Why Does Fast Sync Restart

As stated in Péter Szilágyi's comment above, you will have to wait for --fast syncing to complete, otherwise you will have to restart the process again. The message you should see on your console when --fast syncing has completed is "fast sync complete, auto disabling" as shown below:

I0416 17:16:12.631667 30629 blockchain.go:1251] imported 195 block(s) (0 queued 0 ignored) including 0 txs in 1.235990428s. #384 [d707e667 / d3d5d5c1] I0416 17:16:12.631825 30629 sync.go:180] fast sync complete, auto disabling I0416 17:16:48.831757 30629 blockchain.go:1251] imported 4 block(s) (0 queued 0 ignored) including 0 txs in 12.933585ms. #388 [bbb506ab / 0ace7268] 

And to restart, you will have to clear your chaindata folder - see "How do I reset my blockchain and run geth --fast" below.

Ethereum Mining after Fast Sync

Sync the blockchain, and when you have the latest blocks being sycned, you can type the following command in your console:

miner.start(n) 

where n is the number of threads you want your CPU to mine with.

I'm assuming here that you want to mine the blockchain with a regular CPU, and not a graphics processing unit (GPU). You may want to refer to Is CPU mining even worth the Ether? .

If you do have a GPU on your computer, you may first want to search this site for "mining" Q&As, or ask a separate question if you cannot find an answer. Here is one Q&A - How to mine Ether on GNU + Linux? .

Note that you will have to firstly create an account into which your mining rewards get paid into. See "But I do have a GPU and want to mine with it" below.

How should I proceed?

See details below.

What should I do to stay synced?

You should only need to run geth --fast console for the first time. The --fast option will not sync the blocks any faster after the first time. You can omit the --fast parameters in subsequent runs of geth.

When you run geth for the first time without the --fast parameter, geth may take a few days to download the blockchain from other computers over the Internet - this time depends on the speed of your network connection and your computer CPU.

If you do use geth --fast for the first time in your fresh installation, geth --fast will take several hours to download the blockchain - again this would depend on your network connection and your CPU.

After your initial download of the blockchain using geth --fast, you only run geth without the --fast parameter. The synching now will be fast as only the new blocks need to be download from other Ethereum nodes over the Internet and they are being produced at an average rate of about one block every 14 to 15 seconds.

If you want to reset your blockchain and re-download the blockchain using --fast, see the section below "How do I reset my blockchain and run geth --fast".

Did I do some wrong or geth --fast is not for mining?

geth --fast is used to INITIALLY download a copy the current blockchain from other Ethereum nodes over the Internet. As answered in What is Geth's "fast" sync, and why is it faster? :

Instead of processing the entire block-chain one link at a time, and replay all transactions that ever happened in history, fast syncing downloads the transaction receipts along the blocks, and pulls an entire recent state database.

geth --fast is NOT for mining. It is just the first step of downloading a copy of the blockchain. You will subsequently need a continuously syncing copy of the blockchain if you want to mine.

Was any other step that I missed?

Not that I can tell. It is unusual that your chain will start syncing from the beginning, unless it did not complete correctly or there are some configuration problems. Try clearing your chaindata directory and re-sync your blockchain. You should not need to re-sync from scratch after this.

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The Details

I'm assuming that you want to run the syncing command in one window (#1) and attach another geth console in another window (#2). And when you want to exit from your console, use the Control-D (^D) keystroke. If you you Control-C multiple times, or kill the process in other ways (kill in Linux or Mac, or Task Manager in Windows), your blockchain data can get corrupted (only very rarely - happened to me once).

Syncing for the first time

In window #1, run the command:

geth --fast console 

In window #2, run the following command to attach to the geth --fast console instance above:

geth attach 

You don't need the --rpc flags for this as communication between these two geth instances will be done over the IPC protocol. The IPC protocol only runs within the local computer through a file descriptor. The RPC protocol can be used for communication across different computers.

Syncing after the first time

In window #1, run the command:

geth console 

In window #2, run the following command to attach to the geth console instance above:

geth attach 

Console message difference between --fast and normal syncing

The following messages are displayed on the geth --fast console screen - note the header(s) and receipt(s):

I0416 13:35:53.497422 30629 blockchain.go:889] imported 192 header(s) (0 ignored) in 71.941018ms. #6336 [2edbbc3f… / b80c9ac3…] I0416 13:35:54.263134 30629 blockchain.go:1044] imported 192 receipt(s) (0 ignored) in 55.447062ms. #6336 [2edbbc3f… / b80c9ac3…] I0416 13:35:54.683682 30629 blockchain.go:889] imported 192 header(s) (0 ignored) in 73.050377ms. #6528 [8ab9a7af… / f2ffecac…] 

And the following messages are displayed on the geth console screen - note the block(s):

I0416 13:32:23.331906 30581 blockchain.go:1251] imported 256 block(s) (0 queued 0 ignored) including 0 txs in 979.938402ms. #6366 [66dcf4c1 / c5d009a1] I0416 13:32:24.169955 30581 blockchain.go:1251] imported 256 block(s) (0 queued 0 ignored) including 0 txs in 836.388044ms. #6622 [e11a3fa9 / d211c2e1] I0416 13:32:24.974790 30581 blockchain.go:1251] imported 256 block(s) (0 queued 0 ignored) including 0 txs in 803.457715ms. #6878 [c9f9ae12 / 238493b8] 

Here is the transition when the --fast syncing has completed and normal syncing starts:

I0416 17:16:12.631667 30629 blockchain.go:1251] imported 195 block(s) (0 queued 0 ignored) including 0 txs in 1.235990428s. #384 [d707e667 / d3d5d5c1] I0416 17:16:12.631825 30629 sync.go:180] fast sync complete, auto disabling I0416 17:16:48.831757 30629 blockchain.go:1251] imported 4 block(s) (0 queued 0 ignored) including 0 txs in 12.933585ms. #388 [bbb506ab / 0ace7268] 

How do I reset my blockchain and run geth --fast

The blockchain data, by default, is stored in the following locations (reference Backup & Restore):

• Mac: ~/Library/Ethereum/chaindata
• Linux: ~/.ethereum/chaindata
• Windows: %APPDATA%\Ethereum\chaindata

Delete the contents of the directory above, or move it to another location and when you have successfully synced you data then delete the old copy.

Once the data in the chaindata directory is removed, you should be able to --fast sync again.

But I do have a GPU and want to mine with it

In this case you will need another application like ethminer that will perform the mining operations on the GPU. Communications between geth and ethminer does not work via IPC. You will need to enable the RPC communications using:

geth --rpc console 

geth uses the default --rpcaddr 127.0.0.1 and --rpcport 8545. Start your ethminer with the following command

ethminer -F http://127.0.0.1:8545 -G 

The -G parameter is the instruction for ethminer to perform the mining computations using your GPU.

Before you can run the commands above to mine, you will have to create an account into which any mining rewards will be paid into. Run the following command

geth account new 

You will be prompted for a password twice, then you are good to run the commands above.

Related Questions

The moderators may mark this question as a duplicate as there are several questions on this site that are possibly related:

• What is the difference between "geth" and "geth --fast"?
• How to delete or reset the blockchain in geth? (OSX)
• Why isn't fast sync the default?
• Why is fast sync not working with geth 1.1?
• How can I empty the blockchain?

But I hope that this is a more complete guide to get you past your sync problems.