Chapter 20 The unix library: Unix system calls

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

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

Programs that use the unix library must be linked as follows:
        nmlc other options unix.cma other files
  MacOS:
A fairly complete emulation of the Unix system calls is provided in the MacOS version of Objective Caml. The end of this chapter gives more information on the functions that are not supported under MacOS.
  Windows:
A fairly complete emulation of the Unix system calls is provided in the Windows version of Objective Caml. The end of this chapter gives more information on the functions that are not supported under Windows.
20.1 Module Unix: interface to the Unix system


Error report
type error =
Errors defined in the POSIX standard
    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 *)
Additional errors, mostly BSD
  | 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 *)
All other errors are mapped to EUNKNOWNERR
  | EUNKNOWNERR of int  (* Unknown error *)
The type of error codes.
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. Raise Not_found if the variable is unbound. (This function is identical to Sys.getenv.)
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
  | WSIGNALED of int
  | WSTOPPED of int
The termination status of a process. WEXITED means that the process terminated normally by exit; the argument is the return code. WSIGNALED means that the process was killed by a signal; the argument is the signal number. WSTOPPED means that the process was stopped by a signal; the argument is the signal number.
type wait_flag =
    WNOHANG
  | WUNTRACED
Flags for waitpid. WNOHANG means do not block if no child has died yet, but immediately return with a pid equal to 0. WUNTRACED means report also the children that receive stop signals.
val execv : prog:string -> args:string array -> unit
execv prog args execute the program in file prog, with the arguments args, and the current process environment.
val execve : prog:string -> args:string array -> env:string array -> unit
Same as execv, except that the third argument provides the environment to the program executed.
val execvp : prog:string -> args:string array -> unit
val execvpe : prog:string -> args:string array -> env:string array -> unit
Same as execv and execvp respectively, 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.
val wait : unit -> int * process_status
Wait until one of the children processes die, and return its pid and termination status.
val waitpid : mode:wait_flag list -> int -> int * process_status
Same as wait, but waits for the 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, or also report stopped children.
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 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.
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.
Basic file input/output
type file_descr
The abstract type of file descriptors.
val stdin : file_descr
val stdout : file_descr
val stderr : file_descr
File descriptors for standard input, standard output and 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 *)
The flags to open.
type file_perm = int
The type of file access rights.
val openfile : string -> mode:open_flag list -> perm: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. Return a file descriptor on the named file.
val close : file_descr -> unit
Close a file descriptor.
val read : file_descr -> buf:string -> pos:int -> len:int -> int
read fd buff ofs len reads len characters from descriptor fd, storing them in string buff, starting at position ofs in string buff. Return the number of characters actually read.
val write : file_descr -> buf:string -> pos:int -> len:int -> int
write fd buff ofs len writes len characters to descriptor fd, taking them from string buff, starting at position ofs in string buff. Return the number of characters actually written.
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.
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.
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
  | SEEK_CUR
  | SEEK_END
Positioning modes for lseek. SEEK_SET indicates positions relative to the beginning of the file, SEEK_CUR relative to the current position, SEEK_END relative to the end of the file.
val lseek : file_descr -> int -> mode:seek_command -> int
Set the current position for a file descriptor
val truncate : string -> len:int -> unit
Truncates the named file to the given size.
val ftruncate : file_descr -> len:int -> unit
Truncates the file corresponding to the given descriptor to the given size.
File statistics
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 informations returned by the stat calls.
val stat : string -> stats
Return the information for the named file.
val lstat : string -> stats
Same as 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.
Operations on file names
val unlink : string -> unit
Removes the named file
val rename : src:string -> dst:string -> unit
rename old new changes the name of a file from old to new.
val link : src:string -> dst:string -> unit
link source dest creates a hard link named dest to the file named new.
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 access call.
val chmod : string -> perm:file_perm -> unit
Change the permissions of the named file.
val fchmod : file_descr -> perm:file_perm -> unit
Change the permissions of an opened file.
val chown : string -> uid:int -> gid:int -> unit
Change the owner uid and owner gid of the named file.
val fchown : file_descr -> uid:int -> gid:int -> unit
Change the owner uid and owner gid of an opened file.
val umask : int -> int
Set the process creation mask, and return the previous mask.
val access : string -> perm:access_permission list -> unit
Check that the process has the given permissions over the named file. Raise Unix_error otherwise.
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 : src:file_descr -> dst:file_descr -> unit
dup2 fd1 fd2 duplicates fd1 to fd2, closing fd2 if already opened.
val set_nonblock : file_descr -> unit
val clear_nonblock : file_descr -> unit
Set or clear 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 set_close_on_exec : file_descr -> unit
val clear_close_on_exec : file_descr -> unit
Set or clear 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.
Directories
val mkdir : string -> perm:file_perm -> unit
Create a directory with the given permissions.
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.
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. Raise 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 : 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 -> perm:file_perm -> unit
Create a named pipe with the given permissions.
High-level process and redirection management
val create_process :
  prog:string -> args:string array ->
  stdin:file_descr -> stdout:file_descr -> stderr: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. All file descriptors of the current process are closed in the new process, except those redirected to standard input and outputs.
val create_process_env :
  prog:string -> args:string array -> env:string array ->
  stdin:file_descr -> stdout:file_descr -> stderr:file_descr -> int
create_process_env prog args env new_stdin new_stdout new_stderr works as create_process, except that the extra argument env specifies the environment passed to the program.
val open_process_in: string -> in_channel
val open_process_out: string -> out_channel
val open_process: string -> in_channel * out_channel
High-level pipe and process management. These functions run the given command in parallel with the program, and return channels connected to the standard input and/or the standard output of the command. The command is interpreted by the shell /bin/sh (cf. system). Warning: writes on channels are buffered, hence be careful to call flush at the right times to ensure correct synchronization.
val open_process_full:
      string -> env:string array -> in_channel * out_channel * in_channel
Similar to open_process, but the second argument specifies the environment passed to the command. The result is a triple of channels connected to the standard output, standard input, and standard error of the command.
val close_process_in: in_channel -> process_status
val close_process_out: out_channel -> process_status
val close_process: in_channel * out_channel -> process_status
val close_process_full: in_channel * out_channel * in_channel -> process_status
Close channels opened by open_process_in, open_process_out, open_process and open_process_full, respectively, wait for the associated command to terminate, and return its termination status.
Symbolic links
val symlink : src:string -> dst:string -> unit
symlink source dest creates the file dest as a symbolic link to the file source.
val readlink : string -> string
Read the contents of a link.
Polling
val select :
  read:file_descr list -> write:file_descr list -> except:file_descr list ->
  timeout: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 lockf.
val lockf : file_descr -> mode:lock_command -> len: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 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 (set with F_LOCK or F_TLOCK) prevents any other process from acquiring a read or write lock on the region. A read lock (set with F_RLOCK or F_TRLOCK) prevents any other process from acquiring a write lock on the region, but lets other processes acquire read locks on it.
Signals
val kill : pid:int -> signal:int -> unit
kill pid sig sends signal number sig to the process with id pid.
type sigprocmask_command = SIG_SETMASK | SIG_BLOCK | SIG_UNBLOCK
val sigprocmask: mode: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.
val sigpending: unit -> int list
Return the set of blocked signals that are currently pending.
val sigsuspend: int list -> unit
sigsuspend sigs atomically sets the blocked signals to sig and waits for a non-ignored, non-blocked signal to be delivered. On return, the blocked signals are reset to their initial value.
val pause : unit -> unit
Wait until a non-ignored, non-blocked signal is delivered.
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..59 *)
    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 time, but with resolution better than 1 second.
val gmtime : float -> tm
Convert a time in seconds, as returned by time, into a date and a time. Assumes Greenwich meridian time zone, also known as UTC.
val localtime : float -> tm
Convert a time in seconds, as returned by 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 time. 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. The tm argument is interpreted in the local time zone.
val alarm : int -> int
Schedule a SIGALRM signals after the given number of seconds.
val sleep : int -> unit
Stop execution for the given number of seconds.
val times : unit -> process_times
Return the execution times of the process.
val utimes : string -> access:float -> modif: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.
type interval_timer =
    ITIMER_REAL
  | ITIMER_VIRTUAL
  | ITIMER_PROF
The three kinds of interval timers. 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.
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.
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 disable the timer. Setting s.it_interval to zero causes the timer to be disabled after its next expiration.
User id, group id
val getuid : unit -> int
Return the user id of the user executing the process.
val geteuid : unit -> int
Return the effective user id under which the process runs.
val setuid : int -> unit
Set the real user id and effective user id for the process.
val getgid : unit -> int
Return the group id of the user executing the process.
val getegid : unit -> int
Return the effective group id under which the process runs.
val setgid : int -> unit
Set the real group id and effective group id for the process.
val getgroups : unit -> int array
Return the list of groups to which the user executing the process belongs.
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, or raise Not_found.
val getgrnam : string -> group_entry
Find an entry in group with the given name, or raise Not_found.
val getpwuid : int -> passwd_entry
Find an entry in passwd with the given user id, or raise Not_found.
val getgrgid : int -> group_entry
Find an entry in group with the given group id, or raise Not_found.
Internet addresses
type inet_addr
The abstract type of Internet addresses.
val inet_addr_of_string : string -> inet_addr
val string_of_inet_addr : inet_addr -> string
Conversions between string with the format XXX.YYY.ZZZ.TTT and Internet addresses. inet_addr_of_string raises Failure when given a string that does not match this format.
val inet_addr_any : inet_addr
A special Internet address, for use only with bind, representing all the Internet addresses that the host machine possesses.
Sockets
type socket_domain =
    PF_UNIX                             (* Unix domain *)
  | PF_INET                             (* Internet domain *)
The type of socket domains.
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.
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 :
  domain:socket_domain -> kind:socket_type -> protocol: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 socketpair :
  domain:socket_domain -> kind:socket_type -> protocol: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 -> addr:sockaddr -> unit
Bind a socket to an address.
val connect : file_descr -> addr:sockaddr -> unit
Connect a socket to an address.
val listen : file_descr -> max: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 -> mode: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 recv, recvfrom, send and sendto.
val recv :
        file_descr -> buf:string -> pos:int -> len:int
          -> mode:msg_flag list -> int
val recvfrom :
        file_descr -> buf:string -> pos:int -> len:int
          -> mode:msg_flag list -> int * sockaddr
Receive data from an unconnected socket.
val send : file_descr -> buf:string -> pos:int -> len:int
          -> mode:msg_flag list -> int
val sendto :
        file_descr -> buf:string -> pos:int -> len:int
          -> mode:msg_flag list -> addr:sockaddr -> int
Send data over an unconnected socket.
type socket_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 *)
The socket options settable with setsockopt.
val getsockopt : file_descr -> socket_option -> bool
Return the current status of an option in the given socket.
val setsockopt : file_descr -> socket_option -> bool -> unit
Set or clear an option in the given socket.
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 open_connection; that is, transmit an end-of-file condition to the server reading on the other side of the connection.
val establish_server : (in_channel -> out_channel -> unit) ->
                       addr: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 establish_server never returns normally.
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, or raise Not_found.
val gethostbyaddr : inet_addr -> host_entry
Find an entry in hosts with the given address, or raise Not_found.
val getprotobyname : string -> protocol_entry
Find an entry in protocols with the given name, or raise Not_found.
val getprotobynumber : int -> protocol_entry
Find an entry in protocols with the given protocol number, or raise Not_found.
val getservbyname : string -> protocol:string -> service_entry
Find an entry in services with the given name, or raise Not_found.
val getservbyport : int -> protocol:string -> service_entry
Find an entry in services with the given service number, or raise Not_found.
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 = {
Input modes:
    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. *)
Output modes:
    mutable c_opost: bool;   (* Enable output processing. *)
Control modes:
    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. *)
Local modes:
    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. *)
Control characters:
    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.
type setattr_when = TCSANOW | TCSADRAIN | TCSAFLUSH
val tcsetattr: file_descr -> mode: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.
val tcsendbreak: file_descr -> duration: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).
val tcdrain: file_descr -> unit
Waits until all output written on the given file descriptor has been transmitted.
type flush_queue = TCIFLUSH | TCOFLUSH | TCIOFLUSH
val tcflush: file_descr -> mode: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.
type flow_action = TCOOFF | TCOON | TCIOFF | TCION
val tcflow: file_descr -> mode: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.
val setsid : unit -> int
Put the calling process in a new session and detach it from its controlling terminal.
  MacOS:
Under MacOS, the Unix library is only available in the toplevel application, not in MPW tools. Below is a list of the functions that are not implemented, or only partially implemented, under MacOS. Functions not mentioned are fully implemented and behave as described previously in this chapter.



Functions Comment
chown, fchown not implemented
chroot not implemented
environment, putenv not implemented
execv, execve, execvp, execvpe not implemented
fork not implemented, use threads
getegid, geteuid, getgid, getuid always return 1
getgrnam, getgrgid not implemented
getlogin returns the user name as set in the Internet control panel
getpid returns the low-order 31 bits of the PSN
getppid not implemented
getpwnam, getpwuid not implemented
kill not implemented
link not implemented
mkfifo not implemented
nice not implemented
setgid, setuid not implemented
times only the process user time is returned
umask not implemented
wait not implemented
waitpid not implemented
establish_server not implemented; use threads
terminal functions (tc*) not implemented


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



Functions Comment
fork not implemented, use create_process or threads
wait not implemented, use waitpid
waitpid can only wait for a given PID, not any child process
getppid not implemented (meaningless under Windows)
nice not implemented
in_channel_of_descr does not work on sockets under Windows 95, 98, ME; works fine under NT and 2000
out_channel_of_descr ditto
truncate, ftruncate not implemented
lstat, fstat not implemented
link, symlink, readlink not implemented (no links under Windows)
fchmod not implemented
chown, fchown not implemented (make no sense on a DOS file system)
umask not implemented
set_nonblock, clear_nonblock implemented as dummy functions; use threads instead of non-blocking I/O
rewinddir not implemented; re-open the directory instead
mkfifo not implemented
select implemented, but works only for sockets; use threads if you need to wait on other kinds of file descriptors
lockf not implemented
kill, pause not implemented (no inter-process signals in Windows)
alarm, times not implemented
getitimer, setitimer not implemented
getuid, getgid always return 1
getgid, getegid, getgroups not implemented
setuid, setgid not implemented
getpwnam, getpwuid always raise Not_found
getgrnam, getgrgid always raise Not_found
type socket_domain the domain PF_UNIX is not supported; PF_INET is fully supported
establish_server not implemented; use threads
terminal functions (tc*) not implemented