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(ipc.info)msglimits

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Limis on Message Resources
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Sizeof various structures:
     msqid_ds        52   /* 1 per message  queue .. dynamic */

     msg             16   /* 1 for each message in system .. dynamic */

     msgbuf           8   /* allocated by user */

Limits
   * MSGMNI : number of message queue identifiers ... policy.

   * MSGMAX : max size of message.  Header and message space allocated
     on one page.  MSGMAX = (PAGE_SIZE - sizeof(struct msg)).
     Implementation maximum MSGMAX = 4080.

   * MSGMNB : default max size of a message queue ... policy.  The
     super-user can increase the size of a queue beyond MSGMNB by a
     `msgctl' call.

Unused or unimplemented:
MSGTQL  max number of message headers system-wide.
MSGPOOL total size in bytes of msg pool.