How can I find the hardware model in Linux?

using the dmidecode | grep -A3 '^System Information' command. There you'll find all information from BIOS and hardware. These are examples on three different machines (this is an excerpt of the complete output):

System Information
    Manufacturer: Dell Inc.
    Product Name: Precision M4700

System Information
    Manufacturer: MICRO-STAR INTERANTIONAL CO.,LTD
    Product Name: MS-7368

System Information
    Manufacturer: HP
    Product Name: ProLiant ML330 G6

Try sudo dmidecode -t baseboard for full information on the DMI table contents relevant to your baseboard, in a human readable form. For just the System Product Name, you can use either (type dmidecode -s to get a list of strings keywords):

sudo dmidecode -s system-product-name
sudo dmidecode -s baseboard-product-name

Other relevant options for motherboard info are

sudo dmidecode -s system-version
sudo dmidecode -s baseboard-version
sudo dmidecode -s system-manufacturer
sudo dmidecode -s baseboard-manufacturer

Try sudo dmidecode -s for a full list of system DMI strings available.

For the record, much of this information is available under /sys/devices/virtual/dmi/id on modern Linuces (ie, since at least 2011), and much if it- notably, not including serial numbers- is readable by regular users. To answer the original poster's question, product_name is the file that contains the system's model name.

bios_date
bios_vendor
bios_version
board_asset_tag
board_name
board_serial
board_vendor
board_version
chassis_asset_tag
chassis_serial
chassis_type
chassis_vendor
chassis_version
modalias
power
product_name
product_serial
product_uuid
product_version
smbios_version
subsystem
sys_vendor
uevent

And here would be a handy-dandy script that any user could run, to display the goodness:

#!/bin/bash

cd /sys/devices/virtual/dmi/id/
for f in *; do
        printf "$f "
        cat $f 2>/dev/null || echo "***_Unavailable_***"
done

No filenames have spaces in them, so this information is easily manipulated by utilities such as awk, for your own nefarious purposes!