What version of Go are you using (go version)?

go version go1.10.6 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/root/go"
GORACE=""
GOROOT="/usr/lib/golang"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/golang/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build117311720=/tmp/go-build -gno-record-gcc-switches"

What did you do?

http2 works and GODEBUG=http2server=0 does disable http2.
But GODEBUG=http2debug=1 and GODEBUG=http2debug=2 don't produce any output and the output of them is what I need.
The http2 debug mode should log the output to stdout (the screen) or is it saved in some log file?

What did you expect to see?

http2 debug data

What did you see instead?

Nothing