Common Linux commands (version 2)-permission management commands

Common Linux commands (version 2)-permission management commands
Permission management commands

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

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

E.g. chmod u + wx filename

Chmod o-x filename

Chmod g = 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.

752 rwxr-x-w-

Chmod 777 dir1 // set the directory dir1 to have all permissions for all users

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

Exit: exit

Summary:

Directory:

R-ls

W-rm, touch, mkdir

X-cd

[Therefore, in Linux, basically all directories have the rx permission. Otherwise, it would be more awkward...]

2. chown [change file ownership]/bin/chown

Chown [user] [file name or directory name] # change the file owner

E.g. chown nobody file1 # change the owner of file file1 to "nobody" and "nobody" to the default user.

Appendix-Add a user:

1) useradd afang

2) passwd afang # set a password for the passwd

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

Chgrp [user group] [file or directory] # change the group to which the file or directory belongs

# Must be an existing system group

E. g. chgrp adm file1 # change the file1 group to adm.

# Adm is an existing group in the system.

[How do I use a group to change the user group? Let's study later...]

4. umask/bin/umask # display and set the default file permissions

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

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

# Display 0022: 0-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

666-022 = 644 // is the default permission for creating a file, which does not have the x permission. The File Permission is less than the directory permission. X

Appendix 1: many UNIX systems do not have the-S option, so they can only be calculated based on the above!

Appendix 2-Linux permission rules: default file creation, cannot grant executable permissions (X )! The advantage is that it shields many attacks and viruses.

Appendix 3-change default permission value: umask [mask value] // The Mask value must be calculated first, instead of the initial permission value. It must be the calculated mask value, but do not change it!