• PostgreSQL Synchronous Streaming Database Replication

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    PostgreSQL is a great advanced open source database. It offers many features, one of them being database replication. PostgreSQL 9.4 offers many different solutions to the replication problems, each one of them having it’s number of up’s and down’s. In the end it is up to the system or database administrator to decide which solution […]

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  • Install PostgreSQL 9.4 on CentOS 7

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    PostgreSQL is a database server. It is an object-relational database management system and it’s main purpose is to store data. PostgreSQL calls itself “The world’s most advanced open-source database”. It is a fact that MySQL andPostgreSQL are two most popular open-sourcerelation database management systems (RDMS). It is up to you to choose the one you like the […]

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  • Logs Filled Up My Disk – What To Do

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    A couple days ago i received an alert that one of the disks on our linux production machines is filling up very quickly. It was the application server machine and the logging partition was running out of space rapidly. Logs filled up my disk How logs filled up my disk Gladly the log files are […]

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  • Bash Aliases and SUDO – sudo: ll: command not found

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    I really like to do work on my Linux systems as “root”, to get things done quickly and without any hassle. Yeah i know, bombs away, it is not OK or safe or whatever to use “root” user for everyday things but mainly it is not OK from the auditing point of view. Customers really dislike it […]

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  • Rescan SCSI bus on Linux System

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    SCSI stands for Small Computer System Interface and is a set of standards for transferring data and connecting devices and computers. Sometimes you make changes to disk devices on your Linux box while online which is even more often nowadays using virtual machines. Sometimes you also add a new disk and do not want to […]

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  • Configure Postfix Mail Forward

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    I am running a Postfix with Dovecot for my emails and also make email accounts for my friends from time to time. So last night a friend of mine asked me to configure an email account for him and forward the emails to his gmail account. It is really easy and quick to Configure Postfix […]

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  • Manage and Configure YUM Repository

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    YUM Repositories are warehouses of RPM package files. RPM file is a Red Hat Package Manager file and enables quick and easy software installation on Red Hat/CentOS Linux distributions. YUM Repositories hold a number of RPM package files and enable your server to download and new software. YUM Repositories can hold RPM package files locally […]

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  • Configure Password Policy on CentOS 6

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    Configuring Password Policy on CentOS 6 About Password Policy Password policy is a set of rules that must to be satisfied when setting a password. Password policy is an important factor in computer security, specially since user passwords are too often the main reason for computer system security breaches. This is why most companies and […]

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  • ZenHub is Down Zenoss Problems

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    Last time i experienced problems with Zenoss. Zenoss suddenly stopped getting information from the clients, stopped graphing client data and i did not know what the reason was for this situation. I tried removing and readding the client but the job of adding a new client was even not processed. When i tried to re-model […]

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  • Add Windows Client to Zenoss Monitoring

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    It just so happens, that sometimes you would like to add Windows client to Zenoss monitoring 🙂 . A person would think that this would be quite simple and similar to adding Linux client to Zenoss monitoring, but it is not. The SNMP Windows client Zenoss monitoring is very limited, in fact i could not […]

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  • Add Linux Client to Zenoss Monitoring

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    I have been getting some questions and emails about problems with adding linux client to Zenoss monitoring as explained in my post on Install Zenoss Monitoring Server on CentOS 6. I decided to post the SNMP daemon configuration i use, to add linux client to Zenoss monitoring server and write in general how to get […]

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  • Apache Server Status Module

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    The Apache Server Status module is an addition to Apache HTTP Server. It is a module that enables insights into the Apache HTTP Server performance and statistics. On CentOS Linux, Apache Status module is provided by the httpd RPM package, so if you are running Apache, this module is already installed and wait for it […]

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  • Cron Daemon and Cron Jobs

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    Cron is a daemon on linux and unix based operating systems. Cron is a job scheduler which we can be used to configure jobs or run commands at a specific time in a day, month or year. Cron is quite configurable enabling us to run jobs and commands periodically, at fixed times or dates and also […]

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  • PostgreSQL Create Database and Tablespace

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    This is the next post in a series of posts about PostgreSQL and is actually a continuation from post on “PostgreSQL Create User – Manage Users“. If you followed my post on “PostgreSQL Create User – Manage Users” then you successfully created your firstPostgreSQL users and also assigned them desired rights and privileges. The next step is to […]

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  • PostgreSQL Create User – Manage Users

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    As promised in one of the previous posts on “Install PostgreSQL Database on CentOS 6” here is a post describing how to manage PostgreSQL users (PostgreSQL create user, delete user, …). By now you have probably successfully installed and started PostgreSQL server on your linux machine, but empty PostgreSQL server is not useful in any way. The next […]

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  • SSH Tunnel – Port Forwarding With SSH

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    SSH has a huge number of features, SSH Tunnel being just one of them. SSH Tunnel is a secure connection between two machines and is often refered to as “SSH Tunneling” or also “Port Forwarding”. Using the “ssh” command we can bind a desired port on a local machine to a desired port on a remote […]

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  • Install and Configure Postfix with Dovecot on CentOS 6

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    Want to install and configure Postfix with Dovecot on CentOS 6? Or are you wondering whatPostfix orDovecot is? In case you are wondering (i hope not, since you stumbled on this page), Postfix is a mail server or a bit more fancy word for it – Mail Transfer Agent (MTA). Actually MTA tells you what this application does. It transfers the […]

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  • Secure Your Linux Server With IPTables

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    If you have a Linux server out there somewhere in the internet, you probably want to secure it and reflect some of the most common attacks to your server. If you are just starting out with your first server you must know, your server will be attacked. There are automated bots and scripts that scan […]

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  • Configure IPTables on CentOS 6

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    IPTables is a service on linux systems, which allows a system administrator to configure rules and chains in tables provides by the Linux kernel firewall. IPTables is a Linux firewall service which enables you to accept, reject or drop (,…) packages based on the rules you applied. In this post we will learn how to cofigure iptables […]

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  • FSTAB: Mount Point With Space in Dir Name

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    Today i was re-organizing my desktop computer running Fedora 20. Actually i installed a new SSD drive in it and been throwing data around to organize/create new partitions and filesystems – just the way i like it! 🙂 Since i decided to put my VirtualBox machine files on a separated partition i ran into the […]

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  • Securing SSH Server – sshd_config

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    Secure Shell (SSH) is a cryptographic network protocol for secure data communication. SSH is widely used on linux machines for console access and remote management. It is a server – client oriented network protocol which enables a secure communication between two network computers. The port on which SSH Server runs by default is 22. If […]

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  • Forward & Reverse Apache Proxy – CentOS 7

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    There are two possible configurations for Apache Proxy Server and we will present installation and configuration of both types this how to. Forward Apache Proxy is a proxy configuration that is commonly used in companies and it enables users to access the internet. Users or clients must configure their browsers or operating system to use a proxy server (Forward Apache […]

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  • Increase Root Partition Size – LVM – CentOS

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    Since i have been getting alot of questions on how to increase root partition size on a linux system i decided (finally!) to write a how to about this topic. Linux root partition is different from all other partitions on your system since it holds all of the system files required for your system to run […]

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  • Install Nagios on CentOS 7

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    So CentOS 7 is out and there are quite some differences from it’s predecessor CentOS 6. This is why i decided to write a new how to installing Nagios Core 4.0.8 on the latest fully updated CentOS 7 minimal installation – Install Nagios on CentOS 7. The Firewalld and SELinux are both enabled and running in […]

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  • SSL Library Error: error:0906D06C:PEM

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    Recently i was migrating an Apache HTTP Server (httpd) server from one linux machine to another. The problem was, that on the source linux machine Apache HTTP Server (httpd) was a custom compiled 2.4.4 and we were having constant problems when patching the linux machine (openssl libraries etc.). So we decided to replace the custom compiled Apache HTTP Server (httpd) with […]

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  • Error: bad top line in state file – logrotate.status

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    A while ago i noticed that /var partition on a certain server was almost filled up to a 100% up and started researching what caused this. I noticed that log files in /var/log directory were not rotating. I decided to run the log rotation manually when i got this error “error: bad top line in […]

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  • Install CentOS 7 – CentOS 7 is Here!

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    We all know CentOS – Community Enterprise Operating System as a linux distribution aiming at enterprise class community-supported computing platform. CentOS aims to be 100% compatible with it’s upstream source Red Hat Enterprise Linux (RHEL). CentOS 7 was released on 7 th of July 2014 (RHEL 7 on 10th of June 2014) and its brings some major differences from it’s […]

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  • Install Zenoss Monitoring Server on CentOS 6

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    Zenoss is a free and open source monitoring solution similar to Nagios. It can be used to monitor all sorts of hardware and in case of failures sends out alerts to recipients. Zenoss Core provides a web interface that allows system administrators to monitor availability, inventory/configuration, performance, and events. Compared to Nagios (my personal opinion) Zenoss has alot higher […]

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  • Install PostgreSQL 9.3 on CentOS 6

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    PostgreSQL is a database server. It is an object-relational database management system and it’s main purpose is to store data. PostgreSQL calls itself “The world’s most advanced open-source database”. It is a fact that MySQL and PostgreSQL are two most popular open-source relation database management systems (RDMS). It is up to you to choose the one you […]

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  • Install OwnCloud on CentOS 6

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    OwnCloud is a free and open-source software which enables you to create a private “file-hosting” cloud. OwnCloud is similar to DropBox service with the diference of being free to download and install on your private server. Advantage of OwnCloud over DropBox is that it is private (you manage it yourself) and not limited (only limited by hard disk […]

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  • Manage Users and Groups on Linux

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    If you are a linux system administrator one of the more important things to learn and to know is how to manage users and groups on linux systems. This guide will describe how to add, delete and modify users and groups (manage users and groups) on CentOS 6 linux (same applies to other linux distributions) […]

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  • Build Apache 2.4.9 RPM on CentOS 6

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    We all know Apache HTTP Server. Apache is de-facto web server on UNIX-like systems and is maintained by an  open community of developers of the Apache Software Foundation. Apache HTTP Server is released under the Apache License and is an open-source software. The problem with Apache HTTP Server on CentOS and other RHEL based distros is, […]

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  • Kickstart File on CentOS 6

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    Kickstart file is a great solution which enables you to automate installation of CentOS Linux, Red Hat Enterprise Linux and other Red Hat Linux derivates. Kickstart file is basically a single file containing answers to all the questions that you would normally be asked during a typical installation of your Linux system. Kickstart file can […]

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  • Working with YUM on CentOS 6

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    Yum or Yellowdog Updater Modified is a command line package management solution for Linux systems using RPM‘s like Red Hat Enterprise Linux, CentOS Linux, Fedora,… We can use yum to search, install, remove and check for additional information about RPM packages available to our Linux system. Yum works with local or remote repositories which are […]

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  • Ubuntu NFS Server – Ubuntu Server 12.04

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    NFS is short for Network File System. NFS server allows you to share a filesystem from a computer on the network to other computers on the same network. NFS is a server/client oriented protocol so one computer acts as a server and other computers (clients) connect to it. We will install and configure Ubuntu NFS Server […]

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  • Configure DRBD 8.4 on Ubuntu Server 12.04

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    Distributed Replicated Block Device is a great way to replicate filesystem over the network to another server or host. Distributed Replicated Block Device actually mirrors a whole block device over the network therefore it is often used for High Availability (HA) clusters. Distributed Replicated Block Device is actually a network based RAID 1. Distributed Replicated Block Device has […]

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  • Network Bonding on Ubuntu Server 12.04

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    If you are looking for network card redundancy you can start by confguring network bonding on your Ubuntu Server 12.04 machine. Network cards with network bonding can be joined in multiple configuration options (active/active, active/backup,…). We will configure our network cards in “active/backup” configuration. This is a network bonding fallback configuration which means if one […]

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  • Manage IP Alias on CentOS 6

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    Learn how to use IP aliasing on CentOS 6. IP alias / IP aliasing is assigning multiple IP addresses to a single physical network interface.

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  • Pnp4nagios data migration – convert RRD to XML

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    A while ago i wrote an article about Nagios migration to a new Linux server. This project also included migration of Pnp4nagios data. Since i was migrating Nagios to a new architecture (i386 -> x86_64) i had to convert RRD files to XML, transfer them to the new server and convert them back from XML to RRD. […]

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  • DRBD – How to configure DRBD on CentOS 6

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    DRBD® refers to block devices designed as a building block to form high availability (HA) clusters – Distributed Replicated Block Device. This is done by mirroring a whole block device via an assigned network. Distributed Replicated Block Device can be understood as network based raid-1. So, Distributed Replicated Block Device is actually a network based RAID 1. You are configuring DRBD […]

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  • CentOS Network Bonding

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    There are many situations in which someone would like to configure network bonding or channel bonding on a server… In most cases it is done for the network card redundancy. You can bond two network cards together in an “active/backup” configuration and in case one of your network cards fails all of the traffic will […]

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  • Pnp4Nagios CentOS install

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    PNP is an addon to Nagios which analyzes performance data provided by plugins and stores them automatically into RRD-databases (Round Robin Databases, see RRD Tool). It analyzes performance data provided by Nagios and stores them in RRD-databases. RRD Tool enables you to view performance and availability graphs for your Nagios services or hosts. PNP4Nagios Broker […]

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  • Nagios 3.5.0 RPM install on CentOS 6

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    Thanks to guys from Centos.alt.ru CentALT RPM Repository you can now install Nagios 3.5.0 RPM on CentOS. Nagios 3.5.0 RPM is available in their repository so all you need to do is add their CentALT and EPEL repo to your servers and run “yum install nagios”! Here is a Step-by-Step guide on how to get […]

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  • PING WARNING – DUPLICATES FOUND! – Nagios

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    Lately i was migrating my Nagios monitoring server to a new hardware and also a new CentOS version (CentOS 5.9 -> CentOS 6.4). It was a completely new server with new Linux OS installed and everything was configured perfectly. When i migrated Nagios data to a newly installed server and switched the IP addresses, i started […]

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  • Nagios configuration – How to configure Nagios

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    About Nagios Configuration This is a quick manual on Nagios configuration files. We will be explaining which configuration files you need to edit to add hosts, services, contacts and groups. Learn how to configure your Nagios from Linux console and check the configuration for errors. In this Nagios configuration How To guide we will explain most of […]

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  • Nagios migration to a new Linux server

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    About My Nagios Migration I just finished a project of Nagios migration to a new hardware and also a newer CentOS version and architecture. The IP address of the Nagios server didn’t change! I was migrating Nagios from CentOS 5.9 32bit to CentOS 6.4 64bit and of course the objective was to transfer all of […]

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  • Install NagVis on CentOS 6

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    About NagVis NagVis is an addon to Nagios monitoring and alerting system. It is a way to vizualize Nagios data. It enables you to create maps and schemas of a part or the whole server and network infrastructure. Viewing these maps you can quickly see which hosts and services or even branches of your company […]

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  • MK Livestatus CentOS 6 Install

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    About MK Livestatus MK Livestatus is a completely new approach for accessing status and also historic data from hosts and services in Nagios monitoring and alerting system. Livestatus does not actively write out data. Instead, it opens a socket by which data can be retrieved on demand. The socket allows you to send a request […]

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  • Nagios Core 3.5.0 CentOS 6 Install

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    About Nagios Core Perhaps you’ve heard it before, but let’s hear it again – “Nagios Is The Industry Standard In IT Infrastructure Monitoring”. It is used to for monitoring and alerting of your servers, switches applications and services. It is an open source system, network and application monitoring software. Open source also means it is […]

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  • How to install Ubuntu Linux 12.10

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    This is a quick step-by-step with screenshots on how to install Ubuntu Linux on your machine. We will be installing Ubuntu Desktop edition version 12.10. This is the current version of Ubuntu at the time of my writing. First you need to make sure that you have backed up all your valuable data from the […]

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  • How to install Linux – CentOS minimal install

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    About CentOS CentOS is a Community ENTerprise Operating System and it is a Linux distribution based on Red Hat Enterprise Linux (RHEL). CentOS in mostly installed on servers in enterprise environments. Since we presume you will be installing CentOS on a server only minimal installation CentOS packages is required. This means no GUI (Graphical User Interface) is installed. About […]

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