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.sh see also
.br btree (3),
.br dbopen (3),
.br mpool (3),
.br recno (3)
.pp
.ir "dynamic hash tables" ,
per-ake larson, communications of the acm, april 1988.
.pp
.ir "a new hash package for unix" ,
margo seltzer, usenix proceedings, winter 1991.
.sh colophon
this page is part of release 5.13 of the linux
.i man-pages
project.
a description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.
.\" copyright (c) 2002, 2020 michael kerrisk <[email protected]>
.\"
.\" %%%license_start(verbatim)
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
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.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" since the linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. the author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. the author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" formatted or processed versions of this manual, if unaccompanied by
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.\"
.th shm_open 3 2021-03-22 "linux" "linux programmer's manual"
.sh name
shm_open, shm_unlink \- create/open or unlink posix shared memory objects
.sh synopsis
.nf
.b #include <sys/mman.h>
.br "#include <sys/stat.h>" " /* for mode constants */"
.br "#include <fcntl.h>" " /* for o_* constants */"
.pp
.bi "int shm_open(const char *" name ", int " oflag ", mode_t " mode );
.bi "int shm_unlink(const char *" name );
.fi
.pp
link with \fi\-lrt\fp.
.sh description
.br shm_open ()
creates and opens a new, or opens an existing, posix shared memory object.
a posix shared memory object is in effect a handle which can
be used by unrelated processes to
.br mmap (2)
the same region of shared memory.
the
.br shm_unlink ()
function performs the converse operation,
removing an object previously created by
.br shm_open ().
.pp
the operation of
.br shm_open ()
is analogous to that of
.br open (2).
.i name
specifies the shared memory object to be created or opened.
for portable use,
a shared memory object should be identified by a name of the form
.ir /somename ;
that is, a null-terminated string of up to
.bi name_max
(i.e., 255) characters consisting of an initial slash,
.\" glibc allows the initial slash to be omitted, and makes
.\" multiple initial slashes equivalent to a single slash.
.\" this differs from the implementation of posix message queues.
followed by one or more characters, none of which are slashes.
.\" glibc allows subdirectory components in the name, in which
.\" case the subdirectory must exist under /dev/shm, and allow the
.\" required permissions if a user wants to create a shared memory
.\" object in that subdirectory.
.pp
.i oflag
is a bit mask created by oring together exactly one of
.b o_rdonly
or
.b o_rdwr
and any of the other flags listed here:
.tp