Public bug reported:
In Ubuntu 20.04 (kernel 5.4.0), the /dev/md directory which contains
/dev/md/<NAME> links apparently no longer exists.
# ls -l /dev/md*
brw-rw---- 1 root disk 9, 127 Mar 31 08:46 /dev/md127
#
Compare to an 18.04 system:
$ ls -l /dev/md*
brw-rw---- 1 root disk 9, 0 Mar 26 08:01 /dev/md0
brw-rw---- 1 root disk 9, 1 Mar 26 08:01 /dev/md1
/dev/md:
total 0
lrwxrwxrwx 1 root root 6 Mar 26 08:01 0 -> ../md0
lrwxrwxrwx 1 root root 6 Mar 26 08:01 1 -> ../md1
I've confirmed this is also the case with Debian 10 (also 5.4.0), so it
appears to have been an upstream change. It might be in udev/devtmpfs
or the kernel itself, I don't know which.
However the md(4) manpage still says that it exists:
SYNOPSIS
/dev/mdn
/dev/md/n
/dev/md/name
There are scripts which depend on the /dev/md/n or /dev/md/name link,
e.g. https://github.com/prometheus-community/node-exporter-textfile-
collector-scripts/issues/92, so arguably this is a regression. I'm OK
with it going, but I think the manpage should be updated to reflect this
change.
WORKAROUND: switch to using /dev/disk/by-id/md-name-<FULLNAME>.
# find /dev -lname '*md*'
/dev/log
/dev/disk/by-uuid/f36588df-7e7f-446a-9be4-c0c6d092dcf4
/dev/disk/by-id/md-name-CORE-ELASTIC-VM1:127
/dev/disk/by-id/md-uuid-f6641f8b:65b425e9:298e0ac2:b6c3c83e
/dev/block/9:127
# find /dev -lname '*md*' | xargs ls -l
lrwxrwxrwx 1 root root 8 Mar 31 08:46 /dev/block/9:127 -> ../md127
lrwxrwxrwx 1 root root 11 Mar 31 08:46
/dev/disk/by-id/md-name-CORE-ELASTIC-VM1:127 -> ../../md127
lrwxrwxrwx 1 root root 11 Mar 31 08:46
/dev/disk/by-id/md-uuid-f6641f8b:65b425e9:298e0ac2:b6c3c83e -> ../../md127
lrwxrwxrwx 1 root root 11 Mar 31 08:46
/dev/disk/by-uuid/f36588df-7e7f-446a-9be4-c0c6d092dcf4 -> ../../md127
lrwxrwxrwx 1 root root 28 Mar 31 08:46 /dev/log -> /run/systemd/journal/dev-log
Note that the <FULLNAME> is typically <CREATION_HOST>:<NAME>, and even on older
systems which have /dev/md/ the <NAME> may be different to /dev/md/<NAME>.
** Affects: ubuntu
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1922070
Title:
mdraid: /dev/md directory no longer exists
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