what is meant by umask in linux?

UMASK (User Mask or User file creation MASK) is the default permission or base permissions given when a new file (even folder too, as Linux treats everything as files) is created on a Linux machine. Most of the Linux distros give 022 (0022) as default UMASK. In other words, it is a system default permissions for newly created files/folders in the machine.

For root user default umask value is 022.

For normal user default umask value is 0002

How to check the umask value of the current user (root) ?

using umask to can find the default value

[root@Rhel ~]# umask

0022

when you create a directory default directory permissions is

0777

0022

-------

0755

-------

[root@Rhel ~]# ls -ld /vasu

drwxr-xr-x. 2 root root 6 Nov 24 15:06 /vasu

[root@Rhel ~]#

when you (root)  create a any file the default file permission are 644

[root@Rhel ~]# ls -l

-rw-r--r--. 1 root root 0 Nov 24 15:06 a

how to check the umask value of the normal user (student)?

[student@Rhel ~]$ umask

0002

[student@Rhel ~]$

when you create a directory default directory permissions is

0777

0002

-------

0775

-------

[student@Rhel ~]$ mkdir vasu

[student@Rhel ~]$ ls -l

total 0

drwxrwxr-x. 2 student student 6 Nov 24 15:17 vasu

when you  create a any file the default file permission are 664

[student@Rhel vasu]$ touch a

[student@Rhel vasu]$ ls -l

total 0

-rw-rw-r--. 1 student student 0 Nov 24 15:19 a

[student@Rhel vasu]$

umask and level of security

The umask command be used for setting different security levels as follows:

umask value	Security level	Effective permission (directory)
022	Permissive	755
026	Moderate	751
027	Moderate	750
077	Severe	700

For more information about the umask read the man page of bash or ksh or tcsh shell:

man bash

help umask

man chmod