Mount ReadWrite

To have the boot drive automatically mounted as read/write, create a file at the root of the drive named .readwrite; you can create it with this command:

touch .readwrite

The hidden /etc/rc boot script checks for the existence of the file, and if found, the drive is mounted read/write automatically.

Note that /Users, /etc, /tmp, and /var are mounted on the Scratch volume, which is always writable.

Alternative One Liners

ReadWrite On:

sudo mount -uw /

ReadWrite Off:

sudo mount -ur /

I prefer to leave it mounted read only when I'm not writing