degraded and the GUI becomes unresponsive. This problem ...
26
votes
2answers
64k views

What user should apache and PHP be running as? What permissions should /var/www files have?

I just spun up an Ubuntu 11.10 box and then ran apt-get install apache2 php5 to install apache2 and PHP 5 on the box. Now it is functioning as a "web server" and it loads the "It Works!" page. Now I'm ...
25
votes
1answer
2k views

Were all Unix commands re-written in Linux?

I would like to know which commands were re-written for Linux and which were retained from Unix? I'm new to Linux.
25
votes
4answers
30k views

How can I update to a newer version of Git using apt-get?

I've just set up a new machine with Ubuntu Oneiric 11.10 and then run apt-get update apt-get upgrade apt-get install git Now if I run git --version it tells me I have git version 1.7.5.4 but on my ...
25
votes
5answers
20k views

Why does Linux allow ‘init=/bin/bash’?

I recently found out that if I edit GRUB before booting and I add rw init=/bin/bash I end up with a root shell. Being in a condition that I want to understand everything I would like to know why this ...
25
votes
4answers
1k views

What exactly does init do?

I am creating a linux distro and now I need an init program. I can code in c really well and I know quite a bit about linux (not much but I've been using arch linux for development for 4 years), so I ...