Module Unix

Interface to the Unix system.

Note: all the functions of this module (except error_message and handle_unix_error) are liable to raise the Unix_error exception whenever the underlying system call signals an error.

Error report

type error =
| E2BIG

Argument list too long

| EACCES

Permission denied

| EAGAIN

Resource temporarily unavailable; try again

| EBADF

Bad file descriptor

| EBUSY

Resource unavailable

| ECHILD

No child process

| EDEADLK

Resource deadlock would occur

| EDOM

Domain error for math functions, etc.

| EEXIST

File exists

| EFAULT

Bad address

| EFBIG

File too large

| EINTR

Function interrupted by signal

| EINVAL

Invalid argument

| EIO

Hardware I/O error

| EISDIR

Is a directory

| EMFILE

Too many open files by the process

| ENAMETOOLONG

Filename too long

| ENFILE

Too many open files in the system

| ENODEV

No such device

| ENOENT

No such file or directory

| ENOEXEC

Not an executable file

| ENOLCK

No locks available

| ENOMEM

Not enough memory

| ENOSPC

No space left on device

| ENOSYS

Function not supported

| ENOTDIR

Not a directory

| ENOTEMPTY

Directory not empty

| ENOTTY

Inappropriate I/O control operation

| ENXIO

No such device or address

| EPERM

Operation not permitted

| EPIPE

Broken pipe

| ERANGE

Result too large

| EROFS

Read-only file system

| ESPIPE

Invalid seek e.g. on a pipe

| ESRCH

No such process

| EXDEV

Invalid link

| EWOULDBLOCK

Operation would block

| EINPROGRESS

Operation now in progress

| EALREADY

Operation already in progress

| ENOTSOCK

Socket operation on non-socket

| EDESTADDRREQ

Destination address required

| EMSGSIZE

Message too long

| EPROTOTYPE

Protocol wrong type for socket

| ENOPROTOOPT

Protocol not available

| EPROTONOSUPPORT

Protocol not supported

| ESOCKTNOSUPPORT

Socket type not supported

| EOPNOTSUPP

Operation not supported on socket

| EPFNOSUPPORT

Protocol family not supported

| EAFNOSUPPORT

Address family not supported by protocol family

| EADDRINUSE

Address already in use

| EADDRNOTAVAIL

Can't assign requested address

| ENETDOWN

Network is down

| ENETUNREACH

Network is unreachable

| ENETRESET

Network dropped connection on reset

| ECONNABORTED

Software caused connection abort

| ECONNRESET

Connection reset by peer

| ENOBUFS

No buffer space available

| EISCONN

Socket is already connected

| ENOTCONN

Socket is not connected

| ESHUTDOWN

Can't send after socket shutdown

| ETOOMANYREFS

Too many references: can't splice

| ETIMEDOUT

Connection timed out

| ECONNREFUSED

Connection refused

| EHOSTDOWN

Host is down

| EHOSTUNREACH

No route to host

| ELOOP

Too many levels of symbolic links

| EOVERFLOW

File size or position not representable

| EUNKNOWNERR of int

Unknown error

The type of error codes. Errors defined in the POSIX standard and additional errors from UNIX98 and BSD. All other errors are mapped to EUNKNOWNERR.

exception Unix_error of error * string * string

Raised by the system calls below when an error is encountered. The first component is the error code; the second component is the function name; the third component is the string parameter to the function, if it has one, or the empty string otherwise.

val error_message : error -> string

Return a string describing the given error code.

val handle_unix_error : ('a -> 'b) -> 'a -> 'b

handle_unix_error f x applies f to x and returns the result. If the exception Unix_error is raised, it prints a message describing the error and exits with code 2.

Access to the process environment

val environment : unit -> string array

Return the process environment, as an array of strings with the format ``variable=value''. The returned array is empty if the process has special privileges.

val unsafe_environment : unit -> string array

Return the process environment, as an array of strings with the format ``variable=value''. Unlike environment, this function returns a populated array even if the process has special privileges. See the documentation for unsafe_getenv for more details.

since
4.06.0
val getenv : string -> string

Return the value associated to a variable in the process environment, unless the process has special privileges.

raises Not_found

if the variable is unbound or the process has special privileges.

(This function is identical to Sys.getenv.

val unsafe_getenv : string -> string

Return the value associated to a variable in the process environment.

Unlike getenv, this function returns the value even if the process has special privileges. It is considered unsafe because the programmer of a setuid or setgid program must be careful to avoid using maliciously crafted environment variables in the search path for executables, the locations for temporary files or logs, and the like.

raises Not_found

if the variable is unbound.

since
4.06.0
val putenv : string -> string -> unit

Unix.putenv name value sets the value associated to a variable in the process environment. name is the name of the environment variable, and value its new associated value.

Process handling

type process_status =
| WEXITED of int

The process terminated normally by exit; the argument is the return code.

| WSIGNALED of int

The process was killed by a signal; the argument is the signal number.

| WSTOPPED of int

The process was stopped by a signal; the argument is the signal number.

The termination status of a process. See module Sys for the definitions of the standard signal numbers. Note that they are not the numbers used by the OS.

type wait_flag =
| WNOHANG

Do not block if no child has died yet, but immediately return with a pid equal to 0.

| WUNTRACED

Report also the children that receive stop signals.

Flags for Unix.waitpid.

val execv : string -> string array -> 'a

execv prog args execute the program in file prog, with the arguments args, and the current process environment. These execv* functions never return: on success, the current program is replaced by the new one.

raises Unix.Unix_error

on failure.

val execve : string -> string array -> string array -> 'a

Same as Unix.execv, except that the third argument provides the environment to the program executed.

val execvp : string -> string array -> 'a

Same as Unix.execv, except that the program is searched in the path.

val execvpe : string -> string array -> string array -> 'a

Same as Unix.execve, except that the program is searched in the path.

val fork : unit -> int

Fork a new process. The returned integer is 0 for the child process, the pid of the child process for the parent process.

On Windows: not implemented, use create_process or threads.

val wait : unit -> int * process_status

Wait until one of the children processes die, and return its pid and termination status.

On Windows: Not implemented, use waitpid.

val waitpid : wait_flag list -> int -> int * process_status

Same as Unix.wait, but waits for the child process whose pid is given. A pid of -1 means wait for any child. A pid of 0 means wait for any child in the same process group as the current process. Negative pid arguments represent process groups. The list of options indicates whether waitpid should return immediately without waiting, and whether it should report stopped children.

On Windows, this function can only wait for a given PID, not any child process.

val system : string -> process_status

Execute the given command, wait until it terminates, and return its termination status. The string is interpreted by the shell /bin/sh (or the command interpreter cmd.exe on Windows) and therefore can contain redirections, quotes, variables, etc. The result WEXITED 127 indicates that the shell couldn't be executed.

val getpid : unit -> int

Return the pid of the process.

val getppid : unit -> int

Return the pid of the parent process. On Windows: not implemented (because it is meaningless).

val nice : int -> int

Change the process priority. The integer argument is added to the ``nice'' value. (Higher values of the ``nice'' value mean lower priorities.) Return the new nice value.

On Windows: not implemented.

Basic file input/output

type file_descr

The abstract type of file descriptors.

val stdin : file_descr

File descriptor for standard input.

val stdout : file_descr

File descriptor for standard output.

val stderr : file_descr

File descriptor for standard error.

type open_flag =
| O_RDONLY

Open for reading

| O_WRONLY

Open for writing

| O_RDWR

Open for reading and writing

| O_NONBLOCK

Open in non-blocking mode

| O_APPEND

Open for append

| O_CREAT

Create if nonexistent

| O_TRUNC

Truncate to 0 length if existing

| O_EXCL

Fail if existing

| O_NOCTTY

Don't make this dev a controlling tty

| O_DSYNC

Writes complete as `Synchronised I/O data integrity completion'

| O_SYNC

Writes complete as `Synchronised I/O file integrity completion'

| O_RSYNC

Reads complete as writes (depending on O_SYNC/O_DSYNC)

| O_SHARE_DELETE

Windows only: allow the file to be deleted while still open

| O_CLOEXEC

Set the close-on-exec flag on the descriptor returned by openfile. See set_close_on_exec for more information.

| O_KEEPEXEC

Clear the close-on-exec flag. This is currently the default.

The flags to Unix.openfile.

type file_perm = int

The type of file access rights, e.g. 0o640 is read and write for user, read for group, none for others

val openfile : string -> open_flag list -> file_perm -> file_descr

Open the named file with the given flags. Third argument is the permissions to give to the file if it is created (see umask). Return a file descriptor on the named file.

val close : file_descr -> unit

Close a file descriptor.

val read : file_descr -> bytes -> int -> int -> int

read fd buff ofs len reads len bytes from descriptor fd, storing them in byte sequence buff, starting at position ofs in buff. Return the number of bytes actually read.

val write : file_descr -> bytes -> int -> int -> int

write fd buff ofs len writes len bytes to descriptor fd, taking them from byte sequence buff, starting at position ofs in buff. Return the number of bytes actually written. write repeats the writing operation until all bytes have been written or an error occurs.

val single_write : file_descr -> bytes -> int -> int -> int

Same as write, but attempts to write only once. Thus, if an error occurs, single_write guarantees that no data has been written.

val write_substring : file_descr -> string -> int -> int -> int

Same as write, but take the data from a string instead of a byte sequence.

since
4.02.0
val single_write_substring : file_descr -> string -> int -> int -> int

Same as single_write, but take the data from a string instead of a byte sequence.

since
4.02.0

Interfacing with the standard input/output library

val in_channel_of_descr : file_descr -> Stdlib.in_channel

Create an input channel reading from the given descriptor. The channel is initially in binary mode; use set_binary_mode_in ic false if text mode is desired. Text mode is supported only if the descriptor refers to a file or pipe, but is not supported if it refers to a socket. On Windows, set_binary_mode_in always fails on channels created with this function.

Beware that channels are buffered so more characters may have been read from the file descriptor than those accessed using channel functions. Channels also keep a copy of the current position in the file.

You need to explicitly close all channels created with this function. Closing the channel also closes the underlying file descriptor (unless it was already closed).

val out_channel_of_descr : file_descr -> Stdlib.out_channel

Create an output channel writing on the given descriptor. The channel is initially in binary mode; use set_binary_mode_out oc false if text mode is desired. Text mode is supported only if the descriptor refers to a file or pipe, but is not supported if it refers to a socket. On Windows, set_binary_mode_out always fails on channels created with this function.

Beware that channels are buffered so you may have to flush them to ensure that all data has been sent to the file descriptor. Channels also keep a copy of the current position in the file.

You need to explicitly close all channels created with this function. Closing the channel flushes the data and closes the underlying file descriptor (unless it has already been closed, in which case the buffered data is lost).

val descr_of_in_channel : Stdlib.in_channel -> file_descr

Return the descriptor corresponding to an input channel.

val descr_of_out_channel : Stdlib.out_channel -> file_descr

Return the descriptor corresponding to an output channel.

Seeking and truncating

type seek_command =
| SEEK_SET

indicates positions relative to the beginning of the file

| SEEK_CUR

indicates positions relative to the current position

| SEEK_END

indicates positions relative to the end of the file

Positioning modes for Unix.lseek.

val lseek : file_descr -> int -> seek_command -> int

Set the current position for a file descriptor, and return the resulting offset (from the beginning of the file).

val truncate : string -> int -> unit

Truncates the named file to the given size.

On Windows: not implemented.

val ftruncate : file_descr -> int -> unit

Truncates the file corresponding to the given descriptor to the given size.

On Windows: not implemented.

File status

type file_kind =
| S_REG

Regular file

| S_DIR

Directory

| S_CHR

Character device

| S_BLK

Block device

| S_LNK

Symbolic link

| S_FIFO

Named pipe

| S_SOCK

Socket

type stats = {
st_dev : int;

Device number

st_ino : int;

Inode number

st_kind : file_kind;

Kind of the file

st_perm : file_perm;

Access rights

st_uid : int;

User id of the owner

st_gid : int;

Group ID of the file's group

st_rdev : int;

Device minor number

st_size : int;

Size in bytes

st_atime : float;

Last access time

st_mtime : float;

Last modification time

st_ctime : float;

Last status change time

}

The information returned by the Unix.stat calls.

val stat : string -> stats

Return the information for the named file.

val lstat : string -> stats

Same as Unix.stat, but in case the file is a symbolic link, return the information for the link itself.

val fstat : file_descr -> stats

Return the information for the file associated with the given descriptor.

val isatty : file_descr -> bool

Return true if the given file descriptor refers to a terminal or console window, false otherwise.

File operations on large files

module LargeFile : sig ... end

File operations on large files. This sub-module provides 64-bit variants of the functions Unix.lseek (for positioning a file descriptor), Unix.truncate and Unix.ftruncate (for changing the size of a file), and Unix.stat, Unix.lstat and Unix.fstat (for obtaining information on files). These alternate functions represent positions and sizes by 64-bit integers (type int64) instead of regular integers (type int), thus allowing operating on files whose sizes are greater than max_int.

Mapping files into memory
val map_file : file_descr -> ?⁠pos:int64 -> ('a'b) Bigarray.kind -> 'c Bigarray.layout -> bool -> int array -> ('a'b'c) Bigarray.Genarray.t

Memory mapping of a file as a big array. map_file fd kind layout shared dims returns a big array of kind kind, layout layout, and dimensions as specified in dims. The data contained in this big array are the contents of the file referred to by the file descriptor fd (as opened previously with Unix.openfile, for example). The optional pos parameter is the byte offset in the file of the data being mapped; it defaults to 0 (map from the beginning of the file).

If shared is true, all modifications performed on the array are reflected in the file. This requires that fd be opened with write permissions. If shared is false, modifications performed on the array are done in memory only, using copy-on-write of the modified pages; the underlying file is not affected.

Genarray.map_file is much more efficient than reading the whole file in a big array, modifying that big array, and writing it afterwards.

To adjust automatically the dimensions of the big array to the actual size of the file, the major dimension (that is, the first dimension for an array with C layout, and the last dimension for an array with Fortran layout) can be given as -1. Genarray.map_file then determines the major dimension from the size of the file. The file must contain an integral number of sub-arrays as determined by the non-major dimensions, otherwise Failure is raised.

If all dimensions of the big array are given, the file size is matched against the size of the big array. If the file is larger than the big array, only the initial portion of the file is mapped to the big array. If the file is smaller than the big array, the file is automatically grown to the size of the big array. This requires write permissions on fd.

Array accesses are bounds-checked, but the bounds are determined by the initial call to map_file. Therefore, you should make sure no other process modifies the mapped file while you're accessing it, or a SIGBUS signal may be raised. This happens, for instance, if the file is shrunk.

Invalid_argument or Failure may be raised in cases where argument validation fails.

since
4.06.0

Operations on file names

Removes the named file.

If the named file is a directory, raises:

  • EPERM on POSIX compliant system
  • EISDIR on Linux >= 2.1.132
  • EACCESS on Windows
val rename : string -> string -> unit

rename old new changes the name of a file from old to new, moving it between directories if needed. If new already exists, its contents will be replaced with those of old. Depending on the operating system, the metadata (permissions, owner, etc) of new can either be preserved or be replaced by those of old.

link source dest creates a hard link named dest to the file named source.

File permissions and ownership

type access_permission =
| R_OK

Read permission

| W_OK

Write permission

| X_OK

Execution permission

| F_OK

File exists

Flags for the Unix.access call.

val chmod : string -> file_perm -> unit

Change the permissions of the named file.

val fchmod : file_descr -> file_perm -> unit

Change the permissions of an opened file. On Windows: not implemented.

val chown : string -> int -> int -> unit

Change the owner uid and owner gid of the named file. On Windows: not implemented (make no sense on a DOS file system).

val fchown : file_descr -> int -> int -> unit

Change the owner uid and owner gid of an opened file. On Windows: not implemented (make no sense on a DOS file system).

val umask : int -> int

Set the process's file mode creation mask, and return the previous mask. On Windows: not implemented.

val access : string -> access_permission list -> unit

Check that the process has the given permissions over the named file.

raises Unix_error

otherwise.

On Windows, execute permission X_OK, cannot be tested, it just tests for read permission instead.

Operations on file descriptors

val dup : ?⁠cloexec:bool -> file_descr -> file_descr

Return a new file descriptor referencing the same file as the given descriptor. See set_close_on_exec for documentation on the cloexec optional argument.

val dup2 : ?⁠cloexec:bool -> file_descr -> file_descr -> unit

dup2 fd1 fd2 duplicates fd1 to fd2, closing fd2 if already opened. See set_close_on_exec for documentation on the cloexec optional argument.

val set_nonblock : file_descr -> unit

Set the ``non-blocking'' flag on the given descriptor. When the non-blocking flag is set, reading on a descriptor on which there is temporarily no data available raises the EAGAIN or EWOULDBLOCK error instead of blocking; writing on a descriptor on which there is temporarily no room for writing also raises EAGAIN or EWOULDBLOCK.

val clear_nonblock : file_descr -> unit

Clear the ``non-blocking'' flag on the given descriptor. See Unix.set_nonblock.

val set_close_on_exec : file_descr -> unit

Set the ``close-on-exec'' flag on the given descriptor. A descriptor with the close-on-exec flag is automatically closed when the current process starts another program with one of the exec, create_process and open_process functions.

It is often a security hole to leak file descriptors opened on, say, a private file to an external program: the program, then, gets access to the private file and can do bad things with it. Hence, it is highly recommended to set all file descriptors ``close-on-exec'', except in the very few cases where a file descriptor actually needs to be transmitted to another program.

The best way to set a file descriptor ``close-on-exec'' is to create it in this state. To this end, the openfile function has O_CLOEXEC and O_KEEPEXEC flags to enforce ``close-on-exec'' mode or ``keep-on-exec'' mode, respectively. All other operations in the Unix module that create file descriptors have an optional argument ?cloexec:bool to indicate whether the file descriptor should be created in ``close-on-exec'' mode (by writing ~cloexec:true) or in ``keep-on-exec'' mode (by writing ~cloexec:false). For historical reasons, the default file descriptor creation mode is ``keep-on-exec'', if no cloexec optional argument is given. This is not a safe default, hence it is highly recommended to pass explicit cloexec arguments to operations that create file descriptors.

The cloexec optional arguments and the O_KEEPEXEC flag were introduced in OCaml 4.05. Earlier, the common practice was to create file descriptors in the default, ``keep-on-exec'' mode, then call set_close_on_exec on those freshly-created file descriptors. This is not as safe as creating the file descriptor in ``close-on-exec'' mode because, in multithreaded programs, a window of vulnerability exists between the time when the file descriptor is created and the time set_close_on_exec completes. If another thread spawns another program during this window, the descriptor will leak, as it is still in the ``keep-on-exec'' mode.

Regarding the atomicity guarantees given by ~cloexec:true or by the use of the O_CLOEXEC flag: on all platforms it is guaranteed that a concurrently-executing Caml thread cannot leak the descriptor by starting a new process. On Linux, this guarantee extends to concurrently-executing C threads. As of Feb 2017, other operating systems lack the necessary system calls and still expose a window of vulnerability during which a C thread can see the newly-created file descriptor in ``keep-on-exec'' mode.

val clear_close_on_exec : file_descr -> unit

Clear the ``close-on-exec'' flag on the given descriptor. See Unix.set_close_on_exec.

Directories

val mkdir : string -> file_perm -> unit

Create a directory with the given permissions (see umask).

val rmdir : string -> unit

Remove an empty directory.

val chdir : string -> unit

Change the process working directory.

val getcwd : unit -> string

Return the name of the current working directory.

val chroot : string -> unit

Change the process root directory. On Windows: not implemented.

type dir_handle

The type of descriptors over opened directories.

val opendir : string -> dir_handle

Open a descriptor on a directory

val readdir : dir_handle -> string

Return the next entry in a directory.

raises End_of_file

when the end of the directory has been reached.

val rewinddir : dir_handle -> unit

Reposition the descriptor to the beginning of the directory

val closedir : dir_handle -> unit

Close a directory descriptor.

Pipes and redirections

val pipe : ?⁠cloexec:bool -> unit -> file_descr * file_descr

Create a pipe. The first component of the result is opened for reading, that's the exit to the pipe. The second component is opened for writing, that's the entrance to the pipe. See set_close_on_exec for documentation on the cloexec optional argument.

val mkfifo : string -> file_perm -> unit

Create a named pipe with the given permissions (see umask). On Windows: not implemented.

High-level process and redirection management

val create_process : string -> string array -> file_descr -> file_descr -> file_descr -> int

create_process prog args new_stdin new_stdout new_stderr forks a new process that executes the program in file prog, with arguments args. The pid of the new process is returned immediately; the new process executes concurrently with the current process. The standard input and outputs of the new process are connected to the descriptors new_stdin, new_stdout and new_stderr. Passing e.g. stdout for new_stdout prevents the redirection and causes the new process to have the same standard output as the current process. The executable file prog is searched in the path. The new process has the same environment as the current process.

val create_process_env : string -> string array -> string array -> file_descr -> file_descr -> file_descr -> int

create_process_env prog args env new_stdin new_stdout new_stderr works as Unix.create_process, except that the extra argument env specifies the environment passed to the program.

val open_process_in : string -> Stdlib.in_channel

High-level pipe and process management. This function runs the given command in parallel with the program. The standard output of the command is redirected to a pipe, which can be read via the returned input channel. The command is interpreted by the shell /bin/sh (or cmd.exe on Windows), cf. system.

val open_process_out : string -> Stdlib.out_channel

Same as Unix.open_process_in, but redirect the standard input of the command to a pipe. Data written to the returned output channel is sent to the standard input of the command. Warning: writes on output channels are buffered, hence be careful to call Pervasives.flush at the right times to ensure correct synchronization.

val open_process : string -> Stdlib.in_channel * Stdlib.out_channel

Same as Unix.open_process_out, but redirects both the standard input and standard output of the command to pipes connected to the two returned channels. The input channel is connected to the output of the command, and the output channel to the input of the command.

val open_process_full : string -> string array -> Stdlib.in_channel * Stdlib.out_channel * Stdlib.in_channel

Similar to Unix.open_process, but the second argument specifies the environment passed to the command. The result is a triple of channels connected respectively to the standard output, standard input, and standard error of the command.

val close_process_in : Stdlib.in_channel -> process_status

Close channels opened by Unix.open_process_in, wait for the associated command to terminate, and return its termination status.

val close_process_out : Stdlib.out_channel -> process_status

Close channels opened by Unix.open_process_out, wait for the associated command to terminate, and return its termination status.

val close_process : (Stdlib.in_channel * Stdlib.out_channel) -> process_status

Close channels opened by Unix.open_process, wait for the associated command to terminate, and return its termination status.

val close_process_full : (Stdlib.in_channel * Stdlib.out_channel * Stdlib.in_channel) -> process_status

Close channels opened by Unix.open_process_full, wait for the associated command to terminate, and return its termination status.

symlink ?to_dir source dest creates the file dest as a symbolic link to the file source. On Windows, ~to_dir indicates if the symbolic link points to a directory or a file; if omitted, symlink examines source using stat and picks appropriately, if source does not exist then false is assumed (for this reason, it is recommended that the ~to_dir parameter be specified in new code). On Unix, ~to_dir is ignored.

Windows symbolic links are available in Windows Vista onwards. There are some important differences between Windows symlinks and their POSIX counterparts.

Windows symbolic links come in two flavours: directory and regular, which designate whether the symbolic link points to a directory or a file. The type must be correct - a directory symlink which actually points to a file cannot be selected with chdir and a file symlink which actually points to a directory cannot be read or written (note that Cygwin's emulation layer ignores this distinction).

When symbolic links are created to existing targets, this distinction doesn't matter and symlink will automatically create the correct kind of symbolic link. The distinction matters when a symbolic link is created to a non-existent target.

The other caveat is that by default symbolic links are a privileged operation. Administrators will always need to be running elevated (or with UAC disabled) and by default normal user accounts need to be granted the SeCreateSymbolicLinkPrivilege via Local Security Policy (secpol.msc) or via Active Directory.

has_symlink can be used to check that a process is able to create symbolic links.

Returns true if the user is able to create symbolic links. On Windows, this indicates that the user not only has the SeCreateSymbolicLinkPrivilege but is also running elevated, if necessary. On other platforms, this is simply indicates that the symlink system call is available.

since
4.03.0

Read the contents of a symbolic link.

Polling

val select : file_descr list -> file_descr list -> file_descr list -> float -> file_descr list * file_descr list * file_descr list

Wait until some input/output operations become possible on some channels. The three list arguments are, respectively, a set of descriptors to check for reading (first argument), for writing (second argument), or for exceptional conditions (third argument). The fourth argument is the maximal timeout, in seconds; a negative fourth argument means no timeout (unbounded wait). The result is composed of three sets of descriptors: those ready for reading (first component), ready for writing (second component), and over which an exceptional condition is pending (third component).

Locking

type lock_command =
| F_ULOCK

Unlock a region

| F_LOCK

Lock a region for writing, and block if already locked

| F_TLOCK

Lock a region for writing, or fail if already locked

| F_TEST

Test a region for other process locks

| F_RLOCK

Lock a region for reading, and block if already locked

| F_TRLOCK

Lock a region for reading, or fail if already locked

Commands for Unix.lockf.

val lockf : file_descr -> lock_command -> int -> unit

lockf fd cmd size puts a lock on a region of the file opened as fd. The region starts at the current read/write position for fd (as set by Unix.lseek), and extends size bytes forward if size is positive, size bytes backwards if size is negative, or to the end of the file if size is zero. A write lock prevents any other process from acquiring a read or write lock on the region. A read lock prevents any other process from acquiring a write lock on the region, but lets other processes acquire read locks on it.

The F_LOCK and F_TLOCK commands attempts to put a write lock on the specified region. The F_RLOCK and F_TRLOCK commands attempts to put a read lock on the specified region. If one or several locks put by another process prevent the current process from acquiring the lock, F_LOCK and F_RLOCK block until these locks are removed, while F_TLOCK and F_TRLOCK fail immediately with an exception. The F_ULOCK removes whatever locks the current process has on the specified region. Finally, the F_TEST command tests whether a write lock can be acquired on the specified region, without actually putting a lock. It returns immediately if successful, or fails otherwise.

What happens when a process tries to lock a region of a file that is already locked by the same process depends on the OS. On POSIX-compliant systems, the second lock operation succeeds and may "promote" the older lock from read lock to write lock. On Windows, the second lock operation will block or fail.

Signals

Note: installation of signal handlers is performed via the functions Sys.signal and Sys.set_signal.

val kill : int -> int -> unit

kill pid sig sends signal number sig to the process with id pid. On Windows, only the Sys.sigkill signal is emulated.

type sigprocmask_command =
| SIG_SETMASK
| SIG_BLOCK
| SIG_UNBLOCK
val sigprocmask : sigprocmask_command -> int list -> int list

sigprocmask cmd sigs changes the set of blocked signals. If cmd is SIG_SETMASK, blocked signals are set to those in the list sigs. If cmd is SIG_BLOCK, the signals in sigs are added to the set of blocked signals. If cmd is SIG_UNBLOCK, the signals in sigs are removed from the set of blocked signals. sigprocmask returns the set of previously blocked signals.

On Windows: not implemented (no inter-process signals on Windows).

val sigpending : unit -> int list

Return the set of blocked signals that are currently pending.

On Windows: not implemented (no inter-process signals on Windows).

val sigsuspend : int list -> unit

sigsuspend sigs atomically sets the blocked signals to sigs and waits for a non-ignored, non-blocked signal to be delivered. On return, the blocked signals are reset to their initial value.

On Windows: not implemented (no inter-process signals on Windows).

val pause : unit -> unit

Wait until a non-ignored, non-blocked signal is delivered.

On Windows: not implemented (no inter-process signals on Windows).

Time functions

type process_times = {
tms_utime : float;

User time for the process

tms_stime : float;

System time for the process

tms_cutime : float;

User time for the children processes

tms_cstime : float;

System time for the children processes

}

The execution times (CPU times) of a process.

type tm = {
tm_sec : int;

Seconds 0..60

tm_min : int;

Minutes 0..59

tm_hour : int;

Hours 0..23

tm_mday : int;

Day of month 1..31

tm_mon : int;

Month of year 0..11

tm_year : int;

Year - 1900

tm_wday : int;

Day of week (Sunday is 0)

tm_yday : int;

Day of year 0..365

tm_isdst : bool;

Daylight time savings in effect

}

The type representing wallclock time and calendar date.

val time : unit -> float

Return the current time since 00:00:00 GMT, Jan. 1, 1970, in seconds.

val gettimeofday : unit -> float

Same as Unix.time, but with resolution better than 1 second.

val gmtime : float -> tm

Convert a time in seconds, as returned by Unix.time, into a date and a time. Assumes UTC (Coordinated Universal Time), also known as GMT. To perform the inverse conversion, set the TZ environment variable to "UTC", use mktime, and then restore the original value of TZ.

val localtime : float -> tm

Convert a time in seconds, as returned by Unix.time, into a date and a time. Assumes the local time zone. The function performing the inverse conversion is mktime.

val mktime : tm -> float * tm

Convert a date and time, specified by the tm argument, into a time in seconds, as returned by Unix.time. The tm_isdst, tm_wday and tm_yday fields of tm are ignored. Also return a normalized copy of the given tm record, with the tm_wday, tm_yday, and tm_isdst fields recomputed from the other fields, and the other fields normalized (so that, e.g., 40 October is changed into 9 November). The tm argument is interpreted in the local time zone.

val alarm : int -> int

Schedule a SIGALRM signal after the given number of seconds.

On Windows: not implemented.

val sleep : int -> unit

Stop execution for the given number of seconds.

val sleepf : float -> unit

Stop execution for the given number of seconds. Like sleep, but fractions of seconds are supported.

since
4.03.0
val times : unit -> process_times

Return the execution times of the process. On Windows, it is partially implemented, will not report timings for child processes.

val utimes : string -> float -> float -> unit

Set the last access time (second arg) and last modification time (third arg) for a file. Times are expressed in seconds from 00:00:00 GMT, Jan. 1, 1970. If both times are 0.0, the access and last modification times are both set to the current time.

type interval_timer =
| ITIMER_REAL

decrements in real time, and sends the signal SIGALRM when expired.

| ITIMER_VIRTUAL

decrements in process virtual time, and sends SIGVTALRM when expired.

| ITIMER_PROF

(for profiling) decrements both when the process is running and when the system is running on behalf of the process; it sends SIGPROF when expired.

The three kinds of interval timers.

type interval_timer_status = {
it_interval : float;

Period

it_value : float;

Current value of the timer

}

The type describing the status of an interval timer

val getitimer : interval_timer -> interval_timer_status

Return the current status of the given interval timer.

On Windows: not implemented.

val setitimer : interval_timer -> interval_timer_status -> interval_timer_status

setitimer t s sets the interval timer t and returns its previous status. The s argument is interpreted as follows: s.it_value, if nonzero, is the time to the next timer expiration; s.it_interval, if nonzero, specifies a value to be used in reloading it_value when the timer expires. Setting s.it_value to zero disables the timer. Setting s.it_interval to zero causes the timer to be disabled after its next expiration.

On Windows: not implemented.

User id, group id

val getuid : unit -> int

Return the user id of the user executing the process. On Windows, always return 1.

val geteuid : unit -> int

Return the effective user id under which the process runs. On Windows, always return 1.

val setuid : int -> unit

Set the real user id and effective user id for the process. On Windows: not implemented.

val getgid : unit -> int

Return the group id of the user executing the process. On Windows, always return 1.

val getegid : unit -> int

Return the effective group id under which the process runs. On Windows, always return 1.

val setgid : int -> unit

Set the real group id and effective group id for the process. On Windows: not implemented.

val getgroups : unit -> int array

Return the list of groups to which the user executing the process belongs. On Windows, always return [|1|].

val setgroups : int array -> unit

setgroups groups sets the supplementary group IDs for the calling process. Appropriate privileges are required. On Windows: not implemented.

val initgroups : string -> int -> unit

initgroups user group initializes the group access list by reading the group database /etc/group and using all groups of which user is a member. The additional group group is also added to the list. On Windows: not implemented.

type passwd_entry = {
pw_name : string;
pw_passwd : string;
pw_uid : int;
pw_gid : int;
pw_gecos : string;
pw_dir : string;
pw_shell : string;
}

Structure of entries in the passwd database.

type group_entry = {
gr_name : string;
gr_passwd : string;
gr_gid : int;
gr_mem : string array;
}

Structure of entries in the groups database.

val getlogin : unit -> string

Return the login name of the user executing the process.

val getpwnam : string -> passwd_entry

Find an entry in passwd with the given name.

raises Not_found

if no such entry exist.

On Windows, always raise Not_found.

val getgrnam : string -> group_entry

Find an entry in group with the given name.

raises Not_found

if no such entry exist.

On Windows, always raise Not_found.

val getpwuid : int -> passwd_entry

Find an entry in passwd with the given user id.

raises Not_found

if no such entry exist.

On Windows, always raise Not_found.

val getgrgid : int -> group_entry

Find an entry in group with the given group id.

raises Not_found

if no such entry exist.

On Windows, always raise Not_found.

Internet addresses

type inet_addr

The abstract type of Internet addresses.

val inet_addr_of_string : string -> inet_addr

Conversion from the printable representation of an Internet address to its internal representation. The argument string consists of 4 numbers separated by periods (XXX.YYY.ZZZ.TTT) for IPv4 addresses, and up to 8 numbers separated by colons for IPv6 addresses.

raises Failure

when given a string that does not match these formats.

val string_of_inet_addr : inet_addr -> string

Return the printable representation of the given Internet address. See Unix.inet_addr_of_string for a description of the printable representation.

val inet_addr_any : inet_addr

A special IPv4 address, for use only with bind, representing all the Internet addresses that the host machine possesses.

val inet_addr_loopback : inet_addr

A special IPv4 address representing the host machine (127.0.0.1).

val inet6_addr_any : inet_addr

A special IPv6 address, for use only with bind, representing all the Internet addresses that the host machine possesses.

val inet6_addr_loopback : inet_addr

A special IPv6 address representing the host machine (::1).

Sockets

type socket_domain =
| PF_UNIX

Unix domain

| PF_INET

Internet domain (IPv4)

| PF_INET6

Internet domain (IPv6)

The type of socket domains. Not all platforms support IPv6 sockets (type PF_INET6). Windows does not support PF_UNIX.

type socket_type =
| SOCK_STREAM

Stream socket

| SOCK_DGRAM

Datagram socket

| SOCK_RAW

Raw socket

| SOCK_SEQPACKET

Sequenced packets socket

The type of socket kinds, specifying the semantics of communications. SOCK_SEQPACKET is included for completeness, but is rarely supported by the OS, and needs system calls that are not available in this library.

type sockaddr =
| ADDR_UNIX of string
| ADDR_INET of inet_addr * int

The type of socket addresses. ADDR_UNIX name is a socket address in the Unix domain; name is a file name in the file system. ADDR_INET(addr,port) is a socket address in the Internet domain; addr is the Internet address of the machine, and port is the port number.

val socket : ?⁠cloexec:bool -> socket_domain -> socket_type -> int -> file_descr

Create a new socket in the given domain, and with the given kind. The third argument is the protocol type; 0 selects the default protocol for that kind of sockets. See set_close_on_exec for documentation on the cloexec optional argument.

val domain_of_sockaddr : sockaddr -> socket_domain

Return the socket domain adequate for the given socket address.

val socketpair : ?⁠cloexec:bool -> socket_domain -> socket_type -> int -> file_descr * file_descr

Create a pair of unnamed sockets, connected together. See set_close_on_exec for documentation on the cloexec optional argument.

val accept : ?⁠cloexec:bool -> file_descr -> file_descr * sockaddr

Accept connections on the given socket. The returned descriptor is a socket connected to the client; the returned address is the address of the connecting client. See set_close_on_exec for documentation on the cloexec optional argument.

val bind : file_descr -> sockaddr -> unit

Bind a socket to an address.

val connect : file_descr -> sockaddr -> unit

Connect a socket to an address.

val listen : file_descr -> int -> unit

Set up a socket for receiving connection requests. The integer argument is the maximal number of pending requests.

type shutdown_command =
| SHUTDOWN_RECEIVE

Close for receiving

| SHUTDOWN_SEND

Close for sending

| SHUTDOWN_ALL

Close both

The type of commands for shutdown.

val shutdown : file_descr -> shutdown_command -> unit

Shutdown a socket connection. SHUTDOWN_SEND as second argument causes reads on the other end of the connection to return an end-of-file condition. SHUTDOWN_RECEIVE causes writes on the other end of the connection to return a closed pipe condition (SIGPIPE signal).

val getsockname : file_descr -> sockaddr

Return the address of the given socket.

val getpeername : file_descr -> sockaddr

Return the address of the host connected to the given socket.

type msg_flag =
| MSG_OOB
| MSG_DONTROUTE
| MSG_PEEK

The flags for Unix.recv, Unix.recvfrom, Unix.send and Unix.sendto.

val recv : file_descr -> bytes -> int -> int -> msg_flag list -> int

Receive data from a connected socket.

val recvfrom : file_descr -> bytes -> int -> int -> msg_flag list -> int * sockaddr

Receive data from an unconnected socket.

val send : file_descr -> bytes -> int -> int -> msg_flag list -> int

Send data over a connected socket.

val send_substring : file_descr -> string -> int -> int -> msg_flag list -> int

Same as send, but take the data from a string instead of a byte sequence.

since
4.02.0
val sendto : file_descr -> bytes -> int -> int -> msg_flag list -> sockaddr -> int

Send data over an unconnected socket.

val sendto_substring : file_descr -> string -> int -> int -> msg_flag list -> sockaddr -> int

Same as sendto, but take the data from a string instead of a byte sequence.

since
4.02.0

Socket options

type socket_bool_option =
| SO_DEBUG

Record debugging information

| SO_BROADCAST

Permit sending of broadcast messages

| SO_REUSEADDR

Allow reuse of local addresses for bind

| SO_KEEPALIVE

Keep connection active

| SO_DONTROUTE

Bypass the standard routing algorithms

| SO_OOBINLINE

Leave out-of-band data in line

| SO_ACCEPTCONN

Report whether socket listening is enabled

| TCP_NODELAY

Control the Nagle algorithm for TCP sockets

| IPV6_ONLY

Forbid binding an IPv6 socket to an IPv4 address

The socket options that can be consulted with Unix.getsockopt and modified with Unix.setsockopt. These options have a boolean (true/false) value.

type socket_int_option =
| SO_SNDBUF

Size of send buffer

| SO_RCVBUF

Size of received buffer

| SO_ERROR

Deprecated. Use Unix.getsockopt_error instead.

| SO_TYPE

Report the socket type

| SO_RCVLOWAT

Minimum number of bytes to process for input operations

| SO_SNDLOWAT

Minimum number of bytes to process for output operations

The socket options that can be consulted with Unix.getsockopt_int and modified with Unix.setsockopt_int. These options have an integer value.

type socket_optint_option =
| SO_LINGER

Whether to linger on closed connections that have data present, and for how long (in seconds)

The socket options that can be consulted with Unix.getsockopt_optint and modified with Unix.setsockopt_optint. These options have a value of type int option, with None meaning ``disabled''.

type socket_float_option =
| SO_RCVTIMEO

Timeout for input operations

| SO_SNDTIMEO

Timeout for output operations

The socket options that can be consulted with Unix.getsockopt_float and modified with Unix.setsockopt_float. These options have a floating-point value representing a time in seconds. The value 0 means infinite timeout.

val getsockopt : file_descr -> socket_bool_option -> bool

Return the current status of a boolean-valued option in the given socket.

val setsockopt : file_descr -> socket_bool_option -> bool -> unit

Set or clear a boolean-valued option in the given socket.

val getsockopt_int : file_descr -> socket_int_option -> int

Same as Unix.getsockopt for an integer-valued socket option.

val setsockopt_int : file_descr -> socket_int_option -> int -> unit

Same as Unix.setsockopt for an integer-valued socket option.

val getsockopt_optint : file_descr -> socket_optint_option -> int option

Same as Unix.getsockopt for a socket option whose value is an int option.

val setsockopt_optint : file_descr -> socket_optint_option -> int option -> unit

Same as Unix.setsockopt for a socket option whose value is an int option.

val getsockopt_float : file_descr -> socket_float_option -> float

Same as Unix.getsockopt for a socket option whose value is a floating-point number.

val setsockopt_float : file_descr -> socket_float_option -> float -> unit

Same as Unix.setsockopt for a socket option whose value is a floating-point number.

val getsockopt_error : file_descr -> error option

Return the error condition associated with the given socket, and clear it.

High-level network connection functions

val open_connection : sockaddr -> Stdlib.in_channel * Stdlib.out_channel

Connect to a server at the given address. Return a pair of buffered channels connected to the server. Remember to call Pervasives.flush on the output channel at the right times to ensure correct synchronization.

val shutdown_connection : Stdlib.in_channel -> unit

``Shut down'' a connection established with Unix.open_connection; that is, transmit an end-of-file condition to the server reading on the other side of the connection. This does not fully close the file descriptor associated with the channel, which you must remember to free via Pervasives.close_in.

val establish_server : (Stdlib.in_channel -> Stdlib.out_channel -> unit) -> sockaddr -> unit

Establish a server on the given address. The function given as first argument is called for each connection with two buffered channels connected to the client. A new process is created for each connection. The function Unix.establish_server never returns normally.

On Windows, it is not implemented. Use threads.

Host and protocol databases

type host_entry = {
h_name : string;
h_aliases : string array;
h_addrtype : socket_domain;
h_addr_list : inet_addr array;
}

Structure of entries in the hosts database.

type protocol_entry = {
p_name : string;
p_aliases : string array;
p_proto : int;
}

Structure of entries in the protocols database.

type service_entry = {
s_name : string;
s_aliases : string array;
s_port : int;
s_proto : string;
}

Structure of entries in the services database.

val gethostname : unit -> string

Return the name of the local host.

val gethostbyname : string -> host_entry

Find an entry in hosts with the given name.

raises Not_found

if no such entry exist.

val gethostbyaddr : inet_addr -> host_entry

Find an entry in hosts with the given address.

raises Not_found

if no such entry exist.

val getprotobyname : string -> protocol_entry

Find an entry in protocols with the given name.

raises Not_found

if no such entry exist.

val getprotobynumber : int -> protocol_entry

Find an entry in protocols with the given protocol number.

raises Not_found

if no such entry exist.

val getservbyname : string -> string -> service_entry

Find an entry in services with the given name.

raises Not_found

if no such entry exist.

val getservbyport : int -> string -> service_entry

Find an entry in services with the given service number.

raises Not_found

if no such entry exist.

type addr_info = {
ai_family : socket_domain;

Socket domain

ai_socktype : socket_type;

Socket type

ai_protocol : int;

Socket protocol number

ai_addr : sockaddr;

Address

ai_canonname : string;

Canonical host name

}

Address information returned by Unix.getaddrinfo.

type getaddrinfo_option =
| AI_FAMILY of socket_domain

Impose the given socket domain

| AI_SOCKTYPE of socket_type

Impose the given socket type

| AI_PROTOCOL of int

Impose the given protocol

| AI_NUMERICHOST

Do not call name resolver, expect numeric IP address

| AI_CANONNAME

Fill the ai_canonname field of the result

| AI_PASSIVE

Set address to ``any'' address for use with Unix.bind

Options to Unix.getaddrinfo.

val getaddrinfo : string -> string -> getaddrinfo_option list -> addr_info list

getaddrinfo host service opts returns a list of Unix.addr_info records describing socket parameters and addresses suitable for communicating with the given host and service. The empty list is returned if the host or service names are unknown, or the constraints expressed in opts cannot be satisfied.

host is either a host name or the string representation of an IP address. host can be given as the empty string; in this case, the ``any'' address or the ``loopback'' address are used, depending whether opts contains AI_PASSIVE. service is either a service name or the string representation of a port number. service can be given as the empty string; in this case, the port field of the returned addresses is set to 0. opts is a possibly empty list of options that allows the caller to force a particular socket domain (e.g. IPv6 only or IPv4 only) or a particular socket type (e.g. TCP only or UDP only).

type name_info = {
ni_hostname : string;

Name or IP address of host

ni_service : string;

Name of service or port number

}

Host and service information returned by Unix.getnameinfo.

type getnameinfo_option =
| NI_NOFQDN

Do not qualify local host names

| NI_NUMERICHOST

Always return host as IP address

| NI_NAMEREQD

Fail if host name cannot be determined

| NI_NUMERICSERV

Always return service as port number

| NI_DGRAM

Consider the service as UDP-based instead of the default TCP

Options to Unix.getnameinfo.

val getnameinfo : sockaddr -> getnameinfo_option list -> name_info

getnameinfo addr opts returns the host name and service name corresponding to the socket address addr. opts is a possibly empty list of options that governs how these names are obtained.

raises Not_found

if an error occurs.

Terminal interface

type terminal_io = {
mutable c_ignbrk : bool;

Ignore the break condition.

mutable c_brkint : bool;

Signal interrupt on break condition.

mutable c_ignpar : bool;

Ignore characters with parity errors.

mutable c_parmrk : bool;

Mark parity errors.

mutable c_inpck : bool;

Enable parity check on input.

mutable c_istrip : bool;

Strip 8th bit on input characters.

mutable c_inlcr : bool;

Map NL to CR on input.

mutable c_igncr : bool;

Ignore CR on input.

mutable c_icrnl : bool;

Map CR to NL on input.

mutable c_ixon : bool;

Recognize XON/XOFF characters on input.

mutable c_ixoff : bool;

Emit XON/XOFF chars to control input flow.

mutable c_opost : bool;

Enable output processing.

mutable c_obaud : int;

Output baud rate (0 means close connection).

mutable c_ibaud : int;

Input baud rate.

mutable c_csize : int;

Number of bits per character (5-8).

mutable c_cstopb : int;

Number of stop bits (1-2).

mutable c_cread : bool;

Reception is enabled.

mutable c_parenb : bool;

Enable parity generation and detection.

mutable c_parodd : bool;

Specify odd parity instead of even.

mutable c_hupcl : bool;

Hang up on last close.

mutable c_clocal : bool;

Ignore modem status lines.

mutable c_isig : bool;

Generate signal on INTR, QUIT, SUSP.

mutable c_icanon : bool;

Enable canonical processing (line buffering and editing)

mutable c_noflsh : bool;

Disable flush after INTR, QUIT, SUSP.

mutable c_echo : bool;

Echo input characters.

mutable c_echoe : bool;

Echo ERASE (to erase previous character).

mutable c_echok : bool;

Echo KILL (to erase the current line).

mutable c_echonl : bool;

Echo NL even if c_echo is not set.

mutable c_vintr : char;

Interrupt character (usually ctrl-C).

mutable c_vquit : char;

Quit character (usually ctrl-\).

mutable c_verase : char;

Erase character (usually DEL or ctrl-H).

mutable c_vkill : char;

Kill line character (usually ctrl-U).

mutable c_veof : char;

End-of-file character (usually ctrl-D).

mutable c_veol : char;

Alternate end-of-line char. (usually none).

mutable c_vmin : int;

Minimum number of characters to read before the read request is satisfied.

mutable c_vtime : int;

Maximum read wait (in 0.1s units).

mutable c_vstart : char;

Start character (usually ctrl-Q).

mutable c_vstop : char;

Stop character (usually ctrl-S).

}
val tcgetattr : file_descr -> terminal_io

Return the status of the terminal referred to by the given file descriptor. On Windows, not implemented.

type setattr_when =
| TCSANOW
| TCSADRAIN
| TCSAFLUSH
val tcsetattr : file_descr -> setattr_when -> terminal_io -> unit

Set the status of the terminal referred to by the given file descriptor. The second argument indicates when the status change takes place: immediately (TCSANOW), when all pending output has been transmitted (TCSADRAIN), or after flushing all input that has been received but not read (TCSAFLUSH). TCSADRAIN is recommended when changing the output parameters; TCSAFLUSH, when changing the input parameters.

On Windows, not implemented.

val tcsendbreak : file_descr -> int -> unit

Send a break condition on the given file descriptor. The second argument is the duration of the break, in 0.1s units; 0 means standard duration (0.25s).

On Windows, not implemented.

val tcdrain : file_descr -> unit

Waits until all output written on the given file descriptor has been transmitted.

On Windows, not implemented.

type flush_queue =
| TCIFLUSH
| TCOFLUSH
| TCIOFLUSH
val tcflush : file_descr -> flush_queue -> unit

Discard data written on the given file descriptor but not yet transmitted, or data received but not yet read, depending on the second argument: TCIFLUSH flushes data received but not read, TCOFLUSH flushes data written but not transmitted, and TCIOFLUSH flushes both.

On Windows, not implemented.

type flow_action =
| TCOOFF
| TCOON
| TCIOFF
| TCION
val tcflow : file_descr -> flow_action -> unit

Suspend or restart reception or transmission of data on the given file descriptor, depending on the second argument: TCOOFF suspends output, TCOON restarts output, TCIOFF transmits a STOP character to suspend input, and TCION transmits a START character to restart input.

On Windows, not implemented.

val setsid : unit -> int

Put the calling process in a new session and detach it from its controlling terminal.

On Windows, not implemented.