How to set Java home in JSch to execute a command?

Question

I'm using Jcraft JSch to ssh into a remote machine and execute a command. As it's a non-interactive shell it's not finding Java home. How do I set Java home while using jsch? looking like

((ChannelExec) channel).setEnv("LANG", "UTF-8");
((ChannelExec) channel).setEnv("JAVA_HOME", "/blah/java/J8.0_64/");

is deprecated?

public String sendCommand(String command) {
  StringBuilder outputBuffer = new StringBuilder();

  try {
     Channel channel = sesConnection.openChannel("exec");
     ((ChannelExec) channel).setEnv("LANG", "UTF-8");
     ((ChannelExec) channel).setEnv("JAVA_HOME", "/blah/java/J8.0_64/");
     ((ChannelExec) channel).setCommand(command);
     InputStream commandOutput = channel.getInputStream();
     channel.connect();
     int readByte = commandOutput.read();

     while (readByte != 0xffffffff) {
        outputBuffer.append((char) readByte);
        readByte = commandOutput.read();
     }

     channel.disconnect();
  } catch (IOException ioX) {
     logWarning(ioX.getMessage());
     return null;
  } catch (JSchException jschX) {
     logWarning(jschX.getMessage());
     return null;
  }

  return outputBuffer.toString();
}

Error I'm getting while executing a command

JAVA_HOME not set and cannot find javac to deduce location, please set JAVA_HOME.

((ChannelExec) channel).setCommand(command); Could you edit your question to include an example of the actual command that you're trying to run here? — Kenster
@Kenster ((ChannelExec) channel).setCommand(command) is part of the test method I'm using. Actual test has the command in it and its trying to run a build. The problem is not with the command but looks like it needs the java home to run this command. — arthi

Martin Prikryl Martin Prikryl · Accepted Answer · 2019-09-17T06:51:34

ChannelExec.setEnv on JSch side probably works. But assuming you are connecting to an OpenSSH server, the server must be explicitly configured to allow you to set the LANG and JAVA_HOME environment variables using the AcceptEnv directive. What it probably is not.

You can try the same using PuTTY (Connection > Data > Environment variables). You will probably get "Server refused to set environment variables" message back.

See also How can I set environment variables when I ssh login to my Unix box by passing custom arguments?

Anyway, the correct solution is to fix your server configuration to set the environment correctly even for non-interactive sessions.

Or as a dirty workaround you can set the variables directly in your command:

JAVA_HOME=/blah/java/J8.0_64/; java ...

See also Certain Unix commands fail with "... not found", when executed through Java using JSch.

How to set Java home in JSch to execute a command?

2 Answers