Difference between a controller and a custodian for a cycles wallet?

[bobbylingus]

“dfx canister” command has these options, but what is the difference?

[claudio]

I couldn’t find an answer here Use the default cycles wallet :: Internet Computer but perhaps someone on the appropriate team could shed some light on the difference.

[prithvi]

Not sure if dfx canister has these options, maybe youre thinking of dfx wallet
A Controller is the most privileged role, and can rename the wallet, add entries to the address book, add/remove controllers, authorize/deauthorize custodians. A Custodian can access the wallet information, send cycles, forward calls, and create canisters.

[paulyoung]

Are canister custodians able to upgrade canister code?

The concept of a custodian is not something the IC itself knows - the spec does not even contain the word ‘custodian.’ Since this is a concept that’s entirely defined within canisters, it all depends on the implementation. I’m not sure a canister can be its own controller and self-update, but with a proxy canister (say you’re custodian of A and tell A to upgrade, A sends this command over to B. B is a controller of A, and upgrades A’s code) this would 100% be possible.