I created two accounts and for both the account addresses I provided them with some ether in a customised genesis.json. Then I ran the command
geth - datadir "/tmp/ethereum_dev_mode/" -dev unlock 0,1 -rpc -rpcaddr w.x.y.z -rpccorsdomain "*" -rpcport abcd init "/tmp/ethereum_dev_mode/genesis.json"
This command ran successfully and it created the custom genesis block, allocated cache and file handles ,wrote the genesis state,etc. then I ran the command geth -datadir "/tmp/ethereum_dev_mode/geth/" -fast console "/tmp/ethereum_dev_mode/genesis.json" -dev I got the following error-
Fatal: Error starting protocol stack: database already contains an incompatible genesis block (have 65e04841b69188e8, new e5be92145a301820)
Is is because of a customised genesis file? Even when using the customised genesis file, the init command ran successfully but starting the Dev console failed.