Скачать или смотреть How to Resume a Killed Job in UNIX Shell: A Guide for MacOS Users

Learn how to handle the unfortunate situation of accidentally killing a process in UNIX Shell and discover preventive strategies to avoid future mishaps.
---
This video is based on the question https://stackoverflow.com/q/67736649/ asked by the user 'SoleGoodman' ( https://stackoverflow.com/u/15808649/ ) and on the answer https://stackoverflow.com/a/67738057/ provided by the user 'Dominique' ( https://stackoverflow.com/u/4279155/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Resume a killed job on shell UNIX

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Resume a Killed Job in UNIX Shell: A Guide for MacOS Users

Introduction

Imagine pouring your time into a lengthy process, only to accidentally halt it by pressing ctrl+ C instead of ctrl+ Z. This painful moment is precisely what Pierre experienced—a simulation that lasted 50 hours, suddenly halted before completion due to a simple keystroke error. In this guide, we’ll explore the unfortunate truth behind resuming a killed job and how you might prevent this from happening in the future.

Understanding the Problem

When you run processes in a UNIX shell, you typically have certain control commands at your disposal to manage these processes. The two most common controls are:

ctrl+ C: This command sends an interrupt signal and immediately terminates the running process.

ctrl+ Z: This command pauses the process and sends it to the background, allowing you to resume it later with the fg command.

In Pierre’s case, the accidental use of ctrl+ C spelled doom for a process that was nearly complete. The question now arises: Is there any way to resume a terminated job?

The Solution: Why You Can't Resume a Killed Job

The Harsh Reality

Unfortunately, the answer to Pierre’s inquiry is a definitive no. Once a job has been killed using ctrl+ C, it cannot be resumed. Here's why:

Process Termination: When you kill a process, its execution state is lost forever. The system releases all the resources allocated to it, and any temporary data is wiped clean.

No Resume Option: Resuming a process implies that it can continue from where it left off, but once terminated, there is no remaining context or state for the operating system to refer to in order to continue execution.

Alternative: Restarting with State Management

However, there is a method that can mitigate the consequences of accidentally killing a process before it occurs. By setting up your processes to periodically save their execution state, you can easily restart them without losing progress. Here’s how you can do this:

Design with Checkpoints:

Structure your process to record its progress at certain intervals (e.g., 10% completion marks).

Save the last completed state in a log or temporary file.

Restarting at a Checkpoint:

If your process is interrupted, you can start a new instance of it from the last completed checkpoint.

For example, instead of restarting from scratch, you can execute your process like this:

[[See Video to Reveal this Text or Code Snippet]]

Note: This is not a true resumption; you are merely starting a new instance from the last recorded point.

Prevention Tips for Future Tasks

To assist with avoiding this scenario in the future, consider implementing these strategies:

Use ctrl+ Z Instead: Familiarize yourself with pausing processes over terminating them when in doubt.

Implement Auto-save Features: Design programs that save progress regularly.

Monitor Processes: Use tools and commands (like jobs, bg, and fg) to monitor and control your processes effectively.

Conclusion

While we have explored the unfortunate truth of process management in UNIX—once terminated, a job is gone forever—there are effective strategies to mitigate this risk in the future. By designing with checkpoints and understanding process controls, you can avoid the heartache that Pierre experienced. Always remember to handle those keystrokes wisely!