There are two ways to start a Linux process: 1. Manually starting a process, which refers to directly starting a process by the user inputting a command. Depending on the type and nature of the started process, it can be subdivided into the foreground There are two ways to start and start in the background. 2. Schedule the startup process (set it in advance, and the process can start by itself according to user requirements); in Linux, tasks can be configured to start automatically at a specified time, date, or when the average system load is lower than a specified value.
#The operating environment of this tutorial: linux7.3 system, Dell G3 computer.
In the Linux system, each process has a unique process ID (PID), which facilitates the system to identify and schedule the process. By simply outputting the name of the program that is running the program, you can run the program, essentially starting a process.
Generally speaking, there are two main ways to start a process, namely manual start and scheduled start (set in advance, and the process can start by itself according to user requirements). Manual start can also be divided into foreground. Startup and background startup.
Linux manual startup process
Manual startup process refers to a process that is directly started by the user inputting a command. Depending on the type and nature of the process, it can be subdivided into two methods: foreground startup and background startup.
Starting the process in the foreground
Starting the process in the foreground is the most common way to start the process manually, because when the user enters a command and runs it, a process has already been started. process, and it is a foreground process. At this time, the system is actually in a multi-process state (one is the Shell process and the other is a newly started process).
In fact, there are many processes quietly running in the background when the system is automatic, but for the convenience of readers' understanding, these processes are not included here.
When we start a process in the foreground and the process does not exit, we use the ps command to see the process. For example, we run the top command as a foreground process. The specific command is as follows :
After running, the terminal output is as follows:
We see that at this time, we run the top process in the foreground. Now, we Use the ps command to view the process. The specific command is as follows:
ps -elf |grep top
Copy after login
After running, the terminal output is as follows:
We see that we used the ps command , you can see the running top process. After the test is completed, we press q to exit the top process.
Start the process in the background
The process runs directly from the background and is used relatively rarely, unless the process is very time-consuming and the user is not in a hurry to need its running results. When, for example, the user needs to start a long-running process for formatting text files, in order to prevent the entire Shell from being "occupied" during the formatting process, it is a wiser choice to start the process from the background.
Starting a process from the background is actually adding an "&" symbol at the end of the command. After entering the command and running it, the Shell will provide us with a number, which is the process number of the process. Then the prompt will appear directly, and the user can continue to complete other work. We enter the following code to run the top command in the background. The specific command is as follows:
After running, the terminal output is as follows:
We see that at this time, we run the top process in the background. Now, we use the ps command to view the process. The specific command is as follows:
ps -elf |grep top
Copy after login
Run After that, the terminal output is as follows:
We see that we used the ps command to see the top process running in the background. After the test is completed, we use the kill command to kill Drop the top process that is running the day after tomorrow. The specific command is as follows:
kill 25439
Copy after login
The 25439 here is the process id. We can use this command to kill the process that is running in the background.
Explanation
The above introduces two methods of manual startup. In fact, they have a common feature, that is, new processes are generated by the current Shell process. , in other words, Shell creates a new process, so this relationship is called a parent-child relationship between processes, where Shell is the parent process and the new process is the child process.
It is worth mentioning that a parent process can have multiple child processes, and usually the parent process can be continued only after the child process ends; of course, if it is started from the background, the parent process does not need to wait for the child process.
Linux system scheduling startup process
In Linux systems, tasks can be configured to start automatically at a specified time, date, or when the average system load is lower than a specified value.
For example, Linux is pre-configured to run important system tasks so that the system can be updated in real time. System administrators can also use automated tasks to regularly back up important data.
There are many ways to schedule the startup process, such as through crontab, at and other commands.
Related recommendations: "Linux Video Tutorial"
The above is the detailed content of There are several ways to start a Linux process. For more information, please follow other related articles on the PHP Chinese website!
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
