open(2)                                                   open(2)



NAME
     open - opens a file for reading or writing

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

     int open(path, oflag[,mode])
     char *path;
     int oflag, mode;

DESCRIPTION
     open opens a file descriptor for the named file and sets the
     file status flags according to the value of oflag.  The
     argument path points to a pathname naming a file.  The oflag
     values are constructed by ORing flags from the following
     list (only one of the first three flags below may be used):

     O_RDONLY
          Open for reading only.

     O_WRONLY
          Open for writing only.

     O_RDWR
          Open for reading and writing.

     O_NDELAY or O_NONBLOCK
          Either flag may affect subsequent reads and writes (see
          read(2) and write(2)).

          When opening a FIFO with O_RDONLY or O_WRONLY set and:

          ⊕    if O_NDELAY or O_NONBLOCK is set, an open for
               reading-only returns without delay.  An open for
               writing-only returns an error if no process
               currently has the file open for reading.

          ⊕    if O_NDELAY and O_NONBLOCK are clear, an open for
               reading-only blocks until a process opens the file
               for writing.  An open for writing-only blocks
               until a process opens the file for reading.  When
               opening a file associated with a communication
               line and:

               ⊕    if O_NDELAY or O_NONBLOCK is set, the open
                    returns without waiting for a carrier.

               ⊕    if O_NDELAY and O_NONBLOCK are clear, an open
                    blocks until a carrier is present.




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open(2)                                                   open(2)



     O_APPEND
          If set, the file pointer is set to the end of the file
          prior to each write.

     O_CREAT
          If the file exists, this flag has no effect.
          Otherwise, the owner ID of the file is set to the
          effective user ID of the process, the group ID of the
          file is set to the effective group ID of the process,
          and the low-order 12 bits of the file mode are set to
          the value of mode modified as follows (see creat(2)):

          ⊕    All bits set in the file-mode-creation mask of the
               process are cleared (see umask(2)).

          ⊕    Mode bit 01000 (save text image after execution
               bit) is cleared (see chmod(2)).

     O_TRUNC
          If the file exists, its length is truncated to 0, and
          the mode and owner are unchanged.

     O_EXCL
          If O_EXCL and O_CREAT are set, open fails if the file
          exists.

     O_NOCTTY
          If set, and path identifies a terminal device, the open
          does not cause the terminal device to become the
          controlling terminal for the process.  O_NOCTTY has
          been added for compliance with POSIX.

     The file pointer used to mark the current position within
     the file is set to the beginning of the file.

     The new file descriptor is set to remain open across exec
     system calls.  See fcntl(2).

STATUS MESSAGE AND VALUES
     On successful completion, the file descriptor is returned.
     Otherwise, a value of -1 is returned and errno is set to
     indicate the error.

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

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

     ENAMETOOLONG
          A component of a pathname exceeded NAME_MAX characters,
          or an entire pathname exceeded PATH_MAX.



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open(2)                                                   open(2)



     ELOOP
          Too many symbolic links were encountered in translating
          a pathname.

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

     EACCES
          A component of the path prefix denies search
          permission.

     EACCES
          An oflag permission is denied for the named file.

     EISDIR
          The named file is a directory, and oflag is write or
          read/write.

     EROFS
          The named file resides on a read-only file system, and
          oflag is write or read/write.

     EMFILE
          The per-process open file limit would be exceeded.

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

     ETXTBSY
          The file is a pure-procedure (shared text) file that is
          being executed, and oflag is write or read/write.

             Note:  If you are running a Network File System
             (NFS) and you are accessing a shared binary
             remotely, it is possible that you will not get
             this errno.


     EFAULT
          path points outside the allocated address space of the
          process.

     EEXIST
          O_CREAT and O_EXCL are set, and the named file exists.

     ENXIO
          O_NDELAY is set, the named file is a FIFO, O_WRONLY is
          set, and no process has the file open for reading.

     EINTR



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open(2)                                                   open(2)



          A signal was caught during the open system call.

     ENFILE
          The system file table is full.

     ENOSPC
          The directory or file system that would contain the new
          file cannot be extended.

SEE ALSO
     chmod(2), close(2), creat(2), dup(2), fcntl(2), lseek(2),
     read(2), umask(2), write(2), fopen(3), ferror(3)











































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