--- a/doc/hgrc.5.txt
+++ b/doc/hgrc.5.txt
@@ -401,9 +401,8 @@ ui::
   username;;
     The committer of a changeset created when running "commit".
     Typically a person's name and email address, e.g. "Fred Widget
-    <fred@example.com>".  Default is $EMAIL or username@hostname, unless
-    username is set to an empty string, which enforces specifying the
-    username manually.
+    <fred@example.com>".  Default is $EMAIL. If no default is found,
+    the username have to be specified manually.
   verbose;;
     Increase the amount of output printed.  True or False.  Default is False.
 

--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -226,10 +226,8 @@ class ui(object):
 
         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 $USER or $LNAME or
-        $USERNAME) +"@full.hostname".
+        Abort if no username is found, to force specifying the commit user
+        with line option or repo hgrc.
         """
         user = os.environ.get("HGUSER")
         if user is None:
@@ -237,10 +235,7 @@ class ui(object):
         if user is None:
             user = os.environ.get("EMAIL")
         if user is None:
-            try:
-                user = '%s@%s' % (util.getuser(), socket.getfqdn())
-            except KeyError:
-                raise util.Abort(_("Please specify a username."))
+            raise util.Abort(_("No default username available, use -u"))
         return user
 
     def shortuser(self, user):

--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -519,20 +519,6 @@ def is_win_9x():
     except AttributeError:
         return os.name == 'nt' and 'command' in os.environ.get('comspec', '')
 
-getuser_fallback = None
-
-def getuser():
-    '''return name of current user'''
-    try:
-        return getpass.getuser()
-    except ImportError:
-        # import of pwd will fail on windows - try fallback
-        if getuser_fallback:
-            return getuser_fallback()
-    # raised if win32api not available
-    raise Abort(_('user name not available - set USERNAME '
-                  'environment variable'))
-
 # Platform specific variants
 if os.name == 'nt':
     demandload(globals(), "msvcrt")

--- a/mercurial/util_win32.py
+++ b/mercurial/util_win32.py
@@ -297,5 +297,3 @@ class posixfile_nt(object):
             win32file.SetEndOfFile(self.handle)
         except pywintypes.error, err:
             raise WinIOError(err)
-
-getuser_fallback = win32api.GetUserName

--- a/tests/test-committer
+++ b/tests/test-committer
@@ -10,3 +10,17 @@ touch asdf
 hg add asdf
 hg commit -d '1000000 0' -m commit-1
 hg tip
+
+unset EMAIL
+echo 1 > asdf
+hg commit -d '1000000 0' -m commit-1
+hg commit -d '1000000 0' -u "foo@bar.com" -m commit-1
+hg tip
+echo "[ui]" >> .hg/hgrc
+echo "username = foobar <foo@bar.com>" >> .hg/hgrc
+echo 12 > asdf
+hg commit -d '1000000 0' -m commit-1
+hg tip
+echo 1 > asdf
+hg commit -d '1000000 0' -u "foo@bar.com" -m commit-1
+hg tip

--- a/tests/test-committer.out
+++ b/tests/test-committer.out
@@ -4,3 +4,24 @@ user:        My Name <myname@example.com
 date:        Mon Jan 12 13:46:40 1970 +0000
 summary:     commit-1
 
+abort: No default username available, use -u
+transaction abort!
+rollback completed
+changeset:   1:2becd0bae6e6
+tag:         tip
+user:        foo@bar.com
+date:        Mon Jan 12 13:46:40 1970 +0000
+summary:     commit-1
+
+changeset:   2:7a0176714f78
+tag:         tip
+user:        foobar <foo@bar.com>
+date:        Mon Jan 12 13:46:40 1970 +0000
+summary:     commit-1
+
+changeset:   3:f9b58c5a6352
+tag:         tip
+user:        foo@bar.com
+date:        Mon Jan 12 13:46:40 1970 +0000
+summary:     commit-1
+