Linux is open-source Unix-like operating system based on the Linux kernel. Linux kernel was first released in 1991 by Linus Torvalds.

“proc” filesystem

proc filesystem is a pseudo-filesystem which provides an interface to kernel data structures, it represents information about system and processes in a hierarchical file-like structure. It is commonly mounted at /proc.

Most of the files in the proc filesystem are read-only, but some files are writable, allowing kernel variables to be changed.


  • CPU information: cat /proc/cpuinfo
  • Load average: cat /proc/loadavg

Load average

Load average (LA) represents the average system load – the number of processes executed by the CPU or are waiting for execution. It is displayed for a period of time (1, 5 and 15 minutes) in the output of the top or uptime commands.

It can be also checked using proc filesystem: cat /proc/loadavg. The first three columns is load average. The fourth column shows the number of currently running processes and the total number of processes. The last column displays the last process ID used.

Process states

Linux process states:

  • R (running or runnable): On run queue, is running or waiting for the CPU.
  • S (interruptible sleep): Waiting for an event, such as input from the terminal, will react to signals.
  • D (uninterruptible sleep): Usually IO, cannot be killed or interrupted with a signal.
  • Z (zombie / defunct): Terminated but its exit status is not read by parent process yet.
  • T (stopped): Stopped, for example: kill -STOP <PID>, Ctrl + Z.