Linux Labs
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Users, permissions, and processes / Stage 7 of 13

Managing group membership

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Step 6 of 6 · summary · 2 min

Summary

  • The primary group is recorded in /etc/passwd, supplementary ones in /etc/group; usermod -g changes the first, -G the whole list of the second.
  • You add a group with usermod -aG and remove one with gpasswd -d; look at id before and after.
  • Changing the account does not touch running processes: check granting and removal with a fresh process, sudo -u.
  • At the start of the lesson the request -G lab-writers set the supplementary list anew, and lab-readers dropped out of it.

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Reference for this lesson

Articles

  • File permissions — The Unix permission model — read/write/execute, owner/group/other, special bits.
  • Users and groups — Linux accounts and groups; usermod -G without -a replaces all of a user's supplementary groups instead of adding one.
  • usermod — change an account and its groups — The usermod command changes an existing account — groups, login shell, home directory, name and locking.
  • 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.
Ubuntu 24.04
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