Library /sys$common/syshlp/uafhelp.hlb ADD, Qualifiers, /DEVICE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /DEVICE=device-name

    Specifies the name of the user's default device at login. The
    device-name is a string of 1 to 31 alphanumeric characters. If
    you omit the colon from the device-name value, AUTHORIZE appends
    a colon. The default device is SYS$SYSDISK.

    If you specify a logical name as the device-name (for example,
    DISK1: for DUA1:), you must make an entry for the logical name in
    the LNM$SYSTEM_TABLE in executive mode by using the DCL command
    DEFINE/SYSTEM/EXEC.