Umask set weird result for files when apply value 0666

Question

umask shows the weird results when applying value: 0666

When apply any value for umask that works as aspected, but when apply 0666 then directory got correct permission value but file got weird value.

$ mkdir demo
$ cd demo
$ umask 0666 ../demo
$ mkdir d1 && touch f1
$ umask 0333 ../demo
$ mkdir d2 && touch f2
$ ls -l

drwxrwxr-x 4 riajul riajul 4096 Mar 27 17:33 ./
drwxr-xr-x 4 riajul riajul 4096 Mar 27 17:30 ../
d--x--x--x 2 riajul riajul 4096 Mar 27 17:32 d1/
dr--r--r-- 2 riajul riajul 4096 Mar 27 17:33 d2/
---------- 1 riajul riajul    0 Mar 27 17:32 f1
-r--r--r-- 1 riajul riajul    0 Mar 27 17:33 f2

Why f1's permission different than d1

Example: picture

Answer 1

umask is a mask, applied to file permissions. touch creates files with permission 666 by default; with a mask of 0666, all those permission bits are masked, so you end up with files with no permission bits set.

The umask isn’t set on specific directories, it is managed per process and inherited from the parent process when a process starts. When you run umask 0666 or umask 0333, the current shell’s umask is set to the given value; extra arguments are ignored.

Answer 2

umask created some confusion, so after reading some documentation I got a clear idea.

umask: [ u => User ]

• When we create files or directories, those files got some default permission.
• mask work exactly as do in photo editing tools. It does not set permissions, instead it remove given permissions.

Default_permission = pre-defined_initial_permission – umask_permission

Pre-defined permission are fixed and cannot be changed.

• for directory: 777
• for file : 666

Default umask permissions for user:

• root user : 0022
• normal user : 0002

So Without any change in default umask permissions:

+---------------------------------------------------+
|   User    |   Directory       |   File            |
|---------------+-----------------------+-----------|
|                                                   |
| <user>    | 777 - x   => y    | 666 - x   => y    |
| root      | 777 - 022 => 755  | 666 - 022 => 644  |
| normal    | 777 - 002 => 775  | 666 - 002 => 664  |
|                                                   |
|                                                   |
| NB: 1st bit (0) of umask values: not effect       |
|    permission so it ignored from calculation.     |
|                                                   |
|                                                   |
+---------------------------------------------------+

Umask permission change can be 2 type:

• Temporary : by umask command, closing shell reset to default.
• Permanent : By setting UMASK value in:
  • User Level: ~/.profile, or .bashrc
  • Globally: /etc/profile, /etc/bashrc, or /etc/login.defs

NB: umask substract permissions from user not from particular directory.

• umask: set permission before created.
• chmod: Change permission after created.

$ umask --help
    -S : makes the output symbolic; otherwise an octal number is output
    -p : if MODE is omitted, output in a form that may be reused as input


$ umask     # Show umask of user
$ umask -S  # Show umask of user as symbol instead of number

$ umask 0022 # Set Umask.