The Linux virtual filesystem that exposes kernel data structures is procfs, commonly accessed through the /proc directory. It is a pseudo-filesystem: its entries generally do not represent ordinary files stored on disk, but are generated by the kernel when programs or users read them.
Procfs provides information about running processes and the system as a whole. Directories such as /proc/1234 correspond to process IDs, while files including /proc/cpuinfo, /proc/meminfo, /proc/uptime, and /proc/loadavg expose kernel-maintained details. Tools such as ps, top, free, and uptime obtain much of their information through interfaces like these.
Some /proc entries are writable and allow controlled runtime configuration, especially under /proc/sys. The sysctl command provides a more convenient interface for many of those kernel parameters. This writable aspect is why /proc is more than a static status report, though permissions and kernel policy limit what can be changed.
Sysfs is the common mix-up. Sysfs exposes devices, drivers, and kernel objects, usually under /sys, whereas procfs primarily presents processes and broader system or kernel information under /proc. Both are virtual filesystems, but they serve different interfaces.