Questions specifically about Linux but not specific to a particular distribution. If the question could apply to any Unix-like system, specify your Linux distribution in the body of your question but do not use the /linux tag.

learn more… | top users | synonyms

291
votes
9answers
116k 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 ...
188
votes
3answers
95k views

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 ...
131
votes
16answers
181k 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.
126
votes
6answers
42k views

Is Linux a Unix?

So, there are lots of different versions of Unix out there: HP-UX, AIX, BSD, etc. Linux is considered a Unix clone rather than an implementation of Unix. Are all the "real" Unices actual descendants ...
123
votes
21answers
110k views

How can I get my external IP address in bash?

I need to find my external IP address from a bash script. At the moment I use this function: myip () { lwp-request -o text checkip.dyndns.org | awk '{ print $NF }' } But it depends on ...
115
votes
1answer
238k views

How do you empty the buffers and cache on a Linux system?

Prior to doing some benchmarking work how would one free up the memory (RAM) that the Linux Kernel is consuming for its buffers and cache?
114
votes
1answer
7k views

How is Mono magical?

I'm learning C#, so I made a little C# program that says Hello, World!, then compiled it with mono-csc and ran it with mono: $ mono-csc Hello.cs $ mono Hello.exe Hello, World! I noticed that when I ...
99
votes
3answers
111k views

Why do I need a tty to run sudo if I can sudo without a password?

I have configured sudo to run without a password, but when I try to ssh 'sudo Foo", I still get sudo: sorry, you must have a tty to run sudo. Why does this happen and how can I work around it?
96
votes
8answers
195k views

How can I monitor disk io?

I'd like to do some general disk io monitoring on a debian linux server. What are the tools I should know about that monitor disk io so I can see if a disk's performance is maxed out or spikes at ...
95
votes
1answer
114k views

In Linux “top” command what are us, sy, ni, id, wa, hi, si and st (for CPU usage)?

When I issue $ top in linux, I get a result similar to this (see here). One of the lines has CPU usage information represented like this: Cpu(s): 87.3%us, 1.2%sy, 0.0%ni, 27.6%id, 0.0%wa, ...
93
votes
4answers
54k views

What do the flags in /proc/cpuinfo mean?

How can I tell whether my processor has a particular feature? (64-bit instruction set, hardware-assisted virtualization, cryptographic accelerators, etc.) I know that the file /proc/cpuinfo contains ...
93
votes
9answers
44k views

Why would someone choose FreeBSD over Linux? [closed]

Why would someone choose FreeBSD over Linux? What are the advantages of FreeBSD compared to Linux? (My shared hosting provider uses FreeBSD.)
91
votes
4answers
57k views

How do I read from /proc/$pid/mem under Linux?

The Linux proc(5) man page tells me that /proc/$pid/mem “can be used to access the pages of a process's memory”. But a straightforward attempt to use it only gives me $ cat /proc/$$/mem ...
90
votes
12answers
370k views

How do I find out what hard disks are in the system?

I need to know what hard disks are available, including ones that aren't mounted and possibly aren't formatted. I can't find them in dmesg or /var/log/messages (too much to scroll through). I'm hoping ...
87
votes
2answers
19k views

Why do we use su - and not just su?

I don't understand why su - is preferred over su to login as root.
85
votes
12answers
268k views

How do I set my DNS when resolv.conf is being overwritten?

Most of the info I see online says to edit /etc/resolv.conf, but any changes I make there just get overridden. $ cat /etc/resolv.conf # Dynamic resolv.conf(5) file for glibc resolver(3) generated by ...
80
votes
3answers
14k views

Why is the root directory denoted by a / sign?

I have done some research about this on Google, but the results were cloudy. Why is the / sign used to denote the root directory. Are there any solid reasons behind it?
80
votes
6answers
6k views

How are “/dev” Linux files created?

There are special files in Linux that are not really files... The most notable and clear examples of these are in the dev folder, "files" like: /dev/null - Ignores anything you write to the file ...
76
votes
13answers
13k views

What is the benefit of compiling your own linux kernel?

What benefit could I see by compiling a Linux kernel myself? Is there some efficiency you could create by customizing it to your hardware?
75
votes
9answers
6k views

Does `sl` ever show the current directory?

For those out of the loop, sl is a humourous command line tool that is meant to trip people up if they mistype ls. When invoked it prints a Steam Locomotive. For example: ( ...
73
votes
1answer
214k 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 ...
70
votes
7answers
107k views

What to do when a linux desktop freezes?

I'm a Windows guy, dual booted recently, and now I'm using Linux Mint 12 When a Windows desktop freezes I refresh, or if I am using a program I use alt + F4 to exit the program or I can use ctrl + ...
66
votes
16answers
70k views

Determine the size of a block device

How can I find out the size of a block device, such as /dev/sda? Running ls -l gives no useful information.
64
votes
10answers
49k views

How can I edit multiple files in VIM?

I know I can open multiple files with vim by doing something like vim 2011-12*.log, but how can I switch between files and close the files one at a time? Also, how can I tell the file name of the ...
61
votes
5answers
43k views

What are high memory and low memory on Linux?

I'm interested in the difference between Highmem and Lowmem: Why is there such a differentiation? What do we gain by doing so? What features does each have?
61
votes
5answers
42k views

Can I configure my Linux system for more aggressive file system caching?

I am neither concerned about RAM usage (as I've got enough) nor about losing data in case of an accidental shut-down (as my power is backed, the system is reliable and the data are not critical). But ...
60
votes
8answers
57k views

How do I know if a partition is ext2, ext3, or ext4?

I just formatted stuff. One disk I format as ext2. The other I want to format as ext4. I want to test how they perform. Now, how do I know the kind of file system in a partition?
60
votes
5answers
81k 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 ...
58
votes
10answers
48k views

How do I choose a graphics card for Linux?

I'm building or buying a new Linux system, and I'm trying to select the best graphics card for my needs. How do I go about making this decision? There's dozens of computer-gear review sites which ...
56
votes
2answers
151k 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?
54
votes
6answers
50k 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 ...
54
votes
15answers
6k views

How do you choose a distribution? [closed]

I'm currently looking at putting a Linux (although BSD is still an option) distribution on my old laptop. However, I'm not sure how to wade through all of my options - rolling releases versus not, ...
53
votes
12answers
70k 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 ...
53
votes
2answers
29k views

Kernel inotify watch limit reached

I'm currently facing a problem on a linux box where as root I have commands returning error because inotify watch limit has been reached. # tail -f /var/log/messages [...] tail: cannot watch ...
53
votes
3answers
66k views

How can I use the “mail” command?

I am not great at using the mail command on Linux. How can I get better? I don't even know what program this is. Is it pine? I doubt it. It is in /usr/bin/mail and when I start it is tells me that it ...
52
votes
6answers
47k views

How to know if a disk is an SSD or an HDD

I want to know whether a disk is a solid-state drive or hard disk. lshw is not installed. I do yum install lshw and it says there is no package named lshw. I do not know which version of ...
52
votes
5answers
31k views

Difference between /bin and /usr/bin

I read this up on this website and it doesn't make sense. http://rcsg-gsir.imsb-dsgi.nrc-cnrc.gc.ca/documents/basic/node32.html When UNIX was first written, /bin and /usr/bin physically resided ...
52
votes
7answers
96k 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.
52
votes
1answer
3k views

Diagram of Linux kernel vs. performance tools?

Is there a diagram that shows how the various performance tools such as ip, netstat, perf, top, ps, etc. interact with the various subsystems within the Linux kernel?
52
votes
4answers
3k views

How to compile the C compiler from scratch, then compile Unix/Linux from scratch

Let's say I work for a large services organisation outside the US/UK. We use UNIX and Linux servers extensively. Reading through this article it mentions that it would be easy to insert a backdoor ...
51
votes
11answers
20k views

Is it good to make a separate partition for /boot?

I've seen some people make a separate partition for /boot. What is the benefit of doing this? What problems might I encounter in the future by doing this? Also, except for /home and /boot, which ...
51
votes
3answers
24k views

How do SO (shared object) numbers work?

I'm aware that shared objects under Linux use "so numbers", namely that different versions of a shared object are given different extensions, for example: example.so.1 example.so.2 I understand ...
51
votes
2answers
29k 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 ...
49
votes
7answers
10k views

Can a laptop battery explode while using Linux?

I have a 2013 Retina MacBook Pro, and I really want to install Debian on it. I have the know-how and have had at least three Debian systems before this. I am very knowledgable with the command-line ...
49
votes
11answers
27k views

Easy way to determine virtualization technology

I have command line access to a Linux machine which may or may not be virtualized. I want to determine what kind of virtualization technology it runs on, if any (VMWare, VirtualBox, KVM, OpenVZ, Xen, ...
48
votes
4answers
106k views

What is the difference between reboot , init 6 and shutdown -r now?

I just want to know difference between in reboot init 6 shutdown -r now and which is the safest and the best?
46
votes
11answers
26k views

Recommended reading to better understand Unix/Linux internals [closed]

I've worked on *nix environments for the last four years as a application developer (mostly in C). Please suggest some books/blogs etc. for improving my *nix internals knowledge.
46
votes
4answers
13k 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 ...
46
votes
5answers
34k 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 ...
45
votes
3answers
389k views

How to check OS and version using a Linux command [duplicate]

What is the Linux command to check the server OS and its version? I am connected to the server using shell.