sysadmin

Sysadmin Humor

I laughed out loud when I saw this XKCD comic this morning:

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Apache mod_proxy '[error] (13)Permission denied' error on RHEL

Had an interesting issue today working on a mod_proxy setup of Apache forwarding requests in a reverse proxy setup to a backend Tomcat server. No matter what I did, I kept getting this in Apache's error log:

[error] (13)Permission denied: proxy: AJP: attempt to connect to 10.x.x.x:7009 (virtualhost.virtualdomain.com) failed
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Teaching Java How to Commit Suicide

At $work, we have a lot of java processes that are ran via cron and other wrappers that do some pretty critical tasks. The apps have been written so that the whole thing is wrapped in a try/catch that will call system.exit(1) should something not go right. Our wrapper scripts watch for a non-zero exit code, and alert Nagios if something went wrong.

This works great except for when a VM encounters an outOfMemory exception (OOM). The Java VM attempts to continue on, but if the main thread hits this exception, the entire VM will exit. However, the application code that exits with a status of 1 never gets called, so the application ends up dying with a status of 0. Well, Sun (Oracle now I guess) gave us a new option in Java 6 that was backported to 1.4.2_12 and up that allows us to tell Java to run a shell command when it encounters an OOM exception. By adding the option

-XX:OnOutOfMemoryError="kill -9 %p"

to our Java command line, the VM will execute a shell that calls the kill command, with an argument of the PID of the VM. The -9 option to kill will cause the VM to exit with a non-zero status, so that our wrappers will pick up the error and alert the right people.

Note: this feature was never backported to Java5 - sorry!

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ZFS in the Trenches presentation at LISA 09

Just got the chance to finally sit down and watch Ben Rockwood's presentation at LISA 09: ZFS in the Trenches. If you are even thinking about ZFS and how it works, it's a very informative presentation. There is very little marketing-speak, and he very specifically targets sysadmins as his audience. Great stuff! Of interesting note about his comparison of fsstat vs iostat, our Apache webservers routinely see about 5MB/sec reads being asked of ZFS, but the actual iostat on the disk shows that almost all of that traffic is being served up from ARC.

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QuickTip: Fix Eclipse Galileo buttons on Ubuntu 9.10

There's a nasty upstream bug in GTK present in Ubuntu 9.10 that makes Eclipse Galileo all but unusable -- specifically it makes clicking many buttons with the mouse just stop working. You can use tab and spacebar to make it work, but that's not much of a workaround. All you need to do is set an environment variable before starting Eclipse:

export GDK_NATIVE_WINDOWS=true
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Share Your Eclipse Plugins and Configurations Across Platforms

Over the years, I've come to know and love Eclipse.  Though it has roots in Java, ironically, I use Eclipse for just about everything except for coding Java (if I wrote Java code, I'm sure I'd use Eclipse).  Eclipse is great for browsing Subversion, coding PHP, coding Perl, and even coding shell scripts.  For die hards like me, there's the viPlugin that allows you to use all the vi commands you know and love within Eclipse.  About the time you get your perfect Eclipse setup established, you buy a new laptop on a new platform.  Or, in my case, I have three "primary" development workstations, each on a different OS.  The rest of this article will show you how to hook Dropbox into your Eclipse installation, allowing you to share your plugins and configurations across different versions of Eclipse, on different machines, and even on different platforms.

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NGINX Performs Well on Solaris 10 x86

Just a quick posting of some simple benchmarks today.  Please note, these are not the be all, end all performance results that allow everyone to scream from atop yonder hill that Solaris performs better than Linux!  This was just me doing a little due dilligence.  I like Solaris 10, and wanted to run it on our webservers.  We're looking at using NGINX to serve up some static files, and I wanted to make sure it performed like it should on Solaris 10 before deploying it - you know, right tool for the job and all.  So, disclaimers aside, here's what I found.

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Ask SAJ: What to do with Apache logs > 50GB?

Our site at $work is generating Apache logs that, when combined sequentially into one file, are larger than 50GB in size for one day's worth of traffic. AWStats' perl script pretty much chokes when working on this much data. Last I checked, Webalizer wasn't much different, and probably wouldn't scale up to that amount of data either. Does anyone out there have any advice on a commercial solution for Apache log analysis that can scale up like that?

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Tip for "Split Components Across Domains" Performance Goal from Yahoo!

Just thought I'd pass this little tidbit out there - we fixed it by pure luck on the first try.

Yahoo unselfishly provides a document titled Best Practices for Speeding Up Your Website. While some of the rules offered there aren't applicable for all sites, it's a great document and if you run a website, you should read it.

At $work, part of our last code drop was to push out a feature that enabled "Split Components Across Domains". From the article Performance Research, Part 4: Maximizing Parallel Downloads in the Carpool Lane:

Our rule of thumb is to increase the number of parallel downloads by using at least two, but no more than four hostnames. Once again, this underscores the number one rule for improving response times: reduce the number of components in the page.

I'm here to tell you, if you have AOL users surfing your site, do not use four hostnames.

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Which Directory Server and Why?

One of my projects for 2010 is to get a reliable directory server in place. I was going to post a poll to my readers asking what they felt was the best DS, but Ben Rockrood beat me to it with his article Community Poll: Whats your favorite Directory Server?. It's likely that most of the readers of this blog already read Ben's too, but if you don't it's a great blog to subscribe to. If you have any input into the debate on what DS is the best, head on over and leave a comment!

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