umask is a Unix command which displays or sets the file mode creation mask. That is, it determines what permission bits will not be set when a new file or directory is created. umask is commonly run in a user's startup scripts. "umask 022" means that other people can read the user's files and browse through their directories, but not edit their files. "umask 077" means that other people cannot access the user's files at all. These are the most common umask values.