Sources: https://www.rosehosting.com/blog/generate-password-linux-command-line/

All examples generate a 16 character long password

OpenSSL

$ openssl rand -base64 16 | colrm 17

GPG

$ gpg --gen-random --armor 1 16 | colrm 17

/dev/urandom

$ head /dev/urandom | tr -dc '[:graph:]' | fold -w16 | sed '$d' | shuf -n1

or maybe (piping all above commands to wc gives 17, this below will give 16 characters)

$ cat /dev/urandom | tr -dc [:alnum:] | head -c16

$ cat /dev/urandom | tr -dc [:punct:][:alnum:] | head -c16