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.

Unix:

Programs that use the unix library must be linked in ``custom runtime'' mode, as follows:

        ocamlc -custom other options unix.cma other files -cclib -lunix
        ocamlopt other options unix.cmxa other files -cclib -lunix

For interactive use of the unix library, do:

        ocamlmktop -custom -o mytop unix.cma -cclib -lunix
        ./mytop

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.

Programs that use the unix library must be linked in ``custom runtime'' mode, as follows:

        ocamlc -custom other options unix.cma other files \
                %CAMLLIB%/libunix.lib wsock32.lib
        ocamlopt other options unix.cmxa other files \
                %CAMLLIB%/libunix.lib wsock32.lib

For interactive use of the unix library, do:

        ocamlmktop -custom -o mytop.exe unix.cma \
                %CAMLLIB%/libunix.lib wsock32.lib
        mytop.exe

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         (* 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.

Interface with the parent process

val environment : unit -> string array

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
  | 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 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.

val execv : string -> string array -> unit

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

val execve : string -> string array -> string array -> unit

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

val execvp : string -> string array -> unit
val execvpe : string -> string array -> 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 : 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 -> 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.

val close : file_descr -> unit

Close a file descriptor.

val read : file_descr -> string -> int -> 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 -> string -> int -> 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.

val out_channel_of_descr : file_descr -> out_channel
                             

Create an output channel writing on the given descriptor.

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 -> seek_command -> int

Set the current position for a file descriptor

val truncate : string -> int -> unit

Truncates the named file to the given size.

val 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.

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 : 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 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 -> file_perm -> unit

Change the permissions of the named file.

val fchmod : file_descr -> file_perm -> unit

Change the permissions of an opened file.

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

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

val fchown : file_descr -> int -> 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 -> 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 : file_descr -> 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 -> 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.

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 -> file_perm -> unit

Create a named pipe with the given permissions.

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. 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 :
  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 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 close_process_in: in_channel -> process_status
val close_process_out: out_channel -> process_status
val 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

val symlink : string -> 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 :
  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.

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 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

val kill : int -> int -> unit

kill pid sig sends signal number sig to the process with id pid.

val 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.

val time : unit -> int

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 : int -> tm

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

val localtime : int -> tm

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

val mktime : tm -> int * 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 and tm_yday recomputed from the other fields.

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 =
              "unix_times_bytecode" "unix_times_native"

Return the execution times of the process.

val 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.

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 : 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 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 recv, recvfrom, send and sendto.

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

Receive data from an unconnected socket.

val send : file_descr -> string -> int -> int -> msg_flag list -> int
val sendto :
        file_descr -> string -> int -> int -> msg_flag list -> 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 -> 'a) -> 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 -> string -> service_entry
                                        

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

val 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). *)
  }
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 -> 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 -> 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 -> 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 -> 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.

Windows:

Below is a list of the functions that are not implemented, or only partially implemented, under Windows. 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
truncate, ftruncate	not implemented
lstat, fstat	not implemented
link, symlink, readlink	not implemented (no links under Windows)
chmod, 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
ioctl_int, ioctl_ptr	not implemented (no ioctl in Windows)
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