Tag Archives: linux

Quick Tips, Systems

Add a Swap File to RHEL/CentOS

Leave a comment

Sometimes, due to some new specific server requirements, you will find it necessary to increase your swap space. Even if your swap partition is setup as a Logical Volume, your requirements may exceed what is available. This is where creating a new swap file is the best option. In this example, we are going to add a new 12GB swap file.

Check Current Swap Space

Verify the total amount of used and free physical and swap memory with the free command and the -h human-readable flag

# free -ht
              total        used        free      shared  buff/cache   available
Mem:           755G        321G        3.0G         62G        430G        670G
Swap:            4G          1G          3G
Total:         771G        322G          6G

Display the swap usage summary by device using swapon. Same as cat /proc/swaps

Continue reading Add a Swap File to RHEL/CentOS →
Systems

How to Mount and ISO Image in Solaris and Linux

Leave a comment

Why Bother Mounting an ISO Image?

Sometimes you find yourself in a situation where you need to take an ISO image and utilize it like a CD or DVD. The popularity of virtual machines and the ability to manipulate larger files over high speed Internet increase the chances that you’ll have to work with an ISO image from time to time. Being able to mount an ISO image as though it were an inserted CD/DVD can make manipulating these kinds of files a bit easier– especially if your computer doesn’t have a CD/DVD ROM drive installed.

In Solaris

Let’s say you have a third party program you need to install, but the vendor only gives you an ISO file. Let’s say the name of the file is thirdparty.iso and you have downloaded that file to /export/home/myhome. Here’s an easy way to utilize this file under Solaris: Continue reading How to Mount and ISO Image in Solaris and Linux →

Systems

How to Sub-Delegate Reverse DNS Records Part 2

1 Comment

From the Service Provider’s Perspective

In part one of this topic, we discussed how to manage a sub-delegation for reverse DNS records once your ISP provides this service for you. Here in part two, we’ll discuss how to provide the sub-delegation of a reverse DNS range to another user. So in this situation, think of yourself as the provider offering the service for a customer or end user.

What You’ll Need

After you have received the request from the customer, you will need to confirm that they have created the proper zone for the Continue reading How to Sub-Delegate Reverse DNS Records Part 2 →

Systems

How to Sub-Delegate Reverse DNS Records Part 1

1 Comment

The Purpose of DNS Sub-Delegation

Let’s say you have acquired a static IP range from your ISP. Now that you have that range, you decide you also want to control the PTR records for these addresses as well. But, PTR records typically belong to the ISP. However, you do not want to depend on the ISP for each change you’d like to make; you want more control. How can your gain more control over those PTR records?

The way to gain this control is through DNS Sub-Delegation. DNS Sub-Delegation is when your ISP forwards PTR requests to your name server so that you can have control over your record updates. In other words, the ISP delegates their authority over their PTR records to your DNS server.

Prerequisites

If you understood the implications of that last sentence, you’ll realize that you will need your own local DNS service that controls your domain. After all, if you don’t control your own domain, how are you going to control the PTR records once they are delegated to you? In this post, we’ll assume that you will manage your PTR records with your own DNS server. Continue reading How to Sub-Delegate Reverse DNS Records Part 1 →

Systems

How to Setup a TFTP Server Under CentOS/RHEL 6

5 Comments

Why bother with tftp?

Many network devices such as Cisco routers and switches use tftp in order to download their IOS config updates. tftp can also be used for network based installs or for booting up diskless systems. Knowing how to setup a tftp server comes in quite handy when circumstances like these arise.

Getting started . . .

The Network Topology

Let’s say we’re dealing with a private network– 192.168.100.0/24. We’ll designate our tftp server and tftp test client as 192.168.100.5 and 192.168.100.105 respectively. You will need superuser privileges on both your server and client in order to successfully perform all of these commands.

Get the Necessary Packages

Log on to 192.168.100.5 and download the necessary programs; make sure they survive reboots:


# yum install tftp-server xinetd
# chkconfig tftp on Continue reading How to Setup a TFTP Server Under CentOS/RHEL 6 →