Linux study note _ 3_common Linux commands _ 2 _ permission management commands

Permission management command:

1. chmod [changethe permissions mode of a file]:/bin/chmod

Syntax: chmod [{ugo} {+-=}{ rwx}] [file or directory name] // intuitive

E.g. chmodu + wx filename

Chmodo-x filename

Chmodg = rwx filename

Or: chmod [mode = 421] [file or directory] // recommended

Number of the permission pair:

R-4

W-2

X-1

E. g. rwxr-xr -- 754

Rw-r-x -- x 651.

752rwxr-x-w-

Chmod777 dir1 // set the directory dir1 to have all permissions for all users

Appendix: su-username: users that can be switched // experiment content

Return: exit

Expansion:

2. chown [changefile ownership]/bin/chown

Change file owner

Chown [user] [file name or directory name]

E. g. chown nobody file1 changes the owner of file file1 to nobody, and the nobody is the default user.

Appendix: Add User: 1) useraddafang

2) passwd afang // set a password for the passwd

3. chgrp [change file group ownership]/bin/chgrp

Change the group of a file or directory

Chgrp [user group] [file or directory]

Change the group of the file file1 to adm. adm is an existing group in the system.

Why do I need to change the user group? How do I use the group? Let's study ^_^ later.

4. umask/bin/umask

Display and set default file permissions

Umask [-S]

E. g. umask // view the default permissions.

Display-Special Permission bit, 022-user permission bit [u, o], representing the mask value;

Calculation: 777 -- 022 = 755 // This is the default permission for creating a directory

644 // It is the default permission for creating files, none of which are x

Note: The-S option is not available in many UNIX systems, so it can only be calculated based on the above!

Umask-S //-S displays the default permissions of new files or directories in the form of rwx, which is more intuitive.

* 4.1 change the default permission Value

Umask [mask value] // The Mask value must be calculated first, but do not change it!

Appendix: Linux permission rules: default file creation. executable permissions cannot be granted! X

The advantage is that it shields many attacks and viruses.