Where is bitcoin.conf and why doesn't bitcoind find existing datadir v0.17.1 Just built no gui, no wallet bitcoin on WSL Ubuntu Bionic, Bitcoin v0.17.1.

I want to experiment with bitcoin-cli.

I followed recommendation to run bitcoind -princonsole and it says:
Using config file 


  /home/&lt;myusername&gt;/.bitcoin/bitcoin.conf


This file doesn't exist.

I followed some dense discussion on how should this behave to make dumb users happier on github, supposedly there were some merges, but frankly, I have no clue what was the final conclusion and what is or isn't in 0.17.1

Eventually, I understood that datadir must be specified first.

But that doesn't work for me.

~/bitcoin$ bitcoind -datadir /mnt/d/blockchain -txindex
Error: Specified data directory "" does not exist.


/mnt/d/blockchain definitely exists.

Thanks for any help.

 Many thanks to Nate Eldredge for pointing out a dumb error of mine and hope someone can help parsing and shedding some light on this:

https://github.com/bitcoin/bitcoin/issues/10746

Blockchain download has started and now I am waiting for the end result.
The syntax should be

bitcoind -datadir=/mnt/d/blockchain -txindex


Note the = sign.

This will look for the bitcoin.conf file at /mnt/d/blockchain/bitcoin.conf and will store the blockchain, databases, wallet files, etc, all in /mnt/d/blockchain.  With this option, Bitcoin Core shouldn't read or write anything in ~/.bitcoin at all.