Thanks to Joost Roeleveld and Brian Hesdorfer for helpful answers. Even before getting the new email, I googled on linux boot root delay and found the answer where previous Google search failed to yield results.
That was an old Linux, Slackware 13.0 with kernel 2.6.29.6 where I remember trying to get started with Gentoo but the kernel I built, compile time 130 minutes, failed to boot. It still took many attempts before I was successful with the boot. No Internet access because the kernel is too old and the Ethernet too new. Tom
