The rt (runtime) module provides low-level, non-portable access to the host, and support code for the Hare compiler and standard library. The use of this module is not recommended for most user programs, and any program which uses rt is unlikely to be portable. However, any program which needs to make syscalls directly will have to use rt to do so. Documentation for most interfaces is not provided; refer to the host documentation (e.g. Linux man pages) instead.