--- a/src/Pure/System/linux.scala	Tue Dec 10 20:57:54 2019 +0100
+++ b/src/Pure/System/linux.scala	Tue Dec 10 21:05:07 2019 +0100
@@ -50,6 +50,7 @@
     override def toString: String = description
 
     def is_ubuntu: Boolean = id == "Ubuntu"
+    def is_ubuntu_18_04: Boolean = is_ubuntu && release == "18.04"
   }
 
 
--- a/src/Pure/Tools/phabricator.scala	Tue Dec 10 20:57:54 2019 +0100
+++ b/src/Pure/Tools/phabricator.scala	Tue Dec 10 21:05:07 2019 +0100
@@ -453,6 +453,9 @@
 
       val progress = new Console_Progress
 
+      val release = Linux.Release()
+      if (!release.is_ubuntu_18_04) error("Bad Linux version: Ubuntu 18.04 LTS required")
+
       phabricator_setup(name = name, root = root, repo = repo,
         package_update = package_update, progress = progress)
     })