umask

umask is a command and a function in POSIX environments that sets the file mode creation mask of the current process. The file mode creation mask (also known as the umask) limits the permission modes for files and directories subsequently created by the process. When a shell or other program is creating a file or directory, it specifies the permissions to be granted. The operating system then removes from those the permissions that the file mode creation mask does not allow.

The umask only restricts permissions; it cannot grant extra permissions beyond what is specified by the program that creates the file or directory. When programs create files, they usually specify read and write permissions for all users, and no execute permissions at all (rw-rw-rw- or octal 666 in traditional Unix notation). Files created in this way will not be executable even if the umask would have allowed that.
Posted on May 31st, 2014

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