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System Administration

Add a new user

$ useradd <USERNAME> -u <USER_ID> -s /bin/bash
$ useradd ktrushin -u 1000 -g 1000 --create-home --user-group

Add an existing user to an existing group

$ sudo usermod -aG <group_name> <user_name>

Change user uid and gid

$ usermod -u <NEWUID> <LOGIN>
$ groupmod -g <NEWGID> <GROUP>

Merge two directories:

$ rsync -a source_dir/* dest_dir/

Memory a process consumes (in KB)

$ ps --no-header -C <process_command> -o rss | awk '{rss += $1};END{print rss}'
$ smem -P <process_command> -c pss -H | \
  python3 -c "from fileinput import input; print(sum(map(int, input())))"

List hardware on a PC

$ lshw
$ lspci
$ lsusb
$ inxi

Get date as unixtime

$ date +%s

Convert a date to unixtime

$ date -d "2015-09-04 13:35:00" +%s

Convert unixtime to a date

$ date -d @1451573940

Fix Ctrl-Shift-e in terminator

$ ibus-setup

Then remove the keybinding for Emoji

Restart GUI:

  1. change to another virtual console using <ctrl+alt+f2>
  2. login
  3. run sudo systemctl restart systemd-logind or sudo systemctl restart gdm
  4. change back to the virtual console where GUI is bind to using <ctrl+alt+f7>

Install system monitor GNOME extentions on Ubuntu 20.04:

  • install required packages 
    $ sudo apt-get install gir1.2-gtop-2.0 gir1.2-nm-1.0 gir1.2-clutter-1.0 \
    gnome-system-monitor gnome-shell-extension-system-monitor
  • restart the machine

Install system monitor GNOME extentions on Ubuntu 22.04:

  • remove chrome-gnome-shell 
    $ sudo apt-get purge chrome-gnome-shell
  • install gnome-browser-connector of version 42.0 or higher 
    $ sudo apt-get update && sudo apt-get install gnome-browser-connector
  • alternatively, compile gnome-browser-connector from source and install manually 
    $ sudo apt-get install git meson
$ git clone https://gitlab.gnome.org/nE0sIghT/gnome-browser-connector.git
$ cd gnome-browser-connector
$ meson --prefix=/usr builddir
$ sudo install -C builddir
  • install required packages 
    $ sudo apt-get install gir1.2-gtop-2.0 gir1.2-nm-1.0 gir1.2-clutter-1.0 \
  gnome-system-monitor
  • restart the machine
  • install the system-monitor-next GHOME extension

Lock screen when lid is closed:

  • In Gnome Tweaks, enable General -> Suspend when laptop lid is closed
  • In /etc/systemd/logind.conf, uncomment the HandleLidSwitch and HandleLidSwitchExternalPower and change their values as follows:
HandleLidSwitch=lock
HandleLidSwitchExternalPower=lock

Install Windows 11 into VirtualBox: before installing, disable Setting -> System -> Enable EFI (special OSes only)

Install HP MFP m137fnw:

  1. Connect the printer to the Wi-Fi network via HP Smart app
  2. Discover the printer via Settings->Printers menu
  3. Install airscan:
$ sudo apt-get install sane-airscan
  1. Go to here, choose Linux -> Ubuntu and download the driver.
  2. Untar the driver and execute install.sh with sudo
  3. In the Settings->Printers menu select the printer settings, hit the Printer Details button, update the printer name to the desired one and hit the Install PPD file button, choose the /usr/share/ppd/uld-hp/HP_Laser_MFP_13x_Series.ppd file.

A data scrubbing command to prevent a bit rot on an external flash-memory-based drive (SSD, USB flash drive):

$ sudo dd if=/dev/disk/by-label/<drive_name> of=/dev/null iflag=nocache status=progress