Java – jcmd not found?

By mkyong | Updated: May 11, 2020

Viewed: 4,805 (+28 pv/w)

Tags: docker jcmd jfr

The jcmd is available at the JDK/bin, not JRE. Make sure the installed Java is JDK, not JRE.

Let review the following example, try to use jcmd to enable Java Flight Recorder inside a docker container.

1. DockerFile

A simple Dokcerfile.

FROM adoptopenjdk/openjdk11:alpine-jre

ARG JAR_FILE=target/markdown.jar

WORKDIR /opt/app

COPY ${JAR_FILE} app.jar

ENTRYPOINT ["java","-jar","app.jar"]

2. Docker + jcmd

Access into the docker container’s shell, try jcmd to enable the Java Flight Recorder, but hits command not found?

$ docker exec -it 3d1588519433 sh

/opt/app # jcmd
sh: jcmd: not found

/opt/app # which java
/opt/java/openjdk/bin/java

/opt/app # java -version
openjdk version "11.0.7" 2020-04-14
OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.7+10)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.7+10, mixed mode)
/opt/app #

Solution

Again, the jcmd is available at the JDK/bin, not JRE. The Dockerfile is using the openjdk11:alpine-jre, JRE image.

FROM adoptopenjdk/openjdk11:alpine-jre

To fix it, try to install the JDK image.

FROM adoptopenjdk/openjdk11:alpine

Test it again.

$ docker exec -it <container ID> sh

/opt/app # jcmd

48 jdk.jcmd/sun.tools.jcmd.JCmd
1 app.jar

Done.

References

• docker exec reference
• How to access the Docker container’s shell?
• Java 11 – Java Flight Recorder
• Docker and Java Application Examples