While CentOS and Oracle Enterprise Linux (OEL) claim 100% binary compatibility with RHEL, real-world scenarios often reveal subtle but critical differences. For example, an application requiring RHEL 5 x64 Update 4 might fail on CentOS 5.4 x64 despite sharing the same kernel version (2.6.18-164.el5). The discrepancies often stem from:

# Check release differences
rpm -qa | grep -E 'redhat-release|centos-release|oraclelinux-release'

Even when using the same upstream sources, rebuilds introduce variations:

• Build environment flags: Different compiler optimizations (-O2 vs. -O3)
• Patch backporting: Security patches may apply differently
• Package metadata: Provides/Requires clauses in RPM specs

Example of package divergence:

# Compare two 'identical' packages
rpm -q --changelog httpd | head -5  # RHEL vs CentOS
rpm -q --provides glibc | sort      # OEL vs RHEL

Simply replacing the release package often fails because:

# Common but ineffective workaround
rpm -e --nodeps centos-release
rpm -ivh https://mirror.example.com/redhat-release-5Server-5.4.0.x86_64.rpm

Applications may perform deeper checks:

# Some apps verify through these methods
test -f /etc/redhat-release || exit 1
grep -q "Red Hat" /proc/version || die "Unsupported OS"

Hardware vendors often certify drivers specifically for RHEL:

# Kernel module differences
modinfo tg3 | grep vermagic  # Compare RHEL vs CentOS build strings
ls /lib/modules/$(uname -r)/updates  # Vendor-added drivers

Enterprise software vendors typically:

• Validate only on RHEL for support contracts
• Use RH-specific APIs like libkmod
• Depend on exact SELinux policy versions

# SELinux policy differences
sestatus | grep policy  # Compare policy versions

For applications that absolutely require RHEL:

# Create RHEL-like environment variables
export REDHAT_SUPPORT_PRODUCT="Red Hat Enterprise Linux"
export REDHAT_SUPPORT_PRODUCT_VERSION="5.4"

Container-based solution:

# Dockerfile snippet for RHEL-emulated environment
FROM centos:5
RUN rpm -e --nodeps centos-release && \
    curl -O http://mirror.example.com/redhat-release-5Server-5.4.0.x86_64.rpm && \
    rpm -ivh redhat-release-5Server-5.4.0.x86_64.rpm

---

Many developers assume that RHEL, CentOS, and Oracle Enterprise Linux (OEL) are 100% interchangeable because they share the same upstream source. While they do maintain high compatibility, subtle differences can break applications in production environments.

# Example of version check that might fail:
if [[ $(cat /etc/redhat-release) != *"Red Hat Enterprise Linux"* ]]; then
    echo "Unsupported platform" >&2
    exit 1
fi

The most significant differences occur in:

• Kernel patches (OEL adds UEK, CentOS may delay security patches)
• Hardware enablement drivers
• OpenSSL and cryptographic module implementations
• Backported packages in minor versions

While RHEL 5.4 and CentOS 5.4 share the same source RPMs, their build environments differ:

# Compare build hashes (often different):
rpm -q --qf '%{NAME}-%{VERSION}-%{RELEASE} %{BUILDTIME} %{PAYLOADDIGEST}\n' kernel

Enterprise software often performs deep checks:

// Sample C code from proprietary apps
int verify_rhel() {
    struct utsname sys;
    uname(&sys);
    return strstr(sys.release, "el5") != NULL 
        && access("/etc/redhat-release", F_OK) == 0;
}

These aren't documented in release notes:

• SELinux policy tweaks in OEL
• Different default umask values
• Varied sysctl parameters for Oracle DB optimization

Before deployment:

#!/bin/bash
# Test critical interfaces
ldd /path/to/application/binary | grep 'not found'
strace -e openat /opt/vendor/bin/validate 2>&1 | grep ENOENT

While sometimes helpful, this isn't a complete solution:

# Partial workaround that may break yum:
rpm -e --nodeps redhat-release
rpm -ivh http://mirror.centos.org/centos/7/os/x86_64/Packages/centos-release-7-9.2009.0.el7.centos.x86_64.rpm

For mission-critical deployments, consider:

• Using RHEL developer subscriptions
• Containerizing with RHEL UBI images
• Leveraging CentOS Stream for forward compatibility testing