How to Send Input to a Java Application Using stdin via /proc/{pid}/fd/0

How can I send commands to a Java application running with the command java -jar using stdin via /proc/{pid}/fd/0?

echo "input" > /proc/{pid}/fd/0

In Linux-based systems, you can manipulate process inputs through the /proc filesystem, which provides a direct way to interact with process file descriptors. This guide explains how to send input to a running Java application launched with 'java -jar' using stdin via /proc/{pid}/fd/0.

# Identify the PID of your Java application
ps aux | grep java

# Replace {pid} with the actual PID in the command below
echo "input" > /proc/{pid}/fd/0

Causes

• The Java application is designed to read from standard input (stdin).
• You have the process ID (PID) of the running Java application.

Solutions

• Identify the PID of the Java process using a command like `ps aux | grep java`.
• Construct the command to send input, replacing `{pid}` with the actual process ID.
• Use the echo command (or any other command that generates output) to send input: `echo "your_input" > /proc/{pid}/fd/0`.
• Ensure that your input format matches what the Java application expects.

Mistake: Not having the correct permissions to write to the process's stdin.

Solution: Ensure you have the necessary permissions or run the command as the same user who started the Java application.

Mistake: The Java application not consuming input as expected.

Solution: Verify that the application is designed to read from stdin at the time you are sending input.