Ubuntu Linux setup basics

For username "foo":

$ adduser foo

$ passwd foo

$ sudo usermod -aG sudo foo

$ mkdir -p /home/foo/.ssh

$ cat the_public_key.pem >> /home/foo/.ssh/authorized_keys

$ chown -R foo:foo /home/foo/.ssh

$ chmod 700 /home/foo/.ssh

$ chmod 600 /home/foo/.ssh/authorized_keys

Disable default account:

$ usermod -s /usr/sbin/nologin default_username

Notes:

Not useradd.
Even when logging in with just SSH key, user must have a password. It will only be used for sudo commands.

Sources:

https://unix.stackexchange.com/questions/210228/add-a-user-without-password-but-with-ssh-and-public-key

When Postgres allows any password

Problem: Postgres does not check my password, i.e. it accepts all passwords.

Solution: pg_hba.conf and change trust to md5. Restart postgres. That is all.

(source)

Bash script must run as root

# This script must be run as root

if [ "$(id -u)" != "0" ]; then
    echo "This script must be run as root" 1>&2
    exit 1
fi

Add a password to a MySQL login

Many applications require there to be a password.

SELECT host, user FROM mysql.user;

SET PASSWORD FOR 'bob'@'%.loc.gov' = PASSWORD('newpass');

Remove MySQL user password

root@dsdsdsdsd:~# mysql -p
Enter password:
mysql> use mysql;
mysql> update user set Password='' where User='yourusername';
mysql> commit;
mysql> flush privileges;
mysql> quit;

Bash profile settings

~/.bash_profile gets called when you log in for the first time. It's your user-specific settings.

~/.bashrc gets called when you start a new shell. Only interactive shells and user scripts read this file.

Allow different users to access MySQL

GRANT ALL PRIVILEGES ON *.* TO 'username'@'hostname';

The single quotes around username and hostname are required.