I was ignorant about Linux file permissions and permissions, so I looked it up.
Files handled by Linux are owned by everything from files created by yourself to libraries provided by the system to execution commands. The owner of the file can freely set the access right to the file.
Confirm file owner
$ ls -l /bin/cat
-rwxr-xr-x 1 root(File owner) wheel(The group to which the file belongs) 23648 9 21 2018 /bin/cat
A group is a group of users.
By assigning multiple administrator users to a group called wheel
that manages the system and giving permission to the wheel group, it is possible to give the same authority to multiple users who have the same role.
groups
command.In each file, information that defines the authority *** "Allow anyone to perform what kind of operation" *** is set.
-rwxr-xr-x(File type and file permissions) 1 root(File owner) wheel(The group to which the file belongs) 23648 9 21 2018 /bin/cat
*-: Normal file
The permissions of the files displayed by rwxr-xr-x
are in one block for every three, which means permissions for" owner "," group ", and" other users ", respectively.
Symbols such as r, w, and x mean operations on allowed files. There are three types of operations: "read", "write", and "execute". If not allowed, -
will be displayed.
-rwxr-xr-x 1 root wheel 23648 9 21 2018 /bin/cat
rwx
→" Read "" Write "" Execute "is allowed
r-x
→" Read "and" Execute "are allowed
r-x
→" Read "and" Execute "are allowed
A command to set file and directory permissions. The chmod command has a symbol mode specification and a numerical mode setting.
Added write permission for owner
$ chmod u+w file.txt
Remove write permission for group
#### **`$ chmod g-w file.txt`**
```txt
Make other users' permissions read only
#### **`$ chmod o=r file.txt`**
```txt
#### User specification method in numerical mode
Permission numbers in numeric mode
* r (read): 4
* w (write): 2
* x (execute): 1
#### How to use in numerical mode
Specify the permissions of file.txt to `rwxr-xr-x`
#### **`$ chmod 755 file.txt`**
```txt
## Superuser
Special user with administrator privileges
Normally, it is common to log in as a general user, operate it, and work as a super user only when necessary.
### su command
Command to temporarily become another user
The su command can be any user, but this command is mainly used to become superuser. For security reasons, Linux does not allow you to log in directly as a superuser. First, you need to log in as a general user and become a super user with the su command.
### sudo command
Run the command as another user. If no user is specified, it will be executed as superuser.
## Summary
Somehow I was using the chmod command and the sudo command, so I learned.