Bash:
[root@FreeBSD /usr/home/zoujiaqing]# freebsd-update upgrade -r 12.1-RELEASE && freebsd-update install
src component not installed, skipped
Looking up update.FreeBSD.org mirrors... 3 mirrors found.
Fetching metadata signature for 12.0-RELEASE from update1.freebsd.org... done.
Fetching metadata index... done.
Fetching 1 metadata patches. done.
Applying metadata patches... done.
Fetching 1 metadata files... gunzip: (stdin): unexpected end of file
metadata is corrupt.