How to use a customised Data Directory in Dev mode(private blockchain)

Question

I have created the data directory in /home/ubuntu/ethchain. Then I created two accounts in this directory using the command (ran the command twice) geth -datadir "/home/ubuntu/ethchain" -dev account new Then I run the following command geth -fast console -dev to start the geth instance. Then I run following command geth -datadir "/home/ubuntu/ethchain" -dev attach ipc:/tmp/ethereum_dev_mode/geth.ipc

Now when I run the above command, I expect that since I have mentioned the data directory, any account query which I run in the interactive javascript console,i.e.,eth.accounts should return me details of the accounts I have created in the directory /home/ubuntu/ethchain. But it returns me an empty list. So how do I change the default data directory? Is there any change in some config file?

Answer 1

DevMode seems to be very strict. See source code here: https://github.com/ethereum/go-ethereum/blob/master/cmd/utils/flags.go, in particular the following lines:

Starting at line 798:

if ctx.GlobalBool(DevModeFlag.Name) {
        // --dev mode can't use p2p networking.
        cfg.MaxPeers = 0
        cfg.ListenAddr = ":0"
        cfg.DiscoveryV5Addr = ":0"
        cfg.NoDiscovery = true
        cfg.DiscoveryV5 = false
}

At line 816:

switch {
    case ctx.GlobalIsSet(DataDirFlag.Name):
        cfg.DataDir = ctx.GlobalString(DataDirFlag.Name)
    case ctx.GlobalBool(DevModeFlag.Name):
        cfg.DataDir = filepath.Join(os.TempDir(), "ethereum_dev_mode")
    case ctx.GlobalBool(TestnetFlag.Name):
        cfg.DataDir = filepath.Join(node.DefaultDataDir(), "testnet")
    case ctx.GlobalBool(RinkebyFlag.Name):
        cfg.DataDir = filepath.Join(node.DefaultDataDir(), "rinkeby")
}

At line 991:

case ctx.GlobalBool(DevModeFlag.Name):
    cfg.Genesis = core.DevGenesisBlock()

So based on my understanding of RTFS, whatever DataDir you try to provide, DevMode will always override it.

I suspect that DevMode is more useful for geth developers than it is for developers who want to use a geth private network to play around with smart contracts.

FWIW I wrote up a guide to getting my first private network set up, that might be more use to you than trying to twist DevMode to your needs: https://alanbuxton.wordpress.com/2017/07/19/first-steps-with-ethereum-private-networks-and-smart-contracts-on-ubuntu-16-04/