/proc/sys
TLDR: The `/proc/sys` Linux directory is part of the virtual proc filesystem that provides an interface for dynamically viewing and modifying Linux kernel parameters. It contains tunable settings for various Linux subsystems, such as Linux memory management, Linux networking, and Linux security. Administrators can adjust these parameters at runtime to optimize Linux system performance and behavior, often using tools like sysctl or direct file manipulation.
https://en.wikipedia.org/wiki/Procfs
Each file within `/proc/sys` represents a specific kernel parameter, organized into subdirectories based on functionality, such as `net` for networking settings or `vm` for memory management. For example, the file `/proc/sys/vm/swappiness` controls the system’s swap usage policy, while `/proc/sys/net/ipv4/tcp_syncookies` manages SYN flood protection. These parameters can be read or written to using standard tools like `cat` and `echo`, allowing for real-time adjustments without rebooting the system.
https://www.kernel.org/doc/html/latest/admin-guide/sysctl/index.html
To persist changes across reboots, configurations are typically added to the `/etc/sysctl.conf` file or equivalent files in `/etc/sysctl.d/`. The `/proc/sys` directory is integral to Linux system management, enabling fine-grained control over kernel operations and hardware interactions. It is widely used in system tuning, debugging, and security hardening, making it a critical resource for administrators and developers.