AlmaLinux 10+ Knowledge Patch

Claude's baseline knowledge covers AlmaLinux through 9.3. This skill provides changes from 10.1 (2025-11-24) onwards.

AlmaLinux 10 is based on RHEL 10 (kernel 6.12) but includes several significant deviations that differentiate it from upstream RHEL and other RHEL rebuilds.

Quick Reference

Breaking Changes / Key Differences from RHEL 10

Feature	RHEL 10	AlmaLinux 10
Btrfs	Not supported	Full kernel + userspace; can install/boot from Btrfs
CPU baseline	x86-64-v3 only	x86-64-v2 AND x86-64-v3 builds
CRB repo	Disabled by default	Enabled by default on new installs
SPICE	Removed	Re-enabled (server + client)
Frame pointers	Not default	Enabled by default (system-wide profiling)
KVM on POWER	Removed	Re-enabled
Firefox/Thunderbird	Flatpak-only	Regular RPMs

Btrfs Support

AlmaLinux 10 is the only RHEL-based distro with full Btrfs support. You can use Btrfs as root filesystem during installation.

# Btrfs is available in the default kernel — no extra packages needed
mkfs.btrfs /dev/sda1
mount -o compress=zstd,noatime /dev/sda1 /mnt

# Subvolume management works out of the box
btrfs subvolume create /mnt/@home
btrfs subvolume snapshot -r /mnt/@home /mnt/@home-snapshot

# Check filesystem usage
btrfs filesystem usage /mnt

x86-64-v2 Architecture Support

RHEL 10 raised the CPU baseline to x86-64-v3 (requires AVX2 — Intel Haswell+ / AMD Excavator+). AlmaLinux ships additional x86-64-v2 builds for older CPUs.

Important caveat: Third-party packages built for RHEL 10 target x86-64-v3 only. The v2 support is limited to AlmaLinux's own repository packages — third-party RHEL 10 packages may fail with SIGILL on v2 hardware.

# Check CPU architecture level support
/lib64/ld-linux-x86-64.so.2 --help 2>&1 | grep supported

CRB Repository

On new AlmaLinux 10 installations, CRB (CodeReady Builder) is enabled by default — development headers and build dependencies are available without manual repo activation.

# Previously required on RHEL/AlmaLinux 9:
#   dnf config-manager --set-enabled crb

# On AlmaLinux 10+ new installs, already enabled
dnf repolist | grep crb

# Note: upgrades from AlmaLinux 9 preserve existing repo configuration

Frame Pointers Enabled by Default

All packages are compiled with frame pointers, enabling system-wide profiling without recompilation:

# System-wide profiling works out of the box
perf record -g -a -- sleep 10
perf report

SPICE, KVM on POWER, Firefox/Thunderbird

• SPICE: Re-enabled for server and client (removed in RHEL 10)
• KVM on IBM POWER: Re-enabled in virtualization stack (removed in RHEL 10)
• Firefox/Thunderbird: Shipped as regular RPMs, not Flatpak-only as in RHEL 10

# Regular RPM install (not Flatpak)
dnf install firefox thunderbird

Post-Quantum Cryptography

System-wide crypto policies enable PQC algorithms by default in AlmaLinux 10:

• OpenSSL 3.5: Adds ML-KEM (Kyber), ML-DSA (Dilithium), SLH-DSA (SPHINCS+)
• TLS: Hybrid ML-KEM is in the default TLS group list — connections auto-negotiate PQC when both sides support it
• RPM signatures: RPMv6 supports PQC via Sequoia PGP tools

No configuration needed — PQC is active out of the box with default crypto policies.

See references/pqc-and-crypto.md for algorithm details.

Key Toolchain Versions (AlmaLinux 10.1)

Tool	Version	Notes
GCC	14.3.1	Default compiler
GCC Toolset 15	GCC 15.1	dnf install gcc-toolset-15
Go	1.24
LLVM/Clang	20.1
Rust	1.88
Python	3.12.11	Default system Python
Node.js	24
Podman	5.6
QEMU-KVM	10.0
Kernel	6.12	Frame pointers enabled

See references/toolchain-versions.md for details.

Dockerfile Base Image

FROM almalinux:10
# or for minimal: FROM almalinux:10-minimal (uses microdnf)

Reference Files

File	Contents
almalinux-deviations.md	Full details on AlmaLinux vs RHEL 10 differences
pqc-and-crypto.md	Post-quantum cryptography algorithms and configuration
toolchain-versions.md	Compiler, runtime, and tool versions in 10.1