IT Cheat Sheet Portal

12:00:00 PM ENTERPRISE IT KNOWLEDGEBASE

Active Directory & PowerShell

Domain Controllers, FSMO roles, Group Policy, AD replication, ACL management, and PowerShell ActiveDirectory cmdlets.

ActiveDirectory Module

AD User & Account Management

Everyday Active Directory user provisioning, unlocking, password resets, and auditing.

# Unlock locked user account
Unlock-ADAccount -Identity "jdoe"

# Reset password and require change at next login
Set-ADAccountPassword -Identity "jdoe" -NewPassword (ConvertTo-SecureString "P@ssw0rd123!" -AsPlainText -Force)
Set-ADUser -Identity "jdoe" -ChangePasswordAtLogon $true

# Find locked accounts
Search-ADAccount -LockedOut | Select-Name, SamAccountName, LastLogonDate

# Search users by attribute
Get-ADUser -Filter 'Enabled -eq $true -and Department -eq "IT"' -Properties EmailAddress, Title | Select Name, SamAccountName, EmailAddress, Title

ActiveDirectory Module

Groups, Computer Accounts & Membership

Managing Security/Distribution Groups and querying workstation domain accounts.

# Create Security Group
New-ADGroup -Name "SEC-VPN-Users" -GroupScope Global -GroupCategory Security -Path "OU=Groups,DC=domain,DC=com"

# Add member to group
Add-ADGroupMember -Identity "SEC-VPN-Users" -Members "jdoe", "asmith"

# Query computer OS versions
Get-ADComputer -Filter * -Properties OperatingSystem | Select Name, OperatingSystem

# Join Workstation to Domain
Add-Computer -DomainName "domain.com" -Credential (Get-Credential) -Restart

FSMO Management

FSMO Roles Query, Transfer & Seizure

Identify domain controllers holding FSMO roles and execute role transfers or emergency seizures.

# Query current FSMO role holders
Get-ADDomain | Select-Object SchemaMaster, DomainNamingMaster, PDCEmulator, RIDMaster, InfrastructureMaster
Get-ADForest | Select-Object SchemaMaster, DomainNamingMaster

# Transfer FSMO roles to target DC
Move-ADDirectoryServerOperationMasterRole -Identity "DC02" -OperationMasterRole SchemaMaster, DomainNamingMaster, PDCEmulator, RIDMaster, InfrastructureMaster

# Force Seize FSMO role (Use only when DC is permanently offline)
Move-ADDirectoryServerOperationMasterRole -Identity "DC02" -OperationMasterRole PDCEmulator -Force

GPO & Replication

GPO Diagnostics & Repadmin CLI

Troubleshoot AD replication topology, GPO evaluation, and ACL permissions.

# Force Group Policy update and generate report
gpupdate /force
gpresult /h C:\temp\GPO_Report.html /f

# AD Replication Diagnostics
repadmin /showrepl
repadmin /replsummary
repadmin /syncall /A /e

# Domain Controller Health Check
dcdiag /v /c /d /e /s:DC01.domain.com

# Inspect Active Directory ACLs using DSACLS
dsacls "OU=Workstations,DC=domain,DC=com"

Networking & Subnetting

IP Routing, CIDR subnet reference matrix, DNS troubleshooting tools, socket diagnostics, and iPerf3 throughput testing.

IPv4 Subnet Cheat Sheet

CIDR Subnet Mask Reference Table

CIDR Prefix	Subnet Mask	Wildcard Mask	Total Addresses	Usable Host IPs
/30	255.255.255.252	0.0.0.3	4	2 (Point-to-Point)
/29	255.255.255.248	0.0.0.7	8	6
/28	255.255.255.240	0.0.0.15	16	14
/27	255.255.255.224	0.0.0.31	32	30
/26	255.255.255.192	0.0.0.63	64	62
/25	255.255.255.128	0.0.0.127	128	126
/24	255.255.255.0	0.0.0.255	256	254
/23	255.255.254.0	0.0.1.255	512	510
/22	255.255.252.0	0.0.3.255	1,024	1,022
/16	255.255.0.0	0.0.255.255	65,536	65,534

DNS & Tracing

DNS Lookup & Path Tracing CLI

Commands to test DNS resolution propagation and trace network routing paths.

# Dig lookup specifying DNS Server and Record Type
dig @1.1.1.1 example.com A +short
dig @8.8.8.8 example.com MX +trace

# Windows Nslookup
nslookup -type=TXT _dmarc.example.com 1.1.1.1

# Tracert / Traceroute
tracert -d 8.8.8.8                # Windows (skip reverse DNS)
traceroute -n -m 30 8.8.8.8        # Linux

# Pathping (Windows latency & packet loss per hop)
pathping 8.8.8.8

IP & Sockets

Sockets, ARP & Interface Configuration

Inspect listening sockets, active connections, MAC ARP tables, and network adapters.

# Socket Statistics (Linux replacement for netstat)
ss -tulnp                          # Display listening TCP/UDP ports with PIDs
netstat -ano                       # Windows active connections with PIDs

# ARP Cache Management
arp -a                             # View resolved MAC addresses
arp -d *                           # Clear ARP cache (Windows Admin)

# Windows Netsh Static IP Config
netsh interface ip set address name="Ethernet" static 192.168.1.50 255.255.255.0 192.168.1.1

# iPerf3 Bandwidth Throughput Test
iperf3 -s                          # Run Server
iperf3 -c 192.168.1.50 -t 30 -P 4  # Run Client (4 parallel streams for 30s)

Linux Administration

Systemd, Journalctl, file permissions matrix, SSH key generation, UFW/iptables firewalls, rsync, and process monitoring.

Systemd Services

Systemctl & Journalctl Logs

Managing Linux background services and querying system logs.

# Control system service
sudo systemctl enable --now nginx
sudo systemctl restart nginx
sudo systemctl status nginx

# Inspect journalctl logs
journalctl -u nginx.service -n 100 --no-pager
journalctl -u sshd -f                           # Tail live SSH logs
journalctl -p err..emerg                        # Show errors & emergencies only

File Permissions

Linux Octal Permissions & Ownership

Chmod octal values, user/group ownership, and sticky bits.

# Permissions Quick Matrix: 4=Read, 2=Write, 1=Execute
# 755 = rwxr-xr-x (Standard Dir) | 644 = rw-r--r-- (Standard File)
# 600 = rw------- (SSH Private Key)

sudo chmod 600 ~/.ssh/id_ed25519
sudo chmod 755 /var/www/html
sudo chown -R www-data:www-data /var/www/html

# Find files with insecure permissions (e.g. 777)
find /var/www/ -type f -perm 0777

Users & Security

User Administration & SSH Hardening

Creating users, assigning sudo privileges, and generating Ed25519 SSH keys.

# Add user with home directory and sudo access
sudo useradd -m -s /bin/bash sysadmin
sudo usermod -aG sudo sysadmin

# Generate Ed25519 SSH Keypair
ssh-keygen -t ed25519 -C "[email protected]"

# Copy SSH key to remote host
ssh-copy-id -i ~/.ssh/id_ed25519.pub [email protected]

Storage & Sync

Disk Inspection, Tar & Rsync Operations

Troubleshoot low disk space, compress archives, and perform fast remote file syncs.

# Disk Usage Summary
df -hT                                 # File systems & types
du -sh /* 2>/dev/null | sort -hr | head -n 10   # Top 10 largest folders

# Create Compressed Gzip Archive
tar -czvf backup.tar.gz /etc /var/www

# Synchronize Directory via SSH with Progress
rsync -avzP --delete /local/dir/ [email protected]:/remote/dir/

Hardware Diagnostics & Repair

POST beep codes, SMART drive diagnostic CLI, memory testing, Windows OS recovery (SFC/DISM/Chkdsk), and PSU multimeter testing.

POST Codes

Motherboard BIOS Beep Code Diagnostic Reference

Beep Pattern	Fault Description	Probable Root Cause	Recommended Troubleshooting Step
1 Short Beep	POST Passed Successfully	Normal Boot Routine	None required
Continuous Beeps	Memory / RAM Failure	Bad RAM module or socket dust	Reseat memory sticks; test individual RAM modules in Slot 2.
1 Long, 2 Short	Video / Graphics Adapter Error	Unseated GPU or missing PCIe power cable	Reseat PCIe graphics card; verify 8-pin PCIe power leads.
1 Long, 3 Short	Video RAM / Display Output Error	Faulty GPU VRAM or cable connection	Test with alternative DisplayPort/HDMI cable or iGPU.
5 Short Beeps	CPU Process Failure	CPU improper seating or bent socket pins	Re-mount CPU cooler, check 8-pin EPS 12V motherboard connection.
No Beep / No Fan Rotation	Power Supply / Short Circuit	Faulty PSU, short to chassis, or dead CMOS	Clear CMOS (CR2032 battery removal 5 mins); perform PSU Paperclip test.

Windows Repair

SFC, DISM & Chkdsk Recovery

Sequential CLI repair routine for corrupted Windows system files and disk errors.

# Step 1: Repair Windows Component Store via DISM
DISM /Online /Cleanup-Image /CheckHealth
DISM /Online /Cleanup-Image /RestoreHealth

# Step 2: Run System File Checker to repair OS corruption
sfc /scannow

# Step 3: Schedule disk error repair on reboot
chkdsk C: /f /r

# Step 4: Windows Memory Diagnostic Tool
mdsched.exe

Storage Testing

SMART Health Check (NVMe & SATA)

Detect bad sectors, reallocated sectors, and NVMe wear levels using smartctl.

# Overall Drive Health Summary
sudo smartctl -H /dev/sda
sudo smartctl -H /dev/nvme0n1

# Detailed SMART Attributes Inspection (Look for Reallocated_Sector_Ct)
sudo smartctl -A /dev/sda

# Execute Short Self-Test
sudo smartctl -t short /dev/sda

# Read Diagnostic Test Logs
sudo smartctl -l selftest /dev/sda

Power Supply

ATX 24-Pin PSU Voltage Multimeter Guide

Expected DC voltages when probing 24-pin connector pins against ground (Black Wire).

Wire Color	Signal Name	Expected Voltage	Tolerance
Yellow	+12V (CPU / GPU)	+12.00 VDC	±5% (11.4V to 12.6V)
Red	+5V (Storage / USB)	+5.00 VDC	±5% (4.75V to 5.25V)
Orange	+3.3V (RAM / Chipset)	+3.30 VDC	±5% (3.14V to 3.47V)
Purple	+5VSB (Standby)	+5.00 VDC	±5% (Always Active)
Green	PS_ON# (Power On)	Short to Black (Ground)	Jump to turn on PSU

Thermals & GPU

Thermal Sensors & PCIe Link Status

Inspect CPU temperatures, thermal throttling, and PCIe bus link width.

# Linux Thermal Sensors Check
sensors

# Inspect NVIDIA GPU Temperature & PCIe Speed
nvidia-smi --query-gpu=temperature.gpu,utilization.gpu,pcie.link.gen.current,pcie.link.width.current --format=csv

# Verify PCIe Device Link Speed (e.g. LnkSta: Speed 16GT/s, Width x16)
sudo lspci -vv -s 01:00.0 | grep -E "LnkCap|LnkSta"