How To Check if a Disk is an SSD or an HDD on Linux

By using /sys/block

Since the kernel version 2.6.29, Linux automatically detects SSD.

Verify the disk:

cat /sys/block/sda/queue/rotational

1 = HDD / Hard Drive Disk 0 = SSD / Solid State Disk

It may not work if the disk is a logical device emulated by hardware e.g. a RAID controller.

By using lsblk from util-linux

Use lsblk from the util-linux package:

lsblk -d -o name, rota

NAME ROTA
sda     0
sdb     0
sdc     1

ROTA stands for /Rotational Device/. 0 = false, 1 = true.

By reading random blocks

Read random blocks off the disk

time for i in `seq 1 1000`; do
    dd bs=4k if=/dev/sda count=1 skip=$(( $RANDOM * 128 )) >/dev/null 2>&1;
done

This operation is slow on HDD (few seconds) while fast on SDD (under a second).