When trying to for an install (in this case a format install) of JunOS sometimes the following will occur while logged in as root:

root@% install –format jinstall-YOURPACKAGE-signed.tgz

/sbin/install: Permission denied.

It will install correctly if install it from loader> prompt. You must have your USB drive connected before rebooting. Get there by hitting spacebar during boot:

Hit [Enter] to boot immediately, or space bar for command prompt.

– Press space bar

loader>

Then just install from here:

loader> install –format file:///jinstall-YOURPACKAGE-signed.tgz

BE AWARE THAT THERE ARE THREE SLASHES AFTER IN THAT COMMAND. It’s easy to overlook that if you aren’t copying and pasting.