KrazyWorks

Run Background Tasks via SSH

June 16, 2011 – 12:58 am

The idea here is simple: you need to connect to hosts 1..100 and execute a command in the background. The trick is to make sure the command continues to run after the SSH session terminates. Simply adding the “&” at the end of the command is not the answer here.

CompTIA Fails It’s Own Linux+ Exam

June 4, 2011 – 3:52 am

The CompTIA Linux+ is a certification program designed for people who’ve heard of Linux but can’t yet figure out what it is. Still, one would imagine that people running CompTIA’s Web site should be able to answer at least some of the sample exam questions posted on their site. At the end of the practice exam there is a link that says “Click here for the answers”. But if you click on that link, you will find none…

Shadowbox JS Plugin Breaks WordPress

June 2, 2011 – 12:24 am

Just a quick alert: the latest version (v. 3.0.3.3) of the popular Shadowbox JS plugin for WordPress has a serious bug that exposes your WordPress installation to a major security risk. Incorrectly coded handling of the “player” tag causes all of your NexGEN Gallery images to be displayed on any page that also has single images embedded via WordPress “Add an Image” function.

Disabling WordPress X-FRAME-OPTIONS Support

May 30, 2011 – 3:37 pm

Staring with version 3.1.3, WordPress introduced X-FRAME-OPTIONS support for the admin and login pages. This is a simple defensive measure against sneaky characters trying to encapsulate your blog within their own Web sites using iframes. So this new security was a welcome addition to WP for most users. I was not one of those users.

Password-less SSH and Autofs

May 15, 2011 – 4:04 am

Recently I’ve ran into an unusual problem with SSH on SLES 11 SP1. The system – a small HPC cluster – is configured to use NIS for authentication and automounter maps. Whenever a user logs in, the home directory is automounted from an external NAS. Each user has a ~/.ssh directory with the authorized_keys2 and known_hosts required for password-less SSH access among the cluster nodes.

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.

Load-Testing HPC Linux Clusters with “stress”

April 28, 2011 – 8:43 pm

The “stress” is a simple-to-use load generator for POSIX systems that I found very useful for stress-testing HPC clusters. The current version of the application is 1.0.4 and it was easy to compile and install. Stress can create configurable system load for CPU, memory, I/O, and disks. In the example below we ran “stress” on a SLES 11 HPC cluster with HP CMU 4.2 installed.

Facebook Security for the Lazy

April 28, 2011 – 2:36 am

Every time you use Facebook, you probably have a nagging feeling in the back of your head that someone other than your friends is reading your posts. You should trust that feeling. At the same time, keep in mind that Facebook is a tool designed primarily for sharing personal information with large groups of people you barely know. Facebook is not your personal diary or a substitute for SMS. You just need to assume that everything you post on Facebook inevitably will end up in the hands of someone you don’t like very much. And then you proceed based on that assumption.

Installing Ganglia on RHEL

March 21, 2011 – 2:59 pm

This is a quick follow-up to my earlier post about installing Ganglia from source on SLES. Here we will install Ganglia from precompiled RPMs on an RHEL server. The basic cluster setup for this example remains the same: two clusters: CLUSTER1 and CLUSTER2 with head nodes head_node1 and head_node2

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.

Force NTP Time Update on Linux

February 21, 2011 – 8:36 pm

Imagine this: you created the /etc/ntp.conf file, enabled and started the ntpd service, and… the system time is still off. Is there a way to force time sync with the NTP server? It must be your lucky day. All you have to do is to connect to your box as root and run the following command…

Don’t Be Afraid to Reboot Unix Servers

February 21, 2011 – 8:11 pm

Reboot your Unix servers after making any major changes to the production environment. Should an unexpected problem come up, it will be easier to deal with it when everything is still fresh in your mind and not six months down the road, when you have to do a reboot to replace a failed system board and suddenly discover that some application wouldn’t load, by which time you forgot all about this application and have to start with the first page of the admin guide.

Fixing Your Crappy Cell Phone Photos

February 10, 2011 – 10:11 pm

Some of today’s cell phones feature camera resolution that rivals digital SLRs from two year ago. An 8-megapixel cell phone camera is no longer a novelty. Unfortunately, high resolution is the only good thing cell phone cameras have to offer and it does not translate into better pictures. If you compare photos taken with the most advanced cell phone camera to those taken with a $200 point-and-shoot digital camera, the cell phone invariably loses.

Find Command with Multiple Exec Statements

February 10, 2011 – 12:32 am

This is a very simple one, but somehow I always forget the correct syntax. I want to use the “find” command to locate files and then use several “exec” statements to perform various operations on whatever “find” finds. In the following example I am making sure that all /etc/*.conf files are owned by root and that they don’t have permissions greater than 644.

WordPress 3.0.4 – the Return of the Custom Field Bug

January 31, 2011 – 4:20 pm

After upgrading to the latest stable WordPress version 3.0.4 I ran into an old issue I haven’t see for almost two years. Clicking “Publish” or “Save Draft” when writing a new post seems to remove some custom fields. If you re-add the custom field and click “Update”, the entry stays. But it goes away again once you use the “Save Draft” or “Publish”.

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

iPhone OS 4 Upgrade: One Month Later

October 13, 2010 – 1:36 am

Over a month has passed since I upgraded my iPhone 3Gs to OS 4. There are a couple of significant issues that I noticed. First, the battery life – not particularly impressive to begin with – got shorter. Before I used to get through the day on one charge. I only charged my iPhone overnight. Now, in addition to the nightly charge, I find I need to use the car charger on the way from work to keep the iPhone alive. Since there have been no changes in how I use my iPhone, I have to assume OS 4 causes iPhone to consume more power.

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.

Modifying Solaris Services

September 9, 2010 – 4:33 pm

Recently I ran into an issue: the sshd service on a Solaris 10 box needed to be used with a custom configuration file. By default, the sshd service will use /etc/ssh/sshd_config. I needed it to use /etc/ssh/sshd_config_custom. I could not just modify the default configuration file. Don’t ask why – it’s complicated. So here’s what I ended up doing and this process is applicable to modifying any other Solaris 10 (and above) service.

Substitute Commands Depending on User ID

September 9, 2010 – 2:44 pm

Here is a quick example of how to substitute system commands based on who tries to run them. A customer of mine has recently deployed a security audit application on his servers. The application has a few bugs that the vendor has not yet resolved. For example, the security audit agent looks at the output of the “mount” command to see if any filesystems are mounted without the “nosuid” option.

iPhone 3GS OS4 Upgrade

September 4, 2010 – 5:23 pm

iTunes for Windows must be one of the buggiest, most poorly written applications out there. In terms of wasted months of your life it definitely ranks up there with Lotus Notes and Media Player 12. I don’t know how well iTunes works on a Mac (I like computer mice with twenty buttons, so I never was a big Mac fan), but I think I read somewhere that iTunes for Windows is the leading cause of suicides among iPhone owners.

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.

Editor

Hi Igor

Latest Comments