Daemon tools explained

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Managed WooCommerce Hosting Managed WordPress Private Cloud 8. Security Bulletins Series Technical Support Tutorials InterWorx 2. Have Some Questions? Latest Articles. What is Bare Metal Programming? Read Article. Common Fixes. Open up a terminal and type in this command:. You will see a complete listing of all of the processes that are running. You may not know what some of them are, or what they do, they are listed.

The pstree output is a pretty good illustration as to what is going on with your machine. Looking at the screen shot, a few daemons can be seen here: udisksd , gvfsd , systemd , logind and some others. Again, a daemon is a process that runs in the background and is usually out of the control of the user. It is said that a daemon has no controlling terminal. A process is a running program. At a particular instant of time, it can be either running, sleeping, or zombie a process that completed its task, but waiting for its parent process to accept the return value.

Interactive processes are those which are run by a user at the command line are called interactive processes. Batch processes are processes that are not associated with the command line and are presented from a list of processes. These are best at times when the system usage is low. When I was a full-time system administrator, I often ran disk usage inventories, system behavior analysis scripts, and so on, at night.

Interactive processes and batch jobs are not daemons even though they can be run in the background and can do some monitoring work. They key is that these two types of processes involve human input through some sort of terminal control. Daemons do not need a person to start them up.

We know that a daemon is a computer program that runs as a background process, rather than being under the direct control of an interactive user. When the system boot is complete, the system initialization process starts spawning creating daemons through a method called forking , eliminating the need for a terminal this is what is meant by no controlling terminal.

I will not go into the full details of process forking, but hopefully, I can be just brief enough to show a little background information to describe what is done. While there are other methods to create processes, traditionally, in Linux, the way to create a process is through making a copy of an existing process in order to create a child process.

An exec system call to start another program in then performed. It gets its name from the C programming language. One of the libraries that C uses, is called the standard library, containing methods to perform operating services.

One of these methods, called fork , is dedicated to creating new processes. The process that initiates a fork is considered to be the parent process of the newly created child process. The process that creates daemons is the initialization called init process by forking its own process to create new ones.

Done this way, the init process is the outright parent process. There is another way to spawn a daemon and that is for another process to fork a child process and then die a term often used in place of exit. When the parent dies, the child process becomes an orphan. When a child process is orphaned, it is adopted by the init process. It is important that you do not confuse this with a zombie.