Backtrack How-to Update: Fixing the Passphrase Silliness and Removing the Splash Screen.

by kriggins on March 8, 2012

in Uncategorized

For some time, there has been a bug in the cryptroot script that makes it odd when you enter your passphrase. Some, including me, have also found it kind of annoying that you have to press the F8 key to get to the console to enter your passphrase.

I have updated the how-to with the fix for the cryptroot bug and with instructions on how to remove the splash screen and boot straight to console mode.

Many thanks for James and Greg for figuring out how to so this.

Included below are the instructions which were added to the blog post. These steps can also be taken to correct an already built Backtrack USB drive. Simply boot the drive and follow the instructions below.

-Kevin

Fixing the Passphrase Entry Bug

When we boot our USB drive, it will appear to be stuck on the splash screen. What is actually happening is that the system is waiting on us to enter our luks password. We have two choices for doing so.

The first is to just type it in when we see the splash screen. This works as long as we have waited long enough for the system to be ready for us. However, it's kind of hard to tell what's going on.

The second option is to press the F8 key which takes us to the console. There we will see the system waiting for us to enter our passphrase and this is where this odd bug shows up.

Initially, it will look like 4 characters have already been entered. They haven't been, but that's what it looks like. Then, every type we press a key, it will reprint the line asking us to enter our passphrase. It is actually taking the input correctly, but, man, it's annoying :)

We can fix that. Greg M and James had a conversation in the comments about this topic and found the resources needed to fix it. James was kind enough to send me the changes that need to be made.

As mentioned, the problem is with the cryptroot script. This script is the script that requests our passphrase and mounts the encrypted volume. Kind of important stuff.

Greg and James used a patch file found in this post in the Backtrack Linux forums. Below I have included the actual changes to be made. Alternatively, you can use a patch file. The commands to perform the patch are as follows. BTW - that's a zero in the patch command.

Warning: You can make your system unbootable if the cryptroot script gets corrupted.

cd ~

wget http://www.infosecramblings.com/cryptroot.patch

patch -u /usr/share/initramfs-tools/scripts/local-top/cryptroot ./cryptroot-patch

If you prefer to do it the manual way, open the file /usr/share/initramfs-tools/scripts/local-top/cryptroot in your favorite editor. Go to line 275. You should see the following:

# Try to get a satisfactory password $crypttries times
 	count=0
 	while [ $crypttries -le 0 ] || [ $count -lt $crypttries ]; do

Add the following line right after 'count=0'

echo "Unlocking the disk $cryptsource ($crypttarget)"

The section should now look like this:

count=0
echo "Unlocking the disk $cryptsource ($crypttarget)"
while [ $crypttries -le 0 ] || [ $count -lt $crypttries ]; do

Next, skip down to line 291 and you'll see a the following:

if [ -z "$cryptkeyscript" ]; then
    cryptkey="Unlocking the disk $cryptsource ($crypttarget)\nEnter passphrase: "
if [ -x /bin/plymouth ] && plymouth --ping; then

Replace the middle line, the one that starts with cryptkey, with:

cryptkey="Enter passphrase: "

so that it now looks like this:

if [ -z "$cryptkeyscript" ]; then
    cryptkey="Enter passphrase: "
if [ -x /bin/plymouth ] && plymouth --ping; then

That's it. Save the file and we are ready to rebuild initrd. To do that, execute the following command.

update-initramfs -u

Now, if having to press the F8 key at boot bugs you, you can change the boot sequence to go directly to the console.

Warning: You can make your system unbootable playing around in here :)

To make the system boot to the console, edit the /boot/grub/grub.cfg file, search for the word 'splash', without the quotes, and delete the word  splash and only that word. The line will end up looking like this:

linux /vmliunx-3.2.6 root=/dev/mapper/vg-root ro text vga=791

If all goes well, you are now ready to cross your fingers and reboot.

Previous post:

Next post: