Ensure that / and /usr have read-write permissions before install/rollback.
Ensure that chflags is supported by the file system (i.e. NFS does not support chflags).
aryeeteygerald_rogers.com on Jan 11 2019, 9:29 PM.Authored by
This is a problem for NFS users. Exit early if it isn't supported with an error message with next steps.
Also do both system checks on rollback (since the same issues can occur then as well)
I think this is not complete. For example, /usr may be a symlink to somewhere else, and freebsd-update needs to have write access there (this applies to /boot, /var, etc. too).