Basic knowledge about Linux: running applications

Article title: Linux basic knowledge: running applications. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.
If you enter an executable file name in the command line without any response, there may be three situations:
　　
3.1.3.1 you typed an incorrect file name
　　
Linux strictly distinguishes uppercase and lowercase letters. therefore, make sure that the uppercase and lowercase letters are correct when you type a command. For example, neither Pico nor PICO can start the pico editor.
　　
3.1.3.2 The executable file is not in the PATH specified by PATH
　　
In Linux, the executable file must be in the PATH specified by the PATH environment variable. If the current directory is not in the PATH by default, you need to add a full PATH name before the executable file name to execute it, or perform the following operations:
　　
Cd executable program directory
　　
./Executable file name
　　
You must add the dot and backslash before the executable file name; otherwise, the program will not execute (it is out of security considerations not to save the current directory in the PATH, this makes it difficult for Trojan Horse-type hacking programs to work ).
　　
Use the following command to display the PATH value.
　　
$ Echo $ PATH
　　
If you want to know how to modify the PATH value or put the current directory into the PATH, see Section 3.1.4.
　　
If you do not know the location of your executable file in the directory tree, you can use the following command to find it (for example, to find netscape)
　　
$ Find/-name netscape
　　
Or
　　
$ Locate netscape
　　
You can use the locate command to get the same result more quickly. It uses a pre-established database to work faster. This database is regularly updated by a background process called "cron.
　　
For a root user, the PATH value is different from that of a common user. it generally contains/sbin and/usr/sbin based on the PATH value of a common user. Therefore, if a common user does not specify the complete path of a command during command execution, the command in the/sbin directory cannot be executed. Similarly, after a common user uses the su command to become a super user, the PATH used is still the PATH of the common user. therefore, to execute the/sbin command, you must explicitly specify the PATH.
　　
3.1.3.3 the file may not have an executable attribute specified
　　
If the file does not have an executable attribute, you can modify the attribute value to make it executable. For example, to change the file to an executable file, run the following command:
　　
$ Chmod a + x file
　　
This command will make the file executable to all users.
　　
3.1.4