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Articles in Networking

Troubleshooting InfiniBand Connections

May 4, 2011 – 10:36 am

The following is a brief troubleshooting guide for an InfiniBand network found in common HPC Linux clusters. Running these commands requires OFED 1.5.2 or later package installed on your systems. Additionally, the “pdsh” (parallel shell) command is part of the HP CMU cluster management software (version 4.2.1 used in our example) installed on the head node.

Opening Custom Ports in SuSE Firewall

March 4, 2011 – 2:18 pm

Most of the servers I work with are already behind an enterprise firewall, so I rarely get to configure a software firewall. In the following example, I installed Webmin and Usermin on a SLES 11 server that had SuSE firewall enabled. Webmin and Usermin by default use ports 10000 and 20000, respectively. These ports are not in the list of common services you would find in the SuSE firewall configuration GUI. There are a couple of ways of adding custom ports to the list of the allowed services.

LPI Invents Linux Commands

January 18, 2011 – 7:50 pm

It would appear that in order to obtain Linux Professional Institute’s LPIC-2 certification, one needs to know real Linux commands as well as imaginary ones. On the Sample Questions page for LPIC-2 Exam 2 the LPI Linux gurus pose the following question

Windows 7 Black Screen After Booting

October 5, 2010 – 4:07 am

I had to power-cycle my Windows 7 64-bit laptop. The bootup sequence looked normal and reached a point where I could see the black screen with the mouse cursor. After this stage my desktop would usually appears, but not this time. I could move the mouse and I could even establish a remote desktop connection to my laptop. But I could not log in. Every time it would reach the same point – the black screen with the mouse cursor – and it would stop.

NFS “Not Owner” Error

August 30, 2010 – 11:34 pm

The “not owner” error is displayed on the client system (usually Solaris) when attempting to mount an NFS share from a server. This error may appear even though the share is correctly exported and the client system has full access. If you are getting a “permission denied” error, then this article is not for you and you should check here instead.

Windows Network Troubleshooting Script

January 20, 2010 – 10:15 pm
windows keyboard

I try my best to stay away from Windows. I wish my clients did the same. The usual difficulty of troubleshooting elusive network performance problems is amplified many-fold when there is a Windows computer at the end of the line. With Unix it’s relatively simple: run tests “a”, “b”, “c”, etc and follow the familiar process of elimination. With Windows in the picture the number of steps uses up all of the English alphabet and spills over well into the Russian one. And when you finally reach step “я”, you have to pull out your Chinese dictionary.

Copying Data: Are We There Yet?

December 27, 2009 – 7:12 pm

I am sure this will sound familiar: you are copying a large amount of data – either locally or over the network – and you are wondering how long it will take and if there is a way to make things go faster.You may be surprised, but it does matter what type of files you are copying: 1Gb-worth of many small files will take considerably longer to copy than two 500Mb files. The hardware you are using is an important consideration, but it’s not the only factor limiting data transfer speed.

Printing from SuSE/SLES to a Windows Printer

December 10, 2009 – 5:05 pm

The following document explains how to configure your SuSE or SLES system to be able to print to a remote printer shared from a Windows server. The first step is to install Unix print support …

Reboot Remote Windows Workstation

December 10, 2009 – 9:53 am

When using RDP, sometimes the session may lock up and you may need to reboot your workstation remotely. This can be done using the “shutdown.exe” command from your local PC. First, make sure you can …

Slow SSH login in SuSE Linux

November 3, 2009 – 6:17 pm

Starting with SuSE 10 and including both openSuSE and SLES an annoying SSH problem appeared. When you SSH to the server (via PuTTY and such) you get the “login” prompts right away, but the “password” …

Automatically Validate HTTP Proxies

August 5, 2009 – 4:14 pm

Let’s say you downloaded a long list of Web proxy servers. Now you are stuck with the task of weeding out the proxies that are dead, slow, fake, or otherwise unusable. There are some applications …

Sharing Videos from Linux to Xbox 360

December 19, 2008 – 8:49 pm
old film projector with dramatic lighting

Xbox 360 uses UPnP protocol to stream multimedia files from computers on your home network. Normally, you would have a Windows PC running WMP and sharing files. But what if you have a Linux box …

Linksys WAP54G Secure Configuration

June 11, 2008 – 1:09 pm
wireless access point ap

Below are some basic steps to secure a wireless access point (WAP). The screenshots are for Linksys WAP54G v. 3.04, however, the same steps will apply to wireless access points from other manufacturers. Understand this: …

Migrating email between hosted providers

May 23, 2008 – 9:38 pm

Recently I ran into a small problem. A customer of mine was moving her site to a new hosting provider. Her old provider was Windows-based and her new provider was Linux-based. The old provider did …

Protected: SuSE Mail Transfer Agent Configuration

February 7, 2008 – 3:48 am

There is no excerpt because this is a protected post.

Configuring eMule for Best Performance

December 27, 2006 – 12:22 am

“eMule is a peer-to-peer file sharing application that works with both the eDonkey network and the Kad network. The distinguishing features of eMule are the direct exchange of
sources between client nodes, fast recovery of corrupted …

Simple network monitoring with ping

April 11, 2006 – 10:12 am

In the Spring of 2005 Comcast experienced a major DNS outage. Since then many Comcast users have switched to DNS servers that belong to Verizon and other ISPs. Comcast started taking a lot of flak …

CUPS printing on Solaris 10

February 28, 2006 – 12:08 pm

Download the Companion CD for Solaris 10 GA on: Solaris 10 Companion cd download

Accessing Samba server in DMZ

January 22, 2006 – 2:04 pm
Security concept: Golden closed padlock on digital background, 3d render

This note explains how to access a Samba server located on the “orange” DMZ subnet from a Windows PC on the “green” LAN. The problem for Samba is caused by the firewall blocking NETBIOS responses. …

Installing SuSE Linux 10 on a laptop

December 10, 2005 – 7:53 pm

What’s the best Linux distro for desktop applications? My subjective opinion based on years of Linux experience is that SuSE 10 at the moment offers the best combination of features and user friendliness. The latter, …

Configuring multi-IP network interfaces

December 2, 2005 – 12:18 pm

This article explains how to configure a network interface to support virtual IP addresses. This is useful in a cluster environment or in any high-availability service cnfiguration, when you need to ensure that at least …

Basic Network Configuration Under Solaris

November 26, 2005 – 1:27 pm

The following document provides a general overview of the network configuration process for Solaris. For a detailed review of Solaris network configuration please see Chapter 4 of the O’Reilly Solaris 8 Administration Guide by Paul …