Repository

sudo timedatectl list-timezones
sudo timedatectl set-timezone Asia/Singapore

type:

https://askubuntu.com/questions/863528/whats-the-difference-between-ls-and-la-why-do-they-give-the-same-output

Login shells:

• https://unix.stackexchange.com/questions/10852/whats-the-difference-between-sbin-nologin-and-bin-false
• https://serverfault.com/questions/519215/what-is-the-difference-between-sbin-nologin-and-bin-false
• https://unix.stackexchange.com/questions/155139/does-usr-sbin-nologin-as-a-login-shell-serve-a-security-purpose
• Users: https://www.hostinger.com/tutorials/how-to-see-system-users-in-ubuntu-linux-vps/

Virtual host folder:

• https://unix.stackexchange.com/questions/47436/why-is-the-root-directory-on-a-web-server-put-by-default-in-var-www
• Filesystem Hierarchy Standard: https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard

x11 forwarding:

• X11Forwarding yes in /etc/ssh/sshd_config and install an X11 server on the client machine, e.g. VcXsrv works, and there is a popular option Xming X11 Server for Windows. Ensure xauth is also installed (sudo apt install xauth).
• If using OpenSSL via Powershell, run $env:DISPLAY="127.0.0.1:0" in the client, and export DISPLAY="127.0.0.1:10.0" on the server.
• Establish SSH connection using the -Y flag, e.g. ssh -Y [USERNAME]@[ADDRESS]
• Use xeyes (sudo apt install x11-apps) as a lightweight X11 forwarding test.
• LIBGL_ALWAYS_INDIRECT=1?

Now I have a ton of system stuff on the server as a result of the testing earlier with apt install atom...

• suto apt autoremove [PACKAGE] or sudo apt remove --auto-remove [PACKAGE] removes configs and dependencies.
• sudo apt install aptitude and sudo aptitude purge [PACKAGE] removes orphaned dependencies.
• sudo apt install deborphan and deporphan; sudo apt autoremove $(deporphan) removes more stuff.
• For complete removal, see this SO answer.

GNUPLOT

# Double y-axes
set key autotitle columnhead  # use first line as column title
set ytics autofreq tc lt 1
set y2tics autofreq tc lt 2
plot "data.txt" using 1 w l linetype 1, "" using 2 w l linetype 2 axes x1y2

# Multiplot
set multiplot layout 4,1 rowsfirst  # 4 rows, 1 column
set yrange [200:450]
plot "long_term_trend.txt" using 1 w l
set yrange [350000:430000]
plot "long_term_trend.txt" using 3 w l
set yrange [28.9:29.1]
plot "long_term_trend.txt" using 4 w l
set yrange [41.9:42.1]
plot "long_term_trend.txt" using 5 w l
unset multiplot

See this for a more detailed guide.