Dial-in server

Configure PPP:

# /etc/ppp/options:
asyncmap 0
crtscts
local
lock
passive
proxyarp
lcp-echo-interval 30
lcp-echo-failure 4
netmask 255.255.255.0
192.168.1.7:192.168.1.8
noauth
silent

Setting up alias:

alias ppp="exec /usr/sbin/pppd -detach"

Automating getty:

# /etc/udev/rules.d/99-usb-serial.rules
# get attributes: `udevadm info --attribute-walk -n /dev/...`
# reload rules: `udevadm control --reload-rules`
SUBSYSTEM=="tty", DRIVERS=="pl2303", TAG+="systemd", ENV{SYSTEMD_WANTS}="serial-getty@$name.service"

udev rules, cbrake.