Tech Blog

The find utility has an option to find a file newer than another file. By creating and empty file with a specific creation date we can do the search:

To show all files newer than 2010-01-01 use:

Or to create a tar archive of them use xargs like so:

Easy. Mark

This has been something I've been looking at, but haven't found a compelling reason for one over the other.

Proxy AJP is claimed to be faster as it is a "Wire protocol" but I couldn't find any benchmarks around this.

So I decided to do a very quick and dirty benchmark to satisfy my curiosity. This is not a scientific process, I just ran a simple railo testpage on the same machine with 50 threads of jmeter requests hitting it.

First I enabled proxy_http and ran it four times, then enabled proxy_ajp and repeated. The config is below:

Results:

The results showed that the proxy_http module was faster - i.e. more requests per second could be pushed through.

I'm putting this down to the fact that proxy_ajp has to convert the http request into it's binary format, while proxy_http really just has to pass it along.

In different scenarios and network configurations the results may be different, but for now I'm going to stick with the http proxy.

Proxy AJP has one other benefit, in that is passes along some extra flags such as whether the request is https or not, but for our purposes we don't need this.

Cheers, Mark

I've been doing some more work on configuring railo to work flexibly in the numerous different environments we work in, and also making it simpler to set up.

To that end I investigated the use of mod_proxy for linking it to apache instead of mod_jk.

Advantages of this approach are:

• Simple - communications are in plain http
• Flexible - Load balancing can be easily added at the apache layer
• Simple - No compiling mod_jk

Here are the basic install instructions for Railo/Tomcat/Apache on Ubuntu.

Download & Install Tomcat

Download tomcat and extract content:

Move Tomcat to a more appropriate place:

Download Railo

Download Railo custom version jars file

Extract and move into Tomcat lib directory:

Make Tomcat load the railo jars by editing catalina.properties to change the shared loader path:

Make Tomcat and Railo work together by modifying the web config file:

add the following inside the <web-app> element:

add the following inside <welcome-file-list> element:

Start up tomcat:

Back to Tomcat

Linking with Apache via Mod Proxy

Ensure the modules proxy and proxy_http are enabled. On Ubuntu this is done as follows:

Create vhost

This tells apache to forward all requests for CFM files to the railo instance.

Finally restart apache and railo and you should be good to go.

These are:

• Logging to DB instead of log files
• Runtime configuration of logging.

Logging to DB instead of log files

Coming from a web development background rather than a sysadmin background I'm far more comfortable manipulating and analysing data using SQL. So to be able to log all the queries or just the slow queries for an application to the db during application development or load testing is a huge benefit.

To enable logging to DB you can add the following to your my.cnf

The logs will be written to the 'slow_log' and 'general_log' tables in the mysql database.

Note - logging to tables has more overhead than logging to file, so would suggest using it primarily for development purposes.

Full details of the options are on the mysql manual on log tables

Runtime configuration of logging.

This allows you to turn on and off logging without restarting MySQL - which just saves a little bit of time and makes it much nicer for debugging problems.

To turn on the logging of all queries run:

And to turn them both off use:

If you also want to see queries not using indexes in the slow query log you can set the following variable:

Hope it helps, Mark

I've just received a copy of the Tomcat 6 Developer's Guide from packt publishing to review.

It's nice timing as I've been working with Tomcat 6 a bit lately and in the new year plan to move some of our production systems over to running Railo on top of Tomcat.

After the extremely busy year Learnosity has had I'm looking forward to reading a few books over the break and coming back in the New Year with lots more ideas and technology to implement.

This sets turns it on for everything except gif,jpeg,png or mp3, as these are already well compressed.

Cheers, Mark

In order to come up with a reliable solution to this we decided to use the SSH server we had available and tunnel the windows sharing across the local port forwards, much simpler and more reliable.

Thanks to this article it was a breeze to set up.

Steps are as follows:

• Create loopback adapter on windows
• Configure loopback adapter on windows
• Reboot
• Configure SSH connection
• Test it all out

Create loopback adapter on windows

We'll give your computer an additional (fake) IP address, and we'll port forward to that address instead of the computer's real IP. Windows XP will continue to do file sharing on the real IP address. We'll assign it an IP of 10.0.0.1 (that's what we configured putty to use above.)

1. System->Control Panel->Add Hardware
2. Yes, Hardware is already connected
3. Add a new hardware device (at bottom of list)
4. Install the hardware that I manually select
5. Network adapters
6. Microsoft , Microsoft Loopback Adapter
7. (Go through the installation procedure.)

Configure loopback adapter on windows

1. Open your new fake ethernet adapter (Network Connections) , enter a made-up IP address (I suggest 10.0.0.1, which is a privately routable address that most folk don't use.)
2. Enable Client for Microsoft Networks.
3. Disable File and Printer Sharing for Microsoft Networks
4. Enable Interent Protocol (TCP/IP)
5. Click on properties for TCP/IP.
6. Enter your chosen IP address (10.0.0.1), subnet mask (255.255.255.0). You can leave gateway blank.
7. Under advanced->WINS, Enable LMHosts Lookup and Disable NetBIOS over TCP/IP

Reboot

Configure SSH connection

• Download Putty
• Enter IP address
• Enter Auth Key (if using SSH keys)
• Enter Port forwards for: (these connect the ports on you local machine to
  • 10.0.0.1:137 to 127.0.0.1:137
  • 10.0.0.1:138 to 127.0.0.1:138
  • 10.0.0.1:139 to 127.0.0.1:139
  • 10.0.0.1:445 to 127.0.0.1:445
• Save the config.

Test it all out

• Open putty, load the settings and connect.
• Open Exporer and type in: \\10.0.0.1\

You should now be connected to your remote windows system over a secure encrypted tunnel.

Cheers, Mark

Running the command df was showing lots of free space.

However, a quick google on cp "no space left on device" turned up the suggestion to try:

This showed up the problem straight away - I had run out of inodes.

Once the problem is identified it is generally easy to resolve, so I figured out that there was a cron job that was running a wget task and not discarding the output, and so had saved 600,000+ files in their home directory.

However, when I tried to delete them I encountered another problem:

There were so many files that I couldn't use standard delete commands.

Another quick google turned up this gem:

I ran the following command to check that I was going to delete the correct files:

One final thing was to fix up the cron job that was causing the problem. Adding the parameter --delete-after to wget kept the directory nice and clean.

All fixed. One of the things this has reinforced for me is how important it is to have /home on a seperate partition. If this had not been the case then the problem would have taken longer to happen (due to larger filesystem) but would have been more destructive - as all systems and processes would not have been able to create new files.

• Automatically fixing file system errors
• Ignoring directories from updatedb

Automatically fixing file system errors

If you have a remote server, i.e. at a data center 10km or 1000km away this should prevent some panic when rebooting the server remotely.

Ext2/3 will do a filesystem check after a certain number of reboots or time. Most of the time any errors are fixed automatically, but certain errors by default require the root shell and the administrator to fix them. I've seen a few of these happen, but I have always replied yes to the prompts as I don't know enough about file systems to fix it I said no.

So, to prevent the need to rush to a data center and plug in a keyboard and mouse just to press the "Y" key there is and option to automatically assume yes.

On Ubuntu in the file /etc/default/rcS you need to change the following:

Ignoring directories from updatedb

To tell locate to ignore a directory you need to add it to the PRUNEPATHS line in the /etc/updatedb.conf file like so:

In the above code I have added the /srv entry to make it ignore all my backups which are held under the /srv directory.

Note: These tips were tested on Ubuntu linux, other distributions will have similar functionality but the file locations may vary.

Cheers, Mark

I found this article on Installing Dell OpenManage Server Administrator on Ubuntu x64 on Keith's Code and am posting here with modifications for 32 bit for my own reference

Dell's OpenManage Server Administrator is a powerful tool for keeping track of your server's health and making sure everything is running as it should. Unfortunately, Dell only released packages for RedHat and SuSE, so installing the software on Ubuntu can be tricky, at best.

There is some information on the Internet about getting the package to install on exotic distributions, but I never found anything definitive. This tutorial will guide you through installing the software and getting the web access up and running. 

My setup is: Dell 2950 with 1 Intel 2.2GHz Processor, 2GB RAM, PERC 5/i SCSI Raid Controller with 2 73GB 15K RPM SAS disks running Ubuntu 8.04.2 LTS 32-bit.

1. Install the kernel modules

The first step is installing the needed kernel modules to support IPMI:

Next,you will want to add those modules to the end of the /etc/modules file. This will allow them to be loaded at boot time.

2. Setup Apt to get the OMSA package

As stated before, Dell only released the OpenManage Server Administrator for RedHat and SuSE. However, someone was kind enough to create an installable Debian based package for us. In order to get access to that package, you will need to add the following line to /etc/apt/sources.list:

Then, you will need to install the Pulic Key for that repository. To do that, create a temporary directory in your home folder and run the following commands from that folder:

3. Install the needed packages

Now it's time to install all the packages that will be needed:

4. Start SNMP

The following commands will enable SNMP and get it going:

If you get and error like:

You may need to reconfigure the dynamic linker so that it knows the new libraries are.

5. Start the web services

Start the Dell OMSA web interface:

6. Add a user to access the OMSA site

If your system is setup properly, you shouldn't have a password for the root user. To access the OpenManage client, you need to have root access. There is a way to do this without giving the root user a password. I created a user called dellroot that will be able to access the OMSA client:
sudo useradd dellroot
sudo usermod -g root dellroot
sudo passwd dellroot

Enter a secure password for the user when prompted.

7. Check it out

Now you should be able to access the OpenManage web interface by going to https://<servername>:1311 (e.g., https://www.example.com:1311)

Make sure you are using https and you add the port number of 1311 to the end of the URL. You can login using the dellroot user you just created. 

If you are using firefox, you will have to add a security exception for the self-signed certificate the server is using.

Thanks Keith for the helpful reference.

Cheers, Mark