# Chapter 21 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.

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: A fairly complete emulation of the Unix system calls is provided in the Windows version of OCaml. The end of this chapter gives more information on the functions that are not supported under Windows.

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

> 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` | not implemented
> `link`, `symlink`, `readlink` | not implemented (no links under Windows)
> `access` | execute permission `X_OK` cannot be tested, it just tests for read permission instead
> `fchmod` | not implemented
> `chown`, `fchown` | not implemented (make no sense on a DOS file system)
> `umask` | not implemented
> `set_nonblock`, `clear_nonblock` | implemented as dummy functions; use threads instead of non-blocking I/O
> `rewinddir` | not implemented; re-open the directory instead
> `mkfifo` | not implemented
> `kill`, `pause` | not implemented (no inter-process signals in Windows)
> `alarm`, `times` | not implemented
> `getitimer`, `setitimer` | not implemented
> `getuid`, `getgid` | always return 1
> `getgid`, `getegid`, `getgroups` | not implemented
> `setuid`, `setgid` | not implemented
> `getpwnam`, `getpwuid` | always raise `Not_found`
> `getgrnam`, `getgrgid` | always raise `Not_found`
> type `socket_domain` | the domains `PF_UNIX` and `PF_INET6` are not supported; `PF_INET` is fully supported
> `establish_server` | not implemented; use threads
> terminal functions (`tc*`) | not implemented