Under Linux (and UNIX), everything in the file system, including directories and devices, is a file. And every file on your system has an accompanying set of permissions based on ownership. These permissions provide data security by giving specific permission settings to every single item denoting who may read, write, or execute the file. These permissions are set individually for the file’s owner, for members of the group the file belongs to, and for all others on the system.
You can examine the default permissions for a file you create by using the
umask command, which lists default permissions using the number system explained next, or by using the
touch command and then the
ls command’s long-format listing like this: ...