More for my own reference and in preparation of me completely gutting my system, I’m posting the contents of my .xmodmaprc file which swaps the left control and alt-keys. This allows me to use my linux laptop more like I used my mac, with the command key. Many distributions now let you swap this from a setting but if yours doesn’t here is how to go about it.
Feel free to copy the contents to a file called .xmodmaprc and run it using the xmodmap command:
remove Control = Control_L
$ xmodmap .xmodmaprc
Note that with some modern Desktop Environments like Gnome 3, you can use the Gnome Tweaks package and have the DE handle this for you.