I installed 16.04 Server and I have had a similar message in my logs and this message when I upgrade initramfs packages through normal package upgrade.

Setting up initramfs-tools (0.122ubuntu8.3) ...
update-initramfs: deferring update (trigger activated)
Processing triggers for initramfs-tools (0.122ubuntu8.3) ...
update-initramfs: Generating /boot/initrd.img-4.4.0-38-generic
W: mdadm: /etc/mdadm/mdadm.conf defines no arrays.

Is this normal, or is Ubuntu expecting to find a RAID because of some misconfiguration somewhere?

Here is the contents of /etc/mdadm/mdadm.conf:

# mdadm.conf
# Please refer to mdadm.conf(5) for information about this file.

# by default (built-in), scan all partitions (/proc/partitions) and all
# containers for MD superblocks. alternatively, specify devices to scan, using
# wildcards if desired.
#DEVICE partitions containers

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts

# definitions of existing MD arrays

1 Answer 1


The error says W: mdadm: /etc/mdadm/mdadm.conf defines no arrays.

I reckon that the warning is displayed whenever there's no ARRAY line in mdadm.conf.

The obvious solution would be to add one:

ARRAY <ignore> devices=/dev/sda

Worked for me...

  • Thank you very much, Steffen. This has stopped the warnings.
    – Paul
    Jan 2, 2017 at 19:29
  • 2
    What does it do? It wont show error? Or wont show and still will crash? Or it doesnt crash aalready but just shows error? If just showing then i dont care to add something if not fixing crashing.
    – Kangarooo
    Mar 5, 2017 at 23:48
  • 3
    @Kangarooo There is no "crashing" problem reported anywhere in this question. The problem is just to make a warning go away. Steffen has provided a proper solution by telling mdadm that it should not expect there to be any arrays, which is all the warning was telling about.
    – Paul
    Mar 6, 2017 at 1:01
  • 3
    Interesting: I have two instances of 16.04.4 installed at about the same time on similar hardware. The first has /etc/mdadm/mdadm.conf and therefore gives the error; the second does not even have that file. One wonders what triggers the installation of that file — maybe it figures out (wrongly?) that an array controller is present even if it is not being used? Mar 2, 2018 at 9:19
  • I can't reply to Steffen Breitbach because my "reputation on this website is too low". I followed his instructions about adding ARRAY <ignore> devices=/dev/sda but I get this error -bash: ignore: No such file or directory
    – sumguy
    Aug 3, 2019 at 20:30

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