man qemu contains a bug in description of "-virtfs" command line argument The description of command line argument looks like this: -virtfs fsdriver[,path=path],mount_tag=mount_tag[,security_model=security_model][,writeout=writeout][,readonly][,socket=socket|sock_fd=sock_fd] note, that there is no "id" attribute in the list of parameters. later on the man there the "id" attribute is documented, as it were present: id=id Specifies identifier for this device i think that it was copied from above section (about "-fsdev") without reviewing.