Umask in Linux
Umask, it may be difficult how to define the meaning of umask. : D
Umask is a command that serves to set the default permissions of a file or folder will be created in Linux.
Default umask on linux is worth 022. How to explain these numbers?
Maybe it would be nice if you use a direct example.
For folders, the permissions that are used is 777.
For files, the permissions that are used is 666.
The following equation:
For folder = 777-022 = 755
For file = 666-022 = 644
Maybe it would be nice if you use a direct example.
For folders, the permissions that are used is 777.
For files, the permissions that are used is 666.
The following equation:
For folder = 777-022 = 755
For file = 666-022 = 644
So:
If you would create a new folder, then the new folder has permissions 755 or u = rwx, g = rx, o = rx
If you create a new file, then the new file has permissions 644 or u = rw, g = r -, o = r -
If you would create a new folder, then the new folder has permissions 755 or u = rwx, g = rx, o = rx
If you create a new file, then the new file has permissions 644 or u = rw, g = r -, o = r -
Umask also allows you to set a permission of a directory mounted by Linux at boot time, which is located in the fstab file.
Maybe it is a glimpse of the umask, good luck :)
Setting the UMASK
You can setup the umask value in /etc/bashrc or /etc/profile for all
users. By default, most Linux distros set it to 0022 (022) or 0002
(002).
Open /etc/profile (global) or ~/.bashrc file
# vi /etc/profile
or
$ vi ~/.bashrc
Append/modify the following line to setup a new umask:
umask 022
Save and close the file. Changes will take effect after next login.
But what is 0022 and 0002?
The default umask 0002 is used for regular users. With this mask,
default directory permissions are 775, and default file permissions are
664.
The default umask for the root user is 0022, and as a result,
default directory permissions are 755, and default file permissions are
644.
For directories, the base permissions are 0777 (rwxrwxrwx) and for files they are 0666 (rw-rw-rw).
To calculate directory permissions for a umask value of 022 (root user):
Default permission: 777
Subtract umask value: 022 (-)
Directory permission: 755
To calculate file permissions for a umask value of 022 (root user):
Default permission: 666
Subtract umask value: 022 (-)
File permission: 644
The following example explains the steps needed to set a umask value
that will result in permission values 700 for directories and 600 for
user files. The idea very simply is that only the user will be allowed
to read or write the file, or to access the contents of the directory.
Default permissions: 777 / 666
Subtract umask value: 077 (-)
Resulting permissions: 700 / 600
$ umask 077
$ touch file.txt
$ mkdir directory
$ ls -ld file.txt directory
Output:
drwx------ 2 vivek vivek 4096 2007-02-01 02:21 directory
-rw------- 1 vivek vivek 0 2007-02-01 02:21 file.txt
Sample umask values and permissions
umask value User Group Others
0000 all all all
0007 all all none
0027 all read none
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