Linux file permissions decide who can read, change or run each file. Every file has an owner (user), a group owner, and three sets of permission bits for user (u), group (g) and others (o). The kernel checks them in order: if you are the owner, only the user bits apply; otherwise, if you are in the group, only the group bits apply; otherwise the others bits apply. Getting these right is the foundation of Linux security, and the exam expects you to convert between notations quickly.
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