What is netfilter primarily used for?

Netfilter is primarily a framework provided by the Linux kernel that allows developers to insert hooks into the network stack, enabling the implementation of firewall technology. It allows for the filtering of packets, NAT (Network Address Translation), and connection tracking, which are essential for creating firewalls and network address translation systems.

This capability makes it integral to the functioning of various firewall applications, such as iptables, which use these hooks defined by netfilter to control the flow of network packets based on predefined rules. By using netfilter, system administrators can configure their systems to accept, drop, or modify packets as they pass through the network stack, thereby enhancing security and traffic management in Linux environments.

The other options relate to different aspects of system management and monitoring. Storing system logs pertains to logging services, network performance monitoring involves tools for analyzing traffic and performance metrics, and managing user permissions is concerned with access control and user rights within the system. None of these functions align with the primary role of netfilter, which is specifically focused on network packet filtering and firewall implementation.