Summary of Linux user groups and permissions

User Groups

In Linux, every user must belong to a group, and there are three types of groups in Linux, as follows:

1. File owner
2. User Group
3. Other Groups

File Owner:
The creator of the file is the owner of the file.

User group:
When the current Linux user creates a file, the group to which the file belongs is the group to which the user belongs.

Other groups:
In addition to the file owner and the users in the same group, other users of the system are other groups of the file.

How do we view the currently logged in user and the group to which the user belongs? Enter the terminal and enter the following command:

1. View the logged in user name?
whoami: View logged in user name
2. Check which user group the currently logged-in user belongs to?
groups: Check which user group the currently logged in user belongs to

If you want to view the corresponding detailed information further, you can enter the following command:

1.
cat /etc/passwd|grep loguser to capture detailed information of the user#The echo information is as follows:
>>loguser: x : 889 : 600 : : /home/loguser:/bin/bash
Username: Password: User ID: Group ID: Remarks: User home directory: The directory where the shell is located2.

cat /etc/passwd|grep weblogic to capture detailed information of the user group weblogic: x:500:600::/weblogic:/bin/bash
#The corresponding relationship is consistent with the user's relationship.

Why do we talk about groups? In fact, it is closely related to the permissions discussed next.

File permissions

Every time we view the specific details of the files in the current directory through ll, we can see the following at the beginning of the file:

drwxrwxrwx
lrwxr-xrw-

As shown in the figure, there are 10 digits in total. Excluding the first digit, the remaining 9 digits start from left to right, and every three letters represent a category. It seems that there are three groups in total, and the three categories here correspond to the user groups above:

Remove the first letter:

1. The first three represent: the file owner's permissions on the file
2. The middle three digits represent: the permissions of the group to which the current user belongs to this file
3. The last three digits represent the permissions of other user groups for this file.

The first digit represents the type of file:

1. d directory file.
2. l Symbolic link (pointing to another file, similar to a shortcut in Windows).
3. s Socket file.
4. b block device file, binary file.
5. c Character device file.
6. p Named pipe file.

Let's continue to discuss the meaning of the three letters rwx:

r (Read): For files, it has the permission to read the file contents; for directories, it has the permission to browse the directory.
w (Write): For files, it has the permission to add, modify, and delete file contents; for directories, it has the permission to create, delete, modify, and move files within the directory.
x (Execute): For files, the user has the permission to execute the file; for directories, the user has the permission to enter the directory.
1
2
3
Command to change permissions

The above rwx actually has the following corresponding relationship:

Each letter corresponds to a number
r,w,x --------------- 2^2,2^1,2^0
r:4
w:2
x:1

Students who have studied computer principles must be very familiar with 8421. In fact, this almost corresponds to this meaning.
So sometimes we see the following command to change permissions:

1. Method 1 to modify permissions:

chmod 755 abc
In fact, it is giving permissions to abc: rwx rx rx
rwx =7, rx = 5, rx = 5
It is a corresponding relationship

2. Method 2:

1. u: User permissions
2. g: group permissions
3. o: permissions for other users in different groups
4. r, w, and x have been introduced above and will not be explained again.
5. +: Join
6. -: Remove
7. =:Set
8. chmod u+x abc gives the file owner of abc the permission to execute
   

The above is a summary of the Linux user groups and permissions that I introduced to you. I hope it will be helpful to you. If you have any questions, please leave me a message and I will reply to you in time. I would also like to thank everyone for their support of the 123WORDPRESS.COM website!