diff --git a/error.py b/error.py
index e3cf41c..029e122 100644
--- a/error.py
+++ b/error.py
@@ -64,3 +64,5 @@
      repo or manifest repositories.  In this special case we must
      use exec to re-execute repo with the new code and manifest.
   """
+  def __init__(self, extra_args=[]):
+    self.extra_args = extra_args
diff --git a/hooks/pre-auto-gc b/hooks/pre-auto-gc
new file mode 100755
index 0000000..110e319
--- /dev/null
+++ b/hooks/pre-auto-gc
@@ -0,0 +1,44 @@
+#!/bin/sh
+#
+# An example hook script to verify if you are on battery, in case you
+# are running Linux or OS X. Called by git-gc --auto with no arguments.
+# The hook should exit with non-zero status after issuing an appropriate
+# message if it wants to stop the auto repacking.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+if test -x /sbin/on_ac_power && /sbin/on_ac_power
+then
+	exit 0
+elif test "$(cat /sys/class/power_supply/AC/online 2>/dev/null)" = 1
+then
+	exit 0
+elif grep -q 'on-line' /proc/acpi/ac_adapter/AC/state 2>/dev/null
+then
+	exit 0
+elif grep -q '0x01$' /proc/apm 2>/dev/null
+then
+	exit 0
+elif grep -q "AC Power \+: 1" /proc/pmu/info 2>/dev/null
+then
+	exit 0
+elif test -x /usr/bin/pmset && /usr/bin/pmset -g batt |
+	grep -q "Currently drawing from 'AC Power'"
+then
+	exit 0
+fi
+
+echo "Auto packing deferred; not on AC"
+exit 1
diff --git a/main.py b/main.py
index 0901c84..be8da01 100755
--- a/main.py
+++ b/main.py
@@ -186,11 +186,13 @@
     repo._Run(argv)
   except KeyboardInterrupt:
     sys.exit(1)
-  except RepoChangedException:
-    # If the repo or manifest changed, re-exec ourselves.
+  except RepoChangedException, rce:
+    # If repo changed, re-exec ourselves.
     #
+    argv = list(sys.argv)
+    argv.extend(rce.extra_args)
     try:
-      os.execv(__file__, sys.argv)
+      os.execv(__file__, argv)
     except OSError, e:
       print >>sys.stderr, 'fatal: cannot restart repo after upgrade'
       print >>sys.stderr, 'fatal: %s' % e
diff --git a/project.py b/project.py
index 874a40b..f963576 100644
--- a/project.py
+++ b/project.py
@@ -46,6 +46,32 @@
 def not_rev(r):
   return '^' + r
 
+
+hook_list = None
+def repo_hooks():
+  global hook_list
+  if hook_list is None:
+    d = os.path.abspath(os.path.dirname(__file__))
+    d = os.path.join(d , 'hooks')
+    hook_list = map(lambda x: os.path.join(d, x), os.listdir(d))
+  return hook_list
+
+def relpath(dst, src):
+  src = os.path.dirname(src)
+  top = os.path.commonprefix([dst, src])
+  if top.endswith('/'):
+    top = top[:-1]
+  else:
+    top = os.path.dirname(top)
+
+  tmp = src
+  rel = ''
+  while top != tmp:
+    rel += '../'
+    tmp = os.path.dirname(tmp)
+  return rel + dst[len(top) + 1:]
+
+
 class DownloadedChange(object):
   _commit_cache = None
 
@@ -472,7 +498,10 @@
     self._RepairAndroidImportErrors()
     self._InitMRef()
     return True
-    
+
+  def PostRepoUpgrade(self):
+    self._InitHooks()
+
   def _CopyFiles(self):
     for file in self.copyfiles:
       file._Copy()
@@ -795,14 +824,29 @@
         to_rm = []
       for old_hook in to_rm:
         os.remove(os.path.join(hooks, old_hook))
-
-      # TODO(sop) install custom repo hooks
+      self._InitHooks()
 
       m = self.manifest.manifestProject.config
       for key in ['user.name', 'user.email']:
         if m.Has(key, include_defaults = False):
           self.config.SetString(key, m.GetString(key))
 
+  def _InitHooks(self):
+    hooks = self._gitdir_path('hooks')
+    if not os.path.exists(hooks):
+      os.makedirs(hooks)
+    for stock_hook in repo_hooks():
+      dst = os.path.join(hooks, os.path.basename(stock_hook))
+      try:
+        os.symlink(relpath(stock_hook, dst), dst)
+      except OSError, e:
+        if e.errno == errno.EEXIST:
+          pass
+        elif e.errno == errno.EPERM:
+          raise GitError('filesystem must support symlinks')
+        else:
+          raise
+
   def _InitRemote(self):
     if self.remote.fetchUrl:
       remote = self.GetRemote(self.remote.name)
@@ -842,19 +886,6 @@
     if not os.path.exists(dotgit):
       os.makedirs(dotgit)
 
-      topdir = os.path.commonprefix([self.gitdir, dotgit])
-      if topdir.endswith('/'):
-        topdir = topdir[:-1]
-      else:
-        topdir = os.path.dirname(topdir)
-
-      tmpdir = dotgit
-      relgit = ''
-      while topdir != tmpdir:
-        relgit += '../'
-        tmpdir = os.path.dirname(tmpdir)
-      relgit += self.gitdir[len(topdir) + 1:]
-
       for name in ['config',
                    'description',
                    'hooks',
@@ -866,8 +897,9 @@
                    'rr-cache',
                    'svn']:
         try:
-          os.symlink(os.path.join(relgit, name),
-                     os.path.join(dotgit, name))
+          src = os.path.join(self.gitdir, name)
+          dst = os.path.join(dotgit, name)
+          os.symlink(relpath(src, dst), dst)
         except OSError, e:
           if e.errno == errno.EPERM:
             raise GitError('filesystem must support symlinks')
diff --git a/subcmds/sync.py b/subcmds/sync.py
index 3eb44ed..9af1232 100644
--- a/subcmds/sync.py
+++ b/subcmds/sync.py
@@ -49,6 +49,9 @@
     p.add_option('--no-repo-verify',
                  dest='no_repo_verify', action='store_true',
                  help='do not verify repo source code')
+    p.add_option('--repo-upgraded',
+                 dest='repo_upgraded', action='store_true',
+                 help='perform additional actions after a repo upgrade')
 
   def _Fetch(self, *projects):
     fetched = set()
@@ -67,6 +70,11 @@
     mp = self.manifest.manifestProject
     mp.PreSync()
 
+    if opt.repo_upgraded:
+      for project in self.manifest.projects.values():
+        if project.Exists:
+          project.PostRepoUpgrade()
+
     all = self.GetProjects(args, missing_ok=True)
     fetched = self._Fetch(rp, mp, *all)
 
@@ -77,7 +85,7 @@
         if not rp.Sync_LocalHalf():
           sys.exit(1)
         print >>sys.stderr, 'info: Restarting repo with latest version'
-        raise RepoChangedException()
+        raise RepoChangedException(['--repo-upgraded'])
       else:
         print >>sys.stderr, 'warning: Skipped upgrade to unverified version'