On my Mediawiki install, I cannot compare versions. The "(Difference between revisions)" page shows only the latest version.

I checked that I do have diff:

~# which diff /usr/bin/diff

~# which diff3 /usr/bin/diff3

~# grep diff /etc/mediawiki/LocalSettings.php # Path to the GNU diff3 utility. Used for conflict resolution. $wgDiff3 = "/usr/bin/diff3";

I also added

$wgDiff = "/usr/bin/diff";

to LocalSettings.php.

This is Mediawiki version 1.19.20+dfsg-2.3 on Debian Jessie.

After turning on debugging, I see this:

wfShellExec: 'wikidiff2' '/tmp/diff_N41UBc' '/tmp/diff_HtzBTH' Possibly missing executable file: 'wikidiff2' '/tmp/diff_N41UBc' '/tmp/diff_HtzBTH'

Indeed, I have no such executable. But "apt-cache search wikidiff2" shows only "php-wikidiff2", which is installed.

~# apt-cache search wikidiff2 php-wikidiff2 - external diff engine for mediawiki

So, would someone know what is wrong, or where to look for more clues?