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Comment by smcl | Hacker News Reader

Took me a while (after reading through the reply, to no avail) to figure out what this refers to. Here's the feature this is referring to:

     $ apt-get moo
                     (__) 
                     (oo) 
               /------\/ 
              / |    ||   
             *  /\---/\ 
                ~~   ~~   
    ..."Have you mooed today?"...

Edit: maybe not actually! Just found this too:

    $ aptitude moo
    There are no Easter Eggs in this program.
    $ aptitude -v moo
    There really are no Easter Eggs in this program.

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This is “documented” as well. apt-get has got Super Cow Powers and aptitude has not.

    $ apt-get
    apt 1.0.9.8.4 for amd64 compiled on Dec 11 2016 09:48:19
    Usage: apt-get [options] command
           apt-get [options] install|remove pkg1 [pkg2 ...]
           apt-get [options] source pkg1 [pkg2 ...]
    …
                                            This APT has Super Cow Powers.

    $ aptitude --help
    aptitude 0.6.11
    Usage: aptitude [-S fname] [-u|-i]
           aptitude [options] <action> ...

    …

                      This aptitude does not have Super Cow Powers.

I don't really understand what in this feature makes the build non-reproducible. Judging by the patch it's the call to time(NULL) that seems to be problematic, but I don't understand why.

The output of "apt-get moo" changes on special days (4/1, 12/25, 8/16, 11/7, 2/18). So if another program was using "apt-get moo" in its build script, the build would not be reproducible. With the patch, the SOURCE_DATE_EPOCH environment variable can be set to make "apt-get moo" deterministic.

I don't think anything actually uses "apt-get moo" in its build script.

This kind of patch makes more sense for build tools like "ar" (static library creator). By default, "ar" injects a timestamp into the output file, so the binary is different each build. But, use the "D" flag and "ar" becomes deterministic.

The time-dependent part can be seen here: https://github.com/Debian/apt/blob/master/apt-private/privat...

There is a second part above too:

https://github.com/Debian/apt/blob/master/apt-private/privat...

Yeh I only skimmed the patch but I presumed "reproducable build" referred to the actual binary, and the patch addresses runtime behaviour. Guess I'm missing something.

It doesn't; it makes anyone using the output...

From what I can read in patch file, it seems to be doing something different on April fools day.

Keep adding more v.

Yep it gets good - wasn't sure whether to spoil the fun or not :)

> I got a fever! And the only prescription.. is more -v!

try

  $ apt-get moo moo
  $ apt-get moo moo moo

Try `aptitude -vv moo` :)

Thanks. A nice New Year's gift, to learn Super Cow Powers. Though talking about more -v's, I don't think Aptitude is written in Python, is it?

I recall that aptitude has more messages for more v's.

This is a patch for apt, it does not have anything to do with aptitude.

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