diff --git a/src/Pure/System/linux.scala b/src/Pure/System/linux.scala
new file mode 100644
--- /dev/null
+++ b/src/Pure/System/linux.scala
@@ -0,0 +1,49 @@
+/*  Title:      Pure/System/linux.scala
+    Author:     Makarius
+
+Specific support for Linux, notably Ubuntu/Debian.
+*/
+
+package isabelle
+
+
+import scala.util.matching.Regex
+
+
+object Linux
+{
+  /* check system */
+
+  def check_system(): Unit =
+    if (!Platform.is_linux) error("Not a Linux system")
+
+  def check_system_root(): Unit =
+  {
+    check_system()
+    if (Isabelle_System.bash("id -u").check.out != "0") error("Not running as superuser (root)")
+  }
+
+
+  /* release */
+
+  object Release
+  {
+    private val ID = """^Distributor ID:\s*(\S.*)$""".r
+    private val RELEASE = """^Release:\s*(\S.*)$""".r
+    private val DESCRIPTION = """^Description:\s*(\S.*)$""".r
+
+    def apply(): Release =
+    {
+      val lines = Isabelle_System.bash("lsb_release -a").check.out_lines
+      def find(R: Regex): String = lines.collectFirst({ case R(a) => a }).getOrElse("Unknown")
+      new Release(find(ID), find(RELEASE), find(DESCRIPTION))
+    }
+  }
+
+  final class Release private(val id: String, val release: String, val description: String)
+  {
+    override def toString: String = description
+
+    def is_ubuntu: Boolean = id == "Ubuntu"
+  }
+}
diff --git a/src/Pure/build-jars b/src/Pure/build-jars
--- a/src/Pure/build-jars
+++ b/src/Pure/build-jars
@@ -1,320 +1,321 @@
 #!/usr/bin/env bash
 #
 # Author: Makarius
 #
 # build-jars - build Isabelle/Scala
 #
 # Requires proper Isabelle settings environment.
 
 ## sources
 
 declare -a SOURCES=(
   Admin/afp.scala
   Admin/build_cygwin.scala
   Admin/build_doc.scala
   Admin/build_fonts.scala
   Admin/build_history.scala
   Admin/build_jdk.scala
   Admin/build_log.scala
   Admin/build_polyml.scala
   Admin/build_release.scala
   Admin/build_status.scala
   Admin/check_sources.scala
   Admin/ci_profile.scala
   Admin/components.scala
   Admin/isabelle_cronjob.scala
   Admin/isabelle_devel.scala
   Admin/jenkins.scala
   Admin/other_isabelle.scala
   Concurrent/consumer_thread.scala
   Concurrent/counter.scala
   Concurrent/event_timer.scala
   Concurrent/future.scala
   Concurrent/mailbox.scala
   Concurrent/par_list.scala
   Concurrent/standard_thread.scala
   Concurrent/synchronized.scala
   GUI/color_value.scala
   GUI/gui.scala
   GUI/gui_thread.scala
   GUI/popup.scala
   GUI/wrap_panel.scala
   General/antiquote.scala
   General/bytes.scala
   General/cache.scala
   General/codepoint.scala
   General/comment.scala
   General/completion.scala
   General/csv.scala
   General/date.scala
   General/exn.scala
   General/file.scala
   General/file_watcher.scala
   General/graph.scala
   General/graph_display.scala
   General/graphics_file.scala
   General/http.scala
   General/json.scala
   General/linear_set.scala
   General/logger.scala
   General/long_name.scala
   General/mercurial.scala
   General/multi_map.scala
   General/output.scala
   General/path.scala
   General/position.scala
   General/pretty.scala
   General/properties.scala
   General/rdf.scala
   General/scan.scala
   General/sha1.scala
   General/sql.scala
   General/ssh.scala
   General/symbol.scala
   General/time.scala
   General/timing.scala
   General/untyped.scala
   General/url.scala
   General/utf8.scala
   General/uuid.scala
   General/value.scala
   General/word.scala
   General/xz.scala
   Isar/document_structure.scala
   Isar/keyword.scala
   Isar/line_structure.scala
   Isar/outer_syntax.scala
   Isar/parse.scala
   Isar/token.scala
   ML/ml_console.scala
   ML/ml_lex.scala
   ML/ml_process.scala
   ML/ml_statistics.scala
   ML/ml_syntax.scala
   PIDE/byte_message.scala
   PIDE/command.scala
   PIDE/command_span.scala
   PIDE/document.scala
   PIDE/document_id.scala
   PIDE/document_status.scala
   PIDE/editor.scala
   PIDE/headless.scala
   PIDE/line.scala
   PIDE/markup.scala
   PIDE/markup_tree.scala
   PIDE/protocol.scala
   PIDE/protocol_handlers.scala
   PIDE/protocol_message.scala
   PIDE/prover.scala
   PIDE/query_operation.scala
   PIDE/rendering.scala
   PIDE/resources.scala
   PIDE/session.scala
   PIDE/text.scala
   PIDE/xml.scala
   PIDE/yxml.scala
   ROOT.scala
   System/bash.scala
   System/command_line.scala
   System/cygwin.scala
   System/distribution.scala
   System/getopts.scala
   System/invoke_scala.scala
   System/isabelle_charset.scala
   System/isabelle_fonts.scala
   System/isabelle_process.scala
   System/isabelle_system.scala
   System/isabelle_tool.scala
+  System/linux.scala
   System/numa.scala
   System/options.scala
   System/platform.scala
   System/posix_interrupt.scala
   System/process_result.scala
   System/progress.scala
   System/system_channel.scala
   System/tty_loop.scala
   Thy/bibtex.scala
   Thy/export.scala
   Thy/export_theory.scala
   Thy/file_format.scala
   Thy/html.scala
   Thy/latex.scala
   Thy/present.scala
   Thy/sessions.scala
   Thy/thy_element.scala
   Thy/thy_header.scala
   Thy/thy_syntax.scala
   Tools/build.scala
   Tools/build_docker.scala
   Tools/check_keywords.scala
   Tools/debugger.scala
   Tools/doc.scala
   Tools/dump.scala
   Tools/fontforge.scala
   Tools/main.scala
   Tools/mkroot.scala
   Tools/print_operation.scala
   Tools/profiling_report.scala
   Tools/server.scala
   Tools/server_commands.scala
   Tools/simplifier_trace.scala
   Tools/spell_checker.scala
   Tools/task_statistics.scala
   Tools/update.scala
   Tools/update_cartouches.scala
   Tools/update_comments.scala
   Tools/update_header.scala
   Tools/update_then.scala
   Tools/update_theorems.scala
   library.scala
   pure_thy.scala
   term.scala
   term_xml.scala
   thm_name.scala
   ../Tools/Graphview/graph_file.scala
   ../Tools/Graphview/graph_panel.scala
   ../Tools/Graphview/graphview.scala
   ../Tools/Graphview/layout.scala
   ../Tools/Graphview/main_panel.scala
   ../Tools/Graphview/metrics.scala
   ../Tools/Graphview/model.scala
   ../Tools/Graphview/mutator.scala
   ../Tools/Graphview/mutator_dialog.scala
   ../Tools/Graphview/mutator_event.scala
   ../Tools/Graphview/popups.scala
   ../Tools/Graphview/shapes.scala
   ../Tools/Graphview/tree_panel.scala
   ../Tools/VSCode/src/build_vscode.scala
   ../Tools/VSCode/src/channel.scala
   ../Tools/VSCode/src/document_model.scala
   ../Tools/VSCode/src/dynamic_output.scala
   ../Tools/VSCode/src/grammar.scala
   ../Tools/VSCode/src/preview_panel.scala
   ../Tools/VSCode/src/protocol.scala
   ../Tools/VSCode/src/server.scala
   ../Tools/VSCode/src/state_panel.scala
   ../Tools/VSCode/src/vscode_javascript.scala
   ../Tools/VSCode/src/vscode_rendering.scala
   ../Tools/VSCode/src/vscode_resources.scala
   ../Tools/VSCode/src/vscode_spell_checker.scala
 )
 
 
 ## diagnostics
 
 PRG="$(basename "$0")"
 
 function usage()
 {
   echo
   echo "Usage: isabelle $PRG [OPTIONS]"
   echo
   echo "  Options are:"
   echo "    -f           fresh build"
   echo
   exit 1
 }
 
 function fail()
 {
   echo "$1" >&2
   exit 2
 }
 
 [ -z "$ISABELLE_HOME" ] && fail "Missing Isabelle settings environment"
 
 
 ## process command line
 
 # options
 
 FRESH=""
 
 while getopts "f" OPT
 do
   case "$OPT" in
     f)
       FRESH=true
       ;;
     \?)
       usage
       ;;
   esac
 done
 
 shift $(($OPTIND - 1))
 
 
 # args
 
 [ "$#" -ne 0 ] && usage
 
 
 ## build
 
 TARGET_DIR="$ISABELLE_HOME/lib/classes"
 TARGET="$TARGET_DIR/Pure.jar"
 
 declare -a UPDATED=()
 
 if [ -n "$FRESH" ]; then
   OUTDATED=true
 else
   OUTDATED=false
   if [ ! -e "$TARGET" ]; then
     OUTDATED=true
   else
     for DEP in "${SOURCES[@]}"
     do
       [ ! -e "$DEP" ] && fail "Missing file: $DEP"
       [ "$DEP" -nt "$TARGET" ] && {
         OUTDATED=true
         UPDATED["${#UPDATED[@]}"]="$DEP"
       }
     done
   fi
 fi
 
 if [ "$OUTDATED" = true ]
 then
   echo "### Building Isabelle/Scala ..."
 
   [ "${#UPDATED[@]}" -gt 0 ] && {
     echo "Changed files:"
     for FILE in "${UPDATED[@]}"
     do
       echo "  $FILE"
     done
   }
 
   rm -f "$TARGET"
   rm -rf classes && mkdir classes
 
   SCALAC_OPTIONS="$ISABELLE_SCALAC_OPTIONS -d classes"
 
   (
     classpath classes
     export CLASSPATH="$(platform_path "$ISABELLE_CLASSPATH")"
 
     isabelle_scala scalac $SCALAC_OPTIONS "${SOURCES[@]}" || \
       fail "Failed to compile sources"
   ) || exit "$?"
 
   mkdir -p "$TARGET_DIR" || fail "Failed to create directory $TARGET_DIR"
 
   pushd classes >/dev/null
 
   CHARSET_SERVICE="META-INF/services/java.nio.charset.spi.CharsetProvider"
   mkdir -p "$(dirname "$CHARSET_SERVICE")"
   echo isabelle.Isabelle_Charset_Provider > "$CHARSET_SERVICE"
 
   cp "$ISABELLE_HOME/lib/logo/isabelle_transparent-32.gif" isabelle/.
   cp "$ISABELLE_HOME/lib/logo/isabelle_transparent.gif" isabelle/.
 
   isabelle_jdk jar cfe "$(platform_path "$TARGET")" isabelle.Main META-INF isabelle || \
     fail "Failed to produce $TARGET"
 
   popd >/dev/null
 
   rm -rf classes
 fi