/proc filesystem in Linux: a window into the kernel

/proc is a virtual filesystem through which the kernel exposes processes and system state as files.

Common cases

cat /proc/cpuinfo        # processor details
cat /proc/meminfo        # memory state
cat /proc/loadavg        # the load average
cat /proc/$$/status      # the status of the current shell ($$ is its PID)

How it works: there are no files on disk

/proc is not on a disk: the kernel builds its contents fresh every time you read them. Every process has a directory /proc/<PID>, and files like /proc/meminfo give a live snapshot of the system right now. That is why cat /proc/loadavg shows fresh numbers every time. The ps, free and top commands just read /proc under the hood and format it. To change kernel behaviour you use the neighbouring /proc/sys.

Used in

You need this in the lesson The kernel via /proc. The theory is the chapter The Linux kernel at work.

See also

Kernel parameters: sysctl, Memory: free, Load average.

Try it

Open the sandbox: a real throwaway Linux terminal in your browser. Run the commands above by hand - the container is deleted when you leave.