These questions are about Linux in general -- NOT specific to a particular distribution. If the question just happens to be in a Linux environment, please specify your Linux distribution in the body of your question, but do NOT use the /linux tag.

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37
votes
4answers
51k 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 ...
37
votes
5answers
45k 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 ...
36
votes
2answers
40k views

how can I recursively delete empty directories in my home directory? [duplicate]

Possible Duplicate: How to remove all empty directories in a subtree? I create directories very often, scattered over my home directory, and I find it very hard to locate and delete them. I ...
36
votes
6answers
66k views

disable transparent hugepages

We are installing SAP HANA in a RAID machine. As part of the installation step, it is mentioned that, To disable the usage of transparent hugepages set the kernel settings at runtime with echo ...
36
votes
5answers
84k views

How can I find the hardware model in Linux?

I used a system information utility to take the model number of a system, and also of the motherboard. DMI System Manufacturer LENOVO DMI System Product 2306CTO DMI System Version ...
36
votes
3answers
131k views

SSH login with clear text password as a parameter? [duplicate]

I need to login to a user that I've created on a remote host running Ubuntu. I can't use an ssh key because the ssh login will happen from a bash script ran within a server that I won't have access to ...
36
votes
1answer
22k views

Linux: What is a tainted kernel?

Under certain conditions, the Linux kernel may become tainted. For example, loading a proprietary video driver into the kernel taints the kernel. This condition may be visible in system logs, kernel ...
36
votes
7answers
2k views

ZFS under Linux, does it work?

Could I get ZFS to work properly in Linux? Are there any caveats / limitations?
36
votes
5answers
133k views

ssh_exchange_identification: Connection closed by remote host (not using hosts.deny)

I'm not using hosts.allow or hosts.deny, further more SSH works from my windows-machine (same laptop, different hard drive) but not my Linux machine. ssh -vvv root@host -p port gives: OpenSSH_6.6, ...
35
votes
12answers
188k views

How to remove all the files in a directory?

I am trying to remove all files and subdirectories in a directory. I used rm -r to remove all files, but I want to remove all files and subdirectories, excluding the top directory itself. For example,...
35
votes
2answers
47k views

Get the chmod numerical value for a file

In FreeBSD and also in Linux, how can I get the numerical chmod value of a file? For example, 644 instead of -rw-r--r--? I need an automatic way for a Bash script.
35
votes
3answers
34k views

What is stored in /dev/pts files and can we open them?

According to my knowledge, /dev/pts files are created for ssh or telnet sessions.
34
votes
1answer
23k views

Linux LXC vs FreeBSD jail

Are there any notable differences between LXC (Linux containers) and FreeBSD's jails in terms of security, stability & performance? On first look, both approaches look very similar.
34
votes
2answers
90k views

ifconfig command not found

I've just installed CentOS7 as a virtual machine on my mac (osx10.9.3 + virtualbox) .Running ifconfig returns command not found. Also running sudo /sbin/ifconfig returns commmand not found. I am root. ...
34
votes
7answers
47k views

Linux: allowing an user to listen to a port below 1024

I need to allow an user (different from root) to run a server listening on port 80. Is there any way to do this?
34
votes
2answers
1k views

Why and how are some shared libraries runnable, as though they are executables?

On 32-bit Linux systems, invoking this $ /lib/libc.so.6 and on 64-bit systems this $ /lib/x86_64-linux-gnu/libc.so.6 in a shell, provides an output like this: GNU C Library stable release ...
34
votes
2answers
31k views

What is difference between User space and Kernel space?

Is Kernel space used when Kernel is executing on the behalf of the user program i.e. System Call? Or is it the address space for all the Kernel threads (for example scheduler)? If it is the first one,...
34
votes
3answers
60k views

Can I connect to Windows machine from Linux shell?

I can connect to Linux machines from Windows using PuTTY/SSH. I want to do the other way round - connect to a Windows machine from Linux. Is this possible?
33
votes
4answers
2k 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
5answers
56k 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 ...
33
votes
7answers
143k views

How to move all files and folders via mv command

How can I move all files and folders from one directory to another via mv command?
33
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 ...
33
votes
3answers
22k views

How much RAM does the kernel use?

This question is motivated by my shock when I discovered that Mac OS X kernel uses 750MB of RAM. I have been using Linux for 20 years, and I always "knew" that the kernel RAM usage is dwarfed by X (...
33
votes
2answers
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 ...
32
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.
32
votes
3answers
5k views

What is the difference between these commands for bringing down a Linux server?

Reading "What is the difference between Halt and Shutdown commands?" , I generally have an idea what does the command shutdown does, with or without -h/-r options. The "halt" command performs ...
32
votes
3answers
93k views

linux + add X days to date and get new virtual date

I have Linux ( RH 5.3) machine I need to add/calculate 10 days plus date so then I will get new date (expiration date)) for example # date Sun Sep 11 07:59:16 IST 2012 So I need to get ...
32
votes
5answers
25k views

How can I limit the bandwidth used by a process?

I have a CentOS 5.7 server that will be backing up its files nightly. I am concerned that visitors to the various sites that the server hosts will experience degraded performance while the backup is ...
32
votes
4answers
9k 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 ...
32
votes
1answer
84k views

How to see process created by specific user in Unix/linux

I want to see list of process created by specific user or group of user in Linux Can I do it using ps command or is there any other command to achieve this?
32
votes
3answers
3k 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 ...
32
votes
3answers
66k views

Linux: How to find the device driver used for a device?

If my target has one device connected and many drivers for that device loaded, how can I understand what device is using which driver?
31
votes
4answers
15k views

What makes OSX programs not runnable on Linux?

I know there are many differences between OSX and Linux, but what makes them so totally different, that makes them fundamentally incompatible?
31
votes
4answers
59k views

How to make log-rotate change take effect

I followed this link to change log-rotate configuration for RHEL 6 After I made the change to config file, what should I do to let this take effect?
31
votes
2answers
12k views

Can I watch the progress of a `sync` operation?

I've copied a large file to a USB disk mounted on a Linux system with async. This returns to a command prompt relatively quickly, but when I type sync, of course, it all has to go to disk, and that ...
31
votes
4answers
3k 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 ...
31
votes
1answer
29k views

Getting information about a process' memory usage from /proc/pid/smaps

For a given process in /proc/<pid>/smaps, for a given mapping entry what are: Shared_Clean Shared_Dirty Private_Clean Private_Dirty Is Shared_Clean + Shared_Dirty the amount of memory that ...
31
votes
2answers
91k 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 ...
30
votes
3answers
4k 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 ...
30
votes
5answers
32k 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 ...
30
votes
5answers
10k views

Where does uname get its information from?

Where does uname really get its information from? I figure this is something that should be straightforward. Unfortunately, I can't find any header containing just that information. Say someone ...
30
votes
2answers
58k views

Too many levels of symbolic links

I created this file structure: test/src test/firefox When I run this command: ln -s test/src test/firefox I would expect a symbolic link test/firefox/src to be created pointing to test/src, ...
30
votes
5answers
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 ...
30
votes
1answer
21k views

How OOM killer decides which process to kill first?

This answer explains the actions taken by the kernel when an OOM situation is encountered based on the value of sysctl vm.overcommit_memory. When overcommit_memory is set to 0 or 1, overcommit is ...
30
votes
1answer
11k views

What are ConsoleKit and PolicyKit? How do they work?

I've seen that recent GNU/Linux are using ConsoleKit and PolicyKit. What are they for? How do they work? The best answer should explain what kind of problem each one tries to solve, and how they ...
29
votes
5answers
11k views

Understanding UNIX permissions and their attributes

I've never really got how chmod worked up until today. I followed a tutorial that explained a big deal to me. For example, I've read that you've got three different permission groups: owner (u) ...
29
votes
4answers
3k views

Is slash (/) part of the name of Linux root directory?

Is the slash (/) really part of the name of the Linux root directory? Or is it just a symbol for it? What about /etc and so on?
29
votes
2answers
22k views

What is the proper sudoers syntax to add a user?

According to the comments in /etc/sudoers (Fedora 13): ## Syntax: ## ## user MACHINE=COMMANDS ## ## The COMMANDS section may have other options added to it. My two related questions: What ...
29
votes
4answers
163k views

Linux: set date through command line

How to change the system date in Linux ? I want to change: Only Year Only Month Only Date Any combination of above three
29
votes
3answers
4k views

Way to instantly fill up/use up lots of disk space?

On a Linux VM I would like to TEST the NAGIOS monitoring more deeply than just switching off the VM or disconnecting the virtual NIC; I would like to test or "enforce a disk space alarm" through ...