Linux umask and chmod

Function Description: Specifies the default permission mask when creating a file.

Syntax:Umask[-S] [permission mask]

Note:UmaskYou can set the [permission mask]. The [permission mask] is composed of three Octal numbers. After the existing access permissions are removed from the permission mask, the preset permissions for file creation can be generated.

Parameters:
-S indicates the permission mask in text format.

When you first log on to the system, the u m a s k Command determines the default mode of file creation. This command actually corresponds
The C h m o d command is the opposite. Your system administrator must set a reasonable u m a s k value for you to ensure that
Files have the desired default permissions to prevent other users from having the write permission on your files.
Example:

  $ umask u=rwx,g=rwx,o=  $ umask   0007  $ mkdir fu  $ touch bar  $ ls -l  drwxrwx--- 2 dave dave 512 Sep  1 20:59 fu  -rw-rw---- 1 dave dave   0 Sep  1 20:59 bar

$ umask 0022  $ mkdir xdir  $ touch xfile  $ ls -l  drwxr-xr-x 2 dave dave 512 Aug 18 20:59 xdir  -rw-r--r-- 1 dave dave   0 Aug 18 20:59 xfile
 
Enter at the terminal:
Ls-l File Viewing permission
These are the main reasons:
-RW-r --
A total of 10 digits
The first one represents the type (Directory D or file -)
The three RW in the middle indicates that the owner (User) has the Read and Write rights.
Then the three RW-indicate that the group has the Read and Write rights.
The last three R groups indicate that others (other) only have read permission.
Meaning of each character:
R indicates that the file can be read)
W indicates that the file can be written)
X indicates that the file can be executed (if it is a program)
-The permission has not been granted.
Chmod o + w xxx. XXX
Grant other users the permission to write the file XXX. XXX.
Chmod go-rw xxx. XXX
Deletes the read and write permissions of group groups and other persons in XXX. XXX.
Where:
U stands for the owner (User)
G indicates the group in which the owner is located)
O stands for others, but not u and g (other)
A Represents all people, including U, G, and O
Action:
+ Indicates adding permissions.
-Indicates the permission to be deleted.
= Indicates that it is the only permission
Numeric representation:
Chmod 755 File
File Usage: The owner has the read and write permissions. users in the same group and other users only have the read and execution permissions.