diff --git a/weed-shell.md b/weed-shell.md
index 4de793c..3c89409 100644
--- a/weed-shell.md
+++ b/weed-shell.md
@@ -24,6 +24,8 @@ Type:	"help <command>" for help on <command>
   fs.mv                         	# move or rename a file or a folder
   fs.pwd                        	# print out current directory
   fs.tree                       	# recursively list all files under a directory
+  lock                          	# lock in order to exclusively manage the cluster
+  unlock                        	# unlock the cluster-wide lock
   volume.balance                	# balance all volumes among volume servers
   volume.configure.replication  	# change volume replication value
   volume.copy                   	# copy a volume from one volume server to another volume server
@@ -35,10 +37,9 @@ Type:	"help <command>" for help on <command>
   volume.move                   	# move a live volume from one volume server to another volume server
   volume.tier.download          	# download the dat file of a volume from a remote tier
   volume.tier.upload            	# upload the dat file of a volume to a remote tier
-  volume.unmount                	# unmount a volume from one volume server
+  volume.unmount                	# unmount a volume from one volume server```
 ```
 
-
 For example:
 ```
 $ weed shell
@@ -46,18 +47,28 @@ $ weed shell
 block:2715	byte:  31895432	/objects
 ```
 
+For most volume operations, you would need to prevent other possible concurrent operations. To do so, lock this way:
+```
+> lock
+> volume.fix.replication
+> volume.mount ...
+> ...
+> unlock
+```
+
 Another example: sometimes one of your volume server may go down, and a new volume server is added. Here is the command you can run to fix volumes that are under replicated:
+
 ```
 # check any volume that are under replicated, and there are servers that meet the replica placement requirement
-$ echo "volume.fix.replication -n " | weed shell
+$ echo "lock; volume.fix.replication -n ; unlock" | weed shell
 replicating volume 241 001 from localhost:8080 to dataNode 127.0.0.1:7823 ...
 
 # found one, let's really do it
-$ echo "volume.fix.replication" | weed shell
+$ echo "lock; volume.fix.replication ; unlock" | weed shell
 replicating volume 241 001 from localhost:8080 to dataNode 127.0.0.1:7823 ...
 
 # all volumes are replicated now
-$ echo "volume.fix.replication -n" | weed shell
+$ echo "lock; volume.fix.replication -n ; unlock" | weed shell
 no under replicated volumes
 
 ```
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