diff --git a/lib/spack/llnl/util/lock.py b/lib/spack/llnl/util/lock.py
index 2cab436e2d..55837c371e 100644
--- a/lib/spack/llnl/util/lock.py
+++ b/lib/spack/llnl/util/lock.py
@@ -127,8 +127,9 @@ def _lock(self, op, timeout=_default_timeout):
 
                 return
 
-            except IOError as error:
-                if error.errno == errno.EAGAIN or error.errno == errno.EACCES:
+            except IOError as e:
+                if e.errno in (errno.EAGAIN, errno.EACCES):
+                    # EAGAIN and EACCES == locked by another process
                     pass
                 else:
                     raise
@@ -197,6 +198,8 @@ def acquire_read(self, timeout=_default_timeout):
             tty.debug('READ LOCK: {0.path}[{0._start}:{0._length}] [Acquiring]'
                       .format(self))
             self._lock(fcntl.LOCK_SH, timeout=timeout)   # can raise LockError.
+            tty.debug('READ LOCK: {0.path}[{0._start}:{0._length}] [Acquired]'
+                      .format(self))
             self._reads += 1
             return True
         else:
@@ -219,6 +222,8 @@ def acquire_write(self, timeout=_default_timeout):
                 'WRITE LOCK: {0.path}[{0._start}:{0._length}] [Acquiring]'
                 .format(self))
             self._lock(fcntl.LOCK_EX, timeout=timeout)   # can raise LockError.
+            tty.debug('WRITE LOCK: {0.path}[{0._start}:{0._length}] [Acquired]'
+                      .format(self))
             self._writes += 1
             return True
         else:
diff --git a/lib/spack/spack/test/lock.py b/lib/spack/spack/test/lock.py
index 7cf4571016..347b72b575 100644
--- a/lib/spack/spack/test/lock.py
+++ b/lib/spack/spack/test/lock.py
@@ -22,37 +22,178 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
-"""
-These tests ensure that our lock works correctly.
+"""These tests ensure that our lock works correctly.
+
+This can be run in two ways.
+
+First, it can be run as a node-local test, with a typical invocation like
+this::
+
+    spack test lock
+
+You can *also* run it as an MPI program, which allows you to test locks
+across nodes.  So, e.g., you can run the test like this::
+
+    mpirun -n 7 spack test lock
+
+And it will test locking correctness among MPI processes.  Ideally, you
+want the MPI processes to span across multiple nodes, so, e.g., for SLURM
+you might do this::
+
+    srun -N 7 -n 7 -m cyclic spack test lock
+
+You can use this to test whether your shared filesystem properly supports
+POSIX reader-writer locking with byte ranges through fcntl.
+
+If you want to test on multiple filesystems, you can modify the
+``locations`` list below.  By default it looks like this::
+
+    locations = [
+        tempfile.gettempdir(),  # standard tmp directory (potentially local)
+        '/nfs/tmp2/%u',         # NFS tmp mount
+        '/p/lscratch*/%u'       # Lustre scratch mount
+    ]
+
+Add names and paths for your preferred filesystem mounts to test on them;
+the tests are parametrized to run on all the filesystems listed in this
+dict.  Note that 'tmp' will be skipped for MPI testing, as it is often a
+node-local filesystem, and multi-node tests will fail if the locks aren't
+actually on a shared filesystem.
+
 """
 import os
 import shutil
-import functools
 import tempfile
 import traceback
+import glob
+import getpass
+from contextlib import contextmanager
 from multiprocessing import Process
 
 import pytest
 
-from llnl.util.filesystem import join_path, touch, mkdirp
+from llnl.util.filesystem import join_path, touch
 from llnl.util.lock import *
 from spack.util.multiproc import Barrier
 
 
-# This is the longest a failed test will take, as the barriers will
-# time out and raise an exception.
+#
+# This test can be run with MPI.  MPI is "enabled" if we can import
+# mpi4py and the number of total MPI processes is greater than 1.
+# Otherwise it just runs as a node-local test.
+#
+# NOTE: MPI mode is different from node-local mode in that node-local
+# mode will spawn its own test processes, while MPI mode assumes you've
+# run this script as a SPMD application.  In MPI mode, no additional
+# processes are spawned, and you need to ensure that you mpirun the
+# script with enough processes for all the multiproc_test cases below.
+#
+# If you don't run with enough processes, tests that require more
+# processes than you currently have will be skipped.
+#
+mpi = False
+comm = None
+try:
+    from mpi4py import MPI
+    comm = MPI.COMM_WORLD
+    if comm.size > 1:
+        mpi = True
+except:
+    pass
+
+
+"""This is a list of filesystem locations to test locks in.  Paths are
+expanded so that %u is replaced with the current username. '~' is also
+legal and will be expanded to the user's home directory.
+
+Tests are skipped for directories that don't exist, so you'll need to
+update this with the locations of NFS, Lustre, and other mounts on your
+system.
+"""
+locations = [
+    tempfile.gettempdir(),
+    os.path.join('/nfs/tmp2/', getpass.getuser()),
+    os.path.join('/p/lscratch*/', getpass.getuser()),
+]
+
+"""This is the longest a failed multiproc test will take.
+Barriers will time out and raise an exception after this interval.
+In MPI mode, barriers don't time out (they hang).  See mpi_multiproc_test.
+"""
 barrier_timeout = 5
 
+"""This is the lock timeout for expected failures.
+This may need to be higher for some filesystems."""
+lock_fail_timeout = 0.1
 
-@pytest.fixture()
-def lock_path():
-    tempdir = tempfile.mkdtemp()
-    lock_file = join_path(tempdir, 'lockfile')
+
+@contextmanager
+def read_only(path):
+    orginal_mode = os.stat(path).st_mode
+    os.chmod(path, 0o444)
+    yield
+    os.chmod(path, orginal_mode)
+
+
+@pytest.fixture(scope='session', params=locations)
+def lock_test_directory(request):
+    """This fixture causes tests to be executed for many different mounts.
+
+    See the ``locations`` dict above for details.
+    """
+    return request.param
+
+
+@pytest.fixture(scope='session')
+def lock_dir(lock_test_directory):
+    parent = next((p for p in glob.glob(lock_test_directory)
+                   if os.path.exists(p) and os.access(p, os.W_OK)), None)
+    if not parent:
+        # Skip filesystems that don't exist or aren't writable
+        pytest.skip("requires filesystem: '%s'" % lock_test_directory)
+    elif mpi and parent == tempfile.gettempdir():
+        # Skip local tmp test for MPI runs
+        pytest.skip("skipping local tmp directory for MPI test.")
+
+    tempdir = None
+    if not mpi or comm.rank == 0:
+        tempdir = tempfile.mkdtemp(dir=parent)
+    if mpi:
+        tempdir = comm.bcast(tempdir)
+
+    yield tempdir
+
+    if mpi:
+        # rank 0 may get here before others, in which case it'll try to
+        # remove the directory while other processes try to re-create the
+        # lock.  This will give errno 39: directory not empty.  Use a
+        # barrier to ensure everyone is done first.
+        comm.barrier()
+
+    if not mpi or comm.rank == 0:
+        shutil.rmtree(tempdir)
+
+
+@pytest.fixture
+def private_lock_path(lock_dir):
+    """In MPI mode, this is a private lock for each rank in a multiproc test.
+
+    For other modes, it is the same as a shared lock.
+    """
+    lock_file = join_path(lock_dir, 'lockfile')
+    if mpi:
+        lock_file += '.%s' % comm.rank
     yield lock_file
-    shutil.rmtree(tempdir)
 
 
-def multiproc_test(*functions):
+@pytest.fixture
+def lock_path(lock_dir):
+    """This lock is shared among all processes in a multiproc test."""
+    lock_file = join_path(lock_dir, 'lockfile')
+    yield lock_file
+
+
+def local_multiproc_test(*functions):
     """Order some processes using simple barrier synchronization."""
     b = Barrier(len(functions), timeout=barrier_timeout)
     procs = [Process(target=f, args=(b,)) for f in functions]
@@ -65,6 +206,52 @@ def multiproc_test(*functions):
         assert p.exitcode == 0
 
 
+def mpi_multiproc_test(*functions):
+    """SPMD version of multiproc test.
+
+    This needs to be run like so:
+
+           srun spack test lock
+
+    Each process executes its corresponding function.  This is different
+    from ``multiproc_test`` above, which spawns the processes. This will
+    skip tests if there are too few processes to run them.
+    """
+    procs = len(functions)
+    if procs > comm.size:
+        pytest.skip("requires at least %d MPI processes" % procs)
+
+    comm.Barrier()  # barrier before each MPI test
+
+    include = comm.rank < len(functions)
+    subcomm = comm.Split(include)
+
+    class subcomm_barrier(object):
+        """Stand-in for multiproc barrier for MPI-parallel jobs."""
+        def wait(self):
+            subcomm.Barrier()
+
+    if include:
+        try:
+            functions[subcomm.rank](subcomm_barrier())
+        except:
+            # aborting is the best we can do for MPI tests without
+            # hanging, since we're using MPI barriers. This will fail
+            # early and it loses the nice pytest output, but at least it
+            # gets use a stacktrace on the processes that failed.
+            traceback.print_exc()
+            comm.Abort()
+    subcomm.Free()
+
+    comm.Barrier()  # barrier after each MPI test.
+
+
+"""``multiproc_test()`` should be called by tests below.
+``multiproc_test()`` will work for either MPI runs or for local runs.
+"""
+multiproc_test = mpi_multiproc_test if mpi else local_multiproc_test
+
+
 #
 # Process snippets below can be composed into tests.
 #
@@ -91,7 +278,7 @@ def fn(barrier):
         lock = Lock(lock_path, start, length)
         barrier.wait()  # wait for lock acquire in first process
         with pytest.raises(LockError):
-            lock.acquire_write(0.1)
+            lock.acquire_write(lock_fail_timeout)
         barrier.wait()
     return fn
 
@@ -101,7 +288,7 @@ def fn(barrier):
         lock = Lock(lock_path, start, length)
         barrier.wait()  # wait for lock acquire in first process
         with pytest.raises(LockError):
-            lock.acquire_read(0.1)
+            lock.acquire_read(lock_fail_timeout)
         barrier.wait()
     return fn
 
@@ -111,7 +298,9 @@ def fn(barrier):
 # exclusive lock is held.
 #
 def test_write_lock_timeout_on_write(lock_path):
-    multiproc_test(acquire_write(lock_path), timeout_write(lock_path))
+    multiproc_test(
+        acquire_write(lock_path),
+        timeout_write(lock_path))
 
 
 def test_write_lock_timeout_on_write_2(lock_path):
@@ -258,7 +447,8 @@ def test_write_lock_timeout_on_read_ranges_3(lock_path):
 def test_write_lock_timeout_on_read_ranges_4(lock_path):
     multiproc_test(
         acquire_read(lock_path, 0, 64),
-        timeout_write(lock_path, 10, 1), timeout_write(lock_path, 32, 1))
+        timeout_write(lock_path, 10, 1),
+        timeout_write(lock_path, 32, 1))
 
 
 def test_write_lock_timeout_on_read_ranges_5(lock_path):
@@ -268,6 +458,7 @@ def test_write_lock_timeout_on_read_ranges_5(lock_path):
         timeout_write(lock_path, 127, 1),
         timeout_write(lock_path, 90, 10))
 
+
 #
 # Test that exclusive locks time while lots of shared locks are held.
 #
@@ -339,12 +530,19 @@ def test_write_lock_timeout_with_multiple_readers_3_2_ranges(lock_path):
 #
 # Test that read can be upgraded to write.
 #
-def test_upgrade_read_to_write(lock_path):
+def test_upgrade_read_to_write(private_lock_path):
+    """Test that a read lock can be upgraded to a write lock.
+
+    Note that to upgrade a read lock to a write lock, you have the be the
+    only holder of a read lock.  Client code needs to coordinate that for
+    shared locks.  For this test, we use a private lock just to test that an
+    upgrade is possible.
+    """
     # ensure lock file exists the first time, so we open it read-only
     # to begin wtih.
-    touch(lock_path)
+    touch(private_lock_path)
 
-    lock = Lock(lock_path)
+    lock = Lock(private_lock_path)
     assert lock._reads == 0
     assert lock._writes == 0
 
@@ -368,26 +566,28 @@ def test_upgrade_read_to_write(lock_path):
     assert lock._writes == 0
     assert lock._file is None
 
+
 #
 # Test that read-only file can be read-locked but not write-locked.
 #
-def test_upgrade_read_to_write_fails_with_readonly_file(lock_path):
+def test_upgrade_read_to_write_fails_with_readonly_file(private_lock_path):
     # ensure lock file exists the first time, so we open it read-only
     # to begin wtih.
-    touch(lock_path)
-    os.chmod(lock_path, 0o444)
+    touch(private_lock_path)
 
-    lock = Lock(lock_path)
-    assert lock._reads == 0
-    assert lock._writes == 0
+    with read_only(private_lock_path):
+        lock = Lock(private_lock_path)
+        assert lock._reads == 0
+        assert lock._writes == 0
 
-    lock.acquire_read()
-    assert lock._reads == 1
-    assert lock._writes == 0
-    assert lock._file.mode == 'r'
+        lock.acquire_read()
+        assert lock._reads == 1
+        assert lock._writes == 0
+        assert lock._file.mode == 'r'
+
+        with pytest.raises(LockError):
+            lock.acquire_write()
 
-    with pytest.raises(LockError):
-        lock.acquire_write()
 
 #
 # Longer test case that ensures locks are reusable. Ordering is
@@ -404,7 +604,7 @@ def p1(barrier):
         lock.release_write()   # release and others acquire read
         barrier.wait()  # ---------------------------------------- 3
         with pytest.raises(LockError):
-            lock.acquire_write(0.1)
+            lock.acquire_write(lock_fail_timeout)
         lock.acquire_read()
         barrier.wait()  # ---------------------------------------- 4
         lock.release_read()
@@ -413,9 +613,9 @@ def p1(barrier):
         # p2 upgrades read to write
         barrier.wait()  # ---------------------------------------- 6
         with pytest.raises(LockError):
-            lock.acquire_write(0.1)
+            lock.acquire_write(lock_fail_timeout)
         with pytest.raises(LockError):
-            lock.acquire_read(0.1)
+            lock.acquire_read(lock_fail_timeout)
         barrier.wait()  # ---------------------------------------- 7
         # p2 releases write and read
         barrier.wait()  # ---------------------------------------- 8
@@ -425,9 +625,9 @@ def p1(barrier):
         # p3 upgrades read to write
         barrier.wait()  # ---------------------------------------- 10
         with pytest.raises(LockError):
-            lock.acquire_write(0.1)
+            lock.acquire_write(lock_fail_timeout)
         with pytest.raises(LockError):
-            lock.acquire_read(0.1)
+            lock.acquire_read(lock_fail_timeout)
         barrier.wait()  # ---------------------------------------- 11
         # p3 releases locks
         barrier.wait()  # ---------------------------------------- 12
@@ -441,9 +641,9 @@ def p2(barrier):
         # p1 acquires write
         barrier.wait()  # ---------------------------------------- 1
         with pytest.raises(LockError):
-            lock.acquire_write(0.1)
+            lock.acquire_write(lock_fail_timeout)
         with pytest.raises(LockError):
-            lock.acquire_read(0.1)
+            lock.acquire_read(lock_fail_timeout)
         barrier.wait()  # ---------------------------------------- 2
         lock.acquire_read()
         barrier.wait()  # ---------------------------------------- 3
@@ -465,9 +665,9 @@ def p2(barrier):
         # p3 upgrades read to write
         barrier.wait()  # ---------------------------------------- 10
         with pytest.raises(LockError):
-            lock.acquire_write(0.1)
+            lock.acquire_write(lock_fail_timeout)
         with pytest.raises(LockError):
-            lock.acquire_read(0.1)
+            lock.acquire_read(lock_fail_timeout)
         barrier.wait()  # ---------------------------------------- 11
         # p3 releases locks
         barrier.wait()  # ---------------------------------------- 12
@@ -481,9 +681,9 @@ def p3(barrier):
         # p1 acquires write
         barrier.wait()  # ---------------------------------------- 1
         with pytest.raises(LockError):
-            lock.acquire_write(0.1)
+            lock.acquire_write(lock_fail_timeout)
         with pytest.raises(LockError):
-            lock.acquire_read(0.1)
+            lock.acquire_read(lock_fail_timeout)
         barrier.wait()  # ---------------------------------------- 2
         lock.acquire_read()
         barrier.wait()  # ---------------------------------------- 3
@@ -495,9 +695,9 @@ def p3(barrier):
         # p2 upgrades read to write
         barrier.wait()  # ---------------------------------------- 6
         with pytest.raises(LockError):
-            lock.acquire_write(0.1)
+            lock.acquire_write(lock_fail_timeout)
         with pytest.raises(LockError):
-            lock.acquire_read(0.1)
+            lock.acquire_read(lock_fail_timeout)
         barrier.wait()  # ---------------------------------------- 7
         # p2 releases write & read
         barrier.wait()  # ---------------------------------------- 8
@@ -517,6 +717,7 @@ def p3(barrier):
 
     multiproc_test(p1, p2, p3)
 
+
 def test_transaction(lock_path):
     def enter_fn():
         vals['entered'] = True
@@ -542,6 +743,7 @@ def exit_fn(t, v, tb):
     assert vals['exited']
     assert not vals['exception']
 
+
 def test_transaction_with_exception(lock_path):
     def enter_fn():
         vals['entered'] = True
@@ -574,6 +776,7 @@ def do_write_with_exception():
     assert vals['exited']
     assert vals['exception']
 
+
 def test_transaction_with_context_manager(lock_path):
     class TestContextManager(object):
 
@@ -634,6 +837,7 @@ def exit_fn(t, v, tb):
     assert not vals['exited_fn']
     assert not vals['exception_fn']
 
+
 def test_transaction_with_context_manager_and_exception(lock_path):
     class TestContextManager(object):
         def __enter__(self):