Summary

Unix is a multi_user, multi_tasking operating system. The file_system is a single tree with the root_directory at /. Work happens in the shell. Run commands with arguments, chain via pipes, and use redirection for standard_input and standard_output. processes have process_id and exit_status. permissions combine user_group_others and rwx_bits. environment_variables like the path_variable control lookup. Core tools include ls, cd, cp, mv, rm, grep, cat, chmod, ps, and kill.