Table of Contents

Helpful Ubuntu/Linux Commands and Procedures

Miscellaneous/General Commands

Disable Ubuntu Pro "Ads", Etc.

sudo pro config set apt_news=false

List hard drive serial numbers

lsblk --nodeps -o name,serial

List processes and the ports they are listening on

netstat -tulpn | grep LISTEN

or 

ss -tulpn | grep LISTEN

Reload systemd manager configuration after changes made

sudo systemctl daemon-reload

List all installed packages

apt list --installed

Search for available packages

apt-cache search <keyword>

Changing default editor for visudo

sudo update-alternatives --config editor

If visudo complains about a missing defaults.vim file, it can be fixed thusly: 

sudo touch ~root/.exrc

Disable GUI screen lock

Settings -> Privacy -> Screen Lock

Disable GUI screen blanking

Settings -> Power -> Blank Screen

Create Samba User

sudo smbpasswd -a <username>

List Samba Users

sudo pdbedit -L

Determine the date the system was installed (not 100% reliable)

tune2fs -l /dev/vda2 | grep ‘Filesystem created:’ (replace vda2 with device where root filesystem is located)

Copy an existing partition to a new partition

sudo rsync -aAXv --info=progress2 --exclude='/lost+found' /disk2/ /newdisk/

Finding largest files/directories

du -a /dir/ | sort -n -r | head -n 20 (replace 20 with the # of lines you wish to have returned)

Find the oldest file in a directory (and it's subdirectories)

find . -type f -printf '%T+ %p\n' | sort | head -n 1

Finding files by file name (or file name portion)

find . -iname <filename to search for>

Disable colors in the vi editor by default

Create (or edit, if it exists) ~/.vimrc; into this file add the command syntax off, and save the file.

Find files consuming the root file system

mkdir /tmp/rootbind
mount --bind / /tmp/rootbind
du -d 1 -h /tmp/rootbind

Solution for Linux systems not visible in the "Network Neighborhood" on Windows machines

apt install wsdd

View video resolution capabilities

xrandr -q

Converting OTA DVR recordings to .MP4

OTA DVR recordings are saved as .ts files, which are not compatible with DaVinci Resolve (my video editor of choice). For this reason, we must convert the files into a format that “DR” can comprehend. We can do this on linux using the ffmpeg package: 

ffmpeg -i <inputfile.ts> -vcodec copy -acodec copy <outputfile.mp4>

Overwrite/blast the boot block on the hard drive (ONLY when you want to re-install the operating system!) 

dd if=/dev/zero of=/dev/sda count=1 bs=512

Generate password hashes (useful for Ansible playbooks amongst other things)

mkpasswd --method=sha-512

Generate random keys

openssl rand -base64 48

Example of referencing an Ansible Vault

ansible-playbook playbook.yml --vault-password-file ~/.ansible_vault_pass

Extracting encrypted/password protected .ZIP files

.zip files that have been encrypted with AES-256 cannot be extracted via the default 'unzip' program that the distro installs. Instead, one must install 7zip. Perform the following steps: 

apt update
apt install 7zip

Once installed, use the 7zz command to extract the file (you will be prompted for the password used to initially encrypt the archive if one was used): 

7zz x <filename>

Cookbook for passing client IP address to systems behind a reverse proxy

On the reverse proxy:

Ensure that websockets support is enabled

On the host:

Create /etc/apache2/conf-available/remoteip.conf with the following contents: 

RemoteIPHeader X-Forwarded-For
RemoteIPTrustedProxy x.x.x.x (replace w/ IP address of trusted proxy)

Execute the commands: 

ln /etc/apache2/conf-available/remoteip.conf /etc/apache2/conf-enabled/remoteip.conf
ln /etc/apache2/mods-available/remoteip.load /etc/apache2/mods-enabled/remoteip.load

Edit /etc/apache2/apache2.conf and find the LogFormat lines. Change each occurrence of %h to %a.

Restart apache.

Create new GPT disk partition

sudo into an elevated shell and then perform the following: 

parted /dev/sdX (where X is the letter of the drive to be manipulated)
mklabel gpt
Acknowledge the warning if one is given
unit TB
mkpart primary 0.00TB 2.00TB (or 3.00TB, 4.00TB, etc. depending on the size to be created)
print (to view the new partition)
quit (to exit parted)

Then proceed to format the new drive, i.e. mkfs -t ext4 /dev/sdb1

Updating Network Settings

Changing the server's IP address

sudo vi /etc/netplan/00-installer-config.yaml
find the existing IP and change it to the desired IP; 'wq' out of the file
sudo netplan apply

Changing the server's host name

hostnamectl set-hostname [new host name]

Changing the server's DNS settings

Edit the /etc/netplan/50-cloud-init.yaml file appropriately (file name may vary)
Apply the changes with the sudo netplan apply command

Disabling the local DNS resolver

This becomes necessary if a DNS server is deployed on the local system, since it will conflict with the local resolver unless it is first disabled.

Edit /etc/systemd/resolved.conf and change DNSStubListener to “no”: 

DNSStubListener=no

Update the resolv.conf symlink: 

sudo ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf

Restart systemd-resolved: 

sudo systemctl restart systemd-resolved

Validate that the system is no longer listening on port 53: 

ss -tulpn | grep 53

Creating SSH Keys

To create an ed25519 key - 

ssh-keygen -t ed25519 -C "<comment>" -f ~/.ssh/<keyname>