9.4 Under Linux and BSD-like platforms

baseunix
Basic Unix operations, basically a subset of the POSIX specification. Using this unit should ensure portability across most unix systems.
clocale
This unit initializes the internationalization settings in the sysutils unit with settings obtained through the C library.
cthreads
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.
cwstrings
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.
errors
Returns a string describing an operating system error code.
Libc
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.
oldlinux
This unit is deprecated. This unit provides access to the linux operating system. It provides most file and I/O handling routines that you may need. It implements most of the standard C library constructs that you will find on a Unix system. It is recommended, however, that you use the baseunix, unixtype and unix units. They are more portable.
ports
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 ruit or setuid root, and are a serious security risk on your system.
termio
Terminal control routines, which are compatible to the C library routines.
unix
Extended Unix operations.
unixtype
All types used commonly on Unix platforms.