On Thursday 24 August 2017 12:30:37 Dan Ritter wrote: > On Thu, Aug 24, 2017 at 10:43:56AM -0500, David Wright wrote: > > On Thu 24 Aug 2017 at 10:20:52 (-0400), Dan Ritter wrote: > > > There are, of course, five different ways to do this (at a > > > minimum): > > > > > > 1. /dev/sda1 is based on discovery order. Changes in discovery > > > order may indicate a significant problem that you need to > > > investigate -- or not. > > > > I'm having difficulty imagining a scenario where the identity > > of sdaX, in particular, is unimportant (for most people). > > Say you boot from /dev/nvme0n1p1 (a high speed NVMe SSD) and > have /dev/sda, b, c and d in an mdadm RAID10. > > mdadm will scan all disks looking for its signature, and will > assemble them into /dev/md/0 regardless of physical disk > location. So it really won't matter to you whether you have the > same disks in /dev/sdX from boot to boot as long as they are > all there. > > But for most people, most of the time, swapping /dev/sda and > /dev/sdc would be a problem. > > > But in connection with the original NIC discussion, the absence > > of disk/by-uuid would be sorely missed if it weren't there, which > > is why some improvement on eth0, eth1 assignment was needed, > > and the result was a very flexible system IMO. > > > > > 6. Various advanced systems -- mdadm, LVM, btrfs, ZFS, hardware > > > RAID -- have their own ideas about what to do and how to do it, > > > which may include any of the above methods as well as their own > > > peculiarities. > > > > > > That said, if you have a laptop or a desktop with 1-2 disks, you > > > are probably going to be perfectly happy with either /dev/sda1 or > > > LABEL=root-$HOSTNAME addressing. > > > > With two disks on a BIOS computer, you have an immediate problem, > > don't you? That what disk-swapping was all about. And that was when > > everything was on ATA. > > On a well-working computer, device discovery order is constant without > physical changes. sda will always be sda, until it breaks or > something else (bad) happens. > > > But now look at the debates here on, for example, how an SD card > > is going to appear to the system. The schematic diagram of any > > laptop looks like a forest of USBs (and other types) so which is > > going to win the race to become sda? > > They don't. The SATA, SATA-DOM or NVMe disk selected by the UEFI or > BIOS will become sda. Or if you've got an internal USB port with a > stick in it, that might be a selected candidate. In no case > should it change without hardware failure or physical > rearrangement. > > The question is, how will your newly plugged in SD card become > sdk rather than sdj, and the answer is that mass storage devices > that are expected to be rearranged should be treated differently > from those which are expected to always be available from > boot-time onwards. > > > > Getting back to the original point, NIC names -- virtually every > > > computer has exactly one or two NICs, and is best served by eth0 > > > and wlan0. The computers with 3-5 NICs are usually best served > > > that way. More complex naming schemes are helpful when you have a > > > router or switch, and it's nice that Debian supports that, but > > > hardly a good default. > > > > There are plenty of ways that you, or Debian, can set a default. > > But it surprises me that so many people grumble about this change. > > People grumble about changes for several nonexclusive reasons: > > 1. The change broke what they were doing. > 2. The change broke their mental model of what they were doing. > 3. The change did not bring them perceived benefits. > 4. The change appears arbitrary. > 5. The change fixed a problem but they perceive better ways to > solve the problem. > 6. The change creates new problems. > > > The history of computing is littered with statements like > > "virtually every computer has exactly one or two NICs". > > It used to be zero. > > We are currently in the phase of history where this statement is > true. NICs are both ubiquitous and cheap, yet devices tend to > come with one (only an ethernet port or only a wifi radio) or > two (one of each of those, or a wifi radio and a cell radio). > > Devices can add more, but they are always special cases: my > Debian-running firewall has 5 ethernet ports. I occasionally > add a USB ethernet frob in order to isolate a device that I want > to talk to directly. Special cases deserve special treatment. > > I expect the statement to remain true for the next ten years. > > Do you expect differently? If so, why? > > > This list is full of postings about the complex DNS system. But > > how long did /etc/hosts last? Some complexity is unavoidable, > > but if you try to avoid it, you pay for it later. Look at timezones. > > Ever allowing computers' internal clocks to run on local time > > was, with hindsight, a big mistake. Leap seconds might also > > be seen the same way (still under debate). > > /etc/hosts still acts the way it always did -- put in an entry, > it overrides DNS. > That depends entirely on who wrote your /etc/resolv.conf and whether or not your did a sudo chattr +i /etc/resolv.conf, immediately after verifying that it works. (and of course that implies it is a real file, not a softlink to something else. With N-M in the mix and active that is the only way to keep it from tearing down your network configuration and leaving you empty files, and no network, if it cannot find a dhcpd server)
> Timezones are a human legal-social problem, and the ability of > technology to deal with those is known to be problematic. Just as humans are known to be a problem... > -dsr- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene>