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msgget(2)
NAME
  msgget - Return (and possibly create) the ID for a message queue

SYNOPSIS
  #include <sys/msg.h>

  int msgget(
	  key_t key,
	  int msgflg );

  Application developers may want to specify #include statements for
  <sys/types.h> and <sys/ipc.h> before the one for <sys/msg.h> if programs
  are being developed for multiple platforms.  The additional #include
  statements are not required on Tru64 UNIX systems or by ISO or X/Open
  standards, but may be required on other vendors' systems that conform to
  these standards.

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  msgget():  XSH4.0, XSH4.2, XSH5.0

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  key Specifies the key that identifies the message queue. The value for the
      key parameter can be IPC_PRIVATE or a random number other than zero
      (0). To ensure that the msgget() function returns a new message queue
      ID, specify the IPC_PRIVATE keyword.

  msgflg
      Specifies flags that control the msgget() function. Possible values are
      as follows:

      IPC_CREAT
	  Specifies creating a message queue ID.

	  If the specified key does not exist, the msgget() function creates
	  a message queue ID and associates it with the specified key.

	  If the specified key does exist, and IPC_EXCL is not set, the
	  msgget() function returns the message queue ID associated with key.

	  If the specified key does exist and IPC_EXCL is set, the msgget()
	  function fails and returns an error.

      IPC_EXCL
	  Specifies that you want to ensure that your application is the only
	  one using the specified key parameter. If the specified key already
	  exists, the msgget() function fails and returns an error
	  notification.

DESCRIPTION
  The msgget() function returns the message queue ID for the message queue
  identified by the key parameter.  If the message queue ID does not exist,
  the msgget() function attempts to create it.

  If you specify IPC_PRIVATE for the key parameter, the msgget() function
  returns the ID for a private (that is, newly created) message queue.

  The msgflg parameter supplies creation options for the msgget() function.
  The IPC_CREAT flag specifies that you want the kernel to create a message
  queue for your application. The kernel returns the message queue ID to your
  application as the return value of the successful call to the msgget()
  function.

  The msgget() function does not create a message queue ID for your
  application under the following conditions:

    ·  A message queue ID that is associated with the specified key already
       exists. In this case, the msgget() function returns the message queue
       ID associated with the key parameter (unless you have set the IPC_EXCL
       flag).

    ·  You have set the IPC_EXCL flag and another application is using the
       specified key. In this case, the msgget() function fails and returns
       an error to your application.

  After creating a new message queue ID, the msgget() function initializes
  the msqid_ds structure associated with the ID as follows:

    ·  The msg_perm.cuid and msg_perm.uid members are set equal to the
       effective user ID of the calling process.

    ·  The msg_perm.cgid and msg_perm.gid members are set equal to the
       effective group ID of the calling process.

    ·  The low-order nine bits of the msg_perm.mode member are set equal to
       the low-order nine bits of msgflg.

    ·  The msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime members
       are all set equal to zero.

    ·  The msg_ctime member is set equal to the current time.

    ·  The msg_qbytes member is set equal to the system limit.

RETURN VALUES
  Upon successful completion, the msgget() function returns a message queue
  identifier. Otherwise, the function returns a value of -1 and sets errno to
  indicate the error.

ERRORS
  The msgget() function sets errno to the specified values for the following
  conditions:

  [EACCES]
      A message queue identifier exists for the key parameter, but the
      calling process does not have the appropriate privileges to perform the
      operation. The permission is specified by the low-order nine bits of
      the msgflg parameter.

  [EEXIST]
      A message queue identifier exists for the key parameter, and both
      IPC_CREAT and IPC_EXCL are set.

  [ENOENT]
      A message queue identifier does not exist for the key parameter and the
      IPC_CREAT value is not set.

  [ENOSPC]
      A message queue identifier can be created, but the system-imposed limit
      on the maximum number of allowed message queue identifiers has been
      exceeded.

SEE ALSO
  Functions: msgctl(2), msgrcv(2), msgsnd(2), table(2), ftok(3)

  Data Structures: msqid_ds(4)

  Standards: standards(5)

Index for Section 2

Alphabetical listing for M

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