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The Linux kernel has a few sysctrl's related to random devices packaged in a bin_random_table (http://lxr.free-electrons.com/source/kernel/sysctl_binary.c?v=3.2):

static const struct bin_table bin_random_table[] = {
        { CTL_INT,      RANDOM_POOLSIZE,        "poolsize" },
        { CTL_INT,      RANDOM_ENTROPY_COUNT,   "entropy_avail" },
        { CTL_INT,      RANDOM_READ_THRESH,     "read_wakeup_threshold" },
        { CTL_INT,      RANDOM_WRITE_THRESH,    "write_wakeup_threshold" },
        { CTL_UUID,     RANDOM_BOOT_ID,         "boot_id" },
        { CTL_UUID,     RANDOM_UUID,            "uuid" },
        {}
};

I believe RANDOM_UUID is useful in cases /dev/urandom is not available, for example, in chroot environments. But I don't know how RANDOM_BOOT_ID is used.

What is the purpose of RANDOM_BOOT_ID?

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1 Answer 1

up vote 3 down vote accepted

While RANDOM_UUID a type 4 (randomly-generated) UUID that changes every time it's read, RANDOM_BOOT_ID is a similar UUID that changes exactly once per boot. This is useful for configuration or instance differentiation to keep straight properties for your application that should change exactly once per boot.

This value is not typically significant for security or cryptography, but instead is used simply for instance management.

Also, RANDOM_UUID is not a replacement for /dev/random, but rather a source of properly-generated type-4 UUIDs. See how the first digit in the 3rd group is always "4"?

See also:

/proc/sys/kernel/random/uuid
/proc/sys/kernel/random/boot_id
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"RANDOM_UUID is not a replacement for /dev/random" - oh, I did not know that. I wanted to start a bounty and give you an extra 25 for that, but I can't at the moment. Hopefully I can get to it in the future. Thanks. –  jww Feb 19 at 13:37

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