[arch-general] help

Hello.I'm a new users of Archlinux but using Ubuntu for 3 years. I have installed all the system following the guide of beginner's guide. and I found I could not ping to google after I reboot my computer however just as 5 minutes before I had just used pacman to install all the packages i needed. and then I use “systemctl enable dhcpcd@ ” hoping to reset the Internet connection but the shell tells me“ Fail to issue method call:Read-only file system” Does anyone know what's the problem? Thank you!