2.9BSD/usr/man/man2/open.2

.TH OPEN 2 
.UC
.SH NAME
open \- open for reading or writing
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <sys/file.h>
.sp
.B open(name, mode)
.br
.B char *name;
.SH DESCRIPTION
.I Open
opens the file
.I name
for reading
(if
.I mode
is FATT_RDONLY),
writing (if
.I mode
is FATT_WRONLY) or for both reading and writing
(if
.I mode
is FATT_RDWR).
.I Name
is the address of a string of ASCII characters representing
a path name, terminated by a null character.
.PP
The file is positioned at the beginning (byte 0).
The returned file descriptor must be used for subsequent calls
for other input-output functions on the file.
.SH ERRORS
The named file is opened unless one or more of the following is true:
.TP 20
[EINVAL]
The path name contains a non-ASCII byte.
.TP 20
[ENOTDIR]
A component of the path prefix is not a directory.
.TP 20
[EACCES]
A component of the path prefix denies search permission.
.TP 20
[ENOENT]
The named file does not exist.
.TP 20
[EISDIR]
The named file is a directory and the arguments specify it is to be
opened for writing.
.TP 20
[EROFS]
The named file resides on a read-only file system and the file is to
be modified.
.TP 20
[EMFILE]
The maximum number of file descriptors allowed are already open.
.TP 20
[ETXTBSY]
The file is a pure procedure (shared text) file that is being executed
and the
.I open
call requests write access.
.TP 20
[EFAULT]
.I Name
points outside the process's allocated address space.
.TP 20
[ELOOP]
Too many symbolic links were encountered in translating the path name.
.SH "SEE ALSO"
close(2), creat(2), dup(2), read(2), write(2)
.SH ASSEMBLER
(open = 5.)
.br
.B sys open; name; mode
.br
(file descriptor in r0)