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-.TH SHM_OVERVIEW 7 2010-09-10 "Linux" "Linux Programmer's Manual"
-.SH NAME
-shm_overview \- overview of POSIX shared memory
-.SH DESCRIPTION
-The POSIX shared memory API allows processes to communicate information
-by sharing a region of memory.
-
-The interfaces employed in the API are:
-.TP 15
-.BR shm_open (3)
-Create and open a new object, or open an existing object.
-This is analogous to
-.BR open (2).
-The call returns a file descriptor for use by the other
-interfaces listed below.
-.TP
-.BR ftruncate (2)
-Set the size of the shared memory object.
-(A newly created shared memory object has a length of zero.)
-.TP
-.BR mmap (2)
-Map the shared memory object into the virtual address space
-of the calling process.
-.TP
-.BR munmap (2)
-Unmap the shared memory object from the virtual address space
-of the calling process.
-.TP
-.BR shm_unlink (3)
-Remove a shared memory object name.
-.TP
-.BR close (2)
-Close the file descriptor allocated by
-.BR shm_open (3)
-when it is no longer needed.
-.TP
-.BR fstat (2)
-Obtain a
-.I stat
-structure that describes the shared memory object.
-Among the information returned by this call are the object's
-size
-.RI ( st_size ),
-permissions
-.RI ( st_mode ),
-owner
-.RI ( st_uid ),
-and group
-.RI ( st_gid ).
-.TP
-.BR fchown (2)
-To change the ownership of a shared memory object.
-.TP
-.BR fchmod (2)
-To change the permissions of a shared memory object.
-.SS Versions
-POSIX shared memory is supported since Linux 2.4 and glibc 2.2.
-.SS Persistence
-POSIX shared memory objects have kernel persistence:
-a shared memory object will exist until the system is shut down,
-or until all processes have unmapped the object and it has been deleted with
-.BR shm_unlink (3)
-.SS Linking
-Programs using the POSIX shared memory API must be compiled with
-.I cc \-lrt
-to link against the real-time library,
-.IR librt .
-.SS Accessing shared memory objects via the filesystem
-On Linux, shared memory objects are created in a
-.RI ( tmpfs )
-virtual filesystem, normally mounted under
-.IR /dev/shm .
-Since kernel 2.6.19, Linux supports the use of access control lists (ACLs)
-to control the permissions of objects in the virtual filesystem.
-.SH CONFORMING TO
-POSIX.1-2001.
-.SH NOTES
-Typically, processes must synchronize their access to a shared
-memory object, using, for example, POSIX semaphores.
-
-System V shared memory
-.RB ( shmget (2),
-.BR shmop (2),
-etc.) is an older shared memory API.
-POSIX shared memory provides a simpler, and better designed interface;
-on the other hand POSIX shared memory is somewhat less widely available
-(especially on older systems) than System V shared memory.
-.SH SEE ALSO
-.BR fchmod (2),
-.BR fchown (2),
-.BR fstat (2),
-.BR ftruncate (2),
-.BR mmap (2),
-.BR mprotect (2),
-.BR munmap (2),
-.BR shmget (2),
-.BR shmop (2),
-.BR shm_open (3),
-.BR shm_unlink (3),
-.BR sem_overview (7)
-.SH COLOPHON
-This page is part of release 3.79 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
-\%http://www.kernel.org/doc/man\-pages/.
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