Linux will detects SSD automatically.
Since kernel version 2.6.29, you can check
/dev/sda with following command
# cat /sys/block/sda/queue/rotational
The return number
0 shows you
/dev/sda is a SSD, and
1 shows it is a HDD.
Note that this command may not work when your disk is created by hardware RAID.
Another way is to use
lsblk command, a part of the util-linux package.
# lsblk -d -o name,rota
ROTA means rotational device,
1 for true,
0 for false.
This command report the same information as in