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 $
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   4 .\" Copyright (c) 1995 Frank van der Linden
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  17 .\"      This product includes software developed for the NetBSD Project
  18 .\"      by Frank van der Linden
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  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/types.h>
  41 .Fd #include <sys/ipc.h>
  42 .Fd #include <sys/shm.h>
  43 .Ft int
  44 .Fn shmget "key_t key" "int size" "int shmflg"
  45 .Sh DESCRIPTION
  46 .Fn shmget
  47 returns the shared memory identifier associated with the key
  48 .Fa key .
  49 .Pp
  50 A shared memory segment is created if either
  51 .Fa key
  52 is equal to IPC_PRIVATE, or
  53 .Fa key
  54 does not have a shared memory segment identifier associated with it, and the IPC_CREAT
  55 bit is set in
  56 .Fa shmflg.
  57 .Pp
  58 If a new shared memory segment is created, the data structure associated with it (the
  59 .Va shmid_ds
  60 structure, see
  61 .Xr shmctl 2 )
  62 is initialized as follows:
  63 .Bl -bullet
  64 .It
  65 .Va shm_perm.cuid
  66 and
  67 .Va shm_perm.uid
  68 are set to the effective uid of the calling process.
  69 .It
  70 .Va shm_perm.gid
  71 and
  72 .Va shm_perm.cgid
  73 are set to the effective gid of the calling process.
  74 .It
  75 .Va shm_perm.mode
  76 is set to the lower 9 bits of
  77 .Fa shmflg .
  78 .It
  79 .Va shm_lpid ,
  80 .Va shm_nattch ,
  81 .Va shm_atime ,
  82 and
  83 .Va shm_dtime
  84 are set to 0
  85 .It
  86 .Va shm_ctime
  87 is set to the current time.
  88 .It
  89 .Va shm_segsz
  90 is set to the value of
  91 .Fa size .
  92 .El
  93 .Sh RETURN VALUES
  94 Upon successful completion a positive shared memory segment identifier is returned.
  95 Otherwise, -1 is returned and the global variable
  96 .Va errno
  97 is set to indicate the error.
  98 .Sh ERRORS
  99 .Bl -tag -width Er
 100 .It Bq Er EACESS
 101 A shared memory segment is already associated with
 102 .Fa key
 103 and the caller has no permission to access it.
 104 .It Bq Er EEXIST
 105 Both IPC_CREAT and IPC_EXCL are set in
 106 .Fa shmflg ,
 107 and a shared memory segment is already associated with
 108 .Fa key .
 109 .It Bq Er ENOSPC
 110 A new shared memory indentifier could not be created because the system limit
 111 for the number of shared memory identifiers has been reached.
 112 .It Bq Er ENOENT
 113 IPC_CREAT was not set in
 114 .Fa shmflg
 115 and no shared memory segment associated with
 116 .Fa key
 117 was found.
 118 .It Bq Er ENOMEM
 119 There is not enough memory left to created a shared memory segment of the
 120 requested size.
 121 .El
 122 .Sh SEE ALSO
 123 .Xr shmctl 2 ,
 124 .Xr shmat 2 ,
 125 .Xr shmdt 2