1. Each file in Linux is divided into three identities: user, user group, and others according to permissions.
2. One of the most useful features of user groups is that when you are developing resources in a team, each account can have the support of multiple user groups
3. In the file attributes displayed by ls -l, the first field is the permission of the file, with a total of 10 digits, the first one is the file type, and the next three are a group, a total of three groups, which are user, user group, The permissions of others, there are three permissions: r, w, and x
4. If there is one more "." before the file name, it means the file is a "hidden file"
5. Change the user group of the file to support chgrp, the owner of the modified file can use chown, and the permission to modify the file can be chmod
6. There are two methods for chmod to modify permissions, namely the symbolic method and the numerical method. The fractions of r, w, and x in the numerical method are 4, 2, and 1.
7. For files, the effect of permissions is:
r: Read the actual content of this file,
w: The content of the file can be edited, added or modified, but cannot be deleted
x: the file has permission to be executed by the system
8. For directories, the effect of permissions is:
r: can read the list of files in this directory
w: can create, delete, rename, transfer files and directories,
x: The purpose of being able to enter the directory to become the working directory
9. To open the directory for anyone to browse, at least r and x permissions should be given, but w permissions cannot be given casually
10. Limitation of Linux file names: the maximum allowable file name of a single file or directory is 255 characters, and the complete file name including the full path name and directory (/) is 4096 characters
11. According to the official document of FHS, its main purpose is to let users know that installed software is usually placed in which directory
12. The four categories of catalogues developed by FHS are: shareable, unshareable, unchanging, and variable.
13. The three-tier main directory defined by FHS is / , /var , /usr
14. There are five directories that cannot be placed in different partitions from the root directory, namely: /etc, /bin, /lib, /dec, /sbin five