If you receive strange error messages upon Multisystem installation on Debian Jessie:

./gui-detect.sh: line 432: /media/Multisystem/.multisystem-test: Permission denied
cat: /media/Multisystem/.multisystem-test: No such file or directory
cat: /tmp/multisystem/multisystem-laisserpasser-usb: No such file or directory
cat: /tmp/multisystem/multisystem-laisserpasser-usb: No such file or directory

than just edit your /etc/fstab and add following line:

/dev/disk/by-label/Multisystem /media/Multisystem         auto    user,umask=0000,uid=1000,gid=100          0       0