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Comment by phiresky | Hacker News Reader

> I don't know why dd remains the standard for so many tutorials

You can also do something like

    dd if=file.iso of=/dev/disk/by-id/ata-Samsung_SSD_840_EVO_120GB

Where the last part is basically the brand and name of your USB stick, not much guess work required. Though I've never seen that in any tutorials.

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You're not alone. :) The installer for the USB stick Debian Live-based distro I made years ago will only install to a path starting `/dev/disk/by-id/usb-` (or `/dev/loop`).

I've also been doing paths through `/dev/disk/by-id/` in the ops documentation and scripts for my startup.

It's a tiny convention for us promote, and one of countless good practices we exercise, but this particular one can save much misery, at negligible cost.

And early, precarious startups are one of the contexts in which some of these tiny negligible-cost good practices seem to pay off especially well: in an early startup, it's easy for me to imagine a data loss, bad downtime, or missed opportunity ending the company (when a more-established company might be able to weather a mess-up better).

It's really unfortunate how tutorials still spell out all the basics to keep the beginners with them, but then rely on the old-fashioned device names when it comes to writing images. Using sda is fine if you're experienced and know what drive has what name, but technical references should stop relying on them already. It's not like you're getting some useful cross-platform compatibility out of old-fashioned commands or anything, every modern Unix has its own way to specify disk names.

I think the simplest explanation is that the authors themselves never considered the other options or were even aware of them -- they simply are sharing some historical knowledge they had. Very kind and good behavior! But I would imagine it's something rote and probably just a shortcoming in collective knowledge.

In short, I think ignorance is the simpler answer ;)

Yep, every couple of years I need to use dd. Never knew of an alternative to sda.

When I was first learning Linux it was pretty helpful to look at a few random things in /dev and /bin and /etc and learn what they did, whenever I had a few spare minutes.

ZFS has open my eyes to /dev/disk/by-id/. It's the only way when you have many of the exact same make/model/size drives per machine. You will learn by fire the first time you need to determine which drive you need to replace.

>Using sda is fine if you're experienced and know what drive has what name

Not even then. The prospect of making an occasional mistake, while low, is clearly much higher than when you are selecting the disk using its name. Being experienced doesn't excuse you from the responsibility of using a less risky tool.

To avoid mistakes I always do “lsblk” (on Linux) or “diskutil list” (on macOS) or “gpart show” (on FreeBSD) and carefully read the output before I do the dd to something.

Usually on Linux I only use /dev/disk/by-id/foo in scripts and config files. But using it when doing routine stuff with dd is a pretty good idea too.

It’s too bad that macOS and FreeBSD hasn’t anything similar to my knowledge. And since I use both of these operating systems so much, and so often for things involving dd, I think in my case I don’t gain much from doing by-id for dd on Linux unfortunately.

>To avoid mistakes I always do “lsblk”

Even this is faulty solution. By default, it only lists the devices with their "/dev/sd*" names.

I learned of this from this (rather long and detailed) article:

https://perfectmediaserver.com/

It's full of other great nuts-and-bolts advice.

I feel it's important to mention you want by-id as there are 5 permutations of /dev/disk/by-*:

  /dev/disk/by-id
  /dev/disk/by-partlabel
  /dev/disk/by-partuuid
  /dev/disk/by-path
  /dev/disk/by-uuid

What I do to find out which is which is use lsscsi:

    $ lsscsi
    [0:0:0:0]    disk    ATA      ST2000DX001-1NS1 CC41  /dev/sda 
    [3:0:0:0]    cd/dvd  ASUS     SH-224FB         1.00  /dev/sr0 
    [4:0:0:0]    disk    Generic- Multiple Reader  1.11  /dev/sdb

Unfortunately you have to do this again after each reboot, or whenever you plug in an USB stick, so the dev/by-* option does help when you do that repeatedly for the same device.

Excellent suggestion. It also includes the serial number for non-removable devices, like so:

    /dev/disk/by-id/ata-Samsung_SSD_860_PRO_1TB_S42NNF0K123456N -> ../../sdc

TIL! Thank you so much for this. I didn't know.

What happens if you have two?

Lifehack of the month! So obvious and so little used.

I love this tip! I always get sweaty armpits whenever I'm using dd and I check the of parameter several times just to be sure. This will save me from a lot of pit stains.

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