Does MTU matter?

Recently, I have changed my ISP to HKBN. I chose the plan BB10 which provide 10Mb upload and download speed. This is much better than ADSL. For such high bandwidth, I want to use my NSLU2 Linux box to setup a web server at my home.

However, there is some problems. I found that not every machine can access my web server. Ellen using Pacific Supernet cannot access the web server. Besides, a friend of mine using Netvigator faces the same problem. However, the W3C's HTML validate can access my web server to validate my HTML files. Moreover, my company can also access the server.

This is really strange. Today, I try to tackle the problem. I tried to set the server in DMZ at my router but fail. Then, I look for other setting in the router's configuration. I find the item "MTU". MTU stands for "maximum transmission unit". Currently setting is 1500 which is the maximum allowed value. I try to change the value smaller to 1400. It works! However, I want to ask, "Does MTU matter?".

Install Ubuntu Linux Cont'

Today, I go to fine tune the Ubuntu Linux in my desktop. One disadvantage of Ubuntu comparing with Debian is Ubuntu supports less packages officially. For example, the SCIM, a Input Method modules support many languages, is not included in Ubuntu.

To install the SCIM, I includes the "Universe" packages pool in my Ubuntu and install the SCIM. The "Universe" pool contains some extra packages which is not officially support by Ubuntu team. After install the SCIM, I try to run the "Setup" of SCIM. However it can't run properly -- seg. fault. As a Debian user, this problem becomes the weak points of Ubuntu. In Debian, it officially support much more packages than Ubuntu. I think Ubuntu need to put more effort to support more packages.

Finally, I decide to install a Debian on my desktop and give up the fine tuning the Ubuntu. The installation of Debian is more complicated than Ubuntu. Fortunately, I am a experienced Debian User.

After installation complete, the XWindow can start correctly. However, my sound card doesn't work. To solve this, I need to install ALSA package via the "aptitude" (Note: aptitude is a Debian package manager). Moreover, the middle button of my mouse doesn't work and this is similar to the case of Ubuntu. The solution was mentioned yesterday's BLOG entry. Then, I install the SCIM and other Chinese related packages. The SCIM works properly!

Install Ubuntu Linux

According to DistroWatch, Ubuntu Linux is the most popular Linux distribution. Today, I want to experience how good it is.

The installation is quite simple and straight forward. It can detect all my hardware and can run up XWindow without any manual settings. My sound card and CD RW also works properly.

There is one problem on my mouse. The middle key doesn't works. With hours of investigation, I find the solution. The problem is due to the "psmouse" kernel module. It detects my mouse incorrectly. To solve the problem, the parameter "proto=imps" should be used while loading the kernel module. So, I create a file "psmouse" in "/etc/modprode.d" with the following contents:

options psmouse proto=imps 

CSV File Format

CSV stands for Comma Separated Values. It is a common file format for storing tabular data, e.g. spread sheet data. The file format of CSV is simple -- a text file, values are separated by comma (,) and rows are separated by newline. However, there is still some tricky in the format.

The tuck point is how to escape the comma in the values. If a value contains commas, the value should be quoted with double-quote ("). e.g.:

value one,"value two with ',' inside",value three

If a value contains a double-quote, the value should be quoted with double-quote and the double-quote in the value should be escaped with another double-quote. e.g.:

value one,"value two with '""' inside",value three

The specification of the CSV is described in RFC4180.

Even there is an RFC standard for CSV format, there are some deviation standard exists. In some applications, the comma and double-quote is escaped by a back-slash (\). Moreover, the character encoding is not stored in the file format and causes ambiguity. So, it is not trivial while using this format.

Missing Samba after Upgrade Packages

My Old PC is a Debian Linux box. I have not upgraded the packages for a long time. Therefore, yesterday, I run Aptitude to do a mass updates. Today, I find the Samba is removed after the mass updates.

I run Aptitude to figure out the reason. I found the Samba has some broken dependency -- libdb4.1. Then, I search the libdb4.1 on the Web. In the unstable branch of Debian, it only supports AMD64 Architecture. Oh! Some packages in Debian is moving from unstable to stable branch.

So, I edit the "/etc/apt/sources.list" to add the stable repository:

deb http://ftp.hk.debian.org/debian/ stable main non-free contrib

Then run Aptitude and update the package list. The broken dependency problem solve and Samba can be installed.

Free Virtual Machine -- QEMU

Long time ago, I have tried QEMU. I run QEMU in Debian and the guest OS is Win2000. It worked but it was very slow. Recently, I visit the site of QEMU and there is a QEMU Accelerator Module. According to the site, with the accelerator, QEMU's performance is comparable to commercial products.

I want to try QEMU in Windows XP. However, the accelerator for windows is alpha version. Anyway, I still want to try to download and run it on my Win XP. The guest OS is the sample Linux which can be download the QEMU's website. It crashes in LILO. Too bad!!!! After that, I try to run QEMU without the accelerator. It works fine. I think the accelerator for windows need to be improved.

Then, I try another accelerator module -- qvm86. This is a open source accelerator module. This module is even worse. It crashes my WinXP.

Related Links:
Offical site of QEMU
QEMU porting on Windows
QVM86

Trojan Found

Two days ago, my sister reported to me that her computer had torjan. On one hand, IE has many many security bugs. On the other hand, she have not done Windows Update for a long long time. I guess the trojan was planted by visiting some bad web-site. Actually, I have told her don't use IE, use Firefox!

The trojan was found by AVG virus scanner. Actually, there are two trojans found: PSW.Generic.BWM and PSW.Generic.DAP. I search them in google, and nothing related found. The infected file are "WINDOWS\SYSTEM32\msd.dll" and "WINDOWS\SYSTEM32\roddll.dll".

For the filename "roddll.dll", I find some information on the Web. There is a trojan named "Troj/Ragrok-A". This trojan creates "WINDOWS\rundll132.exe" and the "roddll.dll" file. Moreover, it also creates a registry entry to execute the "rundll132.exe" in HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run. So, it is not difficult to remove.

For the "msd.dll", there is not much information find. Anyway, I inspect the HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run in the registry, I find a suspect entry: "WINDOWS\system\rundll32.exe". I search on Google by key words "rundll32.exe" and "trojan". I find that rundll32.exe file is located in the c:\windows\System32 folder. In other cases, rundll32.exe is a virus, spyware, trojan or worm! Then, I remove the entry in the registry, remove the "rundll32.exe" in "WINDOWS\SYSTEM", as well as the "msd.dll". Then, reboot. Everything works fine! The AGV scanner doesn't find any trojan.