Optionally include the install command as found on Juniper products
like EX and SRX. The install command uses pkgfs to extract a kernel,
zero or more modules and a root file system from the specified package
and boots the kernel. The name of the kernel, the list of modules and
the name of the root file system can be specified by putting a
file called "metatags in the package.

The package to use is given by an URL. The schemes supported are
tftp and file. For the file scheme, the disk is currently hardcoded
but that should really look for the package on all devices and
partititions.

Obtained from: Juniper Networks, Inc.