From Debuntu

Over all repositories

Configuration happens in ~/.hgrc . There, you can set your username and enable extensions.

[ui]
username = myuser
[extensions]
hgext.graphlog =
hgext.highlight =

Per repositories

This time, the config is within the repository's .hg/hgrc . There you can set up default values like the default push location, pull, incoming and outgoing:

[defaults]
; push
push=ssh://myhost/repositories/repo1/
; pull
pull=ssh://myhost/repositories/repo1/
[paths]
; outgoing
default-push=ssh://myhost/repositories/repo1/
; incoming
default=ssh://myhost/repositories/repo1/

Reference

$ man hgrc