aide-mémoire

Users and groups in Debian: getting it right

Published by Matthew Davidson on Thu, 19/10/2017 - 1:15pm in

So ideally when I set up a new computer, I want all the users I trust — including, by necessity and regrettably, myself — to be in the staff group, and all the files they create to be by default writable by anyone in that group. This ought to be easy, and in fact now is, but has changed repeatedly over the decades I've been using Debian GNU/Linux, so I can never remember how it's done, hence this note.

You will need to do all this as root, and to be on the safe side, make sure any user(s) you want to put into the staff group are not currently logged in, as files and directories in the affected home directories will be reassigned to the group, which (I guess) won't work for any currently opened by a running process.

If you enable the pam_umask PAM module, you will only need to configure group-writability once, and it will work regardless of whether you're logging in locally, SSHing, or whatever. As root, edit /etc/pam.d/common-session to include this line:

session optional        pam_umask.so

Then edit the umask line in /etc/login.defs like so:

UMASK 002

If yours isn't a fresh Debian install, the umask setting may already have been overridden in one or more of:

  • /etc/profile
  • /etc/bash.bashrc
  • ~/.profile
  • ~/.bashrc

If so, delete or comment out where necessary. (Source)

Adding a user to the staff group is:

usermod -a -G staff myusername

Making staff the user's primary group — the one which by default newly created files and directories are owned by — is just:

usermod -g staff myusername

Too easy.

Saturday, 7 October 2017 - 6:42pm

Published by Matthew Davidson on Sat, 07/10/2017 - 6:42pm in

I should never reboot my computer.

I am so out of touch that I didn't realise that a new version of Debian came out in June. "Splendid!", I thought. So:

# apt-get update
# apt-get dist-upgrade

… then off for a walk while two gigabytes downloaded (really must get rid of all those first-person shooters that are anyway far too violent for a gentleman of my advanced years).

Get through the upgrade, reboot the computer, and my USB WiFi dongle doesn't work. Here's how to diagnose/fix:

# lsusb
Bus 002 Device 002: ID 8087:8000 Intel Corp. 
[…]
Bus 003 Device 003: ID 045e:00cb Microsoft Corp. Basic Optical Mouse v2.0
Bus 003 Device 002: ID 413c:2003 Dell Computer Corp. Keyboard
Bus 003 Device 007: ID 0bda:8178 Realtek Semiconductor Corp. RTL8192CU 802.11n WLAN Adapter
[…]

Yes, I use a Microsoft mouse. Microsoft branded peripherals have generally been pretty darn good. I think this mouse is at least ten years old, and it's as good as the day I bought it. So now I know the WiFi chipset. I go to the Debian Wiki WiFi page, and find that I need the rtl8192cu driver, which is in the (non-free) firmware-realtek package, which is of course already installed because the blasted thing used to work. So now it's just a matter of:

# modprobe rtl8192cu

…and we're back in business. For good measure, I added rtl8192cu to the /etc/modules file, so that maybe I'll survive the next reboot unscathed. Not that I will be rebooting any time soon.