df -x tmpfs fails to exclude udev (/dev)

Thank you for opening this bug and helping make Ubuntu better. Indeed 'stat' states /dev is tmpfs.

But 'mount' gives out the type as 'devtmpfs' (!):

hggdh@chatto:~$ mount | grep udev
udev on /dev type devtmpfs (rw,mode=0755)
hggdh@chatto:~$

and, then, 'df -x devtmpfs' works as expected:

hggdh@chatto:~$ df -x devtmpfs
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/vda 20511356 2518264 16944516 13% /
none 4 0 4 0% /sys/fs/cgroup
tmpfs 50300 232 50068 1% /run
none 5120 0 5120 0% /run/lock
none 251484 52 251432 1% /run/shm
none 102400 0 102400 0% /run/user
hggdh@chatto:~$

 But 'info mount', or 'man mount' do not list 'devtmpfs' as a valid system type. But 'devtmpfs' *is* a kernel-supported type...

I am not sure this is a coreutils issue per se; needs more research.

OTOH, 'stat' *is* coreutils... so confirming. At least 'stat' and 'df' should should agree.

This bug still exists in 15.10 - confirming.

20.04's coreutils still has the behavior described in this bug. /dev is listed as type 'udev' by df but df -x udev does not exclude it; df -x devtmpfs does.

I wonder if one way to at least resolve the confusion might be to make the code that prints the table display devtmpfs devices as 'devtmpfs'. An obvious alternative would be to make '-x udev' be handled like '-x udev -x devtmpfs'. Another alternative would be to overload '-x tmpfs' to exclude also udev and devtmpfs. It's not clear what the best solution would be.

This bug was fixed in the package coreutils - 8.30-3ubuntu3

---------------
coreutils (8.30-3ubuntu3) groovy; urgency=medium

  * d/p/treat-devtmpfs-and-squashfs-as-dummy-filesystems.patch:
    - Avoid displaying snaps in output from df and other tools, by
      excluding display of squashfs filesystems.
      (LP: #1219529, #1756595)
    - Exclude devtmpfs filesystems in output from df and other tools
      since it is a dummy filesystem.
      (LP: #1219529)

 -- Bryce Harrington <email address hidden> Thu, 02 Jul 2020 02:30:48 +0000