Finally to compile the software you use `./build.sh` . It is quite slow
to only use a single thread, so you can use multiple threads, for example 4,
like this:
```
./build.sh -j4
```
Each `build.sh` thread will take ~2GB of RAM so beware of that. If you have
compiled before and just made a change to C++ code, you can probably use
`make` instead and use a high number of threads. For example, if your CPU
has 8 physical cores and 16 "virtual cores" then you can use `make -j16` and
things will compile much faster. Each `make` threads takes only about 200MB of RAM.
If `make` fails in a weird way complaining about Makefiles, you probably need to
run `build.sh`, which takes care of regenerating Makefiles and installing some
additional dependencies.
Sometimes using multiple threads the build can fail, so if it does, try again
with a different number of threads or just one thread before reporting an issue.
# Fresh sync
Many times, you will want to do a "fresh sync" test, to verify code works when syncing from the genesis block, which is a different code path than a "partial sync" which means you already have part of blockchain history and are "catching up" to get in sync.