This chapter presents a collection of problems focused on the topic of access control, offering both theoretical and practical insights. The first part examines foundational access control policies, including discretionary access control (DAC) and mandatory access control (MAC). This section covers key models such as Bell-LaPadula (BLP), which emphasizes confidentiality, and the more general Lattice-Based Access Control (LBAC), which provides a flexible framework for modeling complex access hierarchies. The second part contains exercises related to the access control mechanisms implemented in Linux systems. It includes exercises on the Linux permission model, exploring topics such as file ownership, user groups, and the traditional read/write/execute permission system. Additionally, it examines more advanced mechanisms, including POSIX Access Control Lists (ACLs) for fine-grained permissions and extended features such as capabilities and file attributes. These exercises aim to help readers gain hands-on experience with configuring and analyzing access control in Linux environments.