Linux is the generic term for a UNIX-like open source operating system based on the Linux kernel.

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Multiple Linux sysadmins working as root

In our team we have three seasoned Linux sysadmins having to administer a few dozen Debian servers. Previously we have all worked as root using SSH public key authentication. But we had a discussion ...
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7answers
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How to get e-mail from (failed) cron-jobs in Ubuntu?

I create cron-jobs in Ubuntu by placing the executable in one of /etc/cron.{daily,hourly,monthly,weekly}. There are lots of directories starting with cron: kent@rat:~$ ls -ld /etc/cron* drwxr-xr-x 2 ...
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5answers
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How to install/change locale on Debian?

I've written a web application for which the user interface is in Dutch. I use the system's date and time routines to format date strings in the application. However, the date strings that the system ...
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8answers
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How to display certain lines from a text file in Linux?

I guess everyone knows the useful Linux cmd line utilities head and tail. Head allows you to print the first X lines of a file, tail does the same but prints the end of the file. What is a good ...
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6answers
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How do I list loaded Linux module parameter values?

Is there a standard way to list the parameter values of a loaded Linux module? I'm essentially probing for another answer to this Linux kernel module parameters question, because the module I'm ...
28
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5answers
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How passively monitor for tcp packet loss? (Linux)

How can I passively monitor the packet loss on TCP connections to/from my machine? Basically, I'd like a tool that sits in the background and watches TCP ack/nak/re-transmits to generate a report on ...
28
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5answers
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swap partition vs file for performance?

What is better for performance? A partition closer to the inside of the disk will have slower access times, and we must wait for the drive to switch between the OS and swap partitions. On the other ...
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7answers
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How to check the physical status of an ethernet port in Linux?

I want to check if a specified ethX is physically up or down. How do I do that with the command line?
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3answers
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Did a cat /dev/urandom - Broken terminal

Out of curiosity, when your shell character set breaks from doing something like cat /dev/urandom is there a way to fix that in place?
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3answers
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Turn off the Linux OOM killer by default?

The OOM killer on Linux wreaks havoc with various applications every so often, and it appears that not much is really done on the kernel development side to improve this. Would it not be better, as a ...
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14answers
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File Server - Storage configuration: RAID vs LVM vs ZFS something else…?

We are a small company that does video editing, among other things, and need a place to keep backup copies of large media files and make it easy to share them. I've got a box set up with Ubuntu ...
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4answers
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Why Swap is used when plenty of free memory is left?

I have pretty good web (dedicated) server with good memory resource System information Server load 2.19 (8 CPUs) Memory Used 29.53% (4,804,144 of 16,267,652) Swap Used 10.52% ...
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5answers
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What is “-bash: !”: event not found"

Try executing the following under a bash shell echo "Reboot your instance!" On my installation: root@domU-12-31-39-04-11-83:/usr/local/bin# bash --version GNU bash, version 4.1.5(1)-release ...
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7answers
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Reasons to disable / enable SELinux

In the line of this question on StackOverflow and the completely different crowd we have here, I wonder: what are your reasons to disable SELinux (assuming most people still do)? Would you like to ...
27
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8answers
6k views

How do you setup ssh to authenticate using keys instead of a username / password?

How do you setup ssh to authenticate a user using keys instead of a username / password?
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4answers
23k views

How to sort ps output by process start time?

Is there a way to sort ps output by process start time, so newest are either at the top or bottom ? On Linux ? On SysV5 ? On Mac ?
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6answers
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What happens if I delete lost+found

When you create some Linux filesystems like ext3 a 'lost+found' directory is created. According to this files will be placed there if files were damaged from some kind of system crash. What happens ...
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7answers
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Linux: how to restore config file using apt-get/aptitude?

I've occasionally lost my config file "/etc/mysql/my.cnf", and want to restore it. The file belongs to package mysql-common which is needed for some vital functionality so I can't just purge ...
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1answer
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Why does deleting a big file take longer?

My understanding is that running rm on a file simply unlinks it, marking the space as free in the filesystem. It should then follow that deleting one file always takes roughly the same amount of time ...
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2answers
787 views

Why is it bad to have root writing files to a directory not owned by root?

This came up in a comment to another question and I'd love it if someone could explain the reasons for this to me. I suggested having Apache log the errors for a given VHost to a user's home ...
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4answers
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Does anyone really understand how HFSC scheduling in Linux/BSD works?

I read the original SIGCOMM '97 PostScript paper about HFSC, it is very technically, but I understand the basic concept. Instead of giving a linear service curve (as with pretty much every other ...
26
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14answers
13k views

How do I find out what version of Linux is running?

Sometimes your scripts need to behave differently on different Linux's. How can I determine which version of Linux a script is running on?
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9answers
8k views

How to hide a password passed as command line argument?

I'm running a software daemon that requires for certain actions to enter a passphrase to unlock some features which looks for example like that: $ darkcoind masternode start <mypassphrase> ...
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5answers
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Linux server out of space

I have been asked this question in two consecutive interviews, but after some research and checking with various systems administrators I haven't received a good answer. I am wondering if somebody can ...
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9answers
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Disk full, du tells different. How to further investigate?

I have a SCSI disk in a server (hardware Raid 1), 32G, ext3 filesytem. df tells me that the disk is 100% full. If I delete 1G this is correctly shown. However, if I run a du -h -x / then du tells me ...
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4answers
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Check if port is open or closed on a Linux server?

How can I check if a port is open or closed on a Linux server?
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3answers
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Linux command to inspect TXT records of a domain

Is there a linux shell command that I can use to inspect the TXT records of a domain?
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6answers
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shutdown: What is difference between “Power Off” and “Halt”?

With your typical Linux shutdown command, what is the difference between halting the system and powering off the system?
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3answers
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Linux - How can I see what's waiting for disk IO

I have a server that has a really high load. Nothing is jumping out at me in terms of CPU usage, and it's not swapping. I think it's cause some processes are waiting for disk IO, and I want to see ...
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7answers
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Amazon Linux vs. Ubuntu for Amazon EC2 [closed]

I'm setting up my first website on Amazon EC2, and I'm trying to decide which distro to use. I've used Redhat and CentOS in the past, but I have no bias towards any system, I just want to use whatever ...
26
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6answers
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How can I prevent a DDOS attack on Amazon EC2?

One of the servers I use is hosted on the Amazon EC2 cloud. Every few months we appear to have a DDOS attack on this sever. This slows the server down incredibly. After around 30 minutes, and ...
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4answers
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Where is the statement of deprecation of ifconfig (on linux)?

A lot of people is stating that the ifconfig command is deprecated in favor of the ipone (on linux at least). This is often used as an argumentation to switch from ifconfig to ip (see some comment ...
26
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3answers
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How can I allow one user to su to another without allowing root access?

I'd like to allow certain users to su to another user account without having to know that account's password, but not allow access to any other user account (i.e. root). For instance, I'd like to ...
26
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2answers
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I have a keypair. How do I determine the key length?

Using OpenSSL from the command line in Linux, is there some way to examine a key (either public or private) to determine the key size?
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6answers
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Top-like tool for IP traffic [closed]

I need to keep watch on how much bandwidth some connections are taking in a server, and I know I have seen a top-like tool for that before. However, I can't remember the name of the tool, and I'm not ...
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8answers
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Why rsync is faster than NFS?

Few days ago I noticed something rather odd (at least for me). I ran rsync copying the same data and deleting it afterwards to NFS mount, called /nfs_mount/TEST. This /nfs_mount/TEST is ...
26
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3answers
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What is the difference between unlink and rm?

Is unlink any faster than rm?
26
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1answer
1k views

Minimal rate and default class problem for HTB

I have some doubts about a HTB structure I'm using. My aim is to limit the download and upload speed of users in a local network. Each user of the network has a personal list of domains with a down ...
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4answers
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How to add message that will be read with dmesg?

I am trying to write some custom messages in my dmesg output. I tried: logger "Hello" but this does not work. It exits without error, but no "Hello" appears int the output of: dmesg I am using a ...
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4answers
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How do I verify the speed of my NIC?

I just installed a new gigabit network interface card (NIC) in Linux. How do I tell if it is really set to gigabit speeds? I see ethtool has an option to set the speed, but I can't seem to figure ...
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3answers
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How to get TX/RX bytes without ifconfig?

Since ifconfig is apparently being deprecated in major Linux distributions, I thought I'd learn something about the ip tool that's supposed to be used instead of ifconfig. And here I ran into a ...
25
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13answers
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Linux IO monitoring per file?

I am interested in a utility or process for monitoring disk IO per file on CentOS. On Win2008, the resmon utility allows this type of drilldown, but none of the Linux utilities I have found do this ...
25
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8answers
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How to add a timestamp to bash script log?

I have a constantly running script that I output to a log file: script.sh >> /var/log/logfile I'd like to add a timestamp before each line that is appended to the log. Like: Sat Sep 10 ...
25
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7answers
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Unzipping files that are flying in through a pipe

Can I make unzip or any similar programs work on the standard output? The situation is I'm downloading a zip file, which is supposed to be unzipped on the fly. Related issue: ...
25
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11answers
20k views

How to make `rm` faster on ext3/linux?

I have ext3 filesystem mounted with default options. On it I have some ~ 100GB files. Removal of any of such files takes long time (8 minutes) and causes a lot of io traffic, which increases load on ...
25
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15answers
2k views

How much is IP V6 addressing being used?

Just how much IP V6 addressing is really in typical use out there? I see that Linux/UNIX seems to be ready for this. But I don't see the readiness as much as the Windows side. Especially not for ...
25
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7answers
3k views

Ubuntu, how to setup a new machine like an existing one

I have one machine setup with the apps I need, and I'd like to install the same on a new Ubuntu box. Is there a script that will list all the installed apps, so that I can diff between the boxes and ...
25
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12answers
4k views

Storing and backing up 10 million files on Linux

I run a website where about 10 million files (book covers) are stored in 3 levels of subdirectories, ranging [0-f]: 0/0/0/ 0/0/1/ ... f/f/f/ This leads to around 2400 files per directory, which is ...
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4answers
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Linux/Windows/Unix/… file names: Which characters are allowed? Which are unescaped?

Which characters are allowed and which of them must be escaped on the command line in different operating systems?
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3answers
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The XFS filesystem is broken in RHEL/CentOS 6.x - What can I do about it?

Recent versions of RHEL/CentOS (EL6) brought some interesting changes to the XFS filesystem I've depended on heavily for over a decade. I spent part of last summer chasing down an XFS sparse file ...