write iso directly to flash drive

Here’s a dumb problem you’ve never had:

You need to download an ISO to create a bootable flash drive, but you don’t have enough storage left on your system.

What can you do?

wget to the rescue

wget retrieves files by using popular application layer protocols found within the Internet protocol suite via the commandline. A traditional wget workflow involves specifying a remote source to download and optionally explicitly specifying an output location like so:

wget "https://example.com/file" -O /some/local/location

Since everything is a file, including attached devices, we can write the the downloaded file directly to our attached device.

demo

I’ll be using a live ISO of Fedora 34 in my example along with /dev/sdc on my system. Be sure you specify the correct device (triple-check, then check again).

$ lsblk /dev/sdc
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sdc      8:32   1 57.3G  0 disk
└─sdc1   8:33   1 57.3G  0 part

write the ISO straight to your device:

sudo wget "https://download.fedoraproject.org/pub/fedora/linux/releases/34/Workstation/x86_64/iso/Fedora-Workstation-Live-x86_64-34-1.2.iso" -O /dev/sdc
...
Length: 2007367680 (1.9G) [application/octet-stream]
Saving to: ‘/dev/sdc’

/dev/sdc                                             100%[=====================================================================================================================>]   1.87G  11.5MB/s    in 4m 35s

2021-08-21 16:30:22 (6.95 MB/s) - ‘/dev/sdc’ saved [2007367680/2007367680]

note the new partitions

$ lsblk /dev/sdc
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sdc      8:32   1 57.3G  0 disk
├─sdc1   8:33   1  1.9G  0 part
├─sdc2   8:34   1  9.9M  0 part
└─sdc3   8:35   1 20.9M  0 part

optionally you can use qemu-kvm to verify your device is indeed bootable

sudo qemu-kvm -drive format=raw -hdb /dev/sdc

While this might not be very practical, it’s a neat little “did you know?” that showcases some of the best featues of Unix architecture.


further reading

wget can do a whole bunch that I couldn’t possibly cover here, so I encourage you to learn more if you’re interested.