What's in this computer?

Somebody hands you a server and asks "what is it?". How many CPUs, how much memory, which disks, which Linux, which kernel, and is it even a real machine or a virtual one? Linux can tell you all of that from the command line. This is the first thing a sysadmin does on a new box.

Which Linux, which kernel?

cat /etc/os-release     # the distribution: NAME, VERSION, ID, ID_LIKE
uname -r                # the kernel version, e.g. 5.14.0-570.22.1.el9_6.x86_64
uname -a                # everything: kernel, host name, architecture
hostnamectl             # host name, OS, kernel, hardware vendor and model in one screen

ID_LIKE in os-release tells you the family: rhel centos fedora or debian. Scripts check it to decide between dnf and apt.

CPU and memory

lscpu          # model, CPU(s), cores, threads, caches, virtualisation
nproc          # just the number of CPUs you can use: 4
free -h        # memory and swap, in human units
cat /proc/cpuinfo | grep "model name" | head -1
head -3 /proc/meminfo

/proc isn't a real folder on disk. The kernel makes those files up on the spot when you read them, so they're always current. Tools like lscpu and free mostly just read /proc and format it nicely.

Disks: lsblk vs df

lsblk          # the disks and partitions the kernel sees, mounted or not
df -h          # mounted filesystems and how full they are

lsblk answers "what disks are plugged in?". df answers "how much space is left?". A brand-new disk shows up in lsblk but not in df until you format and mount it. (That's the Linux Sysadmin, lesson 7 lesson.)

Devices on the buses

lspci          # graphics, network cards, disk controllers (the PCI bus)
lspci -k       # …and which kernel driver runs each one
lsusb          # USB devices: keyboard, stick, webcam

Maker, model, serial: dmidecode

sudo dmidecode -s system-manufacturer    # Dell Inc., LENOVO, innotek GmbH (VirtualBox)…
sudo dmidecode -s system-product-name    # the model
sudo dmidecode -t memory                 # RAM sticks and slots
cat /sys/class/dmi/id/product_name       # some of it, without root
systemd-detect-virt                      # kvm, oracle (VirtualBox), vmware, amazon… or none

dmidecode reads tables the firmware (BIOS/UEFI) fills in: the only way to learn a server's serial number without walking to the rack. It needs root because those tables include serial numbers.

Practice: write a machine report 🔍

Find out everything about this server, then save a short report you could send to a teammate.

Quick check