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Linux management basics

User accounts​

Create a user account​

Sudo-enabled account:

sudo useradd -m -s /bin/shell -G sudo <username>

Non-sudo account:

sudo useradd -m -s /bin/shell <username>

Add user to group​

sudo usermod -a -G <group> <username>

Allow passwordless sudo​

Edit the /etc/sudoers file or run sudo visudo:

# All commands for all users in the sudo group
%sudo ALL=(ALL) NOPASSWD:ALL

# Specific command for a specific user
<user> ALL=(ALL) NOPASSWD: <full_path_to_binary>

This will allow all users in the sudo group to run sudo commands without specifying a password.

Create a cron job from the command line​

This is useful for headless installs or dockerfiles.

cronfile="crontab-test-install"

mkdir -p /tmp/crontab-test-install && cd /tmp/crontab-test-install

echo "* * * * * curl https://google.com > /dev/null" >> crontab-test

crontab crontab-test
rm -rf /tmp/crontab-test-install

Fix LF/CRLF issues​

Using vim:

vim <filename> -c "set ff=unix" -c ":wq"

Stop script execution if not running under root​

if [[ $EUID -ne 0 ]]; then
   echo "[ERROR] This script must be run as root"
   exit 1
fi