how to restore boot folder?

No laughing!

I just did sudo rm -vr /boot/*. Is there a way to restore the content?

Just to clarify why I would do this: I have a SD-card with a boot-partition mounted at /media/boot that I wanted to replace.

The computer is still running. What are my options?

Update (my solution): This might be a little unsatisfactory for future reference, but I simply backed up all my files and then reinstalled Ubuntu.

Important note if you have the same problem: Don't turn off your computer until you have everything backuped

You can restore /boot from a live CD using a chroot.

http://ubuntuforums.org/showpost.php?p=11893615&postcount=2

Assuming ubuntu is installed in /dev/sda1 ...

sudo mount /dev/sda1 /mnt
sudo cp /etc/resolv.conf /mnt/etc/

Depending on your configuration, you may also need to copy the hosts file

sudo cp /etc/hosts /mnt/etc/

mount /mnt/dev and chroot, configure the chroot

sudo mount --bind /dev/ /mnt/dev
sudo chroot /mnt /bin/bash
mount -t proc none /proc
mount -t sysfs none /sys
mount -t devpts none /dev/pts

To avoid locale issues and in order to import GPG keys

export HOME=/root
export LC_ALL=C

Restore grub

grub-install /dev/sda

If that does not restore the grub files in /boot, reinstall grub first apt-get install --reinstall grub2 grub-install /dev/sda

Reinstall the kernel

apt-get install --reinstall linux-gnereic

Unless you have backups, then the answer is "You can't."

The OS does not keep a backup of that folder for you (or any other to my knowledge) without you expressly telling it to by installing or configuring a backup program.

Your best way forward IMO is to quickly backup any and all files you need to keep from this machine, and reinstall the operating system. I've marked this answer as community wiki so that if I'm wrong, people can update my answer with a note indicating that there's a better way. You may want to wait a day or two if you can in case anyone posts a better answer.