Update README

README.md

@@ -137,20 +137,36 @@ Stop jails
 ----------
 `gocage stop test`
 
-
 Update jails  
 ----------
 To update jail patch version, use gocage update :  
 `gocage update test`
 
+Update basejails/releases  
+----------
+To update basejails, you need to update the release they are base on. Specify release with -r, and the datastore storing concerned release with -d :  
+`gocage update -d fastgocage -r 14.1-RELEASE`
 
 Upgrade jails  
 ----------
 To upgrade jail to newer release, use gocage upgrade :  
 `gocage upgrade -r 13.2-RELEASE test`
   
-A pre-upgrade snapshot wil be made so we can rollback if needed.  
+A pre-upgrade snapshot wil be made so you can rollback if needed.  
 
+Upgrading basejail/release
+----------
+Upgrading basejails currently needs to be done manually, for each jail.  
+The idea is to stop the jail, change the content of its fstab file to point to the new release, then start jail.  
+If one change the fstab while the jail is running, its system directories won't be unmounted at stop time and this will provoke stop errors.  
+To minimize downtime, the change could be scripted:  
+`gocage stop jail1
+sed -i .bak 's/14.0-RELEASE/14.1-RELEASE/' /iocage/jails/jail1/fstab
+# Avoid race-condition by waiting for the update in fstab
+until grep -q 14.1-RELEASE /iocage/jails/jail1/fstab; do sleep 0.2; done
+gocage start jail1`
+
+You can now update ports.
 
 Delete jails  
 ----------