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OLE: Oracle Linux-Specific Technologies: UEK, Ksplice, Btrfs, and Oracle Cloud Tooling

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Oracle Linux-Specific Technologies: UEK, Ksplice, Btrfs, and Oracle Cloud Tooling

This domain is what distinguishes Oracle Linux from a generic RHEL rebuild: the Unbreakable Enterprise Kernel, zero-downtime patching with Ksplice, the btrfs filesystem, and tooling for Oracle Cloud Infrastructure.

UEK and RHCK

  • UEK is the default kernel; uname -r shows an uek suffix (for example 5.15.0-...el9uek.x86_64), while the Red Hat Compatible Kernel shows a plain el9 build.
  • Packages are kernel-uek, kernel-uek-devel, kernel-uek-modules; third-party modules must match the kernel family (kmod-foo versus kmod-foo-uek).
  • UEK updates come from the release-specific repository such as ol9_UEKR7.

Ksplice

  • Ksplice applies kernel updates to a running kernel without a reboot.
  • uptrack-upgrade -y installs available patches, uptrack-show lists applied ones, and uptrack-uname -r reports the effective (patched) kernel version.
  • It requires an Oracle support entitlement with the Ksplice channel enabled; the ol8_ksplice/equivalent repository and a supported kernel.

Btrfs

  • mkfs.btrfs /dev/vg/lv, mount with -o subvol=, compress=zstd, or noatime.
  • btrfs subvolume create|list|snapshot, btrfs filesystem df /mnt, btrfs send/btrfs receive for incremental copies. Note that df and btrfs filesystem df report differently because of shared extents.

Oracle Cloud tooling

  • OCI instances expose metadata at http://169.254.169.254/opc/v2/; oci-metadata from oci-utils prints instance details.
  • The oci CLI is configured with oci setup config (tenancy, user, fingerprint, key file) and used for commands such as oci compute instance list.
  • cloud-init performs first-boot customization on OCI images; user data and metadata drive it.

Worked example

A production host must take a kernel security fix without a maintenance window. Verify entitlement and the Ksplice repo, run uptrack-upgrade -y, then confirm with uptrack-show and uptrack-uname -r. Reasoning: the running kernel is patched in memory, so uname -r still shows the booted version while uptrack-uname -r reports the effective patched level.

Traps

  • Ksplice patches the kernel, not user-space packages; glibc and OpenSSL still need DNF updates.
  • Loading a non-UEK kmod package against a UEK kernel fails dependency checks.
  • A btrfs snapshot on the same device is not a backup.
  • uptrack-upgrade fails silently for kernels outside Oracle's supported set.