How to increase maximum number of JVM threads (Linux 64bit)

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You can use a sample program to find out the current threads limit.

If you encounter Exception in thread "main" java.lang.OutOfMemoryError: unable to create new native thread, check these:

  1. In small memory machines

    Every Java thread consume its own stack memory. Default stack size is 1024k (= 1M). You can reduce the stack size like java -Xss512k .... JVM cannot be started if the stack size is too low.

    And beware heap memory configurations: (initial) -Xms and (maximum) -Xmx. The more memory is allocated to heap, the less available memory for stack.

  2. System limits

    Some values in ulimit -a can affect a thread limit.

    • max memory size – unlimited on most 64bit machines
    • max user processes – linux treats threads like processes
    • virtual memory – unlimited on most 64bit machines. virtual memory usage is increased by -Xss configuration (default 1024k)

    You can change these values by (temporal) running ulimit command or (permanent) editing /etc/security/limits.conf.

  3. sys.kernel.threads-max

    This value is the system-global (including non-JVM processes) maximum number of threads. Check cat /proc/sys/kernel/threads-max, and increase if necessary.

    echo 999999 > /proc/sys/kernel/threads-max
    or
    sys.kernel.threads-max = 999999 in /etc/sysctl.conf to change permanently.

  4. sys.kernel.pid_max

    If cat /proc/sys/kernel/pid_max is similar to current limit, increase this. Linux treats threads like processes.

    echo 999999 > /proc/sys/kernel/pid_max
    or
    sys.kernel.pid_max = 999999 in /etc/sysctl.conf to change permanently.

    And you may need to increase sys.vm.max_map_count, too.

  5. sys.vm.max_map_count

    cat /proc/sys/vm/max_map_count should be at least (2 x thread-count).

    Attempt to protect stack guard pages failed. and OpenJDK 64-Bit Server VM warning: Attempt to deallocate stack guard pages failed. error messages are emitted by JavaThread::create_stack_guard_pages(), and it calls os::guard_memory(). In Linux, this function is mprotect().

    echo 1999999 > /proc/sys/vm/max_map_count
    or
    sys.vm.max_map_count = 1999999 in /etc/sysctl.conf to change permanently.

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