src/Pure/System/linux.scala

--- a/src/Pure/System/linux.scala	Thu Dec 12 16:12:17 2019 +0100
+++ b/src/Pure/System/linux.scala	Sat Dec 14 16:56:26 2019 +0100
@@ -70,6 +70,9 @@
   def package_install(packages: List[String], progress: Progress = No_Progress): Unit =
     progress.bash("apt-get install -y -- " + Bash.strings(packages), echo = true).check
 
+  def package_installed(name: String): Boolean =
+    Isabelle_System.bash("dpkg-query -s " + Bash.string(name)).ok
+
 
   /* users */