Add section about possible cleanup tasks.

README.md

@@ -93,6 +93,18 @@ Mount the vault with:
 osascript -e 'mount volume "http://localhost:8080/demoVault/"'
 ```
 
+## Manual Cleanup
+
+If a handle to a resource inside the unlocked vault is still open, a graceful unmount is not possible and cryptomator-cli just terminates without executing possible cleanup tasks.
+In that case the message "GRACEFUL UNMOUNT FAILED" is printed to the console/stdout.
+
+On a linux OS with the `LinuxFuseMountProvider`, the manual cleanup task is to unmount and free the mountpoint:
+```
+fusermount -u /path/to/former/mountpoint
+```
+
+For other OSs, there is no cleanup necessary.
+
 ## License
 
 This project is dual-licensed under the AGPLv3 for FOSS projects as well as a commercial license derived from the LGPL for independent software vendors and resellers. If you want to use this library in applications, that are *not* licensed under the AGPL, feel free to contact our [support team](https://cryptomator.org/help/).

src/main/java/org/cryptomator/cli/Unlock.java

@@ -39,6 +39,7 @@ public class Unlock implements Callable<Integer> {
     private static final byte[] PEPPER = new byte[0];
     private static final String CONFIG_FILE_NAME = "vault.cryptomator";
     private static final String MASTERKEY_FILE_NAME = "masterkey.cryptomator";
+    private static final String FORCED_UNMOUNT_MSG = "GRACEFUL UNMOUNT FAILED. Please check if manual cleanups are necessary";
 
     @Spec
     Model.CommandSpec spec;
@@ -86,7 +87,7 @@ public Integer call() throws Exception {
             Runtime.getRuntime().addShutdownHook(new Thread(() -> teardown(mount)));
             Thread.currentThread().join();
         } catch (UnmountFailedException e) {
-            LOG.error("Regular unmount failed. Just terminating process...", e);
+            LOG.error(FORCED_UNMOUNT_MSG, e);
         }
         return 0;
     }
@@ -95,7 +96,7 @@ private void teardown(Mount m) {
         try {
             m.close();
         } catch (IOException | UnmountFailedException e) {
-            LOG.error("Graceful unmount failed, possible cleanup not executed.", e);
+            LOG.error(FORCED_UNMOUNT_MSG, e);
         }
     }