Background process facts for kids

A background process is like a hidden helper on your computer. It's a computer program that runs quietly behind the scenes without you needing to do anything. These processes handle important tasks that keep your computer running smoothly.

Think of them as little workers that do jobs like keeping track of what's happening (logging), checking how your system is doing (monitoring), setting up tasks for later (scheduling), or sending you alerts. Often, a main program starts a background process to do a specific job. Once started, this helper process works on its own, freeing up the main program to do other things.

On Windows computers, a background process can be a program that doesn't show a user interface (like a window you can click on). Or, it can be a special type of program called a Windows service. Regular background programs start like any other app, perhaps from the Start menu. Windows services, however, are managed by a special part of Windows called the Service Control Manager. Since Windows Vista, these services run in their own secure area. Background processes and services can use as much of your computer's power as they need. In fact, on Windows Server systems, these background tasks are expected to be the main users of computer resources.

On Unix or Unix-like systems (like Linux or macOS), a background process is one that isn't directly connected to your terminal (the window where you type commands). This means it won't get keyboard commands from you and usually won't send messages back to that terminal. Even though background processes often do small tasks, any program can be run in the background. It will act like any other program, just without the direct connection to your terminal.

Windows Services

In the Windows NT family of operating systems (which includes most modern Windows versions), a Windows service is a special kind of background process. These services must follow specific rules set by the Service Control Manager, which is the part of Windows that manages them.

Windows services can be set up to start automatically when your computer turns on. They then run in the background as long as Windows is running. You can also start them manually or have them start when a certain event happens. Windows operating systems come with many built-in services. These often run using special user accounts like `System`, `Network Service`, or `Local Service`. You might see them linked to a program called `svchost.exe`. Because they use their own accounts, Windows services can keep working even when no one is logged into the computer.

Before Windows Vista, some services could show windows or interact with your desktop. However, with Windows Vista and newer versions, this feature was removed for security reasons. Services can no longer directly interact with your desktop.

You can manage Windows services in a few main ways:

• The Services tool in Microsoft Management Console.
• The `sc.exe` command-line tool.
• Using Windows PowerShell.

What is a Daemon?

A daemon (pronounced "DAY-mon") is a type of background process that runs continuously. It waits for specific events to happen or conditions to be met. Daemons usually use very little of your computer's power. They perform tasks that don't need much, if any, input from you. When a program is launched as a daemon, it becomes separate from the terminal that started it.

How Daemons Start on Unix

On a Unix-like system, you can start a background process from the command line by adding an "&" symbol at the end of the command. For example, `sleep 1000 &` would run the `sleep` command in the background.

If you have a program that you paused, you can use the `bg` command to make it run in the background again. To bring a background program back to the foreground (so you can interact with it), you use the `fg` command. The `jobs` command will show you all the programs linked to your current terminal. You can use this list to bring background programs to the front.

Normally, when you log out of a Unix session, all the programs you started, including background ones, will stop. This prevents them from becoming "orphan processes" (programs without a parent). When you exit your shell (the program where you type commands), it sends a "hangup" signal (SIGHUP) to all its programs to tell them to stop.

However, there are ways to keep programs running even after you log out:

• You can use a terminal multiplexer (like `screen` or `tmux`). This lets you leave a session running and then disconnect from it. Your programs keep running, and you can connect back to the session later.
• You can start the program using the `nohup` command. This tells the program to ignore the hangup signal.
• You can use the `disown` command after starting a program. This removes it from your job list, so it won't get the hangup signal when you log out.

When programs keep running after you log out, they become orphan processes. The computer's main `init` process (which is like the first program that starts when the system boots) then adopts them. These adopted programs continue to run without a session and are now called daemons.

Example

Here's an example on a Unix system. The `sleep` command was started in the background. Then, the `ps` command was run in the foreground to show running processes. Both were started from the command line.

  PID TT  STAT    TIME COMMAND
54659 10  S    0:00.06 su (zsh)
54703 10  IN   0:00.00 - sleep 1000
54852 10  R+   0:00.00 - ps -U botty -axd

In this output:

• `54703` is the ID of the `sleep` command, running in the background (`IN`).
• `54852` is the ID of the `ps` command, running in the foreground (`R+`).

Background Processes on Smartphones

Many modern smartphone and PDA operating systems (like Android and iOS) can also run background processes. Because smartphones have limited hardware, background processes on them are often restricted. They might only be allowed to do certain tasks or use a limited amount of power.

For example, on Android, background processes might only be allowed to use 5-10% of the CPU (the phone's "brain"). On Apple's iOS, apps can only do a small set of things when running in the background. On both Android and iOS, the system can stop background processes if they are using too much memory. This helps keep your phone running fast and saves battery.

See also

In Spanish: Background para niños

• Batch processing
• Computer multitasking
• Process group