The first file is “index.php” and only requires the removal of the comments around “the_author()” portion.

<small><?php the_time('F jS, Y') ?> <!-- by <?php the_author() ?> --></small>

The second file is “single.php” and requires the addition of a “the_author()” block similar to the following.

on <?php the_time('l, F jS, Y') ?> at <?php the_time() ?> by <?php the_author() ?>

I achieved these changes with the following sed commands.

cd wp-content/themes/default
mv index.php index.php.default
sed 's/<!-- by <?php the_author() ?> -->/by <?php the_author() ?>/' index.php.default > index.php
mv single.php single.php.default
sed "s/on <?php the_time('l, F jS, Y') ?> at <?php the_time() ?>/on <?php the_time('l, F jS, Y') ?> at <?php the_time() ?> by <?php the_author() ?>/" single.php.default > single.php

The better solution is probably to find a theme that does this by default instead of enabling it every time the theme gets updated; however, I haven’t gone looking for a replacement theme yet.

This has been tested with WordPress 2.7.1.

Edit: It is advisable to then set the permissions on those two files back to that of the Apache user:

chown www-data:www-data index.php single.php

This will help prevent possible problems during an upgrade.