RTEMS POSIX API User's Guide
RTEMS provides a single process, multi-threaded execution environment.
In this light, the notion of user and group is somewhat without meaning.
But RTEMS does provide services to provide a synthetic version of
user and group. By default, a single user and group is associated
with the application. Thus unless special actions are taken,
every thread in the application shares the same user and group Id.
The initial rationale for providing user and group Id functionality
in RTEMS was for the filesystem infrastructure to implement
file permission checks. The effective user/group Id capability
has since been used to implement permissions checking by
the ftpd server.
In addition to the "real" user and group Ids, a process may have an effective user/group Id. This allows a process to function using a more limited permission set for certain operations.
RTEMS POSIX API User's Guide
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