Use `sysdig` to trace file accesses by a script

Tracing File Accesses in Linux Using `sysdig`

In the world of Linux, understanding what happens behind the scenes when a script runs can be crucial for debugging and optimizing applications. One powerful tool for tracing system calls and events directly from the Linux kernel is sysdig. In this blog post, we will explore how sysdig can be used to monitor file accesses by a script.

Q&A on Using `sysdig` to Trace file Accesses by a Script

Q1: What is `sysdig`?

A1: sysdig is an open-source system monitoring and activity tracing tool. Unlike traditional tools, it can capture system calls and events directly from the kernel’s syscall interface. This ability makes it extremely powerful for deep system analysis of a running Linux system.

Q2: How can I install `sysdig`?

A2: Installation of sysdig varies based on your Linux distribution. For Debian-based systems like Ubuntu, you can install it using:

sudo apt-get install -y sysdig

For Red Hat-based systems, use:

sudo yum install -y sysdig

Q3: How do I use `sysdig` to monitor file accesses by a script?

A3: To monitor file accesses, sysdig can be invoked with specific filters. The basic syntax to track file open operations by a script looks like this:

sudo sysdig -p "%proc.name %evt.type %evt.arg.name" "proc.name=<script_name> and evt.type=open"

Replace <script_name> with the name of your script. This command filters the events to show only the process name, event type, and the name of the file that the process tried to open.

Background and Further Explanation

sysdig works by interacting directly with the Linux kernel modules to gather data, which allows it to have minimal performance overhead compared to userspace tracing tools. This makes it suitable for production environments where detailed logging and minimal performance impact are crucial.

Here are some other basic sysdig commands to get you started:

List all system events: sudo sysdig
Filter by process name: sudo sysdig proc.name=httpd
Show file reads and writes: sudo sysdig -p"%evt.type %fd.name" evt.is_io=true

Example Script and Usage

Let's use a simple Bash script and demonstrate how sysdig can trace its file interactions.

Create the Script: test_script.sh

#!/bin/bash
echo "Creating a new file..."
touch /tmp/test_file.txt
echo "Writing to file..."
echo "Hello, sysdig!" > /tmp/test_file.txt
echo "Done."

Make it executable:

chmod +x test_script.sh

Trace the Script: Use sysdig to monitor this script's activity.

sudo sysdig -p "%proc.name %evt.type %evt.arg.name" "proc.name=test_script.sh and evt.type=open"

Run the test_script.sh in another terminal while sysdig is monitoring.

Conclusion

In this post, we've explored how to use sysdig, a powerful Linux tool, to trace file accesses by a script. Such capabilities are exceptionally useful for developers and system administrators seeking to pinpoint issues related to file handling, enhance security by monitoring suspicious activities, and optimize system performance by analyzing real-time data from the kernel. By incorporating sysdig into your debugging and monitoring workflows, you can gain deep insights into the behaviors and performance of your applications at the system level.

Tracing File Accesses in Linux Using sysdig

Q&A on Using sysdig to Trace file Accesses by a Script

Q1: What is sysdig?

Q2: How can I install sysdig?

Q3: How do I use sysdig to monitor file accesses by a script?