hacking inside the grub prompt

Yesterday, I was setting up Linux on a new PC and went ahead with a custom partition table using druid. I didn't set up the /boot partition and as a result the grub configuration file (/etc/grub.conf) was incorrect. Then grub stopped at the grub prompt (thus giving me a chance to temporarily correct the problem)

I found this article very helpful in telling grub what I wanted, so that it proceeded with finding the Linux image and loading it.

Incidentally, this machine had a SATA drive, and ata_piix used to complain and kernel panic at boot, I removed the SSC pin (spread spectrum clocking feature) and it booted fine after that.

sudo without password

You can execute root-level commands with sudo without typing passwords by editing /etc/sudoers file to have a line like this (if your user name is alice):

alice (ALL)=ALL NOPASSWD: ALL

The file is read-only. You edit this file with the following command (which opens the file in vi):

visudo -f /etc/sudoers

gcc offseof macro warning

Nathan Sidwell had this really neat trick that gets us around the gcc compiler warning on the usage of the offsetof macro.

Rather than using the offsetof macro, use the one below:

#define myoff(T,m) ((size_t)(&((T *)1)->m) - 1)

The trick is to use the address '1' rather than '0' (which the offsetof macro uses) and thus pacify gcc.

The issue of this compiler warning is a hotly debated issue.

remove carriage returns from Windows files on Linux

Sometimes you have to work with a file created in Windows from Linux. The file has the "\r" (0x0d) that can cause trouble for some Linux apps.

You can easily remove them using "tr" cmd.

cat windows_file | tr -d "\r"

The above command should write the new file to stdout. Save it to a new file, and this will not have "\r" characters.

What problems may happen
The "\r" character is generally interpreted by terminals to move the cursor to the beggining of the current line. The "\n" character moves the cursor to the next line. Generally, a text file created in Windows will have a "\r\n" sequence at the end of each line.

What would happen if you were to remove the last character from each line and try to display it to the terminal? Now after each line, the cursor would advance to the beginning of the line ("\r") but not advance to the next line. Thus each line will overwrite the other.

This could happen if you have a perl script where 'chomp' is used to remove the last character of each line.

cpan2rpm - perl modules and rpms

Today I discovered this amazingly useful utility. This helps in building the perl module rpms that are necessary for other perl module rpms (dependencies) to install.

If you have an rpm install, the dependent rpms need to be listed in the rpm database on your machine. The number 1 source for perl modules is CPAN but they don't necessarily release rpms for the modules. With the cpan2rpm, you can get the required perl module from CPAN, make the rpm and then install the module with rpm.

The really nice thing about cpan2rpm is that it can locate the module from CPAN automatically, for ex: if you invoke it like this: cpan2rpm XML::Simple, it will locate the XML::Simple module from CPAN, copy it over and build the rpm at /usr/src/redhat/RPMS/noarch/perl-XML-Simple-2.14-1.noarch.rpm.

Sometimes, cpan2rpm won't be able to find the module on CPAN. Then you can manually locate it from CPAN archives, download it and then point cpan2rm at the local gzip file and it will go ahead and build the rpm.

ex:
wget http://search.cpan.org/CPAN/authors/id/S/SB/SBURKE/HTML-Format-2.04.tar.gz
cpan2rpm /home/downloads/HTML-Format-1.23.tar.gz

Rather long winded - instead of simply installing the module, but if a latter part of the install uses rpm, you need to make sure the rpm database knows about the dependencies, so this is a necessary step.

Once again, it is a good thing that there's more than one way to do it!

Backing up DVDs - Elizabeth Town

I used DVDShrink to create a backup of this movie. The movie played fine on the hard disk but after copying it over to a DVD, I found that the DVD did not play past chapter 10.

I then used pgcedit to open the movie files on the hard disk. It immediately found the problem - apparently there is a bug in DVDShrink that creates a slightly corrupted index. Pgcedit offerred to correct the problem and change the DVD files accordingly.

After doing this step, I could burn a successful DVD with Roxio.

I'm not sure if DVDShrink encountered some form of copy protection or if it was actually a bug on DVDShrink. Most recently released movies seem to come up with different and newer DRM techniques.

Hotel Rwanda

This is a well made movie about a man who saved 1200 victims from one of the bloodiest massacres in recent history. The movie is based on the true story of Paul Rusesabagina.

Watching this movie, I couldn't quite come to grips with the limits of human atrocities against humans and the inability of the better-off people in the 1st world to act quickly to avoid such horrors.

Human Resources Watch reports the massacre. Reading it leads me to believe that the reason for the lack of intervention was the economics. The cost it took to save a million lives from terrible violence was too much to bear - for the wealthiest of nations.

There was also the fear of loosing personnel. I copy below:

"But instead of using the peacekeeping troops to stop the genocide, the U.N. sought primarily to protect its soldiers from harm. Dallaire was ordered to make avoiding risk to soldiers the priority, not saving the lives of Rwandans. To do so, he regrouped his troops, leaving exposed the Rwandans who had sought shelter in certain outposts under U.N. protection. In the most dramatic case—for which responsibility may belong to commanding officers in Belgium as much as to Dallaire—nearly one hundred Belgian peacekeepers abandoned some two thousand unarmed civilians, leaving them defenseless against attacks by militia and military. As the Belgians went out one gate, the assailants came in the other. More than a thousand Rwandans died there or in flight, trying to reach another U.N. post."

After exploiting Rwanda from 1916 through 1961, Belgium could not deal with the economics of saving a million Tutsi lives. These were the same people Belgium favored during their regime, the people, who under the Belgian command resorted to extreme violence against the Hutus. Some claim that the later uprising of the Hutus against Tutsis were largely due to the ethnic division enforced by Belgium in their divide-and-rule policies.

What is still not clear to me is why the 1st world did not threaten the genocidal government with economic sanctions. This would not have required much capital. Perhaps they looked at the situation from an economic view-point and just said - "why bother, what is in it for me?" I copy below:

"Discussion about the size, mandate, and strategy for a new peacekeeping force continued until May 17, in part because of U.S. rigidity in applying its new standards for approval of peacekeeping operations, in part because of hesitations sparked by RPF opposition to any intervention. Manoeuvering by nations supplying troops and those supplying equipment consumed another two months, so that the second peacekeeping force landed only after the RPF had defeated the genocidal government. The slowness and ineptness of national and international bureaucracies in mounting the operation was not unusual, nor was the attempt by participating nations to get the most or give the least possible. What was extraordinary was that such behavior continued to be acceptable in the context of genocide, by then openly acknowledged by national and international leaders."