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    SubjectRe: /dev/random problem on 2.6.12-rc1
    On Thu, 7 Apr 2005, Matt Mackall wrote:

    > On Thu, Apr 07, 2005 at 05:36:59PM +0200, Simon Derr wrote:
    > >
    > >
    > > On Thu, 7 Apr 2005, Yura Pakhuchiy wrote:
    > >
    > > > On Thu, 2005-04-07 at 14:40 +0200, Patrice Martinez wrote:
    > > > > When using a machine with a 2612-rc 1kernel, I encounter problems
    > > > > reading /dev/random:
    > > > > it simply nevers returns anything, and the process is blocked in the
    > > > > read...
    > > > > The easiest way to see it is to type:
    > > > > od < /dev/random
    > > > >
    > > > > Any idea?
    > > >
    > > > Because, /dev/random use user input, mouse movements and other things to
    > > > generate next random number. Use /dev/urandom if you want version that
    > > > will never block your machine.
    > > >
    > > > Read "man 4 random" for details.
    > > >
    > > Something changed since previous versions of the kernel, I guess.
    > > Running `find /usr | wc' on a ssh session generates both network and disk
    > > activity, and you should not expect any other kind of input on a networked
    > > server.
    >
    Oops, the command is actually "find /usr | xargs wc", witch causes lots of
    disk activity.

    > FYI, network activity only generates entropy on a very small subset of
    > NICs, and probably not the one you're using. This is good, as network
    > activity is assumed passively observable/timable.
    Offtopic, but why isn't the policy the same for all NICs ?

    > > Anyway, still zero bytes coming from /dev/random, for the few minutes I
    > > waited.
    >
    > Are you and Patrice both experiencing this on the same machine?
    Both IA-64, but that's the only common point.

    > What
    > was the last kernel that was known to work for you? Do you see the
    > contents of /proc/sys/kernel/random/entropy_avail change over time?
    > Are there any other entropy consumers on your machine?
    None that I am aware of.

    I run:
    # dd if=/dev/random bs=1 count=1 | od

    Another shell:
    # lsof /dev/random
    COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
    dd 1496 root 0r CHR 1,8 99952 /dev/random

    Now, find /usr | xargs wc running in background.

    About /proc/sys/kernel/random/entropy_avail:
    (5 second refresh interval)

    0
    0
    0
    0
    [lots of 0]
    0
    0
    0
    6
    0
    8
    2
    0
    0
    [lots of 0]
    0
    0
    0
    3
    1
    0
    0
    [lots of 0]
    0
    0
    0

    ...


    After 10 minutes, dd is still running.

    This is on Linux 2.6.12-rc1-bk1, same results for 2.6.12-rc2.

    And /dev/random works fine on the same machine with Linux 2.6.11.
    (i.e when running "find /usr | xargs wc", /dev/random spits out lots of
    bytes)


    Simon.

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