Im am install garb from you repositary on Debian jessi, and configure.
#cat /etc/default/garb
GALERA_NODES="192.168.0.1:4567 192.168.0.2:4567 192.168.0.3:4567"
GALERA_GROUP="cluster"
GALERA_OPTIONS="gmcast.listen_addr=192.168.0.4"
LOG_FILE="/var/log/garb.log"

After run i am see in garb.log Warning: open file(gvwstate.dat.tmp) failed(Permission denied)

I am strace garbd and see garb open this file without any path.
I am test set set in start-stop-daemon set option '-d /tmp' no result.
Only set -o root -c root that helped, garb create file in '/' direcory and start as root, but this insecure.
Need parameter for set garb directory, or if this temp file need garb create this file in system /tmp directory.