Attach to a detached process using `reptyr` (external tool) from a script

How to Attach to a Detached Process Using `reptyr` in a Linux Bash Script?

In managing Linux servers or local machines, one common challenge is handling processes that have been started in one terminal and needing them to be controlled from another session. This might happen when you accidentally close a terminal or disconnect from an SSH session, leaving a vital process running detached. This guide explores how to use reptyr, a handy utility tool, to reattach these detached processes to a new terminal.

Q: What is `reptyr`?

A: reptyr is a utility in Linux that allows you to take an already running process and attach it to a new terminal. It's particularly useful if you started a long-running process in one SSH or terminal session and need to move it to another after disconnecting or accidentally closing the original session.

Q: How do I install `reptyr`?

A: Installing reptyr is straightforward on most Linux distributions. On Ubuntu or Debian systems, you can install it using:

sudo apt-get install reptyr

For Fedora or CentOS, use:

sudo yum install reptyr

Q: How can I use `reptyr` to attach to a detached process?

A: Follow these steps to attach to a detached process: 1. Find the PID (Process ID) of the detached process using tools like ps, top or pgrep. 2. Use the reptyr command followed by the PID to reattach the process: bash sudo reptyr PID

Background and Examples

Understanding Processes

Every running application on a Linux system is considered a process, each uniquely identified by a PID. Sometimes, particularly when accessing servers, you might need to run commands that take a long time to complete. If you start such a process within a terminal session and disconnect, the process continues but may become unmanageable because it's detached from any terminal.

Simple Use Case with `reptyr`

Let's consider a simple example of starting a lengthy operation, such as a large file download using wget:

wget -b http://example.com/largefile.iso

If you've issued this command and detached your terminal, you can reclaim control over this process. First, find the PID:

ps aux | grep wget

Then, use reptyr:

sudo reptyr PID

Executable Script Demonstration

#!/bin/bash
# Script to demonstrate reattaching to a detached process using reptyr

# Starting a long-running process
echo "Starting a long-running process...;"
sleep 300 &
PID=$!

echo "Process started in background with PID: $PID"
echo "Detaching the process... (simulate closing terminal)"
disown $PID

# Wait a couple of seconds to mimic exiting and logging back in
sleep 2

echo "Simulate re-login and reattach the process using reptyr"
sudo reptyr $PID

# Now you would have control over the "sleep 300" process again

Summary Conclusion

Handling detached processes efficiently can make managing long-running tasks on Linux more manageable. reptyr provides a powerful, yet simple solution for these scenarios. Whether used through interactive shells or integrated within scripts for automation, reptyr ensures that important processes are never out of control just because of a disconnected session or a closed terminal. Knowing how to use such tools enhances your capabilities in system administration and process management in Unix-like environments.

How to Attach to a Detached Process Using reptyr in a Linux Bash Script?

Q: What is reptyr?

Q: How do I install reptyr?

Q: How can I use reptyr to attach to a detached process?