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Users, permissions, and processes / Stage 1 of 13

Users, groups, and process identity

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Step 7 of 7 · summary · 1 min

Summary

  • The kernel checks file access for a process, by its UID and groups; commands inherit them from the shell.
  • A file's owner is the user of the process that created it; the directory and the reader do not change it.
  • sudo runs one command as another user; test access as the user who needs it, with sudo -u.
  • A root process created the summary at the start, and only its owner may read it: cat as student was refused, sudo cat ran as root.

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Reference for this lesson

Articles

  • bash — the command shell — A command interpreter for interactive input, builtins, and shell scripts.
  • whoami — identify the effective user — whoami prints the user name tied to the process's effective user ID — the account you act as now.
  • The kernel — The core of the operating system: it manages processes, memory, devices, and filesystems; programs request its services through system calls. uname -r prints its version.
  • stat — file metadata — Full file information — size, permissions, owner, timestamps (atime/mtime/ctime), inode.
  • Users and groups — Linux accounts and groups; usermod -G without -a replaces all of a user's supplementary groups instead of adding one.
  • Processes — Viewing processes, signals and priorities; finding the processes that hog CPU or memory.
  • ps — list processes — The ps command lists running processes with PID, owner, state, CPU and memory use, and the command line.
  • sudo — running commands as another user — Grants temporary root rights via sudoers; edit the file only through visudo, or a mistake locks everyone out of sudo.
  • systemd — System and service manager that manages units and their dependencies.
Ubuntu 24.04
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