Why a umask of 0027 creates files like 0640

The User Mask (umask) can be managed with the command umask. A umask is the reverse value of the octal permission set that files and directories are created with.

So, a umask of 0777 creates files with an octal permission value of 0000; no permissions to read, write or execute.

But; there is a strange thing about the umask; it never allows to make files executable. Here is a demonstration of this "flaw"/"security feature".

$ umask 0027
$ touch me
$ ls -l me | awk '{print $1}'

I would have expected 750, instead 640 is produced. This is default security behaviour of UNIX/Linux.


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To work out the file

To work out the file permissions from a umask you subtracted the umask from 777 for directories or from 666 for files.

Your file for example:
umask = 027
777-027 = 750 Directory permissions
666-027 = 640 File permissions

Nice explanation. I

Nice explanation.

I understood clearly by this example.


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