Chapter 13 Control of File Permission
Chapter’s Main Topics
This chapter describes the basic concepts of how a permissions scheme for a file works on a Linux system, and also describes how to change ownership and execution permissions for a file.
It includes descriptions on the following topics:
■ Scheme of file permission
■ Changing the ownership of a file
■ Change execution permission on a file
12.7.7 Assignment of User Account to User Group
12.7.7.1 Review of Processing Method
If a user account is assigned to a user group, that user inherits all the responsibilities and privileges that the group has. Also, when a certain user group is given a certain responsibility and privilege, all users belonging to that user group are given the same responsibility and privilege.
12.7.6 “delgroup” Command – Delete User Group
You will need to delete user groups that are not needed on your system. When deleting a user group, be careful about the user accounts belonging to that group.
When deleting a user group, you can use “delgroup” and “groupdel” commands. The “delgroup” command makes it easy to create user groups. On the other hand, the “groupdel” command can handle relatively detailed processing with very low-level commands, but it is not used for general purposes because it is complex to use.
12.7.5 “addgroup” Command – Create User Group
You can use “addgroup” and “groupadd” commands to create user groups. The “addgroup” command makes it easy to create user groups. On the other hand, the “groupadd” command can handle relatively detailed processing with very low-level commands, but it is complex to use and is not used for general purposes.
12.7.4 Managing Relationship between User and User Group
Raspberry Pi uses several ways to manage the relationship between user groups and users.
If the user account is not assigned to a separate group, but is assigned only to its own self group, the primary group, the relationship is defined using “/etc/passwd” file.
12.7.3 Managing User Group
In the Raspberry Pi system, user groups are managed in “/etc/group” file. The managed data has the following format.
: x: : ….
12.7.2 Relationship between User and User Group
In the Raspberry Pi system, certain user account is always assigned to a specific group. Also, certain user account can belong to more than one group at the same time.
If you do not specify a separate group for a specific user account, the user always belongs to the primary group, which is its own group. This primary group has the same name as its own user account, contains its own user account only, and is created automatically even if you do not create it separately.
12.7 User Group
12.7.1 What is User Group?
In Linux systems, the concept of group is used to distinguish and manage group of users who can handle certain range of tasks in the system. If you distinguish responsibilities and privileges that can handle a certain range of tasks define and manage them as a group, the same responsibilities and privileges apply to all user accounts belonging to that group. Thus you need not to assign responsibilities and privileges one by one for each individual user account, and it is possible to manage them at once by group
12.6.2 Changing User Password
12.6.2.1 Overview of Changing User Password
User password is the most basic means of keeping your system from external threats. Therefore, it is an important task of system management to give appropriate passwords and to manage them well.
12.6 User Change
After the user account is created on the system, there may be a case where the contents of various items defined for the user account need to be changed.
12.6.1 “usermod” Command – Change User
You can use the “usermod” command to change all defined contents of a user account.