kick_user

Write or kick users logged into a Linux server

If you are multiple admins on the same server, it can sometimes be a hassle to shout over the tables to hear if they are logged in or not, or have you ever needed to kick a user/admin from one of your server?
For both scenarios, Linux has some build in features that come in handy!

The tools i am going to show you in this post is:
w (or some like to use “who” but I think “w” gives you more useful information)
write
wall
kill

Here is how to use the above tools
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Linux lockfile explained, how to use them the easy or hard way

What is a lockfile

You may have experienced it before, you create a cronjob to change some data every X hour or minutes and one day this job takes longer than it usually does and cron spawns another job before the first one is finished.
This can result in data corruption or deletion of data that should not have been deleted, all depending on what the cronjob is set up to do

To prevent bad things from happening, a good rule of thumb is to always use a lockfile

A lockfile is a small file, it virtually takes up no space, at least so little you won’t care (The actual size depends on your filesystem). Sometimes it contains a PID, sometimes a timestamp or just plain empty. Depending on how the lockfile is managed

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ilo

Configuring HP iLO through Linux automatically

We only use HP servers and we get more and more every week. Someone has to keep track of all those servers and be able to configure them using iLO in case of a disaster
Installation almost runs automatically, except for iLO configuration.
I have to first find the iLO ip, then login to the web interface, create users, set static IP and what not. It takes time, a lot of it.
If only there was some way to automate it without having to use HP’s software.. but wait, THERE IS!

I already posted how to scan for all HP ILO devices in your subnet, but the basics in the following post on how to configure iLO from your guest Linux OS might make everything a little easier for the sysadmins out there

How to configure HP iLO in Linux

First I will show you the useful commands and an example output for each, and then how to automate the configuration of your HP iLO interface using bash scripting
The script for configuring iLO automatically will be included at the end of this post

Needed packages:

OpenIPMI OpenIPMI-libs OpenIPMI-tools

These packages can be installed through your favorite package manager, below you’ll see the defaults in Debian and CentOS/RHEL

Debian:

apt-get install OpenIPMI OpenIPMI-libs OpenIPMI-tools

CentOS/RHEL:

yum install OpenIPMI OpenIPMI-libs OpenIPMI-tools

Once you got those installed, you can move on and configure or fetch info from iLO through the guest Linux

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Fixing /lib/ld-linux.so.2: bad ELF interpreter: No such file or directory

Today I had to run a script on a 64Bit server, but was met with the following error:

/lib/ld-linux.so.2: bad ELF interpreter: No such file or directory

Reason for the /lib/ld-linux.so.2: bad ELF interpreter: No such file or directory error

The /lib/ld-linux.so.2: bad ELF interpreter: No such file or directory error will happen only on 64 bit systems, the cause is the that 32 bit libraries are missing from the system and the script/program needs them, so it can’t run.

How to fix the /lib/ld-linux.so.2: bad ELF interpreter: No such file or directory error

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mysql-logo

MySQL get size of all databases in megabytes

Why would you want to get the size of all databases in my MySQL?

Reason for this could be many, in my case I wanted to make sure replication worked as expected, I wanted to see the size of my database be the same on all my MySQL servers. And also I was a little curious how big some of my databases was.

There’s not much to write on this matter, just thought somebody could use this query, I know I am going to use this query many times in the future again.

The query for showing databae sizes in MySQL

It’s one tiny query actually. Just fire up a mysql client – phpmyadmin, mysql in terminal or you can even do this in a script.

The query:

SELECT table_schema AS "Database name", SUM(data_length + index_length) / 1024 / 1024 AS "Size (MB)" FROM information_schema.TABLES GROUP BY table_schema;

Sample output:

+----------------------------+-------------+
| Database name              | Size (MB)   |
+----------------------------+-------------+
| information_schema         |  0.15625000 |
| mysql                      |  1.12139893 |
| performance_schema         |  0.00000000 |
| phpmyadmin                 |  0.04900742 |
+----------------------------+-------------+
4 rows in set (0.01 sec)

View network bandwidth for each process in Linux using Nethogs

Have you ever been in the saturation that your Linux server is using a lot of network bandwidth, but it’s a guesswork to find the process using it all?

I just stumbled upon this tool, it’s not a new tools, but it’s extremely useful!

Let’s say you have a server running apache, mysql, ftp, btsync and a lot of other network services. and somehow that server is using up 100Mbit constantly. You want to find out what it is but only got tools like iftop, atop, iptraf and others which are all great tools, but they only show which connections are using the network bandwidth.

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xbindkeys

Make your own keybindings in linux using xbindkeys

Are you like me, who want to listen to music while you work? But then your boss comes over and you quickly have to pause it? Or maybe you just want some key bindings on your linux workstation to make life a lot easier, then look no further! xbindkeys is the solution, and I will show you how in this post! it’s really easy to configure and extremely helpful.

In my example, I will use it to pause/unpause my music when i press CTRL+space no matter what desktop I’m on and even if I’m not in the terminal where MOC (the music player I use) is running.

What you need

xbindkeys is the name of the only package you need for this. It should be in the official repository for your distro. Install examples below:

Debian

apt-get install xbindkeys

Arch Linux

pacman -S xbindkeys

CentOS

yum install xbindkeys

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logtail

Get all new dhcp leases, but only the new leases since last check in bash

I needed to make a bash script for work that got the ip address of all new leases in the dhcp server, but only the new ones.
I spend some time looking for something useful, and therefore I decided to write a short post here to help others since i had a hard time finding it (maybe my google-fu is not as good as it should be)

The script had to do the following:
1. Get all new lines from a log file since last run
2. Get the ip addresses of the new leases
3. Do some stuff with the new ip addresses. This will not be part of this post
4. Run every minute in cron. This will also not be part of this post

In this post I will only cover how i did 1 and 2.

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centos

How to install a CentOS 7 64Bit server

With CentOS 7 just released, I thought it would be a great time to make a CentOS 7 64Bit server installation step-by-step guide, with pictures and everything just like the old CentOS 6.5 64Bit server installation guide.

Requirements for installing a CentOS 7 64Bit server

You don’t need much for this, of course you need a computer or server to install this on, and the only other things you need are a working internet connection on the server and the CentOS 7 64Bit iso.

You can download the iso here: http://centos.skarta.net/7.0.1406/isos/x86_64/CentOS-7.0-1406-x86_64-DVD.iso

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