We will output a summary of reading the "Linux Standard Textbook (PDF)" about Linux, which beginners should understand above all. This time, Chapters 7 and 8 in the latter half.
It takes a lot of time to write each command one by one, so when it comes time to use it, I mainly extract the one that says "The specific method is written here!". Please note.
-To use Linux, you need a user account, but you can use groups to bundle multiple users. -By properly setting groups and users, ** files, directories, arbitrary programs, shell scripts, etc. can be given permission to browse and edit only those who need them **. -Commands marked with # can only be executed with root privileges, and those marked with $ can also be executed with user privileges.
-In addition to the users prepared from the time of installation, the administrator can define users as needed. However, the command in the link does not seem to be applied on Mac **.
There are many things you can do for each, so refer to the article below.
[Useradd] command-create a new user
[Usermod] command-change user account information
[Group add] command-create a new group
[Groupmod] command-change group ID and name
[Groupdel] command-delete a group
@markIT's Linux search display screen
-To use the user's authority, authenticate using the user name and password. The command to register / change the user password is possible with passwd [user name]
.
-Shadow file: The user's password is saved in the shadow file (/ etc / shadow) instead of the password file. The contents of one user (one line) registered in the shadow file looks like this.
account:password:last_changed:may_be_changed:warned:expires:disabled:reserved
item | Contents |
---|---|
account | User's name |
password | Encrypted password |
last_changed | Days from January 1, 1970 to the date the password was last updated |
may_be_changed | Number of days before the password can be changed |
must_be_changed | Number of days before you have to change your password |
warned | The number of days a user will be warned before the password expires |
expires | The number of days before your password expires and your account becomes unusable |
disabled | Days from January 1, 1970 until the account becomes unavailable |
reserved | Reserved field |
-Advantages of creating a group: You can set the access rights of directories on the system to create a directory that can be accessed only by users who belong to a specific group, or only users who belong to a specific group can become root users. It is possible to operate such as. -Root user: A special user who can change system settings, install or delete programs, and create / delete users without usage restrictions.
The su command is a command that allows a user who is already logged in as another user to temporarily become another user.
su
su - [User]
option
su - (Or su- root): Become the root user
su -user Can be the specified user
-You can execute commands with superuser (root) privileges without switching the user to root with the su command.
-The user ID and group ID of the file creator become the owner and owning group of the file. The owner can be changed with the chown command, and the owning group can be changed with the chgrp command.
chown user[.group]directory
chown user[.group]File
chgrp group directory
chgrp group file
* To change, you need to be the root user
-Files can have permissions set at three levels: the user who owns the file, the user who excludes the file owner from the file ownership group, and other users.
-The file has three permissions, ** ① read ② write ③ execute **, for each of the three levels divided by the user.
-The ls -l
command can be used to display the file mode. For example, like this.
$ ls -l
drwxr-xr-x@ 2 user staff 64 7 30 09:46 test
drwxr-xr-x@ 4 user staff 128 7 26 15:38 method
drwxr-xr-x@ 7 user staff 224 7 29 21:37 practice
drwxr-xr-x@ 4 user staff 128 7 24 15:52 Iterative processing
-The meanings of file types r, w, and x are as follows.
item | Contents |
---|---|
r | Read |
w | writing |
x | Run or move directory |
rwx | All three are possible |
To change the access right, follow the steps below.
chmod mode[,mode]...directory
chmod mode[,mode]...File
chmod octal notation mode directory
chmod octadecimal mode file
For other details, share this article because it was concrete and easy to understand.
chmod? chown? File permission system summary for those who do not understand well
-When a new file is created, the file is created with permissions such as 644 or 664, which are the permissions specified for each USER. By using the umask command, it is possible to restrict the creation of files with the specified permissions.
umask [Eighth mode mask value]
-Permissions are set in the form of file mode. Details are linked below
What is Linux file mode? And how to change
What are "file mode" and "permission" in Linux? 【Beginners】
[Useradd] command-create a new user
[Usermod] command-change user account information
[Group add] command-create a new group
[Groupmod] command-change group ID and name
[Groupdel] command-delete a group
@markIT's Linux search display screen
chmod? chown? File permission system summary for those who do not understand well
What is Linux file mode? And how to change
What are "file mode" and "permission" in Linux? 【Beginners】
Recommended Posts