20.2.2 How Shell Runs Commands
20.2.2.1 Types of Kernel’s System Calls
● “fork” system call
This call is one of the system call methods that a process uses to execute another process. When a command needs to be executed, a child process is created and executed separately.
20.2 Batch Run of Commands via Script
Here we will look at the script tool we use to process multiple commands in batch at once. We will discuss the concept of script, how to write a script, how to execute a script, and so on.
20.2.1 Shell and script
20.2.1.1 What is Script?
On Linux systems, Shell plays a central role in executing commands. Among the various Shell programs, BASH is specified as the default shell. BASH receives a command entered by the user in the terminal environment, interprets the meaning of the command, processes the command according to the specified method, and returns the processing result to the user.
20.1.2 Manual Run and Automatic Run
Based on the subject who instructs the processing, the processing method can be divided into the manual execution and utomatic execution can
● Manual execution
In this method, the user instructs to process certain commands. The user determines the required point of time for execution, and the user also determines the contents of the specific command to be entered for execution and instructs the command. The command to be executed here may be an individual command or a bundle of commands defined by a script. Whatever it is, the user will decide the start of the run.
20.1 How to Run Command
There are several ways to execute commands in the Raspberry Pi system. Users can run them one by one, or the computer can handle them automatically. We will take a look at what methods can be used here.
20.1.1 Individual Run and Batch Run
Based on the number of command processed at one time, the processing method can be divided into individual execution and batch execution.
Chapter 20 Batch Run and Automatic Run
Chapter’s Main Topics
This chapter describes the several ways to execute commands on a Linux system. You can execute commands one by one, or you can execute several commands at once. You can also run it manually or let the system run automatically.
In this regard, we will look at the Script tools we use to process multiple commands at once. We will also look at tools that can execute commands at regular intervals.
It includes descriptions on the following topics:
■ Individual execution and batch execution
■ Manual execution and automatic execution
■ Batch execution with script
■ Automatic execution with init script
■ Automatic execution by schedule
17.6.2 Cleaning Program Package File
During the process of installing or upgrading programs, the related program package file is downloaded and stored in the local repository “/var/cache/apt/archives/”. These files are not deleted and remain intact even if the program installation is completed or the program is removed. If these files continue to accumulate, it will take up unnecessary storage space in the system, so it’s a good idea to remove any files that is no longer needed.
17.6 Uninstalling Programs and Cleaning Files
17.6.1 Uninstalling Programs
If you no longer need the installed programs, you should remove them. There are several ways to remove installed programs.
17.5 Installing and Reinstalling Program
17.5.1 Comparison of Installation by Source Distribution Method
In the Raspbian operating system, it is standard to manage and distribute programs using the package repository, but you can distribute, install, and use programs without using this method.
17.5.2 Installing Programs Distributed in Package Repository
● “apt-get install” command – install program
When installing programs in the package repository, use “install” command in “apt-get” command.
17.5.3 Installing Programs Distributed in Package Format
Of course, if the program is configured in a package format but is not registered in the package repository and distributed in a separate way, you can not use the APT tool “apt-get” command, and you have to use the low-level “dpkg” command.