Why are the shmmax and shmall defaults very high in Red Hat Enterprise Linux 5 and 6?

Solution Verified - Updated -

Issue

  • After installing RHEL5, the system sets up kenel.shmmax and kenel.shmall with high values using sysctl.conf :

    #cat /etc/sysctl.conf
    
    [..]
    # Controls the maximum shared segment size, in bytes
    kernel.shmmax = 68719476736
    # 68719476736/1024/1024/1024 = 64,so that means maximum segment size is 64 Gi Byte.
    
    # Controls the maximum number of shared memory segments, in pages
    kernel.shmall = 4294967296
    # 4294967296*4096/1024/1024/1024 = 16384 Gi Byte 
    [..]
    

Environment

  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6

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