Processor manufacturers release stability and security updates to the processor microcode. While microcode can be updated through the BIOS, the Linux kernel is also able to apply these updates during boot. These updates provide bug fixes that can be critical to the stability of your system. Without these updates, you may experience spurious crashes or unexpected system halts that can be difficult to track down.
Users of CPUs belonging to the Intel Haswell and Broadwell processor families in particular must install these microcode updates to ensure system stability. But all Intel users should install the updates as a matter of course.
- 1 Installation
- 2 Enabling Intel microcode updates
- 3 Verifying that microcode got updated on boot
- 4 Which CPUs accept microcode updates
- 5 Enabling Intel early microcode loading in custom kernels
- 6 See also
For AMD processors the microcode updates are available in, which is installed as part of the base system. No further action is needed.
For Intel processors, install the package, and continue reading.
Enabling Intel microcode updates
Microcode must be loaded by the bootloader. Because of the wide variability in users' early-boot configuration, Intel microcode updates may not be triggered automatically by Arch's default configuration. Many AUR kernels have followed the path of the official Arch kernels in this regard.
These updates must be enabled by adding
/boot/intel-ucode.img as the first initrd in the bootloader config file. This is in addition to the normal initrd file. See below for instructions for common bootloaders.
grub-mkconfig will automatically detect the microcode update and configure GRUB appropriately. After installing the package, regenerate the GRUB config to activate loading the microcode update by running:
# grub-mkconfig -o /boot/grub/grub.cfg
Alternatively, users that manage their GRUB config file manually can add
/boot/intel-ucode.img as follows:
... echo 'Loading initial ramdisk' initrd /intel-ucode.img /initramfs-linux.img ...
Repeat it for each menu entry.
/etc/grub.d/to manage your GRUB configuration needs.
initrd option to load the microcode, before the initial ramdisk, as follows:
title Arch Linux linux /vmlinuz-linux initrd /intel-ucode.img initrd /initramfs-linux.img ...
The latest microcode
intel-ucode.img must be available at boot time in your EFI System Partition (ESP). The ESP must be mounted as
/boot in order to have the microcode updated every time is updated. Otherwise, copy
/boot/intel-ucode.img to your ESP at every update of intel-ucode.
EFI boot stub / EFI handover
For kernels that have been generated as a single file containing all initrd, cmdline and kernel, first generate the initrd to integrate by creating a new one as follows:
cat /boot/intel-ucode.img /boot/initramfs-linux.img > my_new_initrd objcopy ... --add-section .initrd=my_new_initrd
Edit boot options in
/boot/refind_linux.conf as per EFI boot stub above, example:
"Boot with standard options" "rw root=UUID=(...) quiet initrd=/boot/intel-ucode.img initrd=/boot/initramfs-linux.img"
Users employing manual stanzas in
esp/EFI/refind/refind.conf to define the kernels should simply add
/boot/intel-ucode.img as required to the options line, and not in the main part of the stanza.
initramfs-linuxinitrd files. The period signs also do not signify any shorthand or missing code; the
INITRDline must be exactly as illustrated below.
Multiple initrd's can be separated by commas in
LABEL arch MENU LABEL Arch Linux LINUX ../vmlinuz-linux INITRD ../intel-ucode.img,../initramfs-linux.img APPEND <your kernel parameters>
LILO and potentially other old bootloaders do not support multiple initrd images. In that case,
initramfs-linux will have to be merged into one image.
intel-ucodemust not be compressed. Otherwise, the kernel might complain that it can only find garbage in the uncompressed image and fail to boot.
intel-ucode.img should be a cpio archive, as in this case. It is advised to check whether the archive is compressed after each microcode update, as there is no guarantee that the image will stay non-compressed in the future.
In order to check whether
intel-ucode is compressed, you can use the
$ file /boot/intel-ucode.img /boot/intel-ucode.img: ASCII cpio archive (SVR4 with no CRC)
initramfs-linuxmust be concatenated on top of the
To merge both images into one image named
initramfs-merged.img, the following command can be used:
# cat /boot/intel-ucode.img /boot/initramfs-linux.img > /boot/initramfs-merged.img
/etc/lilo.conf to load the new image.
... initrd=/boot/initramfs-merged.img ...
lilo as root:
Verifying that microcode got updated on boot
Use dmesg to see if the microcode has been updated:
$ dmesg | grep microcode
On Intel systems one should see something similar to the following on every boot, indicating that microcode is updated very early on:
[ 0.000000] CPU0 microcode updated early to revision 0x1b, date = 2014-05-29 [ 0.221951] CPU1 microcode updated early to revision 0x1b, date = 2014-05-29 [ 0.242064] CPU2 microcode updated early to revision 0x1b, date = 2014-05-29 [ 0.262349] CPU3 microcode updated early to revision 0x1b, date = 2014-05-29 [ 0.507267] microcode: CPU0 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507272] microcode: CPU1 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507276] microcode: CPU2 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507281] microcode: CPU3 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507286] microcode: CPU4 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507292] microcode: CPU5 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507296] microcode: CPU6 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507300] microcode: CPU7 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507335] microcode: Microcode Update Driver: v2.00 <email@example.com>, Peter Oruba
It is entirely possible, particularly with newer hardware, that there is no microcode update for the CPU. In that case, the output may look like this:
[ 0.292893] microcode: CPU0 sig=0x306c3, pf=0x2, revision=0x1c [ 0.292899] microcode: CPU1 sig=0x306c3, pf=0x2, revision=0x1c [ 0.292906] microcode: CPU2 sig=0x306c3, pf=0x2, revision=0x1c [ 0.292912] microcode: CPU3 sig=0x306c3, pf=0x2, revision=0x1c [ 0.292956] microcode: Microcode Update Driver: v2.00 <firstname.lastname@example.org>, Peter Oruba
On AMD systems microcode is updated a bit later in the boot process, so the output would look something like this:
[ 0.807879] microcode: CPU0: patch_level=0x01000098 [ 0.807888] microcode: CPU1: patch_level=0x01000098 [ 0.807983] microcode: Microcode Update Driver: v2.00 <email@example.com>, Peter Oruba [ 16.150642] microcode: CPU0: new patch_level=0x010000c7 [ 16.150682] microcode: CPU1: new patch_level=0x010000c7
Which CPUs accept microcode updates
Users may consult either Intel or AMD at the following links to see if a particular model is supported:
Detecting available microcode update
It is possible to find out if the
intel-ucode.img contains a microcode image for the running CPU with AUR.
- Install (changing initrd is not required for detection)
- Install AUR
# modprobe cpuid
- Extract microcode image and search it for your cpuid:
# bsdtar -Oxf /boot/intel-ucode.img | iucode_tool -tb -lS -
- If an update is available, it should show up below selected microcodes
- The microcode might already be in your vendor bios and not show up loading in dmesg. Compare to the current microcode running
grep microcode /proc/cpuinfo
Enabling Intel early microcode loading in custom kernels
In order for early loading to work in custom kernels, "CPU microcode loading support" needs to be compiled into the kernel, not compiled as a module. This will enable the "Early load microcode" prompt which should be set to "Y".
CONFIG_BLK_DEV_INITRD=Y CONFIG_MICROCODE=y CONFIG_MICROCODE_INTEL=Y