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Installing UPR on USB drive
The fact that UPR resides on read-only media is an important part of the security concept. The squashfs filesystem is read-only by principle,meaning you cannot permanently install anything on it afterwards within the running system. But there are ways to modify the 'host media' of the live system. Because of this, we recommend you stick with CDs. But there are reasons to install UPR to a USB drive, which should have a physical write protect switch in any case. One possible reason could be the use of UPR on netbooks which do not have an optical drive.
We do not recommend using SD cards, because investigations (see here in german or google translated) have shown that some readers do not obey the write protect switch on SD cards.
You need a USB drive with at least 1 GB. ore is of course possible, but will be of no use because of the write protection - except if you intend to build your own UPR and add more packages. The page above lists experiences with some of the few available sticks with hardware write protection.
There are several ways to create a bootable USB drive with UPR: