Umask (File Creation Mask) in Linux

umask is a command that determines the settings of a mask that controls how file permissions are set for newly created files. It also may refer to a function that sets the mask, or it may refer to the mask itself, which is formally known as the file mode creation mask. The mask is a grouping of bits, each of which restricts how its corresponding permission is set for newly created files. The bits in the mask may be changed by invoking the umask command

If no umask were used then the default permission would be :

·        666 for directories

·        666 for files

The umask command using Octal value:

In this mode umask permissions are not represented as characters but a three digit octal number

The table below gives numbers for all for permissions type:

Octal Value	Binary	Directory Permissions	File permissions
0	0	rwx	rw-
1	1	rw-	rw-
2	10	r-x	r--
3	11	r--	r--
4	100	-wx	-w-
5	101	-w-	-w-
6	110	--x	---
7	111	---	---

So if our umask value is 022, then any new created files will by default have the permissions 644 and any new directories created will by default have the permissions 755

umask 022 (permission)

mkdir dir (for making directory)

touch file (create a file)

ls –l (list directories & files)

The umask command using Symbols:

In the symbolic mode you can set permissions of a specific owner. It makes use of mathematical symbols to modify the file permissions 

Operator	Description
+	Adds a permission to a file or directory
-	Removes the permission
=	Sets the permission and overrides the permissions set earlier

 The various owners are represented as  :

User Denotation
u	User/Owner
g	Group
o	Other
a	All

We will be using permissions in characters like rwx:

umask u=rw,g+wr,o= (permission)

The above umask command will set the permissions for user to read and write, for group to read and write and for other no permission