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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22
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3answers
1k views

How can I shutdown a RHEL server at 06:45 tomorrow morning?

I just received notification that our site has a power outage tomorrow morning. I am a Windows admin but I have to cover for our Linux admin who's not around until tomorrow evening. I need to ...
22
votes
3answers
2k 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 ...
22
votes
6answers
10k views

How do I correlate /dev/sd devices to the hardware they represent?

A drive is beginning to fail and I only know the device by its /dev/sdb device file designation. What are the ways that I can use to correlate that device file to an actual hardware device to know ...
22
votes
3answers
2k views

When is a reboot required?

Apart from upgrading the kernel, are there any changes to a Linux system that require a reboot? I know there are situations where a reboot makes things easier, but are there any that cannot be ...
22
votes
4answers
25k 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 ...
22
votes
4answers
3k views

How to find the driver (module) associated with a device on Linux?

On Linux, given: a device, for example /dev/sda, and its major and minor numbers, for example 8, 0, how can I know which module / driver is "driving" it? Can I dig into /sys or /proc to ...
22
votes
3answers
801 views
+300

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 ...
22
votes
2answers
4k views

When was a process started

To know when was a process started, my first guess was to check the time when /proc/<pid>/cmdline was written/modified the last time. ps also shows a START field. I thought both of these ...
22
votes
2answers
95k 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 ...
22
votes
7answers
5k views

How can I use DD to migrate data from an old drive to a new drive?

I am upgrading the internal SATA hard drive on my laptop from a 40G drive to a 160G drive. I have a Linux/Ubuntu desktop which has a SATA card. I would actually like to do the same thing for a couple ...
22
votes
3answers
2k views

How can I set the processor affinity of a process on Linux?

The question is all in the title: How can I set the processor affinity of a process on Linux?
22
votes
3answers
14k views

What are pseudo terminals (pty/tty)?

This might be really basic question but I want to understand it thoroughly. What is a pseudo terminal? (tty/pty) Why do we need them? How they got introduced and what was the need for it? Are they ...
22
votes
4answers
3k views

Kernel Hacking Environment

I have been working in embedded OS like uCOS, ThreadX. While I have coded apps in Linux, now I’m planning to start learning Linux Kernel. I have few questions regarding the environment. Which is ...
22
votes
1answer
6k views

Why doesn't Linux use the IANA Ephemeral port range?

According to Wikipedia The Internet Assigned Numbers Authority (IANA) suggests the range 49152 to 65535 for dynamic or private ports. Many Linux kernels use the port range 32768 to 61000. Even ...
21
votes
4answers
43k views

linux: How can I view all UUIDs for all available disks on my system?

My /etc/fstab contains this: # / was on /dev/sda1 during installation UUID=77d8da74-a690-481a-86d5-9beab5a8e842 / ext4 errors=remount-ro 0 1 There are several other disks on ...
21
votes
3answers
6k views

Why does Linux use a swap partition rather than a file?

It seems to me a swap file is more flexible.
21
votes
2answers
3k views

Where is the fork() on the fork bomb :(){ :|: & };:?

Warning: Running this command in most shells will result in a broken system that will need a forced shutdown to fix I understand the recursive function :(){ :|: & };: and what it does. But I ...
21
votes
11answers
19k views

Linux replacement for Apple Keynote software?

I am trying to migrate from Mac OS X to a Linux distribution, maybe/probably Ubuntu. One of my favorite applications for the Mac was Apple Keynote, which makes amazing sideshow presentations. Is ...
21
votes
3answers
26k 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 ...
21
votes
4answers
1k views

Is there a reason why 'owner' permissions exist? Aren't group permissions enough?

I think I rather understand how file permissions work in linux. However, I don't really understand why they are split into three levels and not into two. I'd like the following issues answered: Is ...
21
votes
4answers
9k views

What doesn't need defragmentation? Linux or the ext2 ext3 FS?

Why don't you have to defrag a Linux system? Because it's using the ext2/ext3 file system or because it's Linux? That's relevant, because a have a double boot system (W7 / Ubuntu) and a common ...
21
votes
3answers
4k views

What does the vm.swappiness parameter really control?

Per the kernel documentation: This control is used to define how aggressive the kernel will swap memory pages. Higher values will increase aggressiveness, lower values decrease the amount of swap. ...
21
votes
2answers
14k views

How to colorize output of ls ?

I'm running CentOS in Linux text mode. When I run the command ls /usr/, the output is too hard to read (dark blue on black). How can I change the text coloring?
21
votes
3answers
9k 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 ...
21
votes
4answers
723 views

Making Linux read swap back into memory

The Linux kernel swaps out most pages from memory when I run an application that uses most of the 16GB of physical memory. After the application finishes every action (typing commands, switching ...
21
votes
2answers
27k 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?
20
votes
4answers
21k views

How to attach terminal to detached process?

I have detached a process from my terminal, like this: $ process & That terminal is now long closed, but process is still running and I want to send some commands to that process's stdin. Is ...
20
votes
6answers
21k views

How to replace one char with another in all filenames of the current directories?

How do you rename all files/subdirs in the current folder? Lets say, I have many files and subdirs that are with spaces and I want to replace all the spaces with an underscore. File 1 File 2 File 3 ...
20
votes
4answers
25k 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 ...
20
votes
5answers
3k 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 ...
20
votes
3answers
54k views

What is the best text-mode browser? [closed]

I am looking for one that is updated frequently and has support for many things. Please also state how to install it.
20
votes
3answers
10k views

File system compatible with all OSes?

I use Linux and Mac OS X on a regular basis, and sometimes I have to use Windows. I need to use a flash drive on all three, and I need a filesystem that will work well on all of them. None of the ...
20
votes
3answers
13k views

How to Determine the Amount of RAM Slots In Use?

I forgot how many RAM modules are installed on my laptop. I do not want to unscrew it but want to look it up on the console. How do I gather this information?
20
votes
6answers
7k views

How does Linux kernel compare to microkernel architectures?

I read once that one advantage of a microkernel architecture is that you can stop/start essential services like networking and filesystems, without needing to restart the whole system. But considering ...
20
votes
6answers
25k 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?
20
votes
1answer
26k views

How is a message queue implemented in the Linux kernel?

I would like to know how Message Queues are implemented in the Linux Kernel.
20
votes
2answers
3k views

How do I make a file NOT modifiable?

While logged in, I can do the following: mkdir foo touch foo/bar chmod 400 foo/bar chmod 500 foo Then I can open vim (not as root), edit bar, force a write with w!, and the file is modified! How ...
20
votes
1answer
17k 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 ...
20
votes
2answers
5k views

How do I remove a file with no permissions?

A hacker has dropped a file in my tmp dir that is causing issues. Nothing malicious except creating GB's of error_log entries because their script is failing. However, the file they are using to ...
20
votes
3answers
71k 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, ...
20
votes
6answers
5k views

What's the most “correct” mount point for a permanent NTFS partition?

I have an NTFS partition (containing a Windows installation from which I dual boot) that I would like to permanently mount from my Linux installation. Problem is, I can't figure out what the ...
20
votes
2answers
50k views

How can I change a user's default group in Linux?

Being new to Linux administration, I'm a little confused about the following commands: useradd usermod groupadd groupmod I've just finished reading the user administration book in the Linux/Unix ...
20
votes
4answers
21k views

How to record Skype video calls on Linux?

I'd like to conduct recorded video interviews with Skype and am looking for a reliable tool to accomplish that. Is there anything out there that's not slow or buggy? I'm running (K)Ubuntu.
19
votes
5answers
3k 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) ...
19
votes
5answers
8k views

What is the difference between ls and l?

I accidentally typed l instead of ls today and found that the command still printed a list of the files in my current directory. Trying l --help brings up the help file for ls suggesting that l is ...
19
votes
7answers
20k views

Disable screen blanking on text console

I'm running linux clusters, mostly on SLES10. The servers are mostly blades, accessed via remote console. There is a real console in the server room, but switched off. I would like to disable the ...
19
votes
8answers
3k views

The most universal scripting language for Linux is?

We are writing scripts for Linux systems, there has been some debate over what would be the most universally Linux present scripting language to use. Bash, SH, Posix? What?
19
votes
5answers
16k 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 ...
19
votes
2answers
79k views

How can get a list of all scheduled cron jobs on my machine?

My sysadmin has set up a bunch of cron jobs on my machine. I'd like to know exactly what is scheduled for what time. How can I get that list?
19
votes
4answers
22k views

What is a spinlock in Linux?

I would like to know about spinlocks in detail? Could someone explain that to me?