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 .\"
   7 .\" Redistribution and use in source and binary forms, with or without
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  15 .\" 3. All advertising materials mentioning features or use of this software
  16 .\"    must display the following acknowledgement:
  17 .\"      This product includes software developed for the NetBSD Project
  18 .\"      by Frank van der Linden
  19 .\" 4. The name of the author may not be used to endorse or promote products
  20 .\"    derived from this software without specific prior written permission
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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 .It
  95 The
  96 .Xr ftok 3
  97 function may be used to generate a key from a pathname.
  98 .El
  99 .Sh RETURN VALUES
 100 Upon successful completion a positive shared memory segment identifier is returned.
 101 Otherwise, -1 is returned and the global variable
 102 .Va errno
 103 is set to indicate the error.
 104 .Sh ERRORS
 105 The
 106 .Fn shmget
 107 system call will fail if:
 108 .Bl -tag -width Er
 109 .\" ===========
 110 .It Bq Er EACCES
 111 A shared memory segment is already associated with
 112 .Fa key
 113 and the caller has no permission to access it.
 114 .\" ===========
 115 .It Bq Er EEXIST
 116 Both IPC_CREAT and IPC_EXCL are set in
 117 .Fa shmflg ,
 118 and a shared memory segment is already associated with
 119 .Fa key .
 120 .\" ===========
 121 .It Bq Er EINVAL
 122 No shared memory segment is to be created,
 123 and a shared memory segment exists for
 124 .Fa key ,
 125 but the size of the segment associated with it
 126 is less than
 127 .Fa size ,
 128 which is non-zero.
 129 .\" ===========
 130 .It Bq Er ENOENT
 131 IPC_CREAT was not set in
 132 .Fa shmflg
 133 and no shared memory segment associated with
 134 .Fa key
 135 was found.
 136 .\" ===========
 137 .It Bq Er ENOMEM
 138 There is not enough memory left to created a shared memory segment of the
 139 requested size.
 140 .\" ===========
 141 .It Bq Er ENOSPC
 142 A new shared memory identifier could not be created because the system limit
 143 for the number of shared memory identifiers has been reached.
 144 .El
 145 .Sh LEGACY SYNOPSIS
 146 .Fd #include <sys/types.h>
 147 .Fd #include <sys/ipc.h>
 148 .Fd #include <sys/shm.h>
 149 .Pp
 150 .Ft int
 151 .br
 152 .Fo shmget
 153 .Fa "key_t key"
 154 .Fa "int size"
 155 .Fa "int shmflg"
 156 .Fc ;
 157 .Pp
 158 All of these include files are necessary.
 159 The type of
 160 .Fa size
 161 has changed.
 162 .Sh SEE ALSO
 163 .Xr ftok 3 ,
 164 .Xr shmat 2 ,
 165 .Xr shmctl 2 ,
 166 .Xr shmdt 2 ,
 167 .Xr compat 5