bsd/man/man2/shmget.2

   1 .\"   $OpenBSD: shmget.2,v 1.2 1996/10/08 01:20:16 michaels Exp $
   2 .\"     $NetBSD: shmget.2,v 1.1 1995/10/16 23:49:32 jtc Exp $
   3 .\"
   4 .\" Copyright (c) 1995 Frank van der Linden
   5 .\" All rights reserved.
   6 .\"
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  16 .\"    must display the following acknowledgement:
  17 .\"      This product includes software developed for the NetBSD Project
  18 .\"      by Frank van der Linden
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  22 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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  32 .\"/
  33 .Dd August 17, 1995
  34 .Dt SHMGET 2
  35 .Os
  36 .Sh NAME
  37 .Nm shmget
  38 .Nd get shared memory area identifier
  39 .Sh SYNOPSIS
  40 .Fd #include <sys/shm.h>
  41 .Ft int
  42 .Fo shmget
  43 .Fa "key_t key"
  44 .Fa "size_t size"
  45 .Fa "int shmflg"
  46 .Fc
  47 .Sh DESCRIPTION
  48 .Fn shmget
  49 returns the shared memory identifier associated with the key
  50 .Fa key .
  51 .Pp
  52 A shared memory segment is created if either
  53 .Fa key
  54 is equal to IPC_PRIVATE, or
  55 .Fa key
  56 does not have a shared memory segment identifier associated with it, and the IPC_CREAT
  57 bit is set in
  58 .Fa shmflg.
  59 .Pp
  60 If a new shared memory segment is created, the data structure associated with it (the
  61 .Va shmid_ds
  62 structure, see
  63 .Xr shmctl 2 )
  64 is initialized as follows:
  65 .Bl -bullet
  66 .It
  67 .Va shm_perm.cuid
  68 and
  69 .Va shm_perm.uid
  70 are set to the effective uid of the calling process.
  71 .It
  72 .Va shm_perm.gid
  73 and
  74 .Va shm_perm.cgid
  75 are set to the effective gid of the calling process.
  76 .It
  77 .Va shm_perm.mode
  78 is set to the lower 9 bits of
  79 .Fa shmflg .
  80 .It
  81 .Va shm_lpid ,
  82 .Va shm_nattch ,
  83 .Va shm_atime ,
  84 and
  85 .Va shm_dtime
  86 are set to 0
  87 .It
  88 .Va shm_ctime
  89 is set to the current time.
  90 .It
  91 .Va shm_segsz
  92 is set to the value of
  93 .Fa size .
  94 .El
  95 .Sh RETURN VALUES
  96 Upon successful completion a positive shared memory segment identifier is returned.
  97 Otherwise, -1 is returned and the global variable
  98 .Va errno
  99 is set to indicate the error.
 100 .Sh ERRORS
 101 The
 102 .Fn shmget
 103 system call will fail if:
 104 .Bl -tag -width Er
 105 .\" ===========
 106 .It Bq Er EACCES
 107 A shared memory segment is already associated with
 108 .Fa key
 109 and the caller has no permission to access it.
 110 .\" ===========
 111 .It Bq Er EEXIST
 112 Both IPC_CREAT and IPC_EXCL are set in
 113 .Fa shmflg ,
 114 and a shared memory segment is already associated with
 115 .Fa key .
 116 .\" ===========
 117 .It Bq Er EINVAL
 118 No shared memory segment is to be created,
 119 and a shared memory segment exists for
 120 .Fa key ,
 121 but the size of the segment associated with it
 122 is less than
 123 .Fa size ,
 124 which is non-zero.
 125 .\" ===========
 126 .It Bq Er ENOENT
 127 IPC_CREAT was not set in
 128 .Fa shmflg
 129 and no shared memory segment associated with
 130 .Fa key
 131 was found.
 132 .\" ===========
 133 .It Bq Er ENOMEM
 134 There is not enough memory left to created a shared memory segment of the
 135 requested size.
 136 .\" ===========
 137 .It Bq Er ENOSPC
 138 A new shared memory identifier could not be created because the system limit
 139 for the number of shared memory identifiers has been reached.
 140 .El
 141 .Sh LEGACY SYNOPSIS
 142 .Fd #include <sys/types.h>
 143 .Fd #include <sys/ipc.h>
 144 .Fd #include <sys/shm.h>
 145 .Pp
 146 .Ft int
 147 .br
 148 .Fo shmget
 149 .Fa "key_t key"
 150 .Fa "int size"
 151 .Fa "int shmflg"
 152 .Fc ;
 153 .Pp
 154 All of these include files are necessary.
 155 The type of
 156 .Fa size
 157 has changed.
 158 .Sh SEE ALSO
 159 .Xr shmat 2 ,
 160 .Xr shmctl 2 ,
 161 .Xr shmdt 2 ,
 162 .Xr compat 5