diff --git a/src/kvsrv1/client.go b/src/kvsrv1/client.go
index 73f1d29..80c3dec 100644
--- a/src/kvsrv1/client.go
+++ b/src/kvsrv1/client.go
@@ -41,7 +41,7 @@ func (ck *Clerk) Get(key string) (string, rpc.Tversion, rpc.Err) {
 // performed at the server. If the server returns ErrVersion on a
 // resend RPC, then Put must return ErrMaybe to the application, since
 // its earlier RPC might have been processed by the server successfully
-// but the response was lost, and the the Clerk doesn't know if
+// but the response was lost, and the Clerk doesn't know if
 // the Put was performed or not.
 //
 // You can send an RPC with code like this:
diff --git a/src/shardkv1/shardctrler/lock/lock.go b/src/shardkv1/shardctrler/lock/lock.go
new file mode 100644
index 0000000..7b5ab5f
--- /dev/null
+++ b/src/shardkv1/shardctrler/lock/lock.go
@@ -0,0 +1,31 @@
+package lock
+
+import (
+
+	"6.5840/kvsrv1"
+	"6.5840/kvsrv1/rpc"
+	"6.5840/shardkv1/shardctrler/param"
+)
+
+
+type Lock struct {
+	ck *kvsrv.Clerk
+
+}
+
+// Use l as the key to store the "lock state" (you would have to decide
+// precisely what the lock state is).
+func MakeLock(ck kvtest.IKVClerk, l string) *Lock {
+	lk := &Lock{ck: ck.(*kvsrv.Clerk)}
+	// You may add code here
+	return lk
+}
+
+
+func (lk *Lock) Acquire() {
+	// You may add code here.
+}
+
+func (lk *Lock) Release() {
+	// You may add code here.
+}
diff --git a/src/shardkv1/shardctrler/lock/lock_test.go b/src/shardkv1/shardctrler/lock/lock_test.go
new file mode 100644
index 0000000..92c9e67
--- /dev/null
+++ b/src/shardkv1/shardctrler/lock/lock_test.go
@@ -0,0 +1,89 @@
+package lock
+
+import (
+	"fmt"
+	//	"log"
+	"strconv"
+	"testing"
+	"time"
+
+	"6.5840/kvsrv1"
+	"6.5840/kvsrv1/rpc"
+	"6.5840/kvtest1"
+)
+
+const (
+	NACQUIRE = 10
+	NCLNT    = 10
+	NSEC     = 2
+)
+
+func oneClient(t *testing.T, me int, ck kvtest.IKVClerk, done chan struct{}) kvtest.ClntRes {
+	lk := MakeLock(ck, "l")
+	ck.Put("l0", "", 0)
+	for i := 1; true; i++ {
+		select {
+		case <-done:
+			return kvtest.ClntRes{i, 0}
+		default:
+			lk.Acquire()
+
+			// log.Printf("%d: acquired lock", me)
+
+			b := strconv.Itoa(me)
+			val, ver, err := ck.Get("l0")
+			if err == rpc.OK {
+				if val != "" {
+					t.Fatalf("%d: two clients acquired lock %v", me, val)
+				}
+			} else {
+				t.Fatalf("%d: get failed %v", me, err)
+			}
+
+			err = ck.Put("l0", string(b), ver)
+			if !(err == rpc.OK || err == rpc.ErrMaybe) {
+				t.Fatalf("%d: put failed %v", me, err)
+			}
+
+			time.Sleep(10 * time.Millisecond)
+
+			err = ck.Put("l0", "", ver+1)
+			if !(err == rpc.OK || err == rpc.ErrMaybe) {
+				t.Fatalf("%d: put failed %v", me, err)
+			}
+
+			// log.Printf("%d: release lock", me)
+
+			lk.Release()
+		}
+	}
+	return kvtest.ClntRes{}
+}
+
+// Run test clients
+func runClients(t *testing.T, nclnt int, reliable bool) {
+	ts := kvsrv.MakeTestKV(t, reliable)
+	defer ts.Cleanup()
+
+	ts.Begin(fmt.Sprintf("Test: %d lock clients", nclnt))
+
+	ts.SpawnClientsAndWait(nclnt, NSEC*time.Second, func(me int, myck kvtest.IKVClerk, done chan struct{}) kvtest.ClntRes {
+		return oneClient(t, me, myck, done)
+	})
+}
+
+func TestOneClientReliable(t *testing.T) {
+	runClients(t, 1, true)
+}
+
+func TestManyClientsReliable(t *testing.T) {
+	runClients(t, NCLNT, true)
+}
+
+func TestOneClientUnreliable(t *testing.T) {
+	runClients(t, 1, false)
+}
+
+func TestManyClientsUnreliable(t *testing.T) {
+	runClients(t, NCLNT, false)
+}
diff --git a/src/shardkv1/shardctrler/shardctrler.go b/src/shardkv1/shardctrler/shardctrler.go
index 3d8743e..d59c0da 100644
--- a/src/shardkv1/shardctrler/shardctrler.go
+++ b/src/shardkv1/shardctrler/shardctrler.go
@@ -39,12 +39,8 @@ func MakeShardCtrler(clnt *tester.Clnt, leases bool) *ShardCtrler {
 // The tester calls InitController() before starting a new
 // controller. In part A, this method doesn't need to do anything. In
 // B and C, this method implements recovery (part B) and uses a lock
-// to become leader (part C). InitController should return
-// rpc.ErrVersion when another controller supersedes it (e.g., when
-// this controller is partitioned during recovery); this happens only
-// in Part C. Otherwise, it returns rpc.OK.
-func (sck *ShardCtrler) InitController() rpc.Err {
-	return rpc.ErrVersion
+// to become leader (part C).
+func (sck *ShardCtrler) InitController() {
 }
 
 // The tester calls ExitController to exit a controller. In part B and
@@ -61,12 +57,11 @@ func (sck *ShardCtrler) InitConfig(cfg *shardcfg.ShardConfig) {
 }
 
 // Called by the tester to ask the controller to change the
-// configuration from the current one to new. It should return
-// rpc.ErrVersion if this controller is superseded by another
-// controller, as in part C.  In all other cases, it should return
-// rpc.OK.
-func (sck *ShardCtrler) ChangeConfigTo(new *shardcfg.ShardConfig) rpc.Err {
-	return rpc.OK
+// configuration from the current one to new.  While the controller
+// changes the configuration it may be superseded by another
+// controller.
+func (sck *ShardCtrler) ChangeConfigTo(new *shardcfg.ShardConfig) {
+	return
 }
 
 // Tester "kills" shardctrler by calling Kill().  For your
diff --git a/src/shardkv1/shardgrp/server.go b/src/shardkv1/shardgrp/server.go
index c6a8e38..a723a95 100644
--- a/src/shardkv1/shardgrp/server.go
+++ b/src/shardkv1/shardgrp/server.go
@@ -14,11 +14,10 @@ import (
 
 
 type KVServer struct {
-	gid    tester.Tgid
-	me     int
-	dead   int32 // set by Kill()
-	rsm    *rsm.RSM
-	frozen bool // for testing purposes
+	gid  tester.Tgid
+	me   int
+	dead int32 // set by Kill()
+	rsm  *rsm.RSM
 
 }
 
diff --git a/src/shardkv1/shardkv_test.go b/src/shardkv1/shardkv_test.go
index 78f0f58..ce37791 100644
--- a/src/shardkv1/shardkv_test.go
+++ b/src/shardkv1/shardkv_test.go
@@ -67,7 +67,7 @@ func TestStaticOneShardGroup5A(t *testing.T) {
 	}
 
 	// disconnect raft leader of shardgrp and check that keys are
-	// still avaialable
+	// still available
 	ts.disconnectClntFromLeader(ck.(*kvtest.TestClerk).Clnt, shardcfg.Gid1)
 
 	for i := 0; i < n; i++ {
@@ -90,18 +90,17 @@ func TestJoinBasic5A(t *testing.T) {
 	cfg, _ := sck.Query()
 
 	gid2 := ts.newGid()
-	err := ts.joinGroups(sck, []tester.Tgid{gid2})
-	if err != rpc.OK {
-		ts.t.Fatalf("joinGroups: err %v", err)
+	if ok := ts.joinGroups(sck, []tester.Tgid{gid2}); !ok {
+		ts.t.Fatalf("TestJoinBasic5A: joinGroups failed")
 	}
 
 	cfg1, _ := sck.Query()
 	if cfg.Num+1 != cfg1.Num {
-		ts.t.Fatalf("wrong num %d expected %d ", cfg1.Num, cfg.Num+1)
+		ts.t.Fatalf("TestJoinBasic5A: wrong num %d expected %d ", cfg1.Num, cfg.Num+1)
 	}
 
 	if !cfg1.IsMember(gid2) {
-		ts.t.Fatalf("%d isn't a member of %v", gid2, cfg1)
+		ts.t.Fatalf("TestJoinBasic5A: %d isn't a member of %v", gid2, cfg1)
 	}
 
 	ts.checkShutdownSharding(gid1, ka, va)
@@ -136,9 +135,8 @@ func TestDeleteBasic5A(t *testing.T) {
 
 	sck := ts.ShardCtrler()
 	gid2 := ts.newGid()
-	err := ts.joinGroups(sck, []tester.Tgid{gid2})
-	if err != rpc.OK {
-		ts.t.Fatalf("joinGroups: err %v", err)
+	if ok := ts.joinGroups(sck, []tester.Tgid{gid2}); !ok {
+		ts.t.Fatalf("TestDeleteBasic5A: joinGroups failed")
 	}
 
 	// push more Get's through so that all peers snapshot
@@ -150,7 +148,7 @@ func TestDeleteBasic5A(t *testing.T) {
 	sz1 := ts.Group(gid1).SnapshotSize()
 	sz2 := ts.Group(gid2).SnapshotSize()
 	if sz1+sz2 > sz+10000 {
-		ts.t.Fatalf("gid1 %d + gid2 %d = %d use too much space %d", sz1, sz2, sz1+sz2, sz)
+		ts.t.Fatalf("TestDeleteBasic5A: gid1 %d + gid2 %d = %d use too much space %d", sz1, sz2, sz1+sz2, sz)
 	}
 }
 
@@ -165,9 +163,8 @@ func TestJoinLeaveBasic5A(t *testing.T) {
 
 	sck := ts.ShardCtrler()
 	gid2 := ts.newGid()
-	err := ts.joinGroups(sck, []tester.Tgid{gid2})
-	if err != rpc.OK {
-		ts.t.Fatalf("joinGroups: err %v", err)
+	if ok := ts.joinGroups(sck, []tester.Tgid{gid2}); !ok {
+		ts.t.Fatalf("TestJoinLeaveBasic5A: joinGroups failed")
 	}
 
 	ts.checkShutdownSharding(gid1, ka, va)
@@ -176,13 +173,9 @@ func TestJoinLeaveBasic5A(t *testing.T) {
 		ts.CheckGet(ck, ka[i], va[i], rpc.Tversion(1))
 	}
 
-	err = ts.leave(sck, shardcfg.Gid1)
-	if err != rpc.OK {
-		ts.t.Fatalf("Leave: err %v", err)
-	}
-	cfg, _ := sck.Query()
-	if cfg.IsMember(shardcfg.Gid1) {
-		ts.t.Fatalf("%d is a member of %v", shardcfg.Gid1, cfg)
+	ts.leave(sck, shardcfg.Gid1)
+	if ok := ts.checkMember(sck, shardcfg.Gid1); ok {
+		ts.t.Fatalf("%d is a member after leave", shardcfg.Gid1)
 	}
 
 	ts.Group(shardcfg.Gid1).Shutdown()
@@ -382,11 +375,11 @@ func TestProgressJoin(t *testing.T) {
 				return
 			default:
 				//log.Printf("join/leave %v", newgid)
-				if err := ts.joinGroups(sck, []tester.Tgid{newgid}); err != rpc.OK {
-					t.Fatalf("joined err %v", err)
+				if ok := ts.joinGroups(sck, []tester.Tgid{newgid}); !ok {
+					t.Fatalf("TestProgressJoin: join failed")
 				}
-				if err := ts.leaveGroups(sck, []tester.Tgid{newgid}); err != rpc.OK {
-					t.Fatalf("leave err %v", err)
+				if ok := ts.leaveGroups(sck, []tester.Tgid{newgid}); !ok {
+					t.Fatalf("TestProgressJoin: leave failed")
 				}
 			}
 		}
@@ -451,12 +444,12 @@ func concurrentClerk(t *testing.T, nclnt int, reliable bool, part string) {
 
 	sck := ts.ShardCtrler()
 	grps := ts.groups(NGRP)
-	if err := ts.joinGroups(sck, grps); err != rpc.OK {
-		t.Fatalf("joinGroups err %v", err)
+	if ok := ts.joinGroups(sck, grps); !ok {
+		t.Fatalf("concurrentClerk: joinGroups failed")
 	}
 
-	if err := ts.leaveGroups(sck, grps); err != rpc.OK {
-		t.Fatalf("leaveGroups err %v", err)
+	if ok := ts.leaveGroups(sck, grps); !ok {
+		t.Fatalf("concurrentClerk: leaveGroups failed")
 	}
 
 	<-ch
@@ -504,10 +497,9 @@ func TestJoinLeave5B(t *testing.T) {
 	ts.Group(gid1).Shutdown()
 
 	gid2 := ts.newGid()
-	ch := make(chan rpc.Err)
+	ch := make(chan bool)
 	go func() {
-		err := ts.joinGroups(sck, []tester.Tgid{gid2})
-		ch <- err
+		ch <- ts.joinGroups(sck, []tester.Tgid{gid2})
 	}()
 
 	select {
@@ -521,9 +513,9 @@ func TestJoinLeave5B(t *testing.T) {
 	ts.Group(gid1).StartServers()
 
 	select {
-	case err := <-ch:
-		if err != rpc.OK {
-			ts.Fatalf("Join returns err %v", err)
+	case ok := <-ch:
+		if !ok {
+			ts.Fatalf("TestJoinLeave5B: Join returned %t", ok)
 		}
 	case <-time.After(time.Second * NSEC):
 		ts.Fatalf("Join didn't complete")
@@ -536,15 +528,13 @@ func TestJoinLeave5B(t *testing.T) {
 
 	ts.Group(gid2).Shutdown()
 
-	ch = make(chan rpc.Err)
 	go func() {
-		err := ts.leave(sck, shardcfg.Gid1)
-		ch <- err
+		ch <- ts.leaveGroups(sck, []tester.Tgid{shardcfg.Gid1})
 	}()
 
 	select {
-	case err := <-ch:
-		ts.Fatalf("Leave finished %v", err)
+	case <-ch:
+		ts.Fatalf("Leave finished")
 	case <-time.After(NSEC * time.Second):
 		// Give give some time to try to join
 	}
@@ -553,9 +543,9 @@ func TestJoinLeave5B(t *testing.T) {
 	ts.Group(gid2).StartServers()
 
 	select {
-	case err := <-ch:
-		if err != rpc.OK {
-			ts.Fatalf("Leave returns err %v", err)
+	case ok := <-ch:
+		if !ok {
+			ts.Fatalf("TestJoinLeave5B: Leave failed %t", ok)
 		}
 	case <-time.After(time.Second * NSEC):
 		ts.Fatalf("Leave didn't complete")
@@ -611,9 +601,7 @@ func TestLeaseBasicRelease5C(t *testing.T) {
 
 	sck0, clnt0 := ts.makeShardCtrlerClnt()
 	go func() {
-		if err := sck0.InitController(); err != rpc.OK {
-			t.Fatalf("failed to init controller %v", err)
-		}
+		sck0.InitController()
 		time.Sleep(200 * time.Millisecond)
 		sck0.ExitController()
 	}()
@@ -624,9 +612,7 @@ func TestLeaseBasicRelease5C(t *testing.T) {
 	sck1, clnt1 := ts.makeShardCtrlerClnt()
 	ch := make(chan struct{})
 	go func() {
-		if err := sck1.InitController(); err != rpc.OK {
-			t.Fatalf("failed to init controller %v", err)
-		}
+		sck1.InitController()
 		time.Sleep(200 * time.Millisecond)
 		sck1.ExitController()
 		ch <- struct{}{}
@@ -650,9 +636,7 @@ func TestLeaseBasicExpire5C(t *testing.T) {
 
 	sck0, clnt0 := ts.makeShardCtrlerClnt()
 	go func() {
-		if err := sck0.InitController(); err != rpc.OK {
-			t.Fatalf("failed to init controller %v", err)
-		}
+		sck0.InitController()
 		for {
 			time.Sleep(10 * time.Millisecond)
 		}
@@ -667,9 +651,7 @@ func TestLeaseBasicExpire5C(t *testing.T) {
 	sck1, clnt1 := ts.makeShardCtrlerClnt()
 	ch := make(chan struct{})
 	go func() {
-		if err := sck1.InitController(); err != rpc.OK {
-			t.Fatalf("failed to init controller %v", err)
-		}
+		sck1.InitController()
 		time.Sleep(100 * time.Millisecond)
 		sck1.ExitController()
 		ch <- struct{}{}
@@ -695,9 +677,7 @@ func TestLeaseBasicRefresh5C(t *testing.T) {
 
 	sck0, clnt0 := ts.makeShardCtrlerClnt()
 	go func() {
-		if err := sck0.InitController(); err != rpc.OK {
-			t.Fatalf("failed to init controller %v", err)
-		}
+		sck0.InitController()
 		time.Sleep(LEADERSEC * param.LEASETIMESEC * time.Second)
 		sck0.ExitController()
 	}()
@@ -709,9 +689,7 @@ func TestLeaseBasicRefresh5C(t *testing.T) {
 	sck1, clnt1 := ts.makeShardCtrlerClnt()
 	ch := make(chan struct{})
 	go func() {
-		if err := sck1.InitController(); err != rpc.OK {
-			t.Fatalf("failed to init controller %v", err)
-		}
+		sck1.InitController()
 		time.Sleep(100 * time.Millisecond)
 		sck1.ExitController()
 		ch <- struct{}{}
@@ -742,9 +720,7 @@ func TestPartitionControllerJoin5C(t *testing.T) {
 	ka, va := ts.SpreadPuts(ck, NKEYS)
 
 	sck, clnt := ts.makeShardCtrlerClnt()
-	if err := sck.InitController(); err != rpc.OK {
-		ts.Fatalf("failed to init controller %v", err)
-	}
+	sck.InitController()
 
 	ch := make(chan rpc.Err)
 	ngid := tester.Tgid(0)
@@ -752,7 +728,8 @@ func TestPartitionControllerJoin5C(t *testing.T) {
 		ngid = ts.newGid()
 		ts.Config.MakeGroupStart(ngid, NSRV, ts.StartServerShardGrp)
 		ts.Group(ngid).Shutdown()
-		ch <- ts.join(sck, ngid, ts.Group(ngid).SrvNames())
+		ts.join(sck, ngid, ts.Group(ngid).SrvNames())
+		ch <- rpc.OK
 	}()
 
 	// sleep for a while to get the chance for the controller to get
@@ -769,9 +746,7 @@ func TestPartitionControllerJoin5C(t *testing.T) {
 
 	// start new controller to supersede partitioned one,
 	sck0 := ts.makeShardCtrler()
-	if err := sck0.InitController(); err != rpc.OK {
-		t.Fatalf("failed to init controller %v", err)
-	}
+	sck0.InitController()
 
 	scfg, _ := sck0.Query()
 	if !scfg.IsMember(ngid) {
@@ -783,10 +758,8 @@ func TestPartitionControllerJoin5C(t *testing.T) {
 	// reconnect old controller, which shouldn't finish ChangeConfigTo
 	clnt.ConnectAll()
 
-	err := <-ch
-	if err == rpc.OK {
-		t.Fatalf("Old leader succeeded %v", err)
-	}
+	// wait for old controller to finish/exit
+	<-ch
 
 	time.Sleep(1 * time.Second)
 
@@ -797,19 +770,64 @@ func TestPartitionControllerJoin5C(t *testing.T) {
 
 // Make a leader controller loses its leadership during join/leave and
 // test if the next controller recovers correctly.
-func TestPartitionRecovery5C(t *testing.T) {
-	const (
-		// NPARTITION = 10
-		NPARTITION = 5
-	)
-
-	ts := MakeTestLeases(t, "Test (5C): controllers with leased leadership ...", true)
+func partitionRecovery5C(t *testing.T, reliable bool, npart, nclnt int) {
+	const NSEC = 60
+	ts := MakeTestLeases(t, "Test (5C): controllers with leased leadership ...", reliable)
 	defer ts.Cleanup()
 	gid := ts.setupKVService()
 	ck := ts.MakeClerk()
-	ka, va := ts.SpreadPuts(ck, NKEYS)
 
-	for i := 0; i < NPARTITION; i++ {
+	ka := make([]string, 0)
+	va := make([]string, 0)
+	if nclnt <= 0 {
+		ka, va = ts.SpreadPuts(ck, NKEYS)
+	}
+
+	ch := make(chan []kvtest.ClntRes)
+	if nclnt > 0 {
+		ka := kvtest.MakeKeys(1)
+		go func(ch chan []kvtest.ClntRes) {
+			rs := ts.SpawnClientsAndWait(nclnt, NSEC*time.Second, func(me int, ck kvtest.IKVClerk, done chan struct{}) kvtest.ClntRes {
+				return ts.OneClientPut(me, ck, ka, done)
+			})
+			ch <- rs
+		}(ch)
+	}
+
+	for i := 0; i < npart; i++ {
 		ts.killCtrler(ck, gid, ka, va)
 	}
+
+	if nclnt > 0 {
+		<-ch
+		ts.CheckPorcupine()
+	}
+}
+
+func TestPartitionRecoveryReliableNoClerk5C(t *testing.T) {
+	const (
+		NPARTITION = 5
+	)
+	partitionRecovery5C(t, true, NPARTITION, 0)
+}
+
+func TestPartitionRecoveryUnreliableNoClerk5C(t *testing.T) {
+	const (
+		NPARTITION = 3
+	)
+	partitionRecovery5C(t, false, NPARTITION, 0)
+}
+
+func TestPartitionRecoveryReliableClerks5C(t *testing.T) {
+	const (
+		NPARTITION = 5
+	)
+	partitionRecovery5C(t, true, NPARTITION, 5)
+}
+
+func TestPartitionRecoveryUnreliableClerks5C(t *testing.T) {
+	const (
+		NPARTITION = 5
+	)
+	partitionRecovery5C(t, false, NPARTITION, 5)
 }
diff --git a/src/shardkv1/test.go b/src/shardkv1/test.go
index 2020f48..045bacf 100644
--- a/src/shardkv1/test.go
+++ b/src/shardkv1/test.go
@@ -50,6 +50,8 @@ func MakeTestMaxRaft(t *testing.T, part string, reliable, leases bool, maxraftst
 	}
 	cfg := tester.MakeConfig(t, 1, reliable, kvsrv.StartKVServer)
 	ts.Test = kvtest.MakeTest(t, cfg, false, ts)
+	// XXX to avoid panic
+	tester.AnnotateTest(part, 1)
 	ts.Begin(part)
 	return ts
 }
@@ -125,48 +127,56 @@ func (ts *Test) StartServerShardGrp(servers []*labrpc.ClientEnd, gid tester.Tgid
 	return shardgrp.StartServerShardGrp(servers, gid, me, persister, ts.maxraftstate)
 }
 
+func (ts *Test) checkMember(sck *shardctrler.ShardCtrler, gid tester.Tgid) bool {
+	cfg, _ := sck.Query()
+	ok := cfg.IsMember(gid)
+	return ok
+}
+
 // Add group gid
-func (ts *Test) join(sck *shardctrler.ShardCtrler, gid tester.Tgid, srvs []string) rpc.Err {
+func (ts *Test) join(sck *shardctrler.ShardCtrler, gid tester.Tgid, srvs []string) {
 	cfg, _ := sck.Query()
 	newcfg := cfg.Copy()
 	ok := newcfg.JoinBalance(map[tester.Tgid][]string{gid: srvs})
 	if !ok {
 		log.Fatalf("join: group %d is already present", gid)
 	}
-	return sck.ChangeConfigTo(newcfg)
+	sck.ChangeConfigTo(newcfg)
 }
 
-func (ts *Test) joinGroups(sck *shardctrler.ShardCtrler, gids []tester.Tgid) rpc.Err {
+func (ts *Test) joinGroups(sck *shardctrler.ShardCtrler, gids []tester.Tgid) bool {
 	for _, gid := range gids {
 		ts.Config.MakeGroupStart(gid, NSRV, ts.StartServerShardGrp)
-		if err := ts.join(sck, gid, ts.Group(gid).SrvNames()); err != rpc.OK {
-			return err
+		ts.join(sck, gid, ts.Group(gid).SrvNames())
+		if ok := ts.checkMember(sck, gid); !ok {
+			return false
 		}
 		time.Sleep(INTERGRPDELAY * time.Millisecond)
 	}
-	return rpc.OK
+	return true
 }
 
 // Group gid leaves.
-func (ts *Test) leave(sck *shardctrler.ShardCtrler, gid tester.Tgid) rpc.Err {
+func (ts *Test) leave(sck *shardctrler.ShardCtrler, gid tester.Tgid) {
 	cfg, _ := sck.Query()
 	newcfg := cfg.Copy()
 	ok := newcfg.LeaveBalance([]tester.Tgid{gid})
 	if !ok {
 		log.Fatalf("leave: group %d is already not present", gid)
 	}
-	return sck.ChangeConfigTo(newcfg)
+	sck.ChangeConfigTo(newcfg)
 }
 
-func (ts *Test) leaveGroups(sck *shardctrler.ShardCtrler, gids []tester.Tgid) rpc.Err {
+func (ts *Test) leaveGroups(sck *shardctrler.ShardCtrler, gids []tester.Tgid) bool {
 	for _, gid := range gids {
-		if err := ts.leave(sck, gid); err != rpc.OK {
-			return err
+		ts.leave(sck, gid)
+		if ok := ts.checkMember(sck, gid); ok {
+			return false
 		}
 		ts.Config.ExitGroup(gid)
 		time.Sleep(INTERGRPDELAY * time.Millisecond)
 	}
-	return rpc.OK
+	return true
 }
 
 func (ts *Test) disconnectRaftLeader(gid tester.Tgid) (int, string) {
@@ -257,9 +267,7 @@ func (ts *Test) killCtrler(ck kvtest.IKVClerk, gid tester.Tgid, ka, va []string)
 	)
 
 	sck, clnt := ts.makeShardCtrlerClnt()
-	if err := sck.InitController(); err != rpc.OK {
-		ts.Fatalf("failed to init controller %v", err)
-	}
+	sck.InitController()
 
 	cfg, _ := ts.ShardCtrler().Query()
 	num := cfg.Num
@@ -270,12 +278,12 @@ func (ts *Test) killCtrler(ck kvtest.IKVClerk, gid tester.Tgid, ka, va []string)
 		for {
 			ngid = ts.newGid()
 			state = JOIN
-			err := ts.joinGroups(sck, []tester.Tgid{ngid})
-			if err == rpc.OK {
+			ts.joinGroups(sck, []tester.Tgid{ngid})
+			if ok := ts.checkMember(sck, ngid); ok {
 				state = LEAVE
-				err = ts.leaveGroups(sck, []tester.Tgid{ngid})
+				ts.leaveGroups(sck, []tester.Tgid{ngid})
 			} else {
-				//log.Printf("deposed err %v", err)
+				//log.Printf("deposed")
 				return
 			}
 		}
@@ -306,9 +314,8 @@ func (ts *Test) killCtrler(ck kvtest.IKVClerk, gid tester.Tgid, ka, va []string)
 
 	// start new controler to pick up where sck left off
 	sck0, clnt0 := ts.makeShardCtrlerClnt()
-	if err := sck0.InitController(); err != rpc.OK {
-		ts.Fatalf("failed to init controller %v", err)
-	}
+
+	sck0.InitController()
 	cfg, _ = sck0.Query()
 	s := "join"
 	if state == LEAVE {
@@ -337,6 +344,8 @@ func (ts *Test) killCtrler(ck kvtest.IKVClerk, gid tester.Tgid, ka, va []string)
 	sck0.ExitController()
 
 	if ts.leases {
+		//log.Printf("reconnect old controller")
+
 		// reconnect old controller, which should bail out, because
 		// it has been superseded.
 		clnt.ConnectAll()
@@ -366,12 +375,15 @@ func (ts *Test) electCtrler(ck kvtest.IKVClerk, ka, va []string) {
 			default:
 				ngid := ts.newGid()
 				sck := ts.makeShardCtrler()
-				if err := sck.InitController(); err != rpc.OK {
-					ts.Fatalf("failed to init controller %v", err)
-				}
+				sck.InitController()
 				//log.Printf("%d(%p): join/leave %v", i, sck, ngid)
-				if err := ts.joinGroups(sck, []tester.Tgid{ngid}); err == rpc.OK {
-					ts.leaveGroups(sck, []tester.Tgid{ngid})
+				ts.joinGroups(sck, []tester.Tgid{ngid})
+				if ok := ts.checkMember(sck, ngid); ok {
+					if ok := ts.leaveGroups(sck, []tester.Tgid{ngid}); !ok {
+						log.Fatalf("electCtrler: %d(%p): leave %v failed", i, sck, ngid)
+					}
+				} else {
+					log.Fatalf("electCtrler: %d(%p): join %v failed", i, sck, ngid)
 				}
 				sck.ExitController()
 			}
diff --git a/src/shardkv1/test.out b/src/shardkv1/test.out
new file mode 100644
index 0000000..31d8045
--- /dev/null
+++ b/src/shardkv1/test.out
@@ -0,0 +1,169 @@
+=== RUN   TestAcquireLockConcurrentReliable5C
+Test (5C): Concurent ctrlers acquiring leadership ... (reliable network)...
+2025/03/20 09:18:33 PecUxIPV: acquire success 1 l 2.999731394s
+2025/03/20 09:18:35 PecUxIPV: Release 3
+2025/03/20 09:18:35 aKDBLFuF: acquire success 4 l 2.999504542s
+2025/03/20 09:18:37 aKDBLFuF: Release 6
+2025/03/20 09:18:37 HxhaFlAP: acquire success 7 l 2.999622621s
+2025/03/20 09:18:39 HxhaFlAP: Release 9
+2025/03/20 09:18:39 LpTmFCGC: acquire success 10 l 2.999747179s
+2025/03/20 09:18:41 LpTmFCGC: Release 13
+2025/03/20 09:18:41 klmldUQn: acquire success 14 l 2.999558604s
+2025/03/20 09:18:43 klmldUQn: Release 17
+2025/03/20 09:18:43 AWgiWKPZ: acquire success 18 l 2.999701903s
+2025/03/20 09:18:46 AWgiWKPZ: Release 21
+  ... Passed --  16.4  1  2061  120
+--- PASS: TestAcquireLockConcurrentReliable5C (16.38s)
+=== RUN   TestAcquireLockConcurrentUnreliable5C
+Test (5C): Concurent ctrlers acquiring leadership ... (unreliable network)...
+2025/03/20 09:19:00 xulPPlwd: acquire success 2 l 2.768860613s
+2025/03/20 09:19:05 xulPPlwd: Release 6
+2025/03/20 09:19:05 SGXgIJeR: acquire success 7 l 2.984694448s
+2025/03/20 09:19:08 SGXgIJeR: Release 11
+2025/03/20 09:19:08 kNvktGla: acquire success 12 l 2.986135242s
+2025/03/20 09:19:13 kNvktGla: Release 17
+2025/03/20 09:19:13 usGKuyeI: acquire success 18 l 2.97484218s
+2025/03/20 09:19:19 usGKuyeI: Release 24
+  ... Passed --  38.4  1  2226  120
+--- PASS: TestAcquireLockConcurrentUnreliable5C (38.37s)
+=== RUN   TestLeaseBasicRelease5C
+Test (5C): release lease ... (reliable network)...
+2025/03/20 09:19:25 fWllyjFs: acquire success 1 l 2.999778852s
+2025/03/20 09:19:25 fWllyjFs: Release 2
+2025/03/20 09:19:25 HqoctgYf: acquire success 3 l 2.999623311s
+2025/03/20 09:19:26 HqoctgYf: Release 4
+  ... Passed --   0.4  1    17    0
+--- PASS: TestLeaseBasicRelease5C (0.42s)
+=== RUN   TestLeaseBasicExpire5C
+Test (5C): lease expiring ... (reliable network)...
+2025/03/20 09:19:26 MgmIiwHw: acquire success 1 l 2.999622077s
+2025/03/20 09:19:29 PviuBaqZ: acquire: MgmIiwHw lease expired -31.512117ms
+2025/03/20 09:19:29 PviuBaqZ: acquire success 2 l 2.9996929s
+2025/03/20 09:19:29 PviuBaqZ: Release 3
+  ... Passed --   3.1  1    81    0
+--- PASS: TestLeaseBasicExpire5C (3.14s)
+=== RUN   TestLeaseBasicRefresh5C
+Test (5C): lease refresh ... (reliable network)...
+2025/03/20 09:19:29 CqhHcMdl: acquire success 1 l 2.999690343s
+  ... Passed --   7.1  1   144    0
+--- PASS: TestLeaseBasicRefresh5C (7.10s)
+=== RUN   TestPartitionControllerJoin5C
+Test (5C): partition controller in join... (reliable network)...
+2025/03/20 09:19:38 CqhHcMdl: Release 9
+2025/03/20 09:19:38 QykadXGi: acquire success 1 l 2.999763148s
+2025/03/20 09:19:43 YWktoCTH: acquire: QykadXGi lease expired -2.003411436s
+2025/03/20 09:19:43 YWktoCTH: acquire success 2 l 2.999580573s
+2025/03/20 09:19:45 YWktoCTH: Release 4
+2025/03/20 09:19:45 QykadXGi: refresher: exit expired -3.255782562s
+  ... Passed --  11.2  1  1011  120
+--- PASS: TestPartitionControllerJoin5C (11.22s)
+=== RUN   TestPartitionRecoveryReliableNoClerk5C
+Test (5C): controllers with leased leadership ... (reliable network)...
+2025/03/20 09:19:50 nLqpPYYg: acquire success 1 l 2.999773699s
+2025/03/20 09:19:56 Yauplngb: acquire: nLqpPYYg lease expired -1.030252686s
+2025/03/20 09:19:56 Yauplngb: acquire success 4 l 2.999760357s
+2025/03/20 09:19:58 Yauplngb: Release 7
+2025/03/20 09:19:58 nLqpPYYg: refresher: exit expired -3.848348135s
+2025/03/20 09:20:00 dsvADejV: acquire success 8 l 2.999675453s
+2025/03/20 09:20:07 jdcPVdvf: acquire: dsvADejV lease expired -1.56610473s
+2025/03/20 09:20:07 jdcPVdvf: acquire success 11 l 2.999839821s
+2025/03/20 09:20:10 jdcPVdvf: Release 15
+2025/03/20 09:20:10 dsvADejV: refresher: exit expired -4.604218577s
+2025/03/20 09:20:12 vzVcVtTQ: acquire success 16 l 2.999743618s
+2025/03/20 09:20:19 valCDRmB: acquire: vzVcVtTQ lease expired -1.988170854s
+2025/03/20 09:20:19 valCDRmB: acquire success 19 l 2.999667662s
+2025/03/20 09:20:22 valCDRmB: Release 22
+2025/03/20 09:20:22 vzVcVtTQ: refresher: exit expired -4.943386258s
+2025/03/20 09:20:23 RJYqYuLF: acquire success 23 l 2.999774783s
+2025/03/20 09:20:30 KaeJpVvL: acquire: RJYqYuLF lease expired -1.222157296s
+2025/03/20 09:20:30 KaeJpVvL: acquire success 26 l 2.999897268s
+2025/03/20 09:20:33 KaeJpVvL: Release 30
+2025/03/20 09:20:33 RJYqYuLF: refresher: exit expired -4.429889332s
+2025/03/20 09:20:34 leVdobnP: acquire success 31 l 2.999770816s
+2025/03/20 09:20:41 DFnmWean: acquire: leVdobnP lease expired -1.756292497s
+2025/03/20 09:20:41 DFnmWean: acquire success 34 l 2.999905276s
+2025/03/20 09:20:44 DFnmWean: Release 38
+2025/03/20 09:20:44 leVdobnP: refresher: exit expired -4.84260629s
+  ... Passed --  59.3  1  5454  660
+--- PASS: TestPartitionRecoveryReliableNoClerk5C (59.30s)
+=== RUN   TestPartitionRecoveryUnreliableNoClerk5C
+Test (5C): controllers with leased leadership ... (unreliable network)...
+2025/03/20 09:21:01 oBRWPJFn: acquire success 1 l 2.999668901s
+2025/03/20 09:21:08 WCfEtCSF: acquire: oBRWPJFn lease expired -1.960469635s
+2025/03/20 09:21:08 WCfEtCSF: acquire success 4 l 2.989064006s
+2025/03/20 09:21:19 WCfEtCSF: Release 15
+2025/03/20 09:21:20 oBRWPJFn: refresher: exit expired -13.623366094s
+2025/03/20 09:21:25 BKOHUPgK: acquire success 16 l 2.974368151s
+2025/03/20 09:21:32 dpZEDTAn: acquire: BKOHUPgK lease expired -1.266079689s
+2025/03/20 09:21:32 dpZEDTAn: acquire success 19 l 2.986737971s
+2025/03/20 09:21:42 dpZEDTAn: Release 29
+2025/03/20 09:21:43 BKOHUPgK: refresher: exit expired -12.408069097s
+2025/03/20 09:21:50 TiapOztE: acquire: dpZEDTAn lease expired -4.992859225s
+2025/03/20 09:21:50 TiapOztE: acquire success 30 l 2.972701594s
+2025/03/20 09:21:57 aDyCYcpR: acquire: TiapOztE lease expired -1.338848496s
+2025/03/20 09:21:57 aDyCYcpR: acquire success 33 l 2.99686939s
+2025/03/20 09:22:07 aDyCYcpR: Release 43
+2025/03/20 09:22:07 TiapOztE: refresher: exit expired -12.147734461s
+  ... Passed --  86.9  1  4985  420
+--- PASS: TestPartitionRecoveryUnreliableNoClerk5C (86.88s)
+=== RUN   TestPartitionRecoveryReliableClerks5C
+Test (5C): controllers with leased leadership ... (reliable network)...
+2025/03/20 09:22:13 vZrMwEsy: acquire success 1 l 2.999893567s
+2025/03/20 09:22:20 AFHDpDYV: acquire: vZrMwEsy lease expired -1.657500925s
+2025/03/20 09:22:20 AFHDpDYV: acquire success 4 l 2.999596975s
+2025/03/20 09:22:22 AFHDpDYV: Release 6
+2025/03/20 09:22:22 vZrMwEsy: refresher: exit expired -3.627083489s
+2025/03/20 09:22:23 tserHLNb: acquire success 7 l 2.999932478s
+2025/03/20 09:22:29 msIfUgIC: acquire: tserHLNb lease expired -1.13789373s
+2025/03/20 09:22:29 msIfUgIC: acquire success 10 l 2.999755401s
+2025/03/20 09:22:31 msIfUgIC: Release 12
+2025/03/20 09:22:31 tserHLNb: refresher: exit expired -3.083945752s
+2025/03/20 09:22:32 YLEIZyDn: acquire success 13 l 2.999940475s
+2025/03/20 09:22:38 TIibzsMc: acquire: YLEIZyDn lease expired -1.017825561s
+2025/03/20 09:22:38 TIibzsMc: acquire success 16 l 2.999907075s
+2025/03/20 09:22:40 TIibzsMc: Release 18
+2025/03/20 09:22:40 YLEIZyDn: refresher: exit expired -2.789136907s
+2025/03/20 09:22:41 knOnYtxW: acquire success 19 l 2.999891429s
+2025/03/20 09:22:47 KyiPMsgB: acquire: knOnYtxW lease expired -1.534324297s
+2025/03/20 09:22:47 KyiPMsgB: acquire success 22 l 2.999822725s
+2025/03/20 09:22:49 KyiPMsgB: Release 24
+2025/03/20 09:22:49 knOnYtxW: refresher: exit expired -3.516354686s
+2025/03/20 09:22:50 wHNCImkl: acquire success 25 l 2.999917928s
+2025/03/20 09:22:56 CSBcxnyr: acquire: wHNCImkl lease expired -1.051161379s
+2025/03/20 09:22:56 CSBcxnyr: acquire success 28 l 2.999745303s
+2025/03/20 09:22:58 CSBcxnyr: Release 31
+2025/03/20 09:22:58 wHNCImkl: refresher: exit expired -3.241024197s
+  ... Passed --  60.1  1 15934 5124
+--- PASS: TestPartitionRecoveryReliableClerks5C (60.14s)
+=== RUN   TestPartitionRecoveryUnreliableClerks5C
+Test (5C): controllers with leased leadership ... (unreliable network)...
+2025/03/20 09:23:14 ydfNYYir: acquire success 1 l 2.871807366s
+2025/03/20 09:23:21 KmfOaYym: acquire: ydfNYYir lease expired -1.96910688s
+2025/03/20 09:23:21 KmfOaYym: acquire success 4 l 2.976357121s
+2025/03/20 09:23:25 KmfOaYym: Release 9
+2025/03/20 09:23:26 ydfNYYir: refresher: exit expired -6.960801287s
+2025/03/20 09:23:27 XErxjiqb: acquire success 10 l 2.994288153s
+2025/03/20 09:23:34 VQFBAKED: acquire: XErxjiqb lease expired -1.186993995s
+2025/03/20 09:23:34 VQFBAKED: acquire success 14 l 2.978008397s
+2025/03/20 09:23:40 VQFBAKED: Release 20
+2025/03/20 09:23:40 XErxjiqb: refresher: exit expired -7.422563867s
+2025/03/20 09:23:41 IqJHVjsW: acquire success 21 l 2.984528802s
+2025/03/20 09:23:47 NAaIOMcb: acquire: IqJHVjsW lease expired -1.19246442s
+2025/03/20 09:23:48 NAaIOMcb: acquire success 25 l 2.521727902s
+2025/03/20 09:23:53 NAaIOMcb: Release 30
+2025/03/20 09:23:53 IqJHVjsW: refresher: exit expired -7.130118022s
+2025/03/20 09:23:54 pwTkolYO: acquire success 32 l 2.761741697s
+2025/03/20 09:24:01 GAueeCFX: acquire: pwTkolYO lease expired -1.496813006s
+2025/03/20 09:24:01 GAueeCFX: acquire success 34 l 2.977558093s
+2025/03/20 09:24:06 GAueeCFX: Release 39
+2025/03/20 09:24:06 pwTkolYO: refresher: exit expired -6.843949894s
+2025/03/20 09:24:09 FIDtQSlF: acquire: GAueeCFX lease expired -15.508321ms
+2025/03/20 09:24:09 FIDtQSlF: acquire success 40 l 2.998464382s
+2025/03/20 09:24:16 wExaLSov: acquire: FIDtQSlF lease expired -1.874162487s
+2025/03/20 09:24:16 wExaLSov: acquire success 43 l 2.860519358s
+2025/03/20 09:24:21 wExaLSov: Release 48
+2025/03/20 09:24:21 FIDtQSlF: refresher: exit expired -6.924846198s
+  ... Passed --  68.4  1 10469 1186
+--- PASS: TestPartitionRecoveryUnreliableClerks5C (68.39s)
+PASS
+ok  	6.5840/shardkv1	351.349s