NIO CommKit Host Interface Installation and System Administration Manual

3-24
Control Tables (from AT&T 255-110-127)
srvtab
A user ID mapping facility is necessary because every user on every remote
host your system communicates with may not have a login on your system.
Some of your systems may have identical password files (for example, each
user has the same login on each system), while other groups of systems may
have no users in common. Commonly administered systems in a computer
center may have administrative logins (for example, root, bin, sys) in com-
mon, while each user login may be unique to a single system. Finally,
numerical user IDs (for example, the user number of each login in the
/etc/passwd file) may be unique across all of the your systems (for example,
user ID 41627 identifies the login for “Rogers” and is only used on systems
where a rgrs login exists) or the numbers may not be unique (for example,
user ID 41627 is “Rogers” on Systems a, b, and c, but is “Gordon” on Sys-
tems d, e, and f.).
These issues must be addressed when setting up your system’s user ID map-
ping methodology. Additional information on the types of user ID mapping
is presented below.
Transparent User ID Mapping
The transparent mode of user ID mapping is specified by the *n and *o user
ID mapping options in the server table. This mode allows incoming calls to
retain the same numerical user ID on the called system as on the calling sys-
tem as long as the numerical user ID appears in a valid /etc/passwd entry on
the called system.
The transparent mode of user ID mapping is intended for use when two or
more systems have the same user population and each numerical user ID
refers to a single user across the set of systems.
During transparent mapping, it is not possible for the server program to ver-
ify that the numerical user ID refers to the same user on both the called and
calling systems. Therefore, the user ID is accepted as long as a valid /etc/
passwd file entry - one that has not expired - exists on the called system.
This mode of user ID mapping should only be used when both the called and
calling systems have the same user population and the user IDs uniquely
identify the same user on both systems. If the same numerical user ID (for
example, 100) refers to different users on the two systems, do not use trans-
parent mapping between those systems: use translated mapping instead.