title: How to resolve featureCompatibilityVersion issue between MongoDB 3.6 and 4.2?
body: <p>I recently uninstalled MongoDB 3.6 and then installed MongoDB 4.2. When I navigated to MongoDB/Server/4.2/bin and executed <em>mongo</em>, I got the following error message:</p>
  
  <pre><code>$ mongod                                                                                                                                                                             
  2019-10-22T21:16:36.723-0400 I  CONTROL  [main] Automatically disabling TLS 1.0, to force-enable TLS 1.0 specify --sslDisabledProtocols 'none'                                       
  2019-10-22T21:16:37.217-0400 I  CONTROL  [initandlisten] MongoDB starting : pid=9376 port=27017 dbpath=C:\data\db\ 64-bit host=DESKTOP-LF34G1M                                       
  2019-10-22T21:16:37.217-0400 I  CONTROL  [initandlisten] targetMinOS: Windows 7/Windows Server 2008 R2                                                                               
  2019-10-22T21:16:37.217-0400 I  CONTROL  [initandlisten] db version v4.2.1                                                                                                           
  2019-10-22T21:16:37.218-0400 I  CONTROL  [initandlisten] git version: edf6d45851c0b9ee15548f0f847df141764a317e                                                                       
  2019-10-22T21:16:37.218-0400 I  CONTROL  [initandlisten] allocator: tcmalloc                                                                                                         
  2019-10-22T21:16:37.218-0400 I  CONTROL  [initandlisten] modules: none                                                                                                               
  2019-10-22T21:16:37.218-0400 I  CONTROL  [initandlisten] build environment:                                                                                                          
  2019-10-22T21:16:37.218-0400 I  CONTROL  [initandlisten]     distmod: 2012plus                                                                                                       
  2019-10-22T21:16:37.218-0400 I  CONTROL  [initandlisten]     distarch: x86_64                                                                                                        
  2019-10-22T21:16:37.219-0400 I  CONTROL  [initandlisten]     target_arch: x86_64                                                                                                     
  2019-10-22T21:16:37.219-0400 I  CONTROL  [initandlisten] options: {}                                                                                                                 
  2019-10-22T21:16:37.230-0400 I  STORAGE  [initandlisten] Detected data files in C:\data\db\ created by the 'wiredTiger' storage engine, so setting the active storage engine to 'wire
  dTiger'.                                                                                                                                                                             
  2019-10-22T21:16:37.231-0400 I  STORAGE  [initandlisten] wiredtiger_open config: create,cache_size=1498M,cache_overflow=(file_max=0M),session_max=33000,eviction=(threads_min=4,threa
  ds_max=4),config_base=false,statistics=(fast),log=(enabled=true,archive=true,path=journal,compressor=snappy),file_manager=(close_idle_time=100000,close_scan_interval=10,close_handle
  _minimum=250),statistics_log=(wait=0),verbose=[recovery_progress,checkpoint_progress],                                                                                               
  2019-10-22T21:16:37.295-0400 I  STORAGE  [initandlisten] WiredTiger message [1571793397:294196][9376:140704250879568], txn-recover: Recovering log 22 through 23                     
  2019-10-22T21:16:37.439-0400 I  STORAGE  [initandlisten] WiredTiger message [1571793397:438812][9376:140704250879568], txn-recover: Recovering log 23 through 23                     
  2019-10-22T21:16:37.561-0400 I  STORAGE  [initandlisten] WiredTiger message [1571793397:560490][9376:140704250879568], txn-recover: Main recovery loop: starting at 22/896 to 23/256 
  2019-10-22T21:16:37.712-0400 I  STORAGE  [initandlisten] WiredTiger message [1571793397:712086][9376:140704250879568], txn-recover: Recovering log 22 through 23                     
  2019-10-22T21:16:37.807-0400 I  STORAGE  [initandlisten] WiredTiger message [1571793397:806834][9376:140704250879568], txn-recover: Recovering log 23 through 23                     
  2019-10-22T21:16:37.883-0400 I  STORAGE  [initandlisten] WiredTiger message [1571793397:882664][9376:140704250879568], txn-recover: Set global recovery timestamp: (0,0)             
  2019-10-22T21:16:37.934-0400 I  RECOVERY [initandlisten] WiredTiger recoveryTimestamp. Ts: Timestamp(0, 0)                                                                           
  2019-10-22T21:16:37.943-0400 I  STORAGE  [initandlisten] Timestamp monitor starting                                                                                                  
  2019-10-22T21:16:37.947-0400 I  CONTROL  [initandlisten]                                                                                                                             
  2019-10-22T21:16:37.947-0400 I  CONTROL  [initandlisten] ** WARNING: Access control is not enabled for the database.                                                                 
  2019-10-22T21:16:37.948-0400 I  CONTROL  [initandlisten] **          Read and write access to data and configuration is unrestricted.                                                
  2019-10-22T21:16:37.948-0400 I  CONTROL  [initandlisten]                                                                                                                             
  2019-10-22T21:16:37.948-0400 I  CONTROL  [initandlisten] ** WARNING: This server is bound to localhost.                                                                              
  2019-10-22T21:16:37.948-0400 I  CONTROL  [initandlisten] **          Remote systems will be unable to connect to this server.                                                        
  2019-10-22T21:16:37.948-0400 I  CONTROL  [initandlisten] **          Start the server with --bind_ip &lt;address&gt; to specify which IP                                                   
  2019-10-22T21:16:37.949-0400 I  CONTROL  [initandlisten] **          addresses it should serve responses from, or with --bind_ip_all to                                              
  2019-10-22T21:16:37.949-0400 I  CONTROL  [initandlisten] **          bind to all interfaces. If this behavior is desired, start the                                                  
  2019-10-22T21:16:37.949-0400 I  CONTROL  [initandlisten] **          server with --bind_ip 127.0.0.1 to disable this warning.                                                        
  2019-10-22T21:16:37.949-0400 I  CONTROL  [initandlisten]                                                                                                                             
  2019-10-22T21:16:37.959-0400 I  SHARDING [initandlisten] Marking collection local.system.replset as collection version: &lt;unsharded&gt;                                                  
  2019-10-22T21:16:37.965-0400 F  CONTROL  [initandlisten] ** IMPORTANT: UPGRADE PROBLEM: Found an invalid featureCompatibilityVersion document (ERROR: BadValue: Invalid value for ver
  sion, found 3.6, expected '4.2' or '4.0'. Contents of featureCompatibilityVersion document in admin.system.version: { _id: "featureCompatibilityVersion", version: "3.6" }. See http:
  //dochub.mongodb.org/core/4.0-feature-compatibility.). If the current featureCompatibilityVersion is below 4.0, see the documentation on upgrading at http://dochub.mongodb.org/core/
  4.0-upgrade-fcv.                                                                                                                                                                     
  2019-10-22T21:16:37.965-0400 I  NETWORK  [initandlisten] shutdown: going to close listening sockets...                                                                               
  2019-10-22T21:16:37.966-0400 I  -        [initandlisten] Stopping further Flow Control ticket acquisitions.                                                                          
  2019-10-22T21:16:37.966-0400 I  STORAGE  [initandlisten] Deregistering all the collections                                                                                           
  2019-10-22T21:16:37.966-0400 I  STORAGE  [initandlisten] Timestamp monitor shutting down                                                                                             
  2019-10-22T21:16:37.967-0400 I  STORAGE  [initandlisten] WiredTigerKVEngine shutting down                                                                                            
  2019-10-22T21:16:37.967-0400 I  STORAGE  [initandlisten] Shutting down session sweeper thread                                                                                        
  2019-10-22T21:16:37.968-0400 I  STORAGE  [initandlisten] Finished shutting down session sweeper thread                                                                               
  2019-10-22T21:16:37.968-0400 I  STORAGE  [initandlisten] Shutting down journal flusher thread                                                                                        
  2019-10-22T21:16:38.037-0400 I  STORAGE  [initandlisten] Finished shutting down journal flusher thread                                                                               
  2019-10-22T21:16:38.037-0400 I  STORAGE  [initandlisten] Shutting down checkpoint thread                                                                                             
  2019-10-22T21:16:38.038-0400 I  STORAGE  [initandlisten] Finished shutting down checkpoint thread                                                                                    
  2019-10-22T21:16:38.038-0400 I  STORAGE  [initandlisten] Downgrading WiredTiger datafiles.                                                                                           
  2019-10-22T21:16:38.188-0400 I  STORAGE  [initandlisten] WiredTiger message [1571793398:187822][9376:140704250879568], txn-recover: Recovering log 23 through 24                     
  2019-10-22T21:16:38.273-0400 I  STORAGE  [initandlisten] WiredTiger message [1571793398:272644][9376:140704250879568], txn-recover: Recovering log 24 through 24                     
  2019-10-22T21:16:38.365-0400 I  STORAGE  [initandlisten] WiredTiger message [1571793398:365403][9376:140704250879568], txn-recover: Main recovery loop: starting at 23/2048 to 24/256
  
  2019-10-22T21:16:38.533-0400 I  STORAGE  [initandlisten] WiredTiger message [1571793398:532944][9376:140704250879568], txn-recover: Recovering log 23 through 24                     
  2019-10-22T21:16:38.642-0400 I  STORAGE  [initandlisten] WiredTiger message [1571793398:642615][9376:140704250879568], txn-recover: Recovering log 24 through 24                     
  2019-10-22T21:16:38.722-0400 I  STORAGE  [initandlisten] WiredTiger message [1571793398:722405][9376:140704250879568], txn-recover: Set global recovery timestamp: (0,0)             
  2019-10-22T21:16:39.004-0400 I  STORAGE  [initandlisten] shutdown: removing fs lock...                                                                                               
  2019-10-22T21:16:39.005-0400 I  CONTROL  [initandlisten] now exiting                                                                                                                 
  2019-10-22T21:16:39.005-0400 I  CONTROL  [initandlisten] shutting down with code:62     
  </code></pre>
  
  <p>The error which confuses me is:
  <code>UPGRADE PROBLEM: Found an invalid featureCompatibilityVersion document (ERROR: BadValue: Invalid value for version, found 3.6, expected '4.2' or '4.0'.</code>
  This does not seem to align with what I'm seeing below:</p>
  
  <pre><code>&gt; db.adminCommand( { getParameter: 1, featureCompatibilityVersion: 1 } )
  { "featureCompatibilityVersion" : { "version" : "4.2" }, "ok" : 1 }
  </code></pre>
  
  <p>How am I able to fix this featureCompatibilityVersion issue?</p>