How can I add the Memtest86+ options back to the Grub menu?

Try opening a terminal and running

sudo chmod +x /etc/grub.d/20_memtest86+
sudo update-grub

Check to see if it's there

grep memtest /boot/grub/grub.cfg

Just done the same as I had it disabled

hob@hob-HP-dx5150-MT:~$ cat /boot/grub/grub.cfg |grep memtest
hob@hob-HP-dx5150-MT:~$ sudo chmod +x /etc/grub.d/20_memtest86+
[sudo] password for hob: 
hob@hob-HP-dx5150-MT:~$ sudo update-grub
Generating grub.cfg ...
Found linux image: /boot/vmlinuz-3.2.0-24-generic
Found initrd image: /boot/initrd.img-3.2.0-24-generic
Found linux image: /boot/vmlinuz-3.2.0-23-generic
Found initrd image: /boot/initrd.img-3.2.0-23-generic
Found memtest86+ image: /boot/memtest86+.bin
Found Ubuntu 11.10 (11.10) on /dev/sda6
Found Trisquel 5.5 (5.5) on /dev/sda8
Found Ubuntu 12.04 LTS (12.04) on /dev/sda9
done
hob@hob-HP-dx5150-MT:~$ cat /boot/grub/grub.cfg |grep memtest
### BEGIN /etc/grub.d/20_memtest86+ ###
menuentry "Memory test (memtest86+)" {
    linux16 /boot/memtest86+.bin
menuentry "Memory test (memtest86+, serial console 115200)" {
    linux16 /boot/memtest86+.bin console=ttyS0,115200n8
### END /etc/grub.d/20_memtest86+ ###

You could try creating the file if it's not there, using nano in a terminal

sudo nano /etc/grub.d/20_memtest86+

or with a gui editor

gksudo gedit /etc/grub.d/20_memtest86+

Fill it with

#!/bin/sh
set -e

if [ -f /usr/lib/grub/grub-mkconfig_lib ]; then
  . /usr/lib/grub/grub-mkconfig_lib
  LX=linux16
elif [ -f /usr/lib/grub/update-grub_lib ]; then
  . /usr/lib/grub/update-grub_lib
  LX=linux
else
  # no grub file, so we notify and exit gracefully
  echo "Cannot find grub config file, exiting." >&2
  exit 0
fi

# We can't cope with loop-mounted devices here.
case ${GRUB_DEVICE_BOOT} in
  /dev/loop/*|/dev/loop[0-9]) exit 0 ;;
esac

prepare_boot_cache="$(prepare_grub_to_access_device ${GRUB_DEVICE_BOOT} | sed -e "s/^/\t/")"

if test -e /boot/memtest86+.bin ; then
  MEMTESTPATH=$( make_system_path_relative_to_its_root "/boot/memtest86+.bin" )
  echo "Found memtest86+ image: $MEMTESTPATH" >&2
  cat << EOF
menuentry "Memory test (memtest86+)" {
EOF
  printf '%s\n' "${prepare_boot_cache}"
  cat << EOF
    $LX $MEMTESTPATH
}
menuentry "Memory test (memtest86+, serial console 115200)" {
EOF
  printf '%s\n' "${prepare_boot_cache}"
  cat << EOF
    $LX $MEMTESTPATH console=ttyS0,115200n8
}
EOF
fi

#if test -e /boot/memtest86+_multiboot.bin ; then
#  MEMTESTPATH=$( make_system_path_relative_to_its_root "/boot/memtest86+_multiboot.bin" )
#  echo "Found memtest86+ multiboot image: $MEMTESTPATH" >&2
#  cat << EOF
#menuentry "Memory test (memtest86+, experimental multiboot)" {
#EOF
#  printf '%s\n' "${prepare_boot_cache}"
#  cat << EOF
#   multiboot   $MEMTESTPATH
#}
#menuentry "Memory test (memtest86+, serial console 115200, experimental multiboot)" {
#EOF
#  printf '%s\n' "${prepare_boot_cache}"
#  cat << EOF
#   multiboot   $MEMTESTPATH console=ttyS0,115200n8
#}
#EOF
#fi

Make sure to run the chmod +x command on it afterwards.

I'd be a bit concerned that it's missing though - do you have everything else in grub.d ?

ls /etc/grub.d/


00_header        10_linux.bak       20_memtest86+  41_custom
05_debian_theme  10_linux.dpkg-old  30_os-prober   README
10_linux         20_linux_xen       40_custom

apt install memtest86+

This will automatically reconfigure grub and add the entry to the boot menu.

If you get the error memtest86+ is already the newest version then use sudo apt-get install --reinstall memtest86+

If all else fails you can get a bootable ISO that you can burn to a CD and boot from. Of course if you are booting UEFI you should be here instead.

I had the same issue, and due to the fact that I have EFI on my laptop the memtest86+ version 4.x shipped by ubuntu won't work, since EFI is only supported by version 5 and newer.

The latest versions are non-GPL and must be downloaded manually from the memtest website(they have ISO and USB images), but at least they are free of charge.

I didn't managed to make this work in 2 days, then I checked Synaptic for grub packages... Seems to be, that the absence of package grub-imageboot are the root of the problem.

sudo apt-get install grub-imageboot

This what I did to add the now latest (non free) memtest86+ to the grub boot menu for UEFI booting. Current memtest version is 8.2. Tools needed: Disk Image Mounter and grub-customizer, the latter is only for convenience :) Files: memtest binary (see below)

1. Download the memtest binary from: https://www.memtest86.com/download.htm The 'Image for creating bootable USB Drive on a Windows/Linux/Mac system' is fine.
2. Extract the IMG file (memtest86-usb.img)
3. open the img file with disk image mounter (right mouse button on Ubuntu)
4. from the mounted image extract /EFI/BOOT/BOOTX64.efi
5. make memtest86 boot directory:

   sudo mkdir /boot/efi/EFI/memtest86

6. copy the BOOTX64.efi to your new folder on the boot partition (eg /boot/efi/EFI/memtest86)
7. open grub-customizer
8. Add menu item, give it a name, choose type: other
9. add the following boot sequence (assuming you boot from hd0):

insmod part_gpt
insmod fat
set root='hd0,gpt2'
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  1A22-970F
else
  search --no-floppy --fs-uuid --set=root 1A22-970F
fi
chainloader /EFI/memtest86/BOOTX64.efi

10. save and quit grub-customizer

11. reboot and enjoy Memtest86

See also this answer on the Unix StackExchange. In short, the Linux Kernel has a simple memory test built in.

Do grep CONFIG_MEMTEST "/boot/config-$(uname -r)" to determine if it's enabled or not (it'll be commented out if it's not enabled).

Then, edit /etc/default/grub and add memtest to GRUB_CMDLINE_LINUX_DEFAULT, run sudo update-grub, and then reboot.

Once it's finished booting up (it'll take longer than normal given it has to also run the memory test), check /var/log/kern.log for the result of the test.