# The unix library: Unix system calls

The `unix` library (distributed in `contrib/libunix`) makes many Unix system calls and system-related library functions available to Caml Light 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 in ``custom runtime'' mode, as follows:

            camlc -custom other options unix.zo other files -lunix

For interactive use of the `unix` library, run `camllight camlunix`.

Mac:
  This library is not available.

PC:
  This library is not available.

## `unix`: interface to the Unix system

### Error report

    type error =
        ENOERR
      | EPERM               (* Not owner *)
      | ENOENT              (* No such file or directory *)
      | ESRCH               (* No such process *)
      | EINTR               (* Interrupted system call *)
      | EIO                 (* I/O error *)
      | ENXIO               (* No such device or address *)
      | E2BIG               (* Arg list too long *)
      | ENOEXEC             (* Exec format error *)
      | EBADF               (* Bad file number *)
      | ECHILD              (* No children *)
      | EAGAIN              (* No more processes *)
      | ENOMEM              (* Not enough core *)
      | EACCES              (* Permission denied *)
      | EFAULT              (* Bad address *)
      | ENOTBLK             (* Block device required *)
      | EBUSY               (* Mount device busy *)
      | EEXIST              (* File exists *)
      | EXDEV               (* Cross-device link *)
      | ENODEV              (* No such device *)
      | ENOTDIR             (* Not a directory*)
      | EISDIR              (* Is a directory *)
      | EINVAL              (* Invalid argument *)
      | ENFILE              (* File table overflow *)
      | EMFILE              (* Too many open files *)
      | ENOTTY              (* Not a typewriter *)
      | ETXTBSY             (* Text file busy *)
      | EFBIG               (* File too large *)
      | ENOSPC              (* No space left on device *)
      | ESPIPE              (* Illegal seek *)
      | EROFS               (* Read-only file system *)
      | EMLINK              (* Too many links *)
      | EPIPE               (* Broken pipe *)
      | EDOM                (* Argument too large *)
      | ERANGE              (* Result too large *)
      | 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 *)
      | ELOOP               (* Too many levels of symbolic links *)
      | ENAMETOOLONG        (* File name too long *)
      | EHOSTDOWN           (* Host is down *)
      | EHOSTUNREACH        (* No route to host *)
      | ENOTEMPTY           (* Directory not empty *)
      | EPROCLIM            (* Too many processes *)
      | EUSERS              (* Too many users *)
      | EDQUOT              (* Disc quota exceeded *)
      | ESTALE              (* Stale NFS file handle *)
      | EREMOTE             (* Too many levels of remote in path *)
      | EIDRM               (* Identifier removed *)
      | EDEADLK             (* Deadlock condition. *)
      | ENOLCK              (* No record locks available. *)
      | ENOSYS              (* Function not implemented *)
      | EUNKNOWNERR

  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.

    value error_message : error -> string

  Return a string describing the given error code.

    value 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.

### Interface with the parent process

    value environment : unit -> string vect

  Return the process environment, as an array of strings with the format ``variable=value''. See also `sys__getenv`.

### Process handling

    type process_status =
        WEXITED of int
      | WSIGNALED of int * bool
      | 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 first argument is the signal number, the second argument indicates whether a ``core dump'' was performed. `WSTOPPED` means that the process was stopped by a signal; the argument is the signal number.

    type wait_flag =
        WNOHANG
      | WUNTRACED

  Flags for `waitopt` and `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.

    value execv : string -> string vect -> unit

  `execv prog args` execute the program in file `prog`, with the arguments `args`, and the current process environment.

    value execve : string -> string vect -> string vect -> unit

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

    value execvp : string -> string vect -> unit

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

    value 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.

    value wait : unit -> int * process_status

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

    value waitopt : wait_flag list -> int * process_status

  Same as `wait`, but takes a list of options to avoid blocking, or also report stopped children. The pid returned is 0 if no child has changed status.

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

  Same as `waitopt`, but waits for the process whose pid is given. Negative pid arguments represent process groups.

    value 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.

    value getpid : unit -> int

  Return the pid of the process.

    value getppid : unit -> int

  Return the pid of the parent process.

    value 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.

    value stdin : file_descr
    value stdout : file_descr
    value 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_NDELAY                            (* 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.

    value open : 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. Return a file descriptor on the named file.

    value close : file_descr -> unit

  Close a file descriptor.

    value read : file_descr -> string -> int -> int -> int

  `read fd buff start 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.

    value write : file_descr -> string -> int -> int -> int

  `write fd buff start 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 (module io).

    value in_channel_of_descr : file_descr -> in_channel

  Create an input channel reading from the given descriptor.

    value out_channel_of_descr : file_descr -> out_channel

  Create an output channel writing on the given descriptor.

    value descr_of_in_channel : in_channel -> file_descr

  Return the descriptor corresponding to an input channel.

    value 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.

    value lseek : file_descr -> int -> seek_command -> int

  Set the current position for a file descriptor

    value truncate : string -> int -> unit

  Truncates the named file to the given size.

    value ftruncate : file_descr -> 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 owner *)
        st_rdev : int;                      (* Device minor number *)
        st_size : int;                      (* Size in bytes *)
        st_atime : int;                     (* Last access time *)
        st_mtime : int;                     (* Last modification time *)
        st_ctime : int }                    (* Last status change time *)

  The informations returned by the `stat` calls.

    value stat : string -> stats

  Return the information for the named file.

    value lstat : string -> stats

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

    value fstat : file_descr -> stats

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

### Operations on file names

    value unlink : string -> unit

  Removes the named file

    value rename : string -> string -> unit

  `rename old new` changes the name of a file from `old` to `new`.

    value link : string -> 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.

    value chmod : string -> file_perm -> unit

  Change the permissions of the named file.

    value fchmod : file_descr -> file_perm -> unit

  Change the permissions of an opened file.

    value chown : string -> int -> int -> unit

  Change the owner uid and owner gid of the named file.

    value fchown : file_descr -> int -> int -> unit

  Change the owner uid and owner gid of an opened file.

    value umask : int -> int

  Set the process creation mask, and return the previous mask.

    value access : string -> access_permission list -> unit

  Check that the process has the given permissions over the named file. Raise `Unix_error` otherwise.

### File descriptor hacking

    value fcntl_int : file_descr -> int -> int -> int

  Interface to `fcntl` in the case where the argument is an integer. The first integer argument is the command code; the second is the integer parameter.

    value fcntl_ptr : file_descr -> int -> string -> int

  Interface to `fcntl` in the case where the argument is a pointer. The integer argument is the command code. A pointer to the string argument is passed as argument to the command.

### Directories

    value mkdir : string -> file_perm -> unit

  Create a directory with the given permissions.

    value rmdir : string -> unit

  Remove an empty directory.

    value chdir : string -> unit

  Change the process working directory.

    value getcwd : unit -> string

  Return the name of the current working directory.

    type dir_handle

  The type of descriptors over opened directories.

    value opendir : string -> dir_handle

  Open a descriptor on a directory

    value readdir : dir_handle -> string

  Return the next entry in a directory. Raise `End_of_file` when the end of the directory has been reached.

    value rewinddir : dir_handle -> unit

  Reposition the descriptor to the beginning of the directory

    value closedir : dir_handle -> unit

  Close a directory descriptor.

### Pipes and redirections

    value 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 entrace to the pipe.

    value dup : file_descr -> file_descr

  Duplicate a descriptor.

    value dup2 : file_descr -> file_descr -> unit

  `dup2 fd1 fd2` duplicates `fd1` to `fd2`, closing `fd2` if already opened.

    value open_process_in: string -> in_channel
    value open_process_out: string -> out_channel
    value 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.

    value close_process_in: in_channel -> process_status
    value close_process_out: out_channel -> process_status
    value close_process: in_channel * out_channel -> process_status

  Close channels opened by `open_process_in`, `open_process_out` and `open_process`, respectively, wait for the associated command to terminate, and return its termination status.

### Symbolic links

    value symlink : string -> string -> unit

  `symlink source dest` creates the file `dest` as a symbolic link to the file `source`.

    value readlink : string -> string

  Read the contents of a link.

### Named pipes

    value mkfifo : string -> file_perm -> unit

  Create a named pipe with the given permissions.

### Special files

    value ioctl_int : file_descr -> int -> int -> int

  Interface to `ioctl` in the case where the argument is an integer. The first integer argument is the command code; the second is the integer parameter.

    value ioctl_ptr : file_descr -> int -> string -> int

  Interface to `ioctl` in the case where the argument is a pointer. The integer argument is the command code. A pointer to the string argument is passed as argument to the command.

### Polling

    value 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, and block if already locked *)
      | F_TLOCK               (* Lock a region, or fail if already locked *)
      | F_TEST                (* Test a region for other process' locks *)

  Commands for `lockf`.

    value 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 `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.

### Signals

    type signal =
        SIGHUP              (* hangup *)
      | SIGINT              (* interrupt *)
      | SIGQUIT             (* quit *)
      | SIGILL              (* illegal instruction (not reset when caught) *)
      | SIGTRAP             (* trace trap (not reset when caught) *)
      | SIGABRT             (* used by abort *)
      | SIGEMT              (* EMT instruction *)
      | SIGFPE              (* floating point exception *)
      | SIGKILL             (* kill (cannot be caught or ignored) *)
      | SIGBUS              (* bus error *)
      | SIGSEGV             (* segmentation violation *)
      | SIGSYS              (* bad argument to system call *)
      | SIGPIPE             (* write on a pipe with no one to read it *)
      | SIGALRM             (* alarm clock *)
      | SIGTERM             (* software termination signal from kill *)
      | SIGURG              (* urgent condition on IO channel *)
      | SIGSTOP             (* sendable stop signal not from tty *)
      | SIGTSTP             (* stop signal from tty *)
      | SIGCONT             (* continue a stopped process *)
      | SIGCHLD             (* to parent on child stop or exit *)
      | SIGIO               (* input/output possible signal *)
      | SIGXCPU             (* exceeded CPU time limit *)
      | SIGXFSZ             (* exceeded file size limit *)
      | SIGVTALRM           (* virtual time alarm *)
      | SIGPROF             (* profiling time alarm *)
      | SIGWINCH            (* window changed *)
      | SIGLOST             (* resource lost (eg, record-lock lost) *)
      | SIGUSR1             (* user defined signal 1 *)
      | SIGUSR2             (* user defined signal 2 *)

  The type of signals.

    type signal_handler =
        Signal_default                      (* Default behavior for the signal *)
      | Signal_ignore                       (* Ignore the signal *)
      | Signal_handle of (unit -> unit)     (* Call the given function
                                               when the signal occurs. *)

  The behavior on receipt of a signal

    value kill : int -> signal -> unit

  Send a signal to the process with the given process id.

    value signal : signal -> signal_handler -> unit

  Set the behavior to be taken on receipt of the given signal.

    value pause : unit -> unit

  Wait until a non-ignored 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.

    value time : unit -> int

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

    value gettimeofday : unit -> float

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

    value gmtime : int -> tm

  Convert a time in seconds, as returned by `time`, into a date and a time. Assumes Greenwich meridian time zone.

    value localtime : int -> tm

  Convert a time in seconds, as returned by `time`, into a date and a time. Assumes the local time zone.

    value alarm : int -> int

  Schedule a `SIGALRM` signals after the given number of seconds.

    value sleep : int -> unit

  Stop execution for the given number of seconds.

    value times : unit -> process_times

  Return the execution times of the process.

    value utimes : string -> int -> int -> 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.

### User id, group id

    value getuid : unit -> int

  Return the user id of the user executing the process.

    value geteuid : unit -> int

  Return the effective user id under which the process runs.

    value setuid : int -> unit

  Set the real user id and effective user id for the process.

    value getgid : unit -> int

  Return the group id of the user executing the process.

    value getegid : unit -> int

  Return the effective group id under which the process runs.

    value setgid : int -> unit

  Set the real group id and effective group id for the process.

    value getgroups : unit -> int vect

  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 vect }

  Structure of entries in the `groups` database.

    value getlogin : unit -> string

  Return the login name of the user executing the process.

    value getpwnam : string -> passwd_entry

  Find an entry in `passwd` with the given name, or raise `Not_found`.

    value getgrnam : string -> group_entry

  Find an entry in `group` with the given name, or raise `Not_found`.

    value getpwuid : int -> passwd_entry

  Find an entry in `passwd` with the given user id, or raise `Not_found`.

    value 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.

    value inet_addr_of_string : string -> inet_addr
    value 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.

### 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.

    type shutdown_command =
        SHUTDOWN_RECEIVE                    (* Close for receiving *)
      | SHUTDOWN_SEND                       (* Close for sending *)
      | SHUTDOWN_ALL                        (* Close both *)

  The type of commands for `shutdown`.

    type msg_flag =
        MSG_OOB
      | MSG_DONTROUTE
      | MSG_PEEK

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

    value 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.

    value socketpair :
            socket_domain -> socket_type -> int -> file_descr * file_descr

  Create a pair of unnamed sockets, connected together.

    value 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.

    value bind : file_descr -> sockaddr -> unit

  Bind a socket to an address.

    value connect : file_descr -> sockaddr -> unit

  Connect a socket to an address.

    value listen : file_descr -> int -> unit

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

    value 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).

    value getsockname : file_descr -> sockaddr

  Return the address of the given socket.

    value getpeername : file_descr -> sockaddr

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

    value recv : file_descr -> string -> int -> int -> msg_flag list -> int
    value recvfrom :
            file_descr -> string -> int -> int -> msg_flag list -> int * sockaddr

  Receive data from an unconnected socket.

    value send : file_descr -> string -> int -> int -> msg_flag list -> int
    value sendto :
            file_descr -> string -> int -> int -> msg_flag list -> sockaddr -> int

  Send data over an unconnected socket.

### High-level network connection functions

    value 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.

    value 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.

    value 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 `establish_server` never returns normally.

### Host and protocol databases

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

  Structure of entries in the `hosts` database.

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

  Structure of entries in the `protocols` database.

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

  Structure of entries in the `services` database.

    value gethostname : unit -> string

  Return the name of the local host.

    value gethostbyname : string -> host_entry

  Find an entry in `hosts` with the given name, or raise `Not_found`.

    value gethostbyaddr : inet_addr -> host_entry

  Find an entry in `hosts` with the given address, or raise `Not_found`.

    value getprotobyname : string -> protocol_entry

  Find an entry in `protocols` with the given name, or raise `Not_found`.

    value getprotobynumber : int -> protocol_entry

  Find an entry in `protocols` with the given protocol number, or raise `Not_found`.

    value getservbyname : string -> string -> service_entry

  Find an entry in `services` with the given name, or raise `Not_found`.

    value getservbyport : int -> 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). *)
      }
    value tcgetattr: file_descr -> terminal_io

  Return the status of the terminal referred to by the given file descriptor.

    type setattr_when = TCSANOW | TCSADRAIN | TCSAFLUSH
    value 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.

    value 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).

    value tcdrain: file_descr -> unit

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

    type flush_queue = TCIFLUSH | TCOFLUSH | TCIOFLUSH
    value 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.

    type flow_action = TCOOFF | TCOON | TCIOFF | TCION
    value 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.