#tips #security #limit_process @unixmens

ایجاد limit در دیتابیس های مختلف


// mysql
select col from tbl limit 20;

// Oracle
select col from tbl where rownum<=20;

// Microsoft SQL
select top 20 col from tbl;

#db #limit @unixmens

systemd-nspawn: A Sandbox for Your Processes

systemd-nspawn is a powerful tool in the Linux world, acting as a lightweight virtual machine or container for running processes in an isolated environment. Think of it as a "sandbox" where you can confine an application and its dependencies without affecting the host system.

Here's what makes `systemd-nspawn` special:

* Isolation: It creates a separate namespace for the running process, isolating its resources (like memory, network, etc.) from the host system. This prevents accidental interference and provides a secure environment for testing or running potentially risky applications.
* Customization: You can easily configure the systemd-nspawn environment with settings for memory, CPU, network, storage, and more. This allows you to tailor the environment to your specific needs.
* Lightweight: Unlike traditional virtual machines, systemd-nspawn is incredibly lightweight, minimizing the overhead and performance impact on the host system.
* Integration with systemd: Being tightly integrated with systemd, it benefits from its advanced features like service management, resource control, and logging.

How does it work?

systemd-nspawn essentially creates a new "machine" that runs a specified systemd-based image or a simple directory containing a root filesystem. When you run a process inside this machine, it executes in this isolated environment.

Key Commands:

* `systemd-nspawn --machine=my-machine --version=my-image --network=none`: This launches a new "my-machine" instance with the specified systemd image, disabling network access.
* `systemd-nspawn --machine=my-machine --bind-ro /path/to/app /path/to/app`: This launches a process in the "my-machine" environment, mounting the specified application directory read-only.
* `systemd-nspawn --machine=my-machine --memory=2G --cpu=1`: This launches a "my-machine" instance with a memory limit of 2GB and 1 CPU core allocated.

Advantages:

* Security: Provides a secure environment for running untrusted applications.
* Resource Control: Enables strict resource limits for memory, CPU, and other resources.
* Consistency: Creates a consistent environment for application development and testing.
* Rollback: Allows for easy rollback to a previous state if needed.

Limitations:

* Limited Hardware Support: systemd-nspawn doesn't support hardware virtualization, so it can't run applications requiring specialized hardware features.
* No Network Access (by default): Network access needs to be explicitly configured.
* Limited Support for Graphics: Graphical applications might not work as expected, as they often rely on specific hardware features.

Use Cases:

* Testing Applications: Create a safe environment for testing applications before deploying them on the production system.
* Running Legacy Applications: Run older applications that require specific system configurations or libraries.
* Isolation of Resources: Limit resource usage for specific processes to prevent them from impacting the host system.
* DevOps: Create consistent environments for development and testing, ensuring that applications behave identically across different systems.

Overall, `systemd-nspawn` is a powerful tool for isolating and controlling processes in a Linux environment. It offers significant advantages in terms of security, resource management, and consistency, making it an invaluable tool for developers, system administrators, and anyone who wants to run applications in a controlled environment.

#memory #ns
#limit

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