Recursively generate MD5 checksums

Garda — Wed, 26 Oct 2011 14:53:27 GMT

I wanted to generate MD5 checksums of a whole bunch of files in a directory. It turns out that this is not as straightforward as it should be. IMO it should be completed with: md5sum -br *

Unfortunately it was not as straightforward. I found this blog entry after searching for a while and adapted this to what I needed. To generate checksums, I used the following:

Code:

find . -type f -print0 | xargs -0 md5sum -b

(Note: for the above to work, "cd" to the top level directiory, or use "find /home/username/folder/" instead of "find .")

Some explanation. The "find" command is used to list filenames based on a particular search. "-type f" lists only files (ie. "-type d" lists only directories). "-print0" is an option to use if the filename contains newline characters, it instead finishes entries with a NULL character. Correspondingly, the "-0" switch needs to be used with "xargs".

"xargs" is used to build commands using piped input. So the above basically repeats everything after the "-0" switch over and over with the input from "find" appended each time. If you want to use a different command, just replace "md5sum -b" with any other command.

Also, if sums are stored to a text file, they can be verified using:

Code:

md5sum -c filename.txt

Add splash image to GRUB

Garda — Mon, 15 Dec 2008 08:59:36 GMT

I wanted to add something to the default GRUB screen that greets you as you start Linux more nicely than monochrome text.
I did this using the splashscreen feature of GRUB version 1, the boot loader that I had installed.
I used Krita for some of the image manipulation, but GIMP is also a good app. On Debian, you can get GIMP as root with

Code:

apt-get install gimp

Splash images in GRUB have to be in .xpm or "X PixMap" format and they have to be 640x480 in size, and 14 colours.
I found a nice image of tux on the internet and converted it to the right format.
For interest, images can be .xpm or .xpm.gz (a gzipped image) which are created using

Code:

cat image.xpm | gzip > image.xpm.gz

Images are completely uncompressed and compressing using gzip does significantly reduce their size, however it's not really necessary given that they are only ~300KB anyway.

I placed the image in /boot/grub

To make the image appear during boot, I added the line to /boot/grub/menu.lst
This file may be called something different depending on your distro.

Code:

splashimage=(hd0,0)/grub/splash.xpm

(hd0,0) may be different depending on the location of where Linux is installed for you. There should be a section in this file that looks something like this:

Code:

title		Linux
root		(hd0,1)
kernel		/vmlinuz root=/dev/hda2 ro

In this case (hd0,1) should be used. This is probably the easiest way of figuring out your drive's GRUB designation.
I'm not sure why, but the splash image line needs to be entered into the GRUB configuration file in the early part of the file before the OS lists, otherwise it does not work.
I could not get really good results with Krita, but I was able to find a nice Debian package (there may be a similar package for other distros) with pre-made images

Code:

apt-get install grub-splashimages

These images are placed in /boot/grub/splashimages/ and can be accessed using a line such as

Code:

splashimage=(hd0,0)/grub/splashimages/debsplash.xpm.gz

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Recursively generate MD5 checksums

Add splash image to GRUB