If you get the error "Cannot start datanode because the configured max locked
memory size... is more than the datanode's available RLIMIT_MEMLOCK ulimit," that
means that the operating system is imposing a lower limit on the amount of memory
that you can lock than what you have configured. To fix this, you must adjust the
ulimit -l value that the DataNode runs with. This value is usually
configured in /etc/security/limits.conf, but this may vary depending on
what operating system and distribution you are using.
You will know that you have correctly configured this value when you can
run ulimit -l from the shell and get back either a higher value
than what you have configured with dfs.datanode.max.locked.memory, or
the string "unlimited", which indicates that there is no limit. Note that it is
typical for ulimit -l to output the memory lock limit in kilobytes
(KB), but dfs.datanode.max.locked.memory must be specified in
bytes.
