V4/man/man2/creat.2

.th CREAT II 8/5/73
.sh NAME
creat  \*-  create a new file
.sh SYNOPSIS
(creat = 8.)
.br
.ft B
sys creat; name; mode
.br
(file descriptor in r0)
.s3
creat(name, mode)
.br
char *name;
.ft R
.sh DESCRIPTION
.it Creat
creates a new file or prepares to rewrite an existing
file called 
.it name,
given as the address of a null-terminated string.
If the file did not exist, it is given
mode
.it mode.
See
chmod(II) for the
construction of the
.it mode
argument.
.s3
If the file did exist, its mode and owner remain unchanged
but it is truncated to 0 length.
.s3
The file is also opened for writing, and its file descriptor
is returned (in r0).
.s3
The
.it mode
given is arbitrary; it need not allow
writing.
This feature is used by programs which deal with temporary
files of fixed names.
The creation is done with
a mode that forbids writing.
Then if a second
instance of the program attempts a
.it creat,
an error is
returned and the program knows that the name is unusable
for the moment.
.sh "SEE ALSO"
write(II), close(II), stat(II)
.sh DIAGNOSTICS
The error bit
(c-bit) may be set if: a needed directory is not searchable;
the file does not exist and the directory
in which it is to be created is not writable; the file
does exist and is unwritable;
the file is a directory;
there are already 10 files open.
.s3
From C, a \*-1 return indicates an error.