Sia's blockchain can take a while to synchronize with the network when installing a new client. While the developers are working on improving the syncing speed, a good workaround for now is to install an auxiliary database.
There are currently two public consensus database downloads available:
Select either link above and download the consensus database provided there.
While the consensus.db file is downloading you need to shut down any running instance of Sia (either siad or Sia-UI). You can close Sia-UI by right clicking the Sia icon in the system tray and choosing “Quit Sia”. On Linux simply closing the Sia-UI window is enough. If you're running the daemon you need to issue a
siac stop command and wait for the shutdown to finish.
When the consensus.db file has finished downloading you need to navigate to your Sia consensus data directory. For users of the commandline client this is in the same place as the
siad executable. If you're using Sia-UI it can be found in an operating system-specific location:
|Operating system||Consensus data directory|
|Mac OS X||
In this directory you'll find the consensus.db and consensus.log files that Sia generated when it first ran. Now you need to replace the consensus.db file in that directory with the one you downloaded.
Now it's time to start Sia again. Sia will automatically detect the new database and start scanning it for transactions that might be related to your wallet. Sia also has to build data related to other modules (such as renting and hosting, even if you don't use them) from the new consensus data. This process is very intensive on the storage medium. If you just downloaded Sia and have never opened it or fully synched before, this process can take several hours, even with a solid state drive - it may take longer on a traditional hard drive.
If you are using the Sia-UI, you'll see a message that loading may take a while after upgrading. If you're using the Sia daemon (siad) via command line, you may see the output hang for a long time. As long as you don't see an error message, Sia is working properly to process the new consensus database and you simply need to wait for it to finish.
Go work on something else and let Sia do it's thing. When it's finished, you'll have a fully operational and synchronized Sia client - congratulations!