Chapter 31 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 -I +unix unix.cma other files
        ocamlopt other options  -I +unix unix.cmxa other files

For interactive use of the unix library, do:

        ocamlmktop -o mytop -I +unix unix.cma

or (if dynamic linking of C libraries is supported on your platform), start ocaml and type

# #directory "+unix";;
# #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.
forknot implemented, use create_process or threads
waitnot implemented, use waitpid
waitpidcan only wait for a given PID, not any child process
getppidnot implemented (meaningless under Windows)
nicenot implemented
truncate, ftruncateimplemented (since 4.10.0)
linkimplemented (since 3.02)
fchmodnot implemented
chown, fchownnot implemented (make no sense on a DOS file system)
umasknot implemented
accessexecute permission X_OK cannot be tested, it just tests for read permission instead
chrootnot implemented
mkfifonot implemented
symlink, readlinkimplemented (since 4.03.0)
killpartially implemented (since 4.00.0): only the sigkill signal is implemented
sigprocmask, sigpending, sigsuspendnot implemented (no inter-process signals on Windows
pausenot implemented (no inter-process signals in Windows)
alarmnot implemented
timespartially implemented, will not report timings for child processes
getitimer, setitimernot implemented
getuid, geteuid, getgid, getegidalways return 1
setuid, setgid, setgroups, initgroupsnot implemented
getgroupsalways returns [|1|] (since 2.00)
getpwnam, getpwuidalways raise Not_found
getgrnam, getgrgidalways raise Not_found
type socket_domainPF_INET is fully supported; PF_INET6 is fully supported (since 4.01.0); PF_UNIX is supported since 4.14.0, but only works on Windows 10 1803 and later.
establish_servernot implemented; use threads
terminal functions (tc*)not implemented
setsidnot implemented