Fix error message when package install fails due to missing Java (#36077)

Currently is `java` is not in $PATH the preinst script fails
prematurely and prevents an appropriate message from getting displayed
to the user.

Make package installation more user friendly when java is not in
$PATH and add a test for it.

Also use a she-bang in the preinst script, as, at least in Debian,
maintainer scripts must start with the #! convention [1].

Relates #31845

[1] https://www.debian.org/doc/debian-policy/ch-maintainerscripts.html

distribution/packages/src/common/scripts/preinst

@@ -1,3 +1,4 @@
+#!/bin/bash
 #
 # This script is executed in the pre-installation phase
 #
@@ -9,16 +10,22 @@
 #       $1=1       : indicates an new install
 #       $1=2       : indicates an upgrade
 
+err_exit() {
+    echo "$@" >&2
+    exit 1
+}
+
 # Check for these at preinst time due to failures in postinst if they do not exist
 if [ -x "$JAVA_HOME/bin/java" ]; then
     JAVA="$JAVA_HOME/bin/java"
+elif command -v java; then
+    JAVA=`command -v java`
 else
-    JAVA=`which java`
+    JAVA=""
 fi
 
 if [ -z "$JAVA" ]; then
-    echo "could not find java; set JAVA_HOME or ensure java is in PATH"
-    exit 1
+    err_exit "could not find java; set JAVA_HOME or ensure java is in PATH"
 fi
 
 case "$1" in
@@ -75,8 +82,7 @@ case "$1" in
     ;;
 
     *)
-        echo "pre install script called with unknown argument \`$1'" >&2
-        exit 1
+        err_exit "pre install script called with unknown argument \`$1'"
     ;;
 esac
 

distribution/src/bin/elasticsearch-env

@@ -45,7 +45,7 @@ else
 fi
 
 if [ ! -x "$JAVA" ]; then
-  echo "could not find java; set JAVA_HOME or ensure java is in PATH"
+  echo "could not find java; set JAVA_HOME or ensure java is in PATH" >&2
   exit 1
 fi
 

qa/vagrant/src/main/java/org/elasticsearch/packaging/test/ArchiveTestCase.java

@@ -111,7 +111,7 @@ public abstract class ArchiveTestCase extends PackagingTestCase {
                 sh.run("chmod -x '" + javaPath + "'");
                 final Result runResult = sh.runIgnoreExitCode(bin.elasticsearch.toString());
                 assertThat(runResult.exitCode, is(1));
-                assertThat(runResult.stdout, containsString("could not find java; set JAVA_HOME or ensure java is in PATH"));
+                assertThat(runResult.stderr, containsString("could not find java; set JAVA_HOME or ensure java is in PATH"));
             } finally {
                 sh.run("chmod +x '" + javaPath + "'");
             }

qa/vagrant/src/main/java/org/elasticsearch/packaging/test/PackageTestCase.java

@@ -70,6 +70,7 @@ public abstract class PackageTestCase extends PackagingTestCase {
             mv(originalJavaPath, relocatedJavaPath);
             final Result installResult = runInstallCommand(distribution());
             assertThat(installResult.exitCode, is(1));
+            assertThat(installResult.stderr, containsString("could not find java; set JAVA_HOME or ensure java is in PATH"));
         } finally {
             mv(relocatedJavaPath, originalJavaPath);
         }