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Practical technology help for homes and small businesses, from someone who knows how to make it work. Based in Martinez, serving Contra Costa County.

Practical IT guides, cheatsheets, and references from Jeremiah Ellington, drawn from more than 20 years of IT work in public sector and higher education.

Contact Info
Email hello@jeremiahellington.com
Location Martinez, CA (Serving Contra Costa County)
Contact Info
Email hello@jeremiahellington.com
Location Martinez, CA (Serving Contra Costa County)
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Technical Cheatsheets

Command references you can print or save as a PDF. Each one lists the versions it was checked against, and commands that can delete data or lock you out are marked.

Cheatsheet

Small Business Cybersecurity Checklist (Printable)

The one-page version of the Small Business Cybersecurity Checklist: what to do this week, this month, this quarter, and on a schedule, with space for your emergency contacts.

Small businesses using Windows/macOS computers and Microsoft 365 or Google Workspace. Companion to the full guide, which explains each item · Updated

Cheatsheet

Mental Subnetting Cheatsheet

One printable page for subnetting IPv4 without a chart: the four steps, the interesting octet for each prefix, mask values and increments, powers of two, and /0, /31 and /32.

IPv4 CIDR prefixes /0 to /32. IPv6 isn't covered · Updated

Cheatsheet

OpenSSL Certificate Inspection and s_client Cheatsheet

OpenSSL commands for reading certificates, requests, CRLs and PFX files, checking a chain, matching a key to its certificate, and testing a live TLS server with s_client, organised around four everyday jobs.

OpenSSL 3.5 LTS on Linux or macOS. Checked against the OpenSSL 3.5 manual pages (docs.openssl.org/3.5) on 2026-10-27, not run against a live server; other 3.x releases may differ in detail · Updated

Cheatsheet

PowerShell Essentials Cheatsheet for IT Admins

Everyday PowerShell for Windows administration: discovery, files, processes and services, networking, event logs, users, disks, remoting and safe-change habits, plus walk-throughs for Active Directory, Entra ID and Exchange (on-premises and online).

PowerShell 7.6 LTS and Windows PowerShell 5.1 on Windows 11 and Windows Server 2019+ (noted where they differ). PowerShell 7.4 and 7.5 reach end of support on November 10, 2026 · Updated

Cheatsheet

Proxmox VE Command-Line Cheatsheet

The Proxmox VE shell commands you'll use most: VMs (qm), containers (pct), storage, backups and restores, templates, networking, updates, and troubleshooting.

Proxmox VE 9.x (9.2 current on 2026-10-27); run as root on the host. Commands checked against Proxmox VE 9.x docs, not lab-tested on a 9.2 host. Most also work on 8.x, which reached end of support in August 2026 · Updated

Cheatsheet

Windows Certificate Commands Cheatsheet

The Windows tools for finding, checking, requesting and installing certificates, organised around four everyday jobs: renewing a server certificate, fixing an untrusted chain, moving a certificate to a new server, and publishing a template on an AD CS issuing CA.

Windows Server 2016 to 2025 and Windows 11: certutil, certreq, certlm.msc and certmgr.msc; the PowerShell Cert: drive in Windows PowerShell 5.1 and PowerShell 7.6 (the -DnsName, -EKU, -ExpiringInDays and -SSLServerAuthentication filters need 5.1 or 7.1 and later); the ADCSAdministration module on an enterprise issuing CA. Checked against Microsoft Learn on 2026-10-27, not lab-tested · Updated