Cactus going yellow :(

[cactusjack]

Hey there, I got a cactus a few months ago and it's starting to turn yellow at the bottom and it looks like there are some small cracks. I had a look online and from what I saw it seems like yellow could be due to not enough water or too much water but I don't know how to tell. Hopefully someone has an idea of what I should do? pics attached, thanks

 

[DirtMechanic]

It seems like that type of plant is built for full sun. I imagine it likes a drier soil, given how it appears built to hold its own water for extended periods of time. I doubt it eats much either, so a rich tropical swampy compost might be the exact opposite of the type soil it would have come from.