# Chapter ‍27 The unix library: Unix system calls

The unix library makes many Unix system calls and system-related library functions available to OCaml programs. This chapter describes briefly the functions provided. Refer to sections 2 ‍and ‍3 of the Unix manual for more details on the behavior of these functions.

- Module Unix: Unix system calls
- Module UnixLabels: Labeled Unix system calls

Not all functions are provided by all Unix variants. If some functions are not available, they will raise Invalid_arg when called.

Programs that use the unix library must be linked as follows:

            ocamlc other options unix.cma other files
            ocamlopt other options unix.cmxa other files

For interactive use of the unix library, do:

            ocamlmktop -o mytop unix.cma
            ./mytop

or (if dynamic linking of C libraries is supported on your platform), start ocaml and type #load "unix.cma";;.

> Windows:The Cygwin port of OCaml fully implements all functions from the Unix module. The native Win32 ports implement a subset of them. Below is a list of the functions that are not implemented, or only partially implemented, by the Win32 ports. Functions not mentioned are fully implemented and behave as described previously in this chapter.

Functions | Comment
fork | not implemented, use create_process or threads
wait | not implemented, use waitpid
waitpid | can only wait for a given PID, not any child process
getppid | not implemented (meaningless under Windows)
nice | not implemented
truncate, ftruncate | implemented (since 4.10.0)
link | implemented (since 3.02)
fchmod | not implemented
chown, fchown | not implemented (make no sense on a DOS file system)
umask | not implemented
access | execute permission X_OK cannot be tested, it just tests for read permission instead
chroot | not implemented
mkfifo | not implemented
symlink, readlink | implemented (since 4.03.0)
kill | partially implemented (since 4.00.0): only the sigkill signal is implemented
sigprocmask, sigpending, sigsuspend | not implemented (no inter-process signals on Windows
pause | not implemented (no inter-process signals in Windows)
alarm | not implemented
times | partially implemented, will not report timings for child processes
getitimer, setitimer | not implemented
getuid, geteuid, getgid, getegid | always return 1
setuid, setgid, setgroups, initgroups | not implemented
getgroups | always returns [|1|] (since 2.00)
getpwnam, getpwuid | always raise Not_found
getgrnam, getgrgid | always raise Not_found
type socket_domain | PF_INET is fully supported; PF_INET6 is fully supported (since 4.01.0); PF_UNIX is not supported
establish_server | not implemented; use threads
terminal functions (tc*) | not implemented
setsid | not implemented