Which feature in Linux defines the default permissions assigned to newly created files and directories?

The umask is the feature in Linux that defines the default permissions assigned to newly created files and directories. When a new file or directory is created, the system applies a set of default permissions, and the umask value determines which of those permissions are removed.

In Linux, permissions for files and directories are typically expressed in terms of read, write, and execute for the owner, group, and others. The umask value is subtracted from the default permission values (typically 666 for files and 777 for directories) to determine the final permission settings. For example, if the umask is set to 022, the resulting permissions for a new directory would be 755 (rwxr-xr-x), where the write permission for the group and others has been masked out.

The other options represent different functionalities: chmod is used to change the permissions of existing files and directories; the sticky bit is a permission that prevents users from deleting files in a directory unless they are the owner; and SUID (Set User ID) allows users to run an executable with the permissions of the executable's owner. These concepts are important in understanding Linux permissions but do not pertain to the setting of default permissions for newly created files and directories.