open.2 (2010 09)

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open(2) open(2)

NAME

open() - open ﬁle for reading or writing

SYNOPSIS

#include <fcntl.h>

int open(const char *path, int oflag, ... /*

[mode_t mode] */ );

Remarks

The ANSI C ", ..." construct speciﬁes a variable length argument list whose optional member is given

in the associated comment (/* */

DESCRIPTION

The

open() system call opens a ﬁle descriptor for the named ﬁle and sets the ﬁle status ﬂags according

to the value of oﬂag.

The path argument points to a path name naming a ﬁle, and must not exceed

PATH_MAX bytes in length.

The oﬂag argument is a value that is the bitwise inclusive OR of ﬂags listed in "Read-Write Flags," "Gen-

eral Flags," "Synchronized I/O Flags," and "Direct I/O Flags" below.

The optional mode argument is only effective when the

O_CREAT ﬂag is speciﬁed.

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).

Read-Write Flags

Exactly one of the

O_RDONLY, O_WRONLY,orO_RDWR ﬂags must be used in composing the value of

oﬂag. If none or more than one is used, the behavior is undeﬁned.

O_RDONLY Open for reading only.

O_WRONLY Open for writing only.

O_RDWR Open for reading and writing.

General Flags

Several of the ﬂags listed below can be changed with the

fcntl() system call while the ﬁle is open. See

fcntl (2) and fcntl (5) for details.

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

O_CREAT If the ﬁle exists, this ﬂag has no effect, except as noted under

O_EXCL below. Oth-

erwise, 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 if the set-group-ID

bit of the parent directory is not set, or to the group ID of the parent directory if the

set-group-ID bit of the parent directory is set.

The ﬁle access permission bits of the new ﬁle mode are set to the value of mode,

modiﬁed as follows (see creat (2)):

• For each bit set in the ﬁle mode creation mask of the process, the corresponding

bit in the new ﬁle mode is cleared (see umask(2)).

• The "save text image after execution" bit of the new ﬁle mode is cleared. See

chmod(2).

• On HFS ﬁle systems with access control lists, three base ACL entries are created

corresponding to the ﬁle access permissions (see acl (5)).

• On JFS ﬁle systems that support access control lists, optional ACL entries are

created corresponding to the parent directory’s default ACL entries (see aclv (5)).

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

O_LARGEFILE

This is a non-standard ﬂag which may be used by 32-bit applications to access ﬁles

larger than 2 GB. See creat64 (2).

O_NDELAY This ﬂag might affect subsequent reads and writes. See read (2) and write(2).

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (4 pages)

PAGE 1
open(2) open(2) NAME open() - open file for reading or writing SYNOPSIS #include int open(const char *path, int oflag, ... /* [mode_t mode] */ ); Remarks The ANSI C ", ..." construct specifies a variable length argument list whose optional member is given in the associated comment (/* */). DESCRIPTION The open() system call opens a file descriptor for the named file and sets the file status flags according to the value of oflag.
PAGE 2
open(2) open(2) When opening a FIFO with O_RDONLY or O_WRONLY set: If O_NDELAY is set: A read-only open() returns without delay. A write-only open() returns an error if no process currently has the file open for reading. If O_NDELAY is clear: A read-only open() does not return until a process opens the file for writing. A write-only open() does not return until a process opens the file for reading.
PAGE 3
open(2) open(2) time) too are the same as their image on disk. RETURN VALUE open() returns the following values: n -1 Successful completion. n is a file descriptor for the opened file. Failure. errno is set to indicate the error. ERRORS If open() fails, errno is set to one of the following values. [EACCES] oflag permission is denied for the named file. [EACCES] A component of the path prefix denies search permission.
PAGE 4
open(2) open(2) types can be kept open for a long time, or indefinitely under some circumstances. EXAMPLES The following call to open() opens file inputfile for reading only and returns a file descriptor for inputfile. For an example of reading from file inputfile, see the read (2) manual entry. int infd; infd = open ("inputfile", O_RDONLY); The following call to open() opens file outputfile for writing and returns a file descriptor for outputfile.