The old Ubuntu versus Rocky Linux argument is apt against dnf and five years of support against ten. Since the Red Hat family moved its 10 series to a newer CPU baseline, the processor answers first. RHEL 10, Rocky Linux 10 and the default AlmaLinux 10 build will not start on a processor below the x86-64-v3 level, which rules out Intel server chips older than Haswell and any Proxmox VM still on its default CPU type. Ubuntu 26.04 LTS and Debian 13 started on every CPU model we tried, down to Proxmox's kvm64.
We build and run Linux servers for businesses in Kenya on dedicated hardware, in Proxmox virtual machines and on machines clients already own, so the distribution question always arrives with a box attached. To answer it with more than a forum thread, we ran each distribution's own C library and shell on nine emulated CPU models (three Proxmox CPU types, five Intel and AMD generations, and the default of the bpg Terraform provider for Proxmox) and recorded which ones started.
Which CPUs can run Rocky Linux 10 and AlmaLinux 10?
For Rocky Linux 10 and the default AlmaLinux 10 build, only x86-64-v3 and above: Intel Haswell and later, and AMD from Excavator on, which covers every EPYC. Intel's Pentium, Celeron and low-power Atom lines carry exceptions in those years (Rocky's notes name two Atom families), so check the chip, not the generation. The Rocky Linux 10 release notes call v3 the baseline and say v2 hardware is no longer supported. AlmaLinux also ships a separate v2 build, which comes up further down. In our run RHEL 10.2, Rocky 10.2 and the default AlmaLinux 10.2 started on 3 of the 9 models. On the other six the loader refused before bash started, with this line on the four v2-level models (on kvm64 and qemu64 the same line ends in x86-64-v2):
Fatal glibc error: CPU does not support x86-64-v3That line comes from glibc's dynamic loader, and every dynamically linked program on the system passes through it. So this is not one package failing. It is every dynamically linked program, refused before it starts.
Sandy Bridge and Ivy Bridge are the trap. Both report AVX, which looks modern enough on a spec sheet. glibc still rated both at v2, because v3 also needs AVX2, BMI1, BMI2, FMA, LZCNT and MOVBE, which neither model has (Sandy Bridge lacks F16C as well). Rocky's notes name that Haswell feature set as the baseline.
- loader and shell started
- Fatal glibc error, bash never started
A row is what glibc measured from the CPU it was shown. A VM is rated on its configured CPU type, so a Haswell host whose VMs were left on x86-64-v2-AES puts every one of them in the middle row.
This was user-mode emulation of the loader and the shell, not a full boot, so we are not telling you what your console will print after the refusal. The refusal itself is the same code path either way.
Why a Proxmox VM refuses Rocky 10
A VM created in the Proxmox web interface gets the CPU type x86-64-v2-AES unless somebody changes it, and the Proxmox VM documentation says so in as many words. We rebuilt that type from Proxmox's own flag list. Rocky 9 ran on it, and so did AlmaLinux 10's v2 build. Rocky 10, RHEL 10 and the default AlmaLinux 10 build did not.
Automation lands lower still. Proxmox's backend default, used when a VM's config names no CPU type at all, is kvm64, and the bpg Terraform provider defaults to qemu64. On both, even Rocky 9 and RHEL 9 refused, with the same message ending in x86-64-v2.
On a single host whose own CPU reports v3, the fix is one setting: x86-64-v3 or host. In a Proxmox cluster it is a decision, because Proxmox tells you to set the lowest CPU generation in the cluster if VMs live-migrate, and a VM whose CPU flags are missing on the target node simply stops. One Ivy Bridge node means no Rocky 10 VM can safely land on it. The CPU type belongs on the checklist after any move onto Proxmox, next to the disk bus a Windows guest boots from.
How to check a server before you choose
The loader tells you itself, with no root needed, on Rocky 9, RHEL 9 or Ubuntu 22.04 and newer:
/lib64/ld-linux-x86-64.so.2 --help | grep x86-64-vRocky 9's loader, run on the Ivy Bridge model, printed this:
x86-64-v4
x86-64-v3
x86-64-v2 (supported, searched)If the x86-64-v3 line does not say (supported, searched), that machine cannot run RHEL 10, Rocky 10 or the default AlmaLinux 10 build. Ubuntu 20.04's older loader does not know --help at all, so on a box that old, grep /proc/cpuinfo for avx2, bmi2, fma and movbe: if any one is missing, it is not v3. Run either check inside the VM rather than on the host, because a guest sees its configured CPU type, not the chip underneath. If that is forty servers rather than one, send us the list instead (details at the end).
Ubuntu vs Rocky Linux vs AlmaLinux once the CPU is settled
| Ubuntu 26.04 LTS | Rocky Linux 10 | AlmaLinux 10 | |
|---|---|---|---|
| Lowest CPU level that ran in our test | x86-64-v1 (kvm64) | x86-64-v3 | x86-64-v3, or v2 with the separate build |
| Free security updates until | May 2031 for Main (May 2036 with Ubuntu Pro) | 31 May 2035 | 31 May 2035 |
| On an older CPU instead | runs as it is | Rocky 9, security fixes to 31 May 2032 | the x86_64_v2 build |
Without a subscription the folklore holds. Rocky and AlmaLinux give you security fixes to May 2035, while Ubuntu's standard window closes in May 2031 and the five years after that come through Ubuntu Pro. Their full support, the years of minor releases that bring new software, ends five years earlier, on 31 May 2030.
Your software decides more than either. If the ERP, the database or the monitoring agent lists Rocky or AlmaLinux, run that. If it lists only RHEL, that is the case for paying for RHEL, and if it lists Ubuntu, run Ubuntu. On a platform the vendor does not list, expect its first reply to a ticket to be a request to reproduce the fault on one it does.
On an old server, two differences between the rebuilds decide it. AlmaLinux ships a second build of version 10 for x86-64-v2 hardware and Rocky does not, and AlmaLinux's notes list drivers it re-enabled for hardware RHEL had disabled, HP Smart Array controllers among them. AlmaLinux's release notes state the catch plainly: third-party packages for RHEL 10 target v3, so the v2 build suits a server that lives on the base package set, or one where you rebuild what you add. AlmaLinux has approved rebuilding EPEL for it, which closes part of that gap.
Which one we would put on your server
A CPU that reports v3, or a VM typed x86-64-v3 (or host on such a CPU). Choose on software and support. Our default is Ubuntu LTS, and Rocky or AlmaLinux when a vendor certifies the Red Hat family and accepts a rebuild.
A v2 CPU (Westmere to Ivy Bridge), or a cluster pinned to x86-64-v2-AES. Ubuntu 26.04 runs as it is. For a Red Hat shaped estate, it turns on what the server runs. On the base package set, we would take AlmaLinux 10's v2 build, with active support to 31 May 2030 and the re-enabled drivers. With third-party RHEL packages on it, we would take Rocky 9, whose general support ends 31 May 2027 and security support 31 May 2032, and plan the hardware refresh inside that window, because third-party RHEL 10 packages target v3.
kvm64 or qemu64. Change the VM's CPU type first. Every Red Hat family image in our run refused there, RHEL 9, Rocky 9 and both AlmaLinux 10 builds included. Ubuntu and Debian started.
If every server you own already reports v3 and your software vendor names the distribution, you do not need us to pick one. Install what the vendor supports. After the install, our server setup checklist covers what comes next.
Where the honest answer is new hardware, we hand over a dedicated server in about 24 hours. Send us the ld.so --help lines (or the CPU model line from lscpu) from each server, which hypervisor and CPU type the VMs use, and what software has to run on them, through the Linux scoping form or on WhatsApp at +254 713 403 044. You get back each server marked runs the 10 series, stays on 9, or goes to Ubuntu, the one distribution we would standardize the estate on, and one monthly figure if you want us to run it. The reading is free and commits you to nothing.