Technically speaking, a process is a series of interdependent operations carries out by a computer. Every time a program is launched or booted, a corresponding process is created.
Process management is at the heart of how modern operating systems manage multitasking operations. Without them, computers would only be able to run a single application at a time, making for a very limited user experience!
Unix organizes these processes by queueing them up, and having them waiting their turn at the CPU. Each process has a ranking, and a turn called a timeslice. Unix, and other related OS's sharing these features are known as time sharing systems. This is very much like a check-out line at the grocery store except the system is very rapid, with most programs taking fewer than a second to execute.
In this section, we'll go over how to examine what processes are doing, and how to interact with processes to stop or pause them as needed.
Upon boot, the very first process to be run is
init (short for initialization). After init is started, a series of shell scripts in /etc called init scripts are executed.
With each consecutive process, a unique identifier is given. Since
init is the first running process, it is given a PID of 1.
Here are a few types of processes you should familiarize yourself with.
Most processes initialized by init are daemon programs (prounounced DEE-man). These processes just sit in the background and perform their tasks without any user interface.
Some example daemon processes are the mail and print daemons, which wait for some mail, or print job to come in.
Processes can launch other processes through appropriate system calls such as fork or spawn. What results is a parent-child process relationship.
If a process is run through the command line interface, or shell, the shell is the parent. Every process has a parent, except the
A zombie (or defunct) process arise when a child process is terminated, but its entry still lives in the process table. All memory and resources are released from the terminated child, and only its entry remains. until the parent process fetches status info for terminated child, this process is known as a zombie.
An orphan process arises when a process is still running, but its parent has died. They are adopted by init.
Now that we understand the concept of processes and learned a little bit of its jargon, let's see how we can view and control processes with shell commands.
This book approaches system administration in a practical way and is an invaluable reference for both new administrators and experienced professionals. It details best practices for every facet of system administration, including storage management, network design and administration, email, web hosting, scripting, and much more.$ Check price
Stretch out your back and relieve your back muscles with inversion therapy. This device counteracts the forces of gravity on the body by decompressing and elongating the spine. By using this product just ten minutes a day, you can be well on your way to improved circulation and posture while relieving muscle aches, back pain and stress.$$ Check price