9.4 Under Linux and BSD-like platforms

Basic Unix operations, basically a subset of the POSIX specification. Using this unit should ensure portability across most unix systems.
This unit initializes the internationalization settings in the sysutils unit with settings obtained through the C library.
This unit should be specified as the first or second unit in the uses clause of your program: it will use the Posix threads implementation to enable threads in your FPC program.
If widestring routines are used, then this unit should be inserted as one of the first units in the uses clause of your program: it will initialize the widestring manager in the system unit with routines that use C library functions to handle Widestring conversions and other widestring operations.
Returns a string describing an operating system error code.
This is the interface to GLibc on a linux I386 system. It will not work for other platforms, and is in general provided for Kylix compatibility.
This implements the various port[] constructs. These are provided for compatibility only, and it is not recommended to use them extensively. Programs using this construct must be run as root or setuid root, and are a serious security risk on your system.
Terminal control routines, which are compatible to the C library routines.
Extended Unix operations.
All types used commonly on Unix platforms.