Warning: risky on production. Snapshot before every major step. This documents what worked once on a CentOS 6.8 i386 VPS that needed amd64 packages.

Overview

  1. Snapshot → yum upgrade on i386 → snapshot again
  2. Force-install an x86_64 kernel RPM, reboot (amd64 kernel + i386 userspace)
  3. Download amd64 builds of all installed i686 packages → remove *.i686.rpm → rpm -iv --force *.rpm → reboot

Step 0 — snapshots

Take a full snapshot in your hypervisor before starting.

Step 1 — latest i386 packages

yum upgrade -y

Snapshot again.

Step 2 — amd64 kernel

Copy an kernel-2.6.32-642.el6.x86_64.rpm (or matching line) to the host:

rpm -Uhv --force --ignorearch kernel-2.6.32-642.el6.x86_64.rpm
reboot

You should boot an x86_64 kernel with i386 userspace.

Step 3 — download amd64 RPM set

mkdir x64 && cd x64
rpm -qa | grep '\.i686' | sed 's/.i686//' | xargs yumdownloader

If a repo fails GPG/metadata (example: APItools_monitor), disable that repo and retry. Some kernel packages may not download — handle separately.

Example messages you can ignore if the rest downloads:

No Match for argument kernel-2.6.32-642.el6.x86_64

Snapshot again before the next step.

Step 4 — replace userspace

rm -f *.i686.rpm
rpm -ivh --force *.rpm
reboot

Result

System ran amd64 userspace on the same data partition. Monitor for broken third-party repos or kmods. Not supported by CentOS — treat as last resort.