Geth version I have:

Version: 1.8.15-unstable
Architecture: amd64
Protocol Versions: [63 62]
Network Id: 1
Go Version: go1.11
Operating System: linux

go version:

$ which go
$ go version
go version go1.11 linux/amd64
$ echo $GOROOT
(Blank line)

geth --fast --cache=1024 ...

The error I am receiving:

flag provided but not defined: -fast

I was able to use --fast flag on the previous versions but now I cannot. Is is because --fast flag removed or something else. How could I fix this error? Is there any alternative flag for --fast?

=> Similar issue.

1 Answer 1


you can use flag --syncmode fast instead

they already update the wiki document https://github.com/ethereum/go-ethereum/wiki/Command-Line-Options


--fast Enable fast syncing through state downloads (replaced by --syncmode)

--light Enable light client mode (replaced by --syncmode)

  • It works! what is difference between --fast and --syncmode fast? @Ha ĐANG
    – alper
    Aug 27, 2018 at 15:06
  • 1
    no difference, --fast is just a shortcut for --syncmode fast and they remove this shortcut in version 1.8.15
    – Tony Dang
    Aug 27, 2018 at 15:07

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