When migrating from Ubuntu to CentOS, understanding package availability and versions is crucial for compatibility planning. Unlike Ubuntu's apt repositories which are easily browsable online, CentOS requires some different approaches to examine packages without a live system.

The CentOS project provides several ways to explore packages:

• CentOS Mirror List: https://www.centos.org/download/mirrors/ - Contains the base packages
• EPEL Repository: https://fedoraproject.org/wiki/EPEL - Additional packages not in base
• CentOS Vault: https://vault.centos.org/ - Historical packages

CentOS repositories contain XML metadata files that list all available packages. You can parse these directly:

# Sample command to view package list from a mirror
curl -s https://mirror.centos.org/centos/7/os/x86_64/repodata/primary.xml.gz | gunzip | grep -E '<name>|<version'

Several websites provide package search capabilities:

• pkgs.org - Search across multiple distros including CentOS
• centos.pkgs.org - Dedicated CentOS package browser
• rpmfind.net - RPM package search engine

Here's a Python script to compare package availability between Ubuntu and CentOS:

import requests

def check_package(pkg_name):
    centos_url = f"https://centos.pkgs.org/search/?search={pkg_name}"
    ubuntu_url = f"https://packages.ubuntu.com/search?keywords={pkg_name}"
    
    print(f"CentOS: {centos_url}")
    print(f"Ubuntu: {ubuntu_url}")

check_package("nginx")
check_package("php-fpm")

Key web server packages that often differ between Ubuntu and CentOS:

Remember that CentOS typically uses older, more stable versions compared to Ubuntu's newer releases. Always verify version compatibility for your applications.

When migrating from Ubuntu to CentOS, examining package availability beforehand is crucial. Here are authoritative online sources for CentOS package metadata:

# Primary mirror structure (replace $VERSION):
https://vault.centos.org/$VERSION/os/x86_64/Packages/
https://vault.centos.org/$VERSION/updates/x86_64/Packages/

For CentOS 7 specifically:

https://vault.centos.org/7.9.2009/os/x86_64/Packages/

Use this Python script to fetch package lists via HTTP:

import requests
from bs4 import BeautifulSoup

def get_centos_packages(version='7'):
    base_url = f"https://vault.centos.org/{version}/os/x86_64/Packages/"
    response = requests.get(base_url)
    soup = BeautifulSoup(response.text, 'html.parser')
    return [a['href'] for a in soup.find_all('a') if a['href'].endswith('.rpm')]

print(get_centos_packages('7.9.2009')[:10])  # Sample output

Key differences in common web server packages:

For EPEL repositories (common for web applications):

https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
https://mirrors.edge.kernel.org/fedora-epel/7/x86_64/Packages/

For automated comparison between systems:

# Ubuntu to CentOS mapping example
package_map = {
    'apache2': 'httpd',
    'libapache2-mod-php': 'mod_php',
    'python3-pip': 'python3-pip'
}

def convert_package(pkg_name):
    return package_map.get(pkg_name, pkg_name)