Why Does JSch Throw a 'Command not found' Error When Executing Unix Commands, and How Can I Fix It?

Troubleshooting "Command not found" Errors When Executing Unix Commands Through Java with JSch

Problem:

Java code using JSch fails to execute certain Unix commands with a "command not found" error, despite being able to execute other simple commands successfully. Specifically, running an Ab-initio graph through Java using the "air sandbox run" command gives the error.

Possible Cause:

The JSch "exec" channel does not allocate a pseudo terminal (PTY) by default, resulting in a different set of startup scripts being sourced or different branches in scripts being taken based on the absence of the TERM environment variable. As a result, the environment may differ from an interactive SSH session, potentially leading to a PATH issue.

Solutions:

1. Fix the command: Use a full path to the "air" executable in the command string to avoid relying on the PATH environment variable.
2. Fix startup scripts: Make sure startup scripts set the PATH the same for both interactive and non-interactive sessions.
3. Use a login shell: Run the command through a login shell (with the "--login" switch) to inherit the current user's environment.
4. Modify the environment: Change the PATH environment variable within the command string to include the path to the "air" executable.
5. Force PTY allocation (not recommended): Enable pseudo terminal allocation for the "exec" channel using the setPty(true) method. However, this can lead to unintended consequences or side effects.

Additional Notes:

• Disabling the pseudo terminal allocation in an SSH client can reproduce the error.
• Other similar issues include commands behaving differently in JSch than in SSH terminals and difficulties exposing user environment variables to the "exec" channel.

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