Simon Krenger

The Linux kernel provides the tmpfs, which basically creates a file system in memory. This temporary file system can be used to store temporary data, such as caches or log files. Read more about tmpfs in the kernel documentation: tmpfs.txt

After reading this excellent article about using tmpfs in Linux, I decided to put it to the test. Even though the Linux kernel already does a good job caching files, I wanted to see the performance of this solution by applying different loads on it. For this, I am using the IOzone tool I already used for my ZFS tests (1) (2) and my Amazon EC2 IO test.

So one might want to ask why you’d want to sacrifice the fantastic stability and openness of Debian to install a vanilla (= original) kernel (Debian currently has 2.6.32). There are quite a few reasons for doing so. For example, the current kernel (2.6.38) has TRIM support, which is something I am looking for when using SSDs. Also, maybe you want to have a bleeding edge kernel just for the fun of it. So lets get started.

First order of business is to download a few packages, download the latest kernel from kernel.org and then unpack the kernel in /usr/src/:

In my traffic logs, I still notice a high interest in my post for the Java Service Wrapper. So I hereby provide a more current version of the Tanuki Java Service Wrapper for Windows x64 (Community Edition).

Also, please note:

While discussing the topic of cloud computing today, my co-worker mentioned the Amazon EC2 service and gave me a quick presentation of the features that are available. Since I am a big fan of virtualisation and the idea of scalable architectures, I immediately thought “This could be great to test some things out and is a wonderful opportunity to play around with different virtual machines”. So I signed up and did some quick tests to look at the IO performance…

I was especially interested in using these machines for storage and maybe some tests with databases. For these tests, my current Virtual Server serves as a reference, simply because EC2 could provide an alternative to that Virtual Server. In my tests, I included the following configurations:

One of the first things I do when I install PuTTY on a new machine, is to change the default color settings to something that is easier to read. This is a problem I have noticed on Red Hat machines, where the terminal color settings are not that great.

When you do an “ls” for example and the output contains folders, these are shown in a dark blue color, which makes it very hard to read on a black background. See the first picture in the gallery below.

Using Red Hat with Samba (Version 3.0.10-1.4E.11), I had the problem that Windows Explorer would not refresh properly when browsing the folders served by Samba. When creating a new folder, nothing showed up and it was necessary to manually refresh the Explorer window to see the “New Folder”. The same symptoms appeared with newly created files.

To fix this, add the following line to the [global] section of your smb.conf (usually located under /etc/samba/smb.conf):

[global]
refresh = 1

Sadly, I could not find this parameter in the official Samba manpages. Should anyone have more information or any documentation on this, feel free to let me know.

During maintenance, I had to disable all constraints of a table. I knew that Oracle SQL Developer (I really like it even though it is a developer tool and not aimed at Database Administrators) had built-in functions to do this, but since I could only access the database machine via SSH, I had to do it in SQL*Plus.

Luckily, SQL Developer is quite transparent about the commands it uses and I could therefore easily see what is going on when you disable all constraints on a table using the GUI. So here it goes…

When I was installing Red Hat Enterprise Linux on a server, the machine suddenly hung at the following line:

PCI: Probing PCI Hardware (Bus 00)

This is a well-known problem (as a simple search on Google will reveal), so to solve it simply add the following parameter to the kernel boot configuration:

Well, you’ve got to go with the time. krenger.ch is now reachable through IPv6 thanks to the IPv6 support of HostEurope:

simon@atlas:~$ ping6 www.krenger.ch
PING www.krenger.ch(2a01:488:66:1000:53a9:2967:0:1) 56 data bytes
64 bytes from 2a01:488:66:1000:53a9:2967:0:1: icmp_seq=1 ttl=64 time=0.022 ms
64 bytes from 2a01:488:66:1000:53a9:2967:0:1: icmp_seq=2 ttl=64 time=0.035 ms
64 bytes from 2a01:488:66:1000:53a9:2967:0:1: icmp_seq=3 ttl=64 time=0.042 ms

After upgrading a database from 10.2.0.1 to 10.2.0.5, I was unable to start the Oracle Enterprise Manager. Whenever I tried to do so, the log showed that it failed to start Database Control. Even when I deconfigured the Enterprise Manager, deleted the repository and started from scratch, I still ran into the same problem. In this post, I will describe the symptoms I encountered and also provide a solution.