Adapted behaviour of ui.username() to documentation and mention it explicitly: Searched in this order: $HGUSER, [ui] section of hgrcs, $EMAIL and stop searching if one of these is set. Abort if found username is an empty string to force specifying the commit user elsewhere, e.g. with line option or repo hgrc. If not found, use $LOGNAME or $USERNAME +"@full.hostname".

#!/bin/sh

mkdir a
cd a
hg init
echo foo > t1
hg add t1
hg commit -m "1" -d "1000000 0"

cd ..
hg clone a b

cd a
echo foo > t2
hg add t2
hg commit -m "2" -d "1000000 0"

cd ../b
echo foo > t3
hg add t3
hg commit -m "3" -d "1000000 0"

hg push ../a
hg pull ../a
hg push ../a
hg up -m
hg commit -m "4" -d "1000000 0"
hg push ../a