Solved [Solved] /var/empty upgrade from 9.2-RELEASE to 10.0-RELEASE

Last week I just upgraded successfully from 8.2-RELEASE to 9.2-RELEASE.

Now is the time to upgrade to 10.0-RELEASE but I always get the same error and after searching for a solution, it does not seems a common problem:

# freebsd-update fetch install
Looking up mirrors... 5 mirrors found.
Fetching metadata signature for 9.2-RELEASE from done.
Fetching metadata index... done.
Inspecting system... done.
Preparing to download files... done.

No updates needed to update system to 9.2-RELEASE-p3.
No updates are available to install.

# freebsd-update upgrade -r 10.0-RELEASE

# freebsd-update install
Installing updates...chflags: ///var/empty: Read-only file system
Re: /var/empty error upgrading from 9.2-RELEASE to 10.0-RELE

If I remember right this is from /var/empty having schg flag on it. You can verify with ls -lod /var/empty. If it does you'll see schg after the group column. To remove it run chflags noschg /var/empty.

EDIT: Now that I think about it, is this on a ZFS file system? It's been awhile since I ran into this problem and it might have been from the ZFS readonly attribute being set.
Re: /var/empty error upgrading from 9.2-RELEASE to 10.0-RELE

Thanks for putting me on track.

I had already tried the following:

# chflags noschg /var/empty
chflags: /var/empty: Read-only file system

But talking about the readonly ZFS attribute, made me found the solution:

# zfs get readonly zroot/var/empty
zroot/var/empty  readonly  on      local

# zfs set readonly=off zroot/var/empty

Then I could proceed with normal upgrade and put back /var/empty readonly later:
# zfs set readonly=on zroot/var/empty