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 users should install the updates as a matter of course.
- 1 Installation
- 2 Enabling early microcode updates
- 3 Late microcode updates
- 4 Verifying that microcode got updated on boot
- 5 Which CPUs accept microcode updates
- 6 Enabling early microcode loading in custom kernels
- 7 See also
For AMD processors, install the package.
For Intel processors, install the package.
Enabling early microcode updates
Microcode must be loaded by the boot loader. Because of the wide variability in users' early-boot configuration, 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.
cpu_manufacturerwith your CPU manufacturer, .i.e
grub-mkconfig will automatically detect the microcode update and configure GRUB appropriately. After installing the microcode 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 is a separate partition) as follows:
... echo 'Loading initial ramdisk' initrd /boot/cpu_manufacturer-ucode.img /boot/initramfs-linux.img ...
Repeat it for each menu entry.
initrd option to load the microcode, before the initial ramdisk, as follows:
title Arch Linux linux /vmlinuz-linux initrd /cpu_manufacturer-ucode.img initrd /initramfs-linux.img ...
The latest microcode
cpu_manufacturer-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 or is updated. Otherwise, copy
/boot/cpu_manufacturer-ucode.img to your ESP at every update of the microcode package.
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/cpu_manufacturer-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=(...) initrd=/boot/cpu_manufacturer-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 is a separate partition) as required to the options line, and not in the main part of the stanza. E.g.:
options "root=root=UUID=(...) rw add_efi_memmap initrd=/boot/cpu_manufacturer-ucode.img"
initramfs-linux.imginitrd 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 ../cpu_manufacturer-ucode.img,../initramfs-linux.img ...
LILO and potentially other old bootloaders do not support multiple initrd images. In that case,
initramfs-linux.img will have to be merged into one image.
initramfs-linux.imgmust 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/cpu_manufacturer-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:
Late microcode updates
Late loading of microcode updates happens after the system has booted. It uses files in
For AMD processors the microcode update files are provided by.
For Intel processors no package provides the microcode update files (FS#59841). To use late loading you need to manually extract
intel-ucode/ from Intel's provided archive.
Enabling late microcode updates
Unlike early loading, late loading of microcode updates on Arch Linux are enabled by default using
/usr/lib/tmpfiles.d/linux-firmware.conf. After boot the file gets parsed by and CPU microcode gets updated.
To manually update the microcode on a running system run:
# echo 1 > /sys/devices/system/cpu/microcode/reload
This allows to apply microcode updates after pacman hook, e.g.:has updated without rebooting the system. You can even automate it with a
[Trigger] Operation = Install Operation = Upgrade Operation = Remove Type = File Target = usr/lib/firmware/amd-ucode/* [Action] Description = Applying CPU microcode updates... When = PostTransaction Depends = sh Exec = /bin/sh -c 'echo 1 > /sys/devices/system/cpu/microcode/reload'
Disabling late microcode updates
For AMD systems the CPU microcode will get updated even if FS#59840). To disable late loading you must override the tmpfile
/usr/lib/tmpfiles.d/linux-firmware.conf. It can be done by creating a file with the same filename in
# ln -s /dev/null /etc/tmpfiles.d/linux-firmware.conf
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: v2.2.
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: v2.2.
On AMD systems using early loading the output would look something like this:
[ 2.119089] microcode: microcode updated early to new patch_level=0x0700010f [ 2.119157] microcode: CPU0: patch_level=0x0700010f [ 2.119171] microcode: CPU1: patch_level=0x0700010f [ 2.119183] microcode: CPU2: patch_level=0x0700010f [ 2.119189] microcode: CPU3: patch_level=0x0700010f [ 2.119269] microcode: Microcode Update Driver: v2.2.
On AMD systems using late loading the output will show the version of the old microcode before reloading the microcode and the new one once it is reloaded. It would look something like this:
[ 2.112919] microcode: CPU0: patch_level=0x0700010b [ 2.112931] microcode: CPU1: patch_level=0x0700010b [ 2.112940] microcode: CPU2: patch_level=0x0700010b [ 2.112951] microcode: CPU3: patch_level=0x0700010b [ 2.113043] microcode: Microcode Update Driver: v2.2. [ 6.429109] microcode: CPU2: new patch_level=0x0700010f [ 6.430416] microcode: CPU0: new patch_level=0x0700010f [ 6.431722] microcode: CPU1: new patch_level=0x0700010f [ 6.433029] microcode: CPU3: new patch_level=0x0700010f [ 6.433073] x86/CPU: CPU features have changed after loading microcode, but might not take effect.
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 .
- Install (changing initrd is not required for detection)
# 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 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
CONFIG_BLK_DEV_INITRD=Y CONFIG_MICROCODE=y CONFIG_MICROCODE_INTEL=Y CONFIG_MICROCODE_AMD=y