Java warnings when running Jenkins agents with Java 25

[richardlau]

e.g.

root@test-hetzner-ubuntu2404-x64-1 ~ # java -version
openjdk version "25.0.3" 2026-04-21
OpenJDK Runtime Environment (build 25.0.3+9-2-24.04.2-Ubuntu)
OpenJDK 64-Bit Server VM (build 25.0.3+9-2-24.04.2-Ubuntu, mixed mode, sharing)
root@test-hetzner-ubuntu2404-x64-1 ~ # systemctl status jenkins.service
● jenkins.service - Jenkins agent
     Loaded: loaded (/usr/lib/systemd/system/jenkins.service; enabled; preset: enabled)
     Active: active (running) since Tue 2026-06-09 06:50:43 CEST; 9h ago
   Main PID: 84335 (java)
      Tasks: 36 (limit: 76800)
     Memory: 201.5M (peak: 203.4M)
        CPU: 2min 54.671s
     CGroup: /system.slice/jenkins.service
             └─84335 /usr/bin/java -Xmx128m -jar /home/iojs/agent.jar -url https://ci.nodejs.org -name test-hetzner-ubuntu2404-x64-1 -secret e357745ed8badc1076eb653e7506902403e5c2e6f68e994f082e7685dc50a236

Jun 09 06:50:44 test-hetzner-ubuntu2404-x64-1 java[84335]: Jun 09, 2026 6:50:44 AM org.jenkinsci.remoting.protocol.impl.BIONetworkLayer$Reader run
Jun 09 06:50:44 test-hetzner-ubuntu2404-x64-1 java[84335]: INFO: Waiting for ProtocolStack to start.
Jun 09 06:50:45 test-hetzner-ubuntu2404-x64-1 java[84335]: Jun 09, 2026 6:50:45 AM hudson.remoting.Launcher$CuiListener status
Jun 09 06:50:45 test-hetzner-ubuntu2404-x64-1 java[84335]: INFO: Remote identity confirmed: 4f:22:06:c2:64:29:f3:3f:6d:7c:d7:01:f2:18:bb:93
Jun 09 06:50:45 test-hetzner-ubuntu2404-x64-1 java[84335]: Jun 09, 2026 6:50:45 AM hudson.remoting.Launcher$CuiListener status
Jun 09 06:50:45 test-hetzner-ubuntu2404-x64-1 java[84335]: INFO: Connected
Jun 09 06:51:01 test-hetzner-ubuntu2404-x64-1 java[84335]: WARNING: A restricted method in java.lang.System has been called
Jun 09 06:51:01 test-hetzner-ubuntu2404-x64-1 java[84335]: WARNING: java.lang.System::load has been called by com.sun.jna.Native in an unnamed module
Jun 09 06:51:01 test-hetzner-ubuntu2404-x64-1 java[84335]: WARNING: Use --enable-native-access=ALL-UNNAMED to avoid a warning for callers in this module
Jun 09 06:51:01 test-hetzner-ubuntu2404-x64-1 java[84335]: WARNING: Restricted methods will be blocked in a future release unless native access is enabled
root@test-hetzner-ubuntu2404-x64-1 ~ #

I don't think this causes us problems today, but may be a problem with a "future release" of Java.

[richardlau]

Upstream Jenkins issue: jenkinsci/jenkins#26518