Know Your Machine: Hardware & Resources at a Glance

You've been handed access to a box you've never seen before. Before you install anything, restart anything, or trust anything a colleague told you about it, answer one question: what actually is this machine?

CPU

nproc

4

nproc prints one number: how many CPUs the shell can actually use right now. On a shared or virtualized box, that can be less than the physical hardware has, so trust nproc over any assumption. For more detail, lscpu prints a much longer report:

lscpu

Architecture:                            x86_64
CPU op-mode(s):                          32-bit, 64-bit
Address sizes:                           46 bits physical, 48 bits virtual
Byte Order:                              Little Endian
CPU(s):                                  4
On-line CPU(s) list:                     0-3
Vendor ID:                               GenuineIntel
Model name:                              Intel(R) Xeon(R) Processor
CPU family:                              6
Model:                                   183
Thread(s) per core:                      1
Core(s) per socket:                      4
Socket(s):                               1
Stepping:                                1
BogoMIPS:                                3993.60

A few lines worth actually reading: CPU(s) matches what nproc told you - the count the OS sees. Model name tells you the actual chip, which matters when you're chasing a performance difference between two boxes. Thread(s) per core being 1 (instead of 2) tells you this CPU isn't using hyperthreading - each core is one real thread, not two logical ones sharing it.

Memory

free -h

               total        used        free      shared  buff/cache   available
Mem:           9.8Gi       445Mi       9.4Gi       996Ki        87Mi       9.4Gi
Swap:             0B          0B          0B

The -h flag means "human-readable" - without it, free prints raw byte counts, which is hard to read at a glance. Two columns matter more than the others: free is memory nothing is using at all, and available is what's actually available to a new process, including memory currently used for disk cache that the kernel will happily give back if asked. available is almost always the number you actually want - a low free value with a high available value is completely normal and not a problem, the kernel is just using spare RAM to cache files for speed. Swap: 0B means there's no swap space configured on this box at all - if RAM runs out here, the kernel has nowhere else to go.

Disks

lsblk

NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
vda  253:0    0  80G  0 disk /

Read this left to right: NAME is the device name (vda, found at /dev/vda). SIZE is its total capacity - 80G here. TYPE says what kind of block device it is (disk - a whole disk, as opposed to part for a partition of one). MOUNTPOINTS shows where it's attached into the filesystem tree - / here means this entire disk is the root filesystem, with no separate partitions carved out of it.

df -h

Filesystem      Size  Used Avail Use% Mounted on
/dev/root        79G  1.8G   73G   3% /
tmpfs           4.9G     0  4.9G   0% /dev/shm
tmpfs           2.0G  228K  2.0G   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs          1003M   12K 1003M   1% /run/user/1001

lsblk told you what storage exists. df -h answers a completely different question: how full is each mounted filesystem right now. Look at the first row: /dev/root has 79G total, 1.8G used, 73G available, and is 3% full - mounted at /. These are not the same question as lsblk's - a disk can exist and still report 100% full in df, and df would never tell you that on its own.

The other rows, the tmpfs ones, aren't disks at all - they're RAM being used as if it were a filesystem, for things like /dev/shm (shared memory) and /run (runtime state). They vanish completely on reboot.

Attached devices

lspci
lsusb

On a fresh Ubuntu box these two commands may not even exist yet - they come from separate packages (pciutils and usbutils) that aren't always preinstalled:

sudo apt install -y pciutils usbutils

Once installed:

$ lspci
00:00.0 Host bridge: Intel Corporation Device 0d57
00:01.0 Mass storage controller: Red Hat, Inc. Virtio 1.0 block device (rev 01)
00:02.0 Ethernet controller: Red Hat, Inc. Virtio 1.0 network device (rev 01)
00:03.0 Unassigned class [ffff]: Red Hat, Inc. Virtio 1.0 socket (rev 01)
00:04.0 Unassigned class [ffff]: Red Hat, Inc. Virtio 1.0 RNG (rev 01)

$ lsusb

Notice every device here says Virtio - that's the standard interface virtual machines use to talk to their host's real hardware without emulating a specific physical chip. Seeing Virtio everywhere in lspci, on any box, is itself a fact worth knowing: it confirms you're inside a VM, not on bare metal. lsusb came back completely empty, and that's expected, not broken - this playground has no USB devices attached, virtual or otherwise.

Write it down

Build the habit of recording what you found before you change anything. Create ~/machine-report.txt with two lines:

cpus=<the number nproc printed>
rootdev=<the device name from df --output=source /, with the /dev/ prefix stripped>