Mercurial ships with many extensions, but none of them is enabled by default. In addition, many other extensions can be downloaded for Mercurial.
If the extension is already present, it can be enabled by editing your Mercurial configuration file.
For example, to enable an extension named Foo, edit your Mercurial configuration file to add these lines:
[extensions] Foo =
If the extensions section already exists with an enabled extension, additional extensions can be enabled by adding a line each.
For example, to additionally enable a Bar extension:
[extensions] Foo = Bar =
Tried with: Mercurial 2.0.2 and Ubuntu 12.04.1 LTS