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148 lines
4.9 KiB
Plaintext
148 lines
4.9 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "SHMGET" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" shmget
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.SH PROLOG
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This manual page is part of the POSIX Programmer's Manual.
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The Linux implementation of this interface may differ (consult
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the corresponding Linux manual page for details of Linux behavior),
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or the interface may not be implemented on Linux.
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.SH NAME
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shmget \- get an XSI shared memory segment
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.SH SYNOPSIS
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.LP
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\fB#include <sys/shm.h>
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.br
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.sp
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int shmget(key_t\fP \fIkey\fP\fB, size_t\fP \fIsize\fP\fB, int\fP
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\fIshmflg\fP\fB); \fP
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\fB
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The \fIshmget\fP() function operates on XSI shared memory (see the
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Base Definitions volume of IEEE\ Std\ 1003.1-2001,
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Section 3.340, Shared Memory Object). It is unspecified whether this
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function
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interoperates with the realtime interprocess communication facilities
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defined in \fIRealtime\fP .
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.LP
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The \fIshmget\fP() function shall return the shared memory identifier
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associated with \fIkey\fP.
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.LP
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A shared memory identifier, associated data structure, and shared
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memory segment of at least \fIsize\fP bytes (see \fI<sys/shm.h>\fP)
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are created for \fIkey\fP if one of the following is true:
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.IP " *" 3
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The argument \fIkey\fP is equal to IPC_PRIVATE.
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.LP
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.IP " *" 3
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The argument \fIkey\fP does not already have a shared memory identifier
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associated with it and (\fIshmflg\fP &IPC_CREAT)
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is non-zero.
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.LP
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.LP
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Upon creation, the data structure associated with the new shared memory
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identifier shall be initialized as follows:
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.IP " *" 3
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The values of \fIshm_perm.cuid\fP, \fIshm_perm.uid\fP, \fIshm_perm.cgid\fP,
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and \fIshm_perm.gid\fP are set equal to the
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effective user ID and effective group ID, respectively, of the calling
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process.
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.LP
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.IP " *" 3
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The low-order nine bits of \fIshm_perm.mode\fP are set equal to the
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low-order nine bits of \fIshmflg\fP.
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.LP
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.IP " *" 3
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The value of \fIshm_segsz\fP is set equal to the value of \fIsize\fP.
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.LP
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.IP " *" 3
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The values of \fIshm_lpid\fP, \fIshm_nattch\fP, \fIshm_atime\fP, and
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\fIshm_dtime\fP are set equal to 0.
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.LP
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.IP " *" 3
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The value of \fIshm_ctime\fP is set equal to the current time.
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.LP
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.LP
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When the shared memory segment is created, it shall be initialized
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with all zero values.
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.SH RETURN VALUE
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.LP
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Upon successful completion, \fIshmget\fP() shall return a non-negative
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integer, namely a shared memory identifier; otherwise,
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it shall return -1 and set \fIerrno\fP to indicate the error.
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.SH ERRORS
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.LP
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The \fIshmget\fP() function shall fail if:
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.TP 7
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.B EACCES
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A shared memory identifier exists for \fIkey\fP but operation permission
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as specified by the low-order nine bits of
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\fIshmflg\fP would not be granted; see \fIXSI Interprocess Communication\fP
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\&.
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.TP 7
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.B EEXIST
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A shared memory identifier exists for the argument \fIkey\fP but (\fIshmflg\fP
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&IPC_CREAT) &&(\fIshmflg\fP
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&IPC_EXCL) is non-zero.
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.TP 7
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.B EINVAL
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A shared memory segment is to be created and the value of size is
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less than the system-imposed minimum or greater than the
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system-imposed maximum.
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.TP 7
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.B EINVAL
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No shared memory segment is to be created and a shared memory segment
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exists for \fIkey\fP but the size of the segment
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associated with it is less than \fIsize\fP and \fIsize\fP is not 0.
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.TP 7
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.B ENOENT
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A shared memory identifier does not exist for the argument \fIkey\fP
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and (\fIshmflg\fP &IPC_CREAT) is 0.
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.TP 7
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.B ENOMEM
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A shared memory identifier and associated shared memory segment shall
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be created, but the amount of available physical memory
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is not sufficient to fill the request.
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.TP 7
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.B ENOSPC
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A shared memory identifier is to be created, but the system-imposed
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limit on the maximum number of allowed shared memory
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identifiers system-wide would be exceeded.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.LP
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None.
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.SH APPLICATION USAGE
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.LP
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The POSIX Realtime Extension defines alternative interfaces for interprocess
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communication. Application developers who need to
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use IPC should design their applications so that modules using the
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IPC routines described in \fIXSI Interprocess Communication\fP can
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be easily modified to use the alternative
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interfaces.
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.SH RATIONALE
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.LP
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None.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIXSI Interprocess Communication\fP, \fIRealtime\fP, \fIshmat\fP()
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, \fIshmctl\fP(), \fIshmdt\fP(), \fIshm_open\fP(), \fIshm_unlink\fP()
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, the Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<sys/shm.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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