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System Information

A handful of read-only commands identify the distribution, kernel, CPU, memory, disks and hardware of an unfamiliar server. They are the first commands to run on any machine before changing it, and the first facts an incident report asks for.

Track: Core · Interview weight: Med

Must-Know Facts

Fact Value Verify with
Distribution and version /etc/os-release (standard on every systemd distribution) cat /etc/os-release
Kernel release Separate from the distribution version uname -r
CPU architecture x86_64 or aarch64 uname -m
Logical CPUs Count of schedulable CPUs nproc
Memory that can be used now available column, not free free -h
Block devices and mounts Tree of disks, partitions and mount points lsblk
Uptime and load Time since boot, ⅕/15-minute load averages uptime
Virtualization Hypervisor type, or none on bare metal systemd-detect-virt, hostnamectl
Firmware tables dmidecode reads SMBIOS; absent on some microVMs sudo dmidecode -t system
Page size 4096 bytes on x86_64 getconf PAGE_SIZE

Distribution and Kernel

/etc/os-release names the distribution; uname reports the running kernel. The two are independent: both playgrounds below run the same 6.1.167 kernel.

uname -srm
uname -o

Output:

Linux 6.1.167 x86_64
GNU/Linux

grep -E '^(NAME|VERSION_ID|ID|ID_LIKE|PLATFORM_ID)=' /etc/os-release
cat /etc/redhat-release

Output:

NAME="Rocky Linux"
ID="rocky"
ID_LIKE="rhel centos fedora"
VERSION_ID="10.2"
PLATFORM_ID="platform:el10"
Rocky Linux release 10.2 (Red Quartz)

grep -E '^(NAME|VERSION_ID|ID|ID_LIKE|VERSION_CODENAME)=' /etc/os-release
lsb_release -a
cat /etc/debian_version

Output:

NAME="Ubuntu"
VERSION_ID="24.04"
VERSION_CODENAME=noble
ID=ubuntu
ID_LIKE=debian
Distributor ID: Ubuntu
Description:    Ubuntu 24.04.4 LTS
Release:    24.04
Codename:   noble
trixie/sid

/etc/debian_version names the Debian branch Ubuntu was based on, not the Ubuntu release.

CPU

lscpu | grep -E '^(Architecture|CPU\(s\)|Model name|Thread|Core|Socket|Hypervisor|Virtualization type)'
nproc

Output:

Architecture:                            x86_64
CPU(s):                                  4
Model name:                              AMD EPYC
Thread(s) per core:                      1
Core(s) per socket:                      4
Socket(s):                               1
Hypervisor vendor:                       KVM
Virtualization type:                     full
4

nproc can report fewer CPUs than lscpu

Logical CPUs equal sockets times cores per socket times threads per core. nproc respects CPU affinity and cgroup limits, so inside a restricted container it can report fewer CPUs than lscpu.

Memory

free -h
grep -E '^(MemTotal|MemAvailable|SwapTotal)' /proc/meminfo
lsmem

Output:

               total        used        free      shared  buff/cache   available
Mem:           7.8Gi       488Mi       7.3Gi       9.0Mi       336Mi       7.4Gi
Swap:             0B          0B          0B
MemTotal:        8212896 kB
MemAvailable:    7712652 kB
SwapTotal:             0 kB
RANGE                                 SIZE  STATE REMOVABLE BLOCK
0x0000000000000000-0x00000000bfffffff   3G online       yes  0-23
0x0000000100000000-0x000000023fffffff   5G online       yes 32-71
# ... (trimmed)

Low free memory is normal

The kernel fills idle RAM with page cache (buff/cache) and releases it on demand. available estimates what new programs can use without swapping; alerts built on free fire on healthy servers.

Disks and Hardware

lsblk -o NAME,SIZE,TYPE,FSTYPE,MOUNTPOINTS
lspci
lsusb
echo "rc=$?"

Output:

NAME SIZE TYPE FSTYPE MOUNTPOINTS
vda   80G disk ext4   /
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)
rc=1

The Virtio devices show a KVM guest; vda is a Virtio disk. lsusb prints nothing and exits 1 because this microVM has no USB bus.

lshw builds a hardware tree from /proc, /sys and PCI data. dmidecode reads the firmware's SMBIOS table (vendor, serial number, BIOS version), which lightweight microVMs do not provide:

sudo lshw -short
sudo dmidecode -t system

Output:

H/W path    Device    Class          Description
================================================
                      system         Computer
/0                    bus            Motherboard
/0/0                  memory         8GiB System memory
/0/1                  processor      AMD EPYC
/0/100                bridge         Intel Corporation
/0/100/1              storage        Virtio 1.0 block device
/0/100/1/0  /dev/vda  volume         80GiB EXT4 volume
/0/100/2              network        Virtio 1.0 network device
# ... (trimmed)
# dmidecode 3.6
Scanning /dev/mem for entry point.
# No SMBIOS nor DMI entry point found, sorry.
Tool Package (RHEL / Ubuntu) Reads
lscpu, lsblk, lsmem util-linux /proc, /sys
lspci pciutils PCI bus
lsusb usbutils USB bus
lshw lshw Combined hardware tree
dmidecode dmidecode SMBIOS firmware table

Uptime and Virtualization

uptime
who -b
cat /proc/loadavg
systemd-detect-virt
getconf PAGE_SIZE

Output:

 13:25:13 up 1 min,  0 user,  load average: 0.26, 0.10, 0.03
         system boot  2026-09-16 13:23
0.26 0.10 0.03 1/112 1475
kvm
4096

In /proc/loadavg, 1/112 is running over total scheduling entities and 1475 is the most recently assigned PID.

Common Errors

# No SMBIOS nor DMI entry point found, sorry.

Cause: the machine (usually a microVM or container) exposes no SMBIOS table.

Fix: use lscpu, lsmem and lspci instead; cloud instances expose vendor data through their metadata service.

Interview Checkpoints

L1: How do you find which distribution and kernel a server runs?

Say first: /etc/os-release for the distribution and uname -r for the kernel; they are separate components with separate versions.

Proof: cat /etc/os-release; uname -r

Follow-up: Why can two different distributions report the same kernel release?

L1: Why is free memory low on a healthy server?

Say first: the kernel uses spare RAM as page cache and gives it back when programs need it; available is the number that matters.

Proof: free -h shows a large buff/cache and an available close to total.

Follow-up: When does low available become a problem?

L2: Report CPU count, memory, disks and uptime of a new server in one pass.

Say first: four read-only commands.

Proof:

nproc; free -h; lsblk; uptime

Follow-up: How do you tell if the machine is a VM? (systemd-detect-virt, lscpu hypervisor line.)

L2: A script must install packages on both Rocky and Ubuntu. How does it choose the package manager?

Say first: source /etc/os-release and branch on ID_LIKE.

Proof:

. /etc/os-release
case "$ID_LIKE" in *rhel*) echo dnf ;; *debian*) echo apt ;; esac

Follow-up: What is ID_LIKE on Debian itself, where it is not set?

L2: nproc reports 2 inside a container, lscpu reports 16. Which is right?

Say first: both; nproc honours the CPU affinity or cgroup limit applied to the process, lscpu reports the host CPUs.

Proof: nproc versus nproc --all.

Follow-up: Which value should a worker pool size itself from?

L3: A monitoring agent reports the wrong hardware vendor and serial on a VM.

Say first: check whether the hypervisor exposes SMBIOS at all.

Proof: sudo dmidecode -t system returns "No SMBIOS nor DMI entry point found"; ls /sys/class/dmi is missing; the agent falls back to defaults.

Follow-up: Where else can the instance identity come from? (Cloud metadata service.)

Captured on Rocky Linux 10.2 and Ubuntu 24.04.4 LTS (iximiuz Labs microVMs, kernel 6.1.167), 2026-09.