How to Access the Files to Back Up
Using Mist - Backup Accounts
Go to the top bar and select ACCOUNTS
-> BACKUP
-> ACCOUNTS
.
This will open a folder. Inside this folder there are keystrore files that have long names starting with UTC--2016-04-14.......
Each of these files represent an account. Back up these up.
Using Mist - Backup Wallet Contracts
Go to the top bar and go ACCOUNTS
-> BACKUP
-> APPLICATION DATA
. This will open a folder. As far as I can tell, just back up this entire folder.
You could also manually add the wallet contracts back at any time, obviously, but this is easier and more convenient.
How to actually back up
You want to store the keystore files in multiple locations & multiple physical locations. Keep in mind, you must prevent loss of both the keystore file and password due to loss or failure of you hard drive, USB drive, or whatever method you are using to back up. You also must keep in mind physical loss / damage of an entire area (think fire or flood).
For example, consider the add'l security of storing things in 3 places, over 1:
- On computer
This way if your house burns down, you still have access to your funds. If your HDD crashes, your still access.
If you do want a paper option, you can import your Mist keystore file into MyEtherWallet (running offline/locally, see #5 here). Follow those instructions and use the View Wallet Info tab in order to access your Mist wallet and then print a paper version.
Using old Mist without the ACCOUNTS
-> BACKUP
available.
On some versions, (0.3.9) there may just be a BACKUP option in the top bar, not under accounts. For old versions (0.3.7 or lower) the backup option is simply not there.
Depending on what OS you have, you need to navigate to the right folder (below) and back these keystore files / the entire keystore folder up.
Accounts
Mac: ~/Library/Ethereum/keystore
Linux: ~/.ethereum/keystore
Windows: %APPDATA%/Ethereum/keystore
Wallet Contracts
The above will only back up your normal accounts. Wallet Contracts can be manually re-added, or you can back up the data folder. As far as I can tell:
Mac: ~/Library/Application Support/Mist/
Linux: ~/.config/Mist
or, in earlier versions: ~/.config/Chromium/Mist
(folder is hidden)
Windows: C:\Users\< Your Username >\AppData\Roaming
-or- ~\AppData\Roaming\Ethereum\keystore
The folders I see online tend to be all over the place. I can confirm that the above certainly hold true to my Mac.
And once again: Back up your KEYSTORE FILES (aka your private key) and your PASSWORDS. Both items are necessary to access your account. Your address (public key) is not actually needed to restore access. 👍
--
Edit: I found this (possibly out of date) list for go (geth) and c++ (eth) clients which may be helpful for some.
Best Answer
If you wish to move an item from one OS to another, it's simply a matter of copying the necessary files to their appropriate folder on the new computer.
For accounts, that's the keystore files under Accounts -> Backup -> Accounts.
For wallet contracts, that's the items in the application data folder.
It may be that the application data differs slightly between one OS to another. If your wallet contract still isn't showing up, click ADD WALLET, click IMPORT WALLET, and then paste the address of your wallet contract and import it.
As a note, while doing this you should always copy file and never delete any files until you are 100% certain you have 100% access to all accounts / wallet contracts.
This has the full breakdown of where the keystore files (accounts) and application data (wallet contracts) are stored on Windows, Mac, and Linux