# open(2)

    NAME
         open - open a file for reading or writing, or create a new file

    SYNOPSIS
         #include <sys/types.h>
         #include <fcntl.h>

         int open(const char *path, int flags [, mode_t mode])

    DESCRIPTION
         Open opens the file path for reading and/or writing, as specified by  the
         flags  argument  and  returns  a  descriptor  for  that  file.  The flags
         argument may indicate the file is to be created if it  does  not  already
         exist (by specifying the O_CREAT flag), in which case the file is created
         with mode mode as described in chmod(2)  and  modified  by  the  process'
         umask value (see umask(2)).

         Path is the address of a string of ASCII characters representing  a  path
         name,  terminated by a null character.  The flags specified are formed by
         or'ing the following values

              O_RDONLY    open for reading only
              O_WRONLY    open for writing only
              O_RDWR      open for reading and writing
              O_NONBLOCK  do not block on open
              O_APPEND    append on each write
              O_CREAT     create file if it does not exist
              O_TRUNC     truncate size to 0
              O_EXCL      error if create and file exists

         Opening a file with O_APPEND set causes each write  on  the  file  to  be
         appended  to  the  end.  If O_TRUNC is specified and the file exists, the
         file is truncated to zero length.  If O_EXCL is set with O_CREAT, then if
         the  file already exists, the open returns an error.  This can be used to
         implement a simple exclusive access locking mechanism.  If O_EXCL is  set
         and  the last component of the pathname is a symbolic link, the open will
         fail even if the symbolic link points to a  non-existent  name.   If  the
         O_NONBLOCK  flag  is  specified  and  the  open  call would result in the
         process being blocked for some reason, the open returns immediately.

         Upon  successful  completion  a  non-negative  integer  termed   a   file
         descriptor  is  returned.   The  file  pointer  used  to mark the current
         position within the file is set to the beginning of the file.

         The new descriptor is set to remain open across execve system calls;  see
         close(2).

         The  system  imposes  a  limit  on  the  number   of   descriptors   open
         simultaneously by one process.

    ERRORS
         The named file is opened unless one or more of the following are true:

         [ENOTDIR]      A component of the path prefix is not a directory.

         [ENAMETOOLONG] The path name exceeds PATH_MAX characters.

         [ENOENT]       O_CREAT is not set and the named file does not exist.

         [ENOENT]       A component of the path name  that  must  exist  does  not
                        exist.

         [EACCES]       Search permission is denied for a component  of  the  path
                        prefix.

         [EACCES]       The required permissions (for reading and/or writing)  are
                        denied for the named file.

         [EACCES]       O_CREAT is specified, the file does  not  exist,  and  the
                        directory  in  which  it  is to be created does not permit
                        writing.

         [EACCES]       A device to be opened  for  writing  is  physically  write
                        protected.

         [ELOOP]        Too many symbolic links were  encountered  in  translating
                        the pathname.  (Minix-vmd)

         [EISDIR]       The named file is a directory, and the  arguments  specify
                        it is to be opened for writing.

         [EROFS]        The named file resides on a read-only file system, and the
                        file is to be modified.

         [EMFILE]       The system limit for open file descriptors per process has
                        already been reached.

         [ENFILE]       The system file table is full.

         [ENXIO]        The named file is a character  special  or  block  special
                        file,  and  the  device  associated with this special file
                        does not exist.

         [ENOSPC]       O_CREAT is specified, the file does  not  exist,  and  the
                        directory  in  which  the  entry for the new file is being
                        placed cannot be extended because there is no  space  left
                        on the file system containing the directory.

         [ENOSPC]       O_CREAT is specified, the file does not exist,  and  there
                        are no free inodes on the file system on which the file is
                        being created.

         [EIO]          An I/O error occurred while making the directory entry  or
                        allocating the inode for O_CREAT.

         [EFAULT]       Path points outside the process's allocated address space.

         [EEXIST]       O_CREAT and O_EXCL were specified and the file exists.

    SEE ALSO
         chmod(2),  close(2),  dup(2),  fcntl(2),  lseek(2),  read(2),   write(2),
         umask(2).