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  sys-
     tem 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  physi-
                    cally write protected.

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

     [EISDIR]       The named file is a directory, and the  argu-
                    ments 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 direc-
                    tory   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).