I'm doing some testing and often find myself needing to generate 6 blocks quickly to confirm some tx. Each block takes a few minutes to generate on my macbook so this slows things down considerably.

Is there a way to adjust difficulty? Note that this is not for testnet in general but for the private testnet in a box with just 2 nodes on my development machine. Thanks!

1 Answer 1


Changing these 2 lines gets what you want. Note that it's quick and dirty and will break non-testnet, so don't use this for anything but testnet:

diff --git a/src/main.cpp b/src/main.cpp
index a9311e2..b3496a1 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -780,7 +780,7 @@ int64 static GetBlockValue(int nHeight, int64 nFees)

 static const int64 nTargetTimespan = 14 * 24 * 60 * 60; // two weeks
-static const int64 nTargetSpacing = 10 * 60;
+static const int64 nTargetSpacing = 10;
 static const int64 nInterval = nTargetTimespan / nTargetSpacing;

@@ -1784,7 +1784,7 @@ bool LoadBlockIndex(bool fAllowNew)
     if (fTestNet)
         hashGenesisBlock = uint256("0x00000007199508e34a9ff81e6ec0c477a4cccff2a4767a8eee39c11db367b008");
-        bnProofOfWorkLimit = CBigNum(~uint256(0) >> 28);
+        bnProofOfWorkLimit = CBigNum(~uint256(0) >> 15);
         pchMessageStart[0] = 0xfa;
         pchMessageStart[1] = 0xbf;
         pchMessageStart[2] = 0xb5;

Here's some debug.log output with those changes. I'm generating a block every 2 seconds or so. If that's too fast, increase the ">> 15" accordingly. Each increment there doubles the time between blocks.

03/05/12 07:21:54 Flushing wallet.dat
Flushed wallet.dat 132ms
askfor block 000000935f454d1641e5   0
sending getdata: block 000000935f454d1641e5
received block 000000935f454d1641e5
SetBestChain: new best=000000935f454d1641e5  height=23  work=559980566
ProcessBlock: ACCEPTED
askfor block 00000c4d375ce8f92166   0
sending getdata: block 00000c4d375ce8f92166
received block 00000c4d375ce8f92166
SetBestChain: new best=00000c4d375ce8f92166  height=24  work=561029143
ProcessBlock: ACCEPTED
askfor block 000007e863a6d86bfb1d   0
sending getdata: block 000007e863a6d86bfb1d
received block 000007e863a6d86bfb1d
SetBestChain: new best=000007e863a6d86bfb1d  height=25  work=562077720
ProcessBlock: ACCEPTED
03/05/12 07:21:59 Flushing wallet.dat
  • This is great thanks! I assume I will have to rebuild bitcoin afterwards, maybe like this bitcoin.stackexchange.com/questions/793/… Haven't managed to pull that off yet but will give it a try, thanks! Mar 6, 2012 at 5:12
  • 1
    Yes, rebuild bitcoin (or just bitcoind, if that's all you're using in your tests), and keep it somewhere separate from the 'real' bitcoin that you use on the non-test network. Mar 6, 2012 at 17:22
  • It worked!! Thanks so much for your help, I really appreciate it. Seriously. Mar 7, 2012 at 6:19

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