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Module Unix

module Unix: sig .. end
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
*)
| EMLINK (*
Too many links
*)
| 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''.
val getenv : string -> string
Return the value associated to a variable in the process environment.
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.
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 Unix.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 Unix.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 Unix.openfile
*)
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 Unix.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.
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.
Interfacing with the standard input/output library
val in_channel_of_descr : file_descr -> 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 -> 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 : in_channel -> file_descr
Return the descriptor corresponding to an input channel.
val descr_of_out_channel : 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_nlink : int; (*
Number of links
*)
   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.
Operations on file names
val unlink : string -> unit
Removes the named file.
val rename : string -> string -> unit
rename old new changes the name of a file from old to new.
val link : string -> string -> unit
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.
Operations on file descriptors
val dup : file_descr -> file_descr
Return a new file descriptor referencing the same file as the given descriptor.
val dup2 : file_descr -> file_descr -> unit
dup2 fd1 fd2 duplicates fd1 to fd2, closing fd2 if already opened.
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 functions.
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 Unix.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.
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 : 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.
val mkfifo : string -> file_perm -> unit
Create a named pipe with the given permissions (see Unix.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 -> 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 -> 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 flush at the right times to ensure correct synchronization.
val open_process : string -> in_channel * 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 ->
       in_channel * out_channel * 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 : 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 : 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 : in_channel * 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 : in_channel * out_channel * in_channel ->
       process_status
Close channels opened by Unix.open_process_full, wait for the associated command to terminate, and return its termination status.
val symlink : ?to_dir:bool -> string -> string -> unit
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 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.

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

val has_symlink : unit -> bool
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.
val readlink : string -> string
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.

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.
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.
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.
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.
val getgrnam : string -> group_entry
Find an entry in group with the given name.
val getpwuid : int -> passwd_entry
Find an entry in passwd with the given user id.
val getgrgid : int -> group_entry
Find an entry in group with the given group id.
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.
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 : 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.
val domain_of_sockaddr : sockaddr -> socket_domain
Return the socket domain adequate for the given socket address.
val socketpair : socket_domain ->
       socket_type -> int -> file_descr * file_descr
Create a pair of unnamed sockets, connected together.
val accept : 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.
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.
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.
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 -> in_channel * out_channel
Connect to a server at the given address. Return a pair of buffered channels connected to the server. Remember to call flush on the output channel at the right times to ensure correct synchronization.
val shutdown_connection : 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 close_in.
val establish_server : (in_channel -> 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.
val gethostbyaddr : inet_addr -> host_entry
Find an entry in hosts with the given address.
val getprotobyname : string -> protocol_entry
Find an entry in protocols with the given name.
val getprotobynumber : int -> protocol_entry
Find an entry in protocols with the given protocol number.
val getservbyname : string -> string -> service_entry
Find an entry in services with the given name.
val getservbyport : int -> string -> service_entry
Find an entry in services with the given service number.
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.
Terminal interface
The following functions implement the POSIX standard terminal interface. They provide control over asynchronous communication ports and pseudo-terminals. Refer to the termios man page for a complete description. 
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.