Linux – Grub makeactive command in Grub2

This is pretty easy. Partition your disk, install Windows and Ubuntu. Use TrueCrypt on the Windows partition, which will encrypt Windows but leave Ubuntu unencrypted.

You'll then find you can probably only boot into Windows, and then through the TrueCrypt bootloader. Sounds like you're there already.

Say your disk is sda, with Windows on sda1 and Linux on sda2 (this is hypothetical, yours looks like it won't be sda2). TrueCrypt will install onto the MBR on sda and overwrite GRUB.

Use the Ubuntu distro CD to boot up a live CD, then chroot into your pre-installed system. Like so:

sudo su -
mkdir -p /mnt/ubuntu
mount /dev/sda2 /mnt/ubuntu
mount --bind /proc /mnt/ubuntu/proc
mount --bind /dev /mnt/ubuntu/dev
chroot /mnt/ubuntu

Then install the GRUB bootloader, but to sda2, rather than sda.

grub-install /dev/sda2 --force

Then, when you reboot, you'll still get the TrueCrypt loader asking you for a password to boot from sda -> sda1 into Windows. But when you press ESCAPE you'll get the option to bypass and boot straight into Linux, but from sda2 rather than the MBR.

But wait

Before you do this, one caveat: if you get your grub-install wrong, and overwrite the sda MBR, or if you do a kernel upgrade which triggers GRUB to overwrite the MBR, you'll find you need to reinstall the TrueCrypt bootloader in order to get back into Windows. This is a massive hassle if you're not prepared.

I'd suggest that before you fiddle with GRUB, you back up the TrueCrypt bootloader stuff from within Linux. That way, when you break TrueCrypt and can only get into Linux, you can easily write it back.

Back up your TrueCrypt boot loader:

dd if=/dev/sda of=~/truecrypt.mbr count=1 bs=512
dd if=/dev/sda of=~/truecrypt.backup count=8 bs=32256 # Just in case

Restore your TrueCrypt boot loader (I call this restore-truecrypt.sh):

sudo dd if=~/truecrypt.mbr of=/dev/sda count=1 bs=512
sudo dd if=~/truecrypt.backup of=/dev/sda count=8 bs=32256
sudo grub-install /dev/sda2 --force

I have both of these sets of commands in little shell scripts, which I keep handy. When I accidentially zap my bootloader (it happens) I don't want to be Googling around for the commands or reading man.

Oh, and a word on compatibility. When I write "GRUB", I meant GRUB 1 or 2. Personally, I do it with GRUB 2 on 10.04 and Windows 7... but it worked fine with older versions of GRUB, Windows and Linux.

CentOS 7 still uses the deprecated vga parameter. You wanted step-by-step, you get it:

1. Make yourself root: sudo su
2. vi /etc/default/grub
3. In Vi, press i or Insert-key on your keyboard to enter the edit mode.
4. Add vga=792 inside the "-quotes for GRUB_CMDLINE_LINUX, f.ex. GRUB_CMDLINE_LINUX="crashkernel=auto rhgb quiet vga=792"
5. Press Esc and type :wq and hit Enter to save and exit Vi.
6. grub2-mkconfig -o /boot/grub2/grub.cfg
7. reboot

This procedure applies not just Mac, but all host operating systems running Virtualbox: Windows, Linux.

@garethTheRed's answer might work in some versions of some Linux distros, but the trick is to find the correct parameters for your environment. At least with some Red Hat distros you need to fall back to old, deprecated habits.