setupLibrary.sh

#!/bin/bash

# Add the new user account
# Arguments:
#   Account Username
#   Account Password
#   Flag to determine if user account is added silently. (With / Without GECOS prompt)
function addUserAccount() {
    local username=${1}
    local password=${2}
    local silent_mode=${3}

    if [[ ${silent_mode} == "true" ]]; then
        sudo adduser --disabled-password --gecos '' "${username}"
    else
        sudo adduser --disabled-password "${username}"
    fi

    echo "${username}:${password}" | sudo chpasswd
    sudo usermod -aG sudo "${username}"
}

# Add the local machine public SSH Key for the new user account
# Arguments:
#   Account Username
#   Public SSH Key
function addSSHKey() {
    local username=${1}
    local sshKey=${2}

    execAsUser "${username}" "mkdir -p ~/.ssh; chmod 700 ~/.ssh; touch ~/.ssh/authorized_keys"
    execAsUser "${username}" "echo \"${sshKey}\" | sudo tee -a ~/.ssh/authorized_keys"
    execAsUser "${username}" "chmod 600 ~/.ssh/authorized_keys"
}

# Execute a command as a certain user
# Arguments:
#   Account Username
#   Command to be executed
function execAsUser() {
    local username=${1}
    local exec_command=${2}

    sudo -u "${username}" -H bash -c "${exec_command}"
}

# Modify the sshd_config file
# shellcheck disable=2116
function changeSSHConfig() {
    sudo sed -re 's/^(\#?)(PasswordAuthentication)([[:space:]]+)yes/\2\3no/' -i."$(echo 'old')" /etc/ssh/sshd_config
    sudo sed -re 's/^(\#?)(PermitRootLogin)([[:space:]]+)(.*)/PermitRootLogin no/' -i /etc/ssh/sshd_config
}

# Setup the Uncomplicated Firewall
function setupUfw() {
    sudo ufw allow OpenSSH
    yes y | sudo ufw enable
}

# Create the swap file based on amount of physical memory on machine (Maximum size of swap is 4GB)
function createSwap() {
   local swapmem=$(($(getPhysicalMemory) * 2))

   # Anything over 4GB in swap is probably unnecessary as a RAM fallback
   if [ ${swapmem} -gt 4 ]; then
        swapmem=4
   fi

   sudo fallocate -l "${swapmem}G" /swapfile
   sudo chmod 600 /swapfile
   sudo mkswap /swapfile
   sudo swapon /swapfile
}

# Mount the swapfile
function mountSwap() {
    sudo cp /etc/fstab /etc/fstab.bak
    echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab
}

# Modify the swapfile settings
# Arguments:
#   new vm.swappiness value
#   new vm.vfs_cache_pressure value
function tweakSwapSettings() {
    local swappiness=${1}
    local vfs_cache_pressure=${2}

    sudo sysctl vm.swappiness="${swappiness}"
    sudo sysctl vm.vfs_cache_pressure="${vfs_cache_pressure}"
}

# Save the modified swap settings
# Arguments:
#   new vm.swappiness value
#   new vm.vfs_cache_pressure value
function saveSwapSettings() {
    local swappiness=${1}
    local vfs_cache_pressure=${2}

    echo "vm.swappiness=${swappiness}" | sudo tee -a /etc/sysctl.conf
    echo "vm.vfs_cache_pressure=${vfs_cache_pressure}" | sudo tee -a /etc/sysctl.conf
}

# Set the machine's timezone
# Arguments:
#   tz data timezone
function setTimezone() {
    local timezone=${1}
    echo "${1}" | sudo tee /etc/timezone
    sudo ln -fs "/usr/share/zoneinfo/${timezone}" /etc/localtime # https://bugs.launchpad.net/ubuntu/+source/tzdata/+bug/1554806
    sudo dpkg-reconfigure -f noninteractive tzdata
}

# Configure Network Time Protocol
function configureNTP() {
    sudo apt-get update
    sudo apt-get --assume-yes install ntp
}

# Gets the amount of physical memory in GB (rounded up) installed on the machine
function getPhysicalMemory() {
    local phymem
    phymem="$(free -g|awk '/^Mem:/{print $2}')"
    
    if [[ ${phymem} == '0' ]]; then
        echo 1
    else
        echo "${phymem}"
    fi
}

# Disables the sudo password prompt for a user account by editing /etc/sudoers
# Arguments:
#   Account username
function disableSudoPassword() {
    local username="${1}"

    sudo cp /etc/sudoers /etc/sudoers.bak
    sudo bash -c "echo '${1} ALL=(ALL) NOPASSWD: ALL' | (EDITOR='tee -a' visudo)"
}

# Reverts the original /etc/sudoers file before this script is ran
function revertSudoers() {
    sudo cp /etc/sudoers.bak /etc/sudoers
    sudo rm -rf /etc/sudoers.bak
}

# Install prerequisite dependencies
# reference: https://linuxconfig.org/how-to-install-docker-on-ubuntu-18-04-bionic-beaver
function installPrerequisite() {
    sudo apt update
    sudo apt install apt-transport-https ca-certificates curl software-properties-common
}

# Install docker
# from: https://www.digitalocean.com/community/tutorials/how-to-install-and-use-docker-on-ubuntu-16-04
function installDocker() {
    curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
    sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
    sudo apt-get update
    sudo apt-get install -y docker-ce
}

# Install docker compose and docker compose command completion
# reference: https://docs.docker.com/compose/install/
#            https://docs.docker.com/compose/completion/
#            https://gist.github.com/wdullaer/f1af16bd7e970389bad3
function installDockerCompose() {
    COMPOSE_VERSION=$(git ls-remote https://github.com/docker/compose | grep refs/tags | grep -oP "[0-9]+\.[0-9][0-9]+\.[0-9]+$" | tail -n 1)
    sudo curl -L "https://github.com/docker/compose/releases/download/$COMPOSE_VERSION/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose
    sudo chmod +x /usr/local/bin/docker-compose
    sudo curl -L "https://raw.githubusercontent.com/docker/compose/$COMPOSE_VERSION/contrib/completion/bash/docker-compose" -o /etc/bash_completion.d/docker-compose
}

# Install lnav - http://lnav.org/
function installLnav() {
    curl -L https://github.com/tstack/lnav/releases/download/v0.8.3/lnav_0.8.3_amd64.deb -o lnav-latest.deb
    sudo dpkg -i lnav-latest.deb
}

# Install mosh
# Incorporate idea from: https://stephen.rees-carter.net/thought/mosh-and-ufw-without-1000-open-ports
# to auto open/close mosh port
function installMosh() {
    sudo apt-get install -y mosh
    sudo ufw allow mosh
    
    # this doesn't seem to work - mosh can't connect - need to check again
    #sudo cp mosh-allow-ufw.sh /usr/local/bin/mosh-allow-ufw.sh
    #sudo chmod +x /usr/local/bin/mosh-allow-ufw.sh
    #sed -i '$ a sudo /usr/local/bin/mosh-allow-ufw.sh' ~/.bashrc
}

# Update packages
function updatePackages() {
    sudo apt-get update
    sudo apt-get upgrade -y
    sudo apt autoremove -y
}