Linux (11) file directory permissions chmod umask chown

A file directory permission definition

chmod directory

First of all, let's meet the permissions definition of the file directory, and see the ls-l results below.

We found a file or directory in front of the 10-bit information, the first bit represents the file type, chmod recursive directory there are probably several types: D for directory-ordinary file B block device (SDA,SDA1) L link file c character file p pipe file s socket file We are familiar with the first four kinds.
The following 9-bit, no 3-bit group, respectively, represents the user (owner/master), user group (owning group/genus),chmod all files in directory   other user's permissions. Symbol expressed as u (user), G (group), O (Others)
Each group has 3 permissions r,w,x the sub-table represents read,chmod directory permissions  write, execute. Digital notation for Rwx=421=7
Rw=42=6 in turn
Three permissions for the detailed meanings of files and directories see the table below

Note that file permissions expire under the root account, login to the general account verification

Modified Chown of the main genus of two genera

Change owner changes the file to which the user belongs
Format chown user filename
Users can also be chown: the user group filename is also modified to belong to the main group
-R parameter can be cascaded

Three-file directory permissions modification

Chmod There are three ways to change file permissions: chmod 777 directory 
1 chmod u=rwx filename
2 chmod u+r filename or chmod u-r filename
Note: u can be changed as G,o, can also be separated by commas, assign value at the same time, chmod cannot access gradlew no such file or directory the following permissions are customized
3 chmod 770 filename directly to U,g,o Modify permissions
4-r parameter can modify permissions for directory Cascade

Four Umask

Umask can be said to be a file permissions open standard, we create a new file or directory will have a default permissions, such as under the ordinary user, create a new file permissions of 664, the directory is 775, at this time we view umask discovery as 0002, the default four bit, the first bit 0 is a complement, The latter three bits represent the reference permission of the U,g,o, and the simple sum we found,
664+002=666 for normal file full permissions
775+002=777 for directory file full permissions
Then means that we do not give the normal file default X permissions, chmod files in directory as far as possible limit the normal user rights, the directory is not controlled from the source, the default maximum permissions.
We can modify the Umask value to modify the preset permissions
The command format is umask xxx xxx, which represents the base permission for three numbers

Five Hidden permissions chattr lsattr

Here are two hidden permissions I permissions and a permission
Command chattr:
chattr [+-=] [i,a] [file or directory name] Example chattr +a test.txt
' +-= ': increase, decrease, set, respectively
' A ': After adding this attribute, can only append cannot delete, non-root user cannot set this attribute;
' I ': added, so that the file can not be deleted, renamed, set link, write, add data;
Let's give an example of how I can see the effect in a directory:

After we add the I permission to the test directory, even the root user can no longer create or delete files inside
Below we add a permission to the directory to see the results

We found that adding a permission to the directory can create a file inside it, but it cannot be deleted
Below we add I and a permission to the file to see the results


Command: lsattr
This command is used to read special permissions for a file or directory, with the syntax lsattr [-ar] [File/directory name]
'-a ': Similar to the-a option for LS, which is listed together with hidden files;
'-R ': listed together with subdirectories ' data

Linux (11) file directory permissions chmod umask chown