The relationship between Linux permissions and Umask

Linux file permissions are primarily defined for three types of objects
Owner: Master, u
Group: Genus, G
Other: Others, O
Each file has three permissions defined for each type of visitor
R:readable
W:writable
X:excutable
rw-r--r--
Top three: Indicates the permissions that the user has
Medium Three-bit: Represents the permissions of the group in which the user resides
The latter three: represents the permissions of other users

Permissions	Binary	Octal
---	000	0
--x	001	1
-w-	010	2
-wx	011	3
r--	100	4
R-x	101	5
rw-	110	6
Rwx	111	7

R: Readable w: writable x: Executable

Umask (reverse mask also called Mask code)
The Umask value can be used to retain the Create file permission

New file Permission: 666-umask If the result has an execute (odd) permission on a bit, its permissions +1

(Example: The file is created by default is not execute permissions, so the maximum permission is 666, if umask=023,666-023=643, this is actually a problem.) Because this allows other users to have execute permissions, which is not allowed by default, it is necessary to carry plus 1, the correct result is 666-023=644, that is, for the file if the result of the reduction contains the execution permissions, you need to add 1 processing. )
New DIR Permission: 777-umask

Default Umask value

Non-privileged user umask is 002
Root Umask is 022.

#umask可以查看当前umask
Four-bit leftmost without tube when viewing umask (is the extended bit sst:suid, SGID, sticky{000-111})

The mask code can be set by itself, using the command:
#umask number
Umask temporary modification is only valid for the current shell

To change changes permanently

Global Settings:/ETC/BASHRC

User settings: ~/.BASHRC

The relationship between Linux permissions and Umask