Sysadmin Cheatsheet

①

Networking Fundamentals

OSI · IPv4 · TCP/UDP · DNS

OSI Model

#	Layer	Protocol / Tech	Key Role
7	Application	HTTP, FTP, DNS, SMTP, SNMP	User-facing data exchange
6	Presentation	SSL/TLS, JPEG, ASCII	Encoding, encryption, compression
5	Session	NetBIOS, RPC, PPTP	Open/maintain/close sessions
4	Transport	TCP, UDP	Segmentation, ports, reliability
3	Network	IP, ICMP, OSPF, BGP	Logical addressing, routing
2	Data Link	Ethernet, MAC, ARP, VLANs	Physical addressing, framing
1	Physical	Cables, hubs, bits, NICs	Raw bit transmission

IPv4 Address Ranges

Range	Type	Notes
`10.0.0.0/8`	Private	Class A, large networks
`172.16.0.0/12`	Private	Class B (172.16-31.x)
`192.168.0.0/16`	Private	Class C, home/SOHO
`127.0.0.0/8`	Loopback	127.0.0.1 = localhost
`169.254.0.0/16`	APIPA	Auto-assigned when DHCP fails
`224.0.0.0/4`	Multicast	One-to-many delivery
`0.0.0.0`	Unspecified	Two distinct uses: binding (0.0.0.0:80 = listen on all interfaces) vs routing (0.0.0.0/0 = default route / gateway of last resort)

DNS Record Types

Record	Purpose	Example
A	IPv4 address	example.com → 93.184.216.34
AAAA	IPv6 address	example.com → 2606:…
CNAME	Canonical alias	www → example.com
MX	Mail server	Priority + mail host
NS	Nameservers	Delegates zone authority
TXT	Text data	SPF, DKIM, site verification
SOA	Zone authority	Primary NS, serial, TTLs
PTR	Reverse DNS	IP → hostname lookup
SRV	Service location	_sip._tcp.example.com

TCP vs UDP

Property	TCP	UDP
Connection	Connection-oriented (3-way handshake)	Connectionless, no handshake
Reliability	Guaranteed delivery, retransmits lost packets	Best-effort, packets may be lost
Ordering	Sequenced delivery guaranteed	Out-of-order delivery possible
Speed	Slower (overhead from acks, windowing)	Faster, minimal overhead
Use cases	HTTP/S, SSH, FTP, SMTP, RDP, databases	DNS, DHCP, VoIP, video streams, NTP

Network Troubleshooting Workflow

Work through these steps in order - each layer rules out the one above it.

Step	Command	What You're Checking
1. Is the host up?	`ping -c 4 <target>`	Basic ICMP reachability - rules out total network failure
2. What path does traffic take?	`traceroute <target>` / `tracert`	Hop-by-hop path - find where packets drop or latency spikes
3. Does DNS resolve?	`dig <hostname>` / `nslookup`	Name resolution - wrong IP or NXDOMAIN means DNS problem
4. Is the port open?	`nc -zv <host> <port>` / `Test-NetConnection`	TCP connectivity to specific port - rules out firewall or service down
5. Is the service listening?	`ss -tlnp` / `netstat -ano`	What's bound to which port locally - service may not be started
6. What does the traffic look like?	`tcpdump -i eth0 host <target>`	Actual packet capture - see resets, retransmits, TLS failures
7. What do the logs say?	`journalctl -u nginx -n 50` / `tail -f /var/log/syslog`	Application and system errors - often the exact answer
8. Is a firewall blocking it?	`iptables -L -n` / `ufw status` / `Get-NetFirewallRule`	Local firewall rules - check both source and destination
9. Is MTU causing fragmentation?	`ping -M do -s 1472 <target>`	Test for MTU/fragmentation issues on VPN or tunnel paths
10. Is the cert valid?	`openssl s_client -connect <host>:443`	TLS handshake, cert expiry, chain validity - for HTTPS issues

HTTP Status Codes

Code	Meaning	Common Cause
`200`	OK	Request succeeded
`201`	Created	POST succeeded, new resource created
`204`	No Content	Success, no body returned (DELETE, PUT)
`301`	Moved Permanently	URL changed forever - clients should update bookmarks
`302`	Found (Temporary Redirect)	Temporary redirect - client keeps using original URL
`304`	Not Modified	Cached version is still valid - no body sent
`400`	Bad Request	Malformed request syntax, invalid parameters
`401`	Unauthorized	Authentication required or failed
`403`	Forbidden	Authenticated but no permission - check ACLs, file permissions
`404`	Not Found	Resource doesn't exist at this URL
`405`	Method Not Allowed	Wrong HTTP verb (GET vs POST) for this endpoint
`408`	Request Timeout	Client too slow - network issue or overloaded server
`429`	Too Many Requests	Rate limit hit - back off and retry
`500`	Internal Server Error	Unhandled exception - check app logs
`502`	Bad Gateway	Upstream server returned invalid response - check backend/proxy
`503`	Service Unavailable	Server overloaded or down for maintenance
`504`	Gateway Timeout	Upstream server too slow - check backend latency and timeouts

②

CIDR & Subnets

Subnet masks · Host counts · Block sizes

CIDR	Subnet Mask	Hosts	Block Size	Example / Use
`/8`	255.0.0.0	16,777,214	16M	10.0.0.0/8 - large org
`/16`	255.255.0.0	65,534	64K	172.16.0.0/16 - campus
`/20`	255.255.240.0	4,094	4K	AWS default VPC subnets
`/24`	255.255.255.0	254	256	192.168.1.0/24 - typical LAN
`/25`	255.255.255.128	126	128	192.168.1.0/25 - split /24 in half
`/26`	255.255.255.192	62	64	192.168.1.0/26 - quarter of a /24
`/27`	255.255.255.224	30	32	192.168.1.0/27 - small dept segment
`/28`	255.255.255.240	14	16	192.168.1.0/28 - server cluster
`/29`	255.255.255.248	6	8	Point-to-point link
`/30`	255.255.255.252	2	4	Router-to-router link
`/31`	255.255.255.254	2	2	RFC 3021 p2p (no broadcast)
`/32`	255.255.255.255	1	1	Single host route / loopback

Tip: Usable hosts = 2ⁿ - 2 (subtract network + broadcast). /31 is the exception (RFC 3021).

③

Ports & VPN Technologies

Well-known ports · VPN protocols

Well-Known Ports

Port(s)	Protocol	Service	Notes
20 / 21	TCP	FTP	20=data, 21=control. Use SFTP/FTPS instead
22	TCP	SSH / SFTP / SCP	Secure remote shell and file transfer
23	TCP	Telnet	Plaintext - disable, use SSH
25	TCP	SMTP	Mail relay between servers
53	TCP/UDP	DNS	UDP for queries, TCP for zone transfers/large
67 / 68	UDP	DHCP	67=server, 68=client
80	TCP	HTTP	Unencrypted web - redirect to 443
88	TCP/UDP	Kerberos	Authentication in AD environments
110	TCP	POP3	Email retrieval - use POP3S (995)
123	UDP	NTP	Time sync - critical for Kerberos/logs
143	TCP	IMAP	Email access - use IMAPS (993)
161 / 162	UDP	SNMP	161=poll, 162=trap. Use v3 with auth
389	TCP/UDP	LDAP	Directory services - use LDAPS (636)
443	TCP	HTTPS	HTTP over TLS. Also used by some VPNs
445	TCP	SMB	Windows file shares - block at perimeter
465 / 587	TCP	SMTPS / SMTP-TLS	Encrypted mail submission
514	UDP	Syslog	Log forwarding - use TLS syslog (6514)
636	TCP	LDAPS	LDAP over TLS
993	TCP	IMAPS	IMAP over TLS
995	TCP	POP3S	POP3 over TLS
1433	TCP	MS SQL Server	Default SQL Server port
1521	TCP	Oracle DB	Oracle database listener
3306	TCP	MySQL / MariaDB	Common web app database port
3389	TCP	RDP	Remote Desktop - never expose to internet
5432	TCP	PostgreSQL	Default Postgres port
5900	TCP	VNC	Remote desktop - use only over VPN/tunnel
6379	TCP	Redis	Historically no auth by default - always bind to localhost and set requirepass before any exposure
8080 / 8443	TCP	HTTP/S Alt	Dev servers, proxies, alt web services
27017	TCP	MongoDB	Historically no auth by default - modern versions enforce localhost binding; always enable auth and restrict access before exposing

VPN Technologies

Type	Protocol	Port(s)	Notes
IPSec / IKEv2	ESP / IKE	UDP 500 / 4500	Fast, native on most OS, preferred for site-to-site
OpenVPN	TLS	UDP/TCP 1194	Flexible, open-source, common for remote access
WireGuard	UDP	51820	Modern, minimal code, fastest throughput. Key-based auth (Curve25519) - no certificates or CA needed, unlike IPSec/OpenVPN
SSL VPN	HTTPS	TCP 443	Works through firewalls, browser or client-based
L2TP/IPSec	L2TP + ESP	UDP 1701 / 500 / 4500	Common legacy, double-encapsulation overhead; 4500 for NAT-T
PPTP	GRE + TCP	TCP 1723	Obsolete - broken crypto, avoid

④

Security, Threats & Hardening

Attacks · Hardening · Crypto · Auth

Threat / Attack Reference

Category	Attack	Description
Phishing	Phishing / Spear / Whaling	Fraudulent emails targeting all users / specific individuals / executives
Phishing	Vishing / Smishing	Voice call or SMS-based social engineering
Web App	SQL Injection	Malicious SQL inserted into input fields to query or corrupt the DB
Web App	XSS (Cross-Site Scripting)	Injected scripts execute in victim's browser via a trusted site
Web App	CSRF	Forged request tricks authenticated user into unwanted action
Web App	IDOR	Accessing objects by changing an ID in the URL/request
Malware	Ransomware	Encrypts files, demands payment for key
Malware	Rootkit	Hides malware presence at OS/kernel level
Malware	Keylogger	Records keystrokes to capture credentials
Network	MITM	Attacker intercepts communication between two parties
Network	ARP Spoofing	Links attacker MAC to legitimate IP to intercept LAN traffic
Network	DDoS / SYN Flood	Overwhelm target with traffic / half-open TCP connections
Social Eng.	Pretexting / Tailgating	Fabricated scenario to obtain info / following into secure area
Insider	Privilege Escalation	Exploiting vuln or misconfiguration to gain higher access

Hardening Checklist

	Action
DO	Disable unused ports and services
DO	Enable MFA / 2FA on all accounts
DO	Apply least privilege (PoLP) everywhere
DO	Patch OS promptly - critical/zero-day: hours to days; standard patches: within 30 days
DO	Enable host-based firewall (UFW/iptables)
DO	Use key-based SSH auth, disable password auth
DO	Disable root SSH login (PermitRootLogin no)
DO	Encrypt data at rest and in transit
DO	Log and monitor all auth events
DON'T	Use default credentials on any device
DON'T	Run services as root unnecessarily
DON'T	Expose RDP / management ports to internet
DON'T	Disable SELinux/AppArmor without a plan
DON'T	Store plaintext credentials in scripts/repos

Cryptography Algorithms

Algorithm	Type	Key Size / Notes
AES-256	Symmetric	256-bit. NIST standard, fastest for bulk data
ChaCha20	Symmetric	Stream cipher, faster than AES on mobile
RSA	Asymmetric	2048+ min (4096 recommended for long-term)
ECDSA / ECDH	Asymmetric	ECC - same security as RSA with shorter keys
Ed25519	Asymmetric	Preferred for SSH keys, fast and secure
SHA-256 / SHA-3	Hash	Use for integrity checks, digital signatures
bcrypt / Argon2	Password hash	Argon2 is winner of Password Hashing Competition
TLS 1.3 / 1.2	Protocol	TLS 1.3 preferred (faster, mandatory forward secrecy); TLS 1.2 still acceptable with modern ciphers. 1.0/1.1 deprecated - disable immediately

Authentication Methods

Method	Use Case
Password + MFA/TOTP	Baseline for all user accounts
SSH Key Pairs (Ed25519)	Server access, CI/CD pipelines
PKI / X.509 Certificates	TLS, client auth, code signing
OAuth 2.0 / OIDC	Web app delegation, "Sign in with Google"
SAML 2.0	Enterprise SSO, IdP federation
Kerberos	Active Directory authentication (tickets)
RADIUS	Network access (WiFi 802.1X, VPN auth)
LDAP / Active Directory	Centralized user/group directory

⑤

OS & Commands

Linux · Windows/PS · Storage · RAID · Backup · AD

Linux - Process & Performance - Reference: ss64.com/bash

Command	Description
`top / htop`	Real-time process monitor. htop is interactive
`ps aux`	All processes with user and CPU/mem usage
`ps aux \| grep nginx`	Find process by name
`kill -9 <PID>`	Force-kill process by PID (SIGKILL)
`pkill -f nginx`	Kill all processes matching name pattern
`systemctl status sshd`	Check service status (systemd)
`systemctl restart nginx`	Restart a systemd service
`systemctl enable nginx`	Enable service to start on boot
`journalctl -u nginx -f`	Follow systemd logs for a service
`free -h`	Memory usage in human-readable format
`vmstat 1`	CPU/IO/memory stats every 1 second
`uptime`	System uptime and load averages (1/5/15 min)

systemd Deep Dive

Command	Description
`systemctl list-units --type=service --state=failed`	Show all failed services - first thing to check after a reboot
`systemctl list-units --type=service --state=running`	All currently running services
`systemctl disable --now nginx`	Stop a service and prevent it starting on boot in one command
`systemctl mask nginx`	Completely prevent a service from starting - stronger than disable, blocks manual start too
`systemctl cat nginx`	Show the full unit file for a service - see ExecStart, dependencies, restart policy
`systemctl daemon-reload`	Reload unit files after editing - required before restarting a modified service
`journalctl -u nginx -n 100 --no-pager`	Last 100 log lines for a service without paging
`journalctl -u nginx --since "1 hour ago"`	Service logs from the last hour - accepts natural language time
`journalctl -p err -b`	Only error-level (and above) messages from current boot
`journalctl -b -1`	Logs from the previous boot - useful after a crash or unexpected reboot
`journalctl --disk-usage`	How much disk space journal logs are consuming
`journalctl --vacuum-time=7d`	Delete journal entries older than 7 days to free disk space

Linux - Networking & Firewall

Command	Description
`ip addr show`	Show all network interfaces and IP addresses
`ip route show`	Display routing table
`ss -tulnp`	TCP/UDP listening ports with process names
`netstat -tulnp`	Listening ports (legacy, use ss on modern systems)
`ping -c 4 8.8.8.8`	Test connectivity (4 packets)
`traceroute 8.8.8.8`	Trace route hops to destination
`nmap -sV -p 1-1000 <IP>`	Scan top 1000 ports with service version
`dig example.com A`	DNS lookup for A record
`curl -I https://example.com`	Fetch HTTP response headers only

Linux - Files, Permissions & Users

Command	Description
`chmod 755 file`	rwxr-xr-x - owner full, group/other read+exec
`chmod u+x script.sh`	Add execute permission for owner
`chown user:group file`	Change file owner and group
`find / -perm -4000`	Find all SUID binaries (privilege escalation risk)
`useradd -m -s /bin/bash u`	Create user with home dir and bash shell
`usermod -aG sudo username`	Add user to sudo group
`passwd username`	Set or change user password
`grep -r "error" /var/log/`	Recursively search logs for "error"
`tail -f /var/log/syslog`	Follow log file in real-time
`df -h`	Disk usage by filesystem in human-readable
`du -sh /var/log/*`	Size of each item in /var/log
`tar -czf out.tar.gz /dir`	Create gzipped tarball of directory
`rsync -avz src/ dest/`	Sync files with verbose output and compression

Common Linux Config Files

File	What it Controls
`/etc/hosts`	Static hostname-to-IP mappings - checked before DNS, useful for local overrides
`/etc/resolv.conf`	DNS server addresses and search domains - often managed by NetworkManager or systemd-resolved
`/etc/fstab`	Filesystems mounted at boot - device, mount point, type, options, dump, fsck order
`/etc/hostname`	System hostname - change here then run `hostnamectl set-hostname` to apply
`/etc/sudoers`	Sudo access rules - always edit with `visudo` to prevent syntax errors locking you out
`/etc/passwd`	User accounts: username, UID, GID, home dir, shell - no passwords stored here
`/etc/shadow`	Hashed passwords and password policy per user - root-readable only
`/etc/group`	Group definitions and membership lists
`/etc/ssh/sshd_config`	SSH server config - PermitRootLogin, PasswordAuthentication, Port, AllowUsers
`/etc/crontab`	System-wide cron schedule - user crons live in `/var/spool/cron/crontabs/`
`/etc/cron.d/`	Drop-in cron files for packages and services - same format as /etc/crontab
`/etc/environment`	System-wide environment variables set at login - plain KEY=value format, no export needed
`/etc/profile.d/`	Shell scripts sourced at login for all users - drop custom env vars and aliases here
`/etc/logrotate.conf`	Log rotation policy - frequency, retention count, compression settings
`/etc/nsswitch.conf`	Name service switch - controls lookup order for hosts, users, groups (files vs DNS vs LDAP)

SSH Key Management

Command / File	Description
`ssh-keygen -t ed25519 -C "user@host"`	Generate Ed25519 key pair - preferred over RSA for new keys
`ssh-keygen -t rsa -b 4096 -C "user@host"`	Generate 4096-bit RSA key pair - use when Ed25519 not supported
`ssh-copy-id user@host`	Copy public key to remote host's authorized_keys in one step
`cat ~/.ssh/id_ed25519.pub >> ~/.ssh/authorized_keys`	Manually append public key to authorized_keys (manual alternative)
`eval $(ssh-agent -s) && ssh-add ~/.ssh/id_ed25519`	Start ssh-agent and load a key - avoids repeated passphrase prompts
`ssh-add -l`	List keys currently loaded in ssh-agent
`ssh -J bastion user@target`	ProxyJump - SSH through a bastion/jump host to reach internal servers
`ssh -L 8080:internal:80 user@bastion`	Local port forward - tunnel local 8080 through bastion to internal:80
`~/.ssh/config`	Per-user SSH config - define Host aliases, IdentityFile, ProxyJump, Port per host
`~/.ssh/authorized_keys`	Public keys allowed to authenticate to this account - must be chmod 600
`~/.ssh/known_hosts`	Fingerprints of hosts you've connected to - mismatch = MITM warning
`/etc/ssh/sshd_config`	Server-side SSH config - PermitRootLogin, PasswordAuthentication, AllowUsers

Package Management

Task	apt (Debian/Ubuntu)	dnf/yum (RHEL/CentOS)	zypper (SUSE)
Install package	`apt install nginx`	`dnf install nginx`	`zypper install nginx`
Remove package	`apt remove nginx`	`dnf remove nginx`	`zypper remove nginx`
Remove + config	`apt purge nginx`	`dnf remove nginx`	`zypper remove --clean-deps nginx`
Update all	`apt update && apt upgrade`	`dnf upgrade`	`zypper update`
Search package	`apt search nginx`	`dnf search nginx`	`zypper search nginx`
Package info	`apt show nginx`	`dnf info nginx`	`zypper info nginx`
List installed	`apt list --installed`	`dnf list installed`	`zypper packages --installed`
Which pkg owns file	`dpkg -S /usr/bin/nginx`	`rpm -qf /usr/sbin/nginx`	`rpm -qf /usr/sbin/nginx`
List pkg files	`dpkg -L nginx`	`rpm -ql nginx`	`rpm -ql nginx`
Add repo	`add-apt-repository ppa:x`	`dnf config-manager --add-repo URL`	`zypper addrepo URL alias`
Clean cache	`apt clean`	`dnf clean all`	`zypper clean`

Linux Filesystem Hierarchy

Path	What Lives Here
`/`	Root of the entire filesystem tree - everything hangs off here
`/bin`	Essential user binaries (ls, cp, mv, bash) needed before /usr is mounted
`/sbin`	Essential system binaries for root (fdisk, ifconfig, init, fsck)
`/usr`	Read-only user data: most installed apps, libraries, and docs go here
`/usr/bin`	Non-essential user commands (gcc, python3, git, curl, vim)
`/usr/local`	Locally compiled or admin-installed software - not managed by the package manager
`/etc`	System-wide configuration files (/etc/ssh/sshd_config, /etc/hosts, /etc/cron.d)
`/var`	Variable data that grows: logs (/var/log), mail, spool, databases, package cache
`/var/log`	System and service logs (syslog, auth.log, dmesg, journald writes here)
`/tmp`	Temporary files - cleared on reboot, world-writable, no exec in hardened configs
`/home`	User home directories (/home/alice). Root's home is /root, not here
`/root`	Home directory for the root account
`/dev`	Device files: disks (/dev/sda), terminals (/dev/tty), null (/dev/null)
`/proc`	Virtual FS exposing kernel and process info (/proc/cpuinfo, /proc/meminfo)
`/sys`	Virtual FS for kernel devices and drivers - used by udev and hardware management
`/boot`	Kernel images, initramfs, and GRUB config - keep separate partition for safety
`/lib`	Shared libraries needed by /bin and /sbin at boot
`/opt`	Optional third-party software installed as self-contained packages (e.g. /opt/splunk)
`/mnt`	Temporary mount point for manually mounted filesystems
`/media`	Auto-mount point for removable media (USB drives, DVDs)
`/srv`	Service data served to the network (web root, FTP files)
`/run`	Runtime data since last boot: PID files, sockets, lock files (tmpfs)

Windows Filesystem Hierarchy

Drive-letter based (C:, D:). NTFS is standard - supports permissions, ACLs, compression, and encryption.

Path	What Lives Here
`C:\`	Root of the drive - each volume has its own root under a drive letter
`C:\Windows`	OS root containing system binaries, configuration files, and critical subdirectories
`C:\Windows\System32`	64-bit system executables, DLLs, and management tools (cmd.exe, notepad.exe, etc.)
`C:\Windows\SysWOW64`	32-bit system binaries for backward compatibility on 64-bit Windows
`C:\Windows\System32\drivers`	Kernel-mode drivers (.sys files) loaded at boot
`C:\Windows\Temp`	System-wide temporary files - safe to clear periodically
`C:\Program Files`	Default install directory for 64-bit applications
`C:\Program Files (x86)`	Default install directory for 32-bit applications on 64-bit Windows
`C:\ProgramData`	System-wide app data and config shared across all users (hidden by default)
`C:\Users\Public`	Shared folder accessible to all local users
`C:\Users\%USERNAME%`	Per-user profile root - contains all personal folders and app data
`...\AppData\Roaming`	Per-user config that follows domain profiles (Outlook, VS Code settings, etc.)
`...\AppData\Local`	Local-only app data: cache, application state, Temp subfolder
`...\AppData\Local\Temp`	User-specific temp files - a common target for malware drops
`...\Desktop / Downloads`	Standard personal folders inside each user profile

PowerShell Essentials - Reference: ss64.com/ps

Command	Description
`Get-Help Get-Process -Full`	Full documentation for any cmdlet - add `-Examples` for just examples, `-Online` to open browser docs
`Get-Help network`	Wildcard search across all help topics - how you discover cmdlets you don't know yet
`Update-Help`	Download latest help files - run once after a fresh install, requires internet
`Get-Command -Verb Get -Noun DNS`	Find cmdlets by verb, noun, or wildcard - the right way to discover what's available
`Get-Command -Module ActiveDirectory`	List every cmdlet in a specific module
`Get-Module -ListAvailable`	All modules installed on the system, whether loaded or not
`Import-Module ActiveDirectory`	Load a module into the current session
`Get-Process \| Get-Member`	Inspect every property and method on an object - essential for building pipelines
`Get-Service \| Select-Object -Property *`	Reveal all properties on an object, not just the default display columns
`Get-History`	Command history for the current session with execution IDs
`Invoke-History 42`	Re-run a command by its history ID
`Get-PSReadLineOption`	View persistent history path - PSReadLine saves history across sessions by default
`Set-ExecutionPolicy RemoteSigned -Scope CurrentUser`	Allow local scripts to run; remote scripts must be signed. Safest policy for daily use
`Get-ExecutionPolicy -List`	Show policy at every scope (MachinePolicy, UserPolicy, Process, CurrentUser, LocalMachine)

Windows / PowerShell & CMD - Reference: ss64.com/ps · ss64.com/nt

Command	Description
`Get-Process`	List all running processes (PS)
`Stop-Process -Name notepad`	Kill process by name (PS)
`Get-Service \| Where Status -eq Running`	List only running services (PS)
`systeminfo`	OS version, RAM, hotfixes, uptime
`net user /domain`	List domain users
`net localgroup administrators`	List local admins
`Get-HotFix \| Sort-Object InstalledOn -Descending`	Installed Windows Updates and KBs, newest first
`Get-ExecutionPolicy`	Check current PowerShell script execution policy
`Get-CimInstance Win32_OperatingSystem \| select LastBootUpTime`	When the system last rebooted
`Get-WinEvent -LogName Security -MaxEvents 50`	Recent Security event log entries (PS)
`Get-WinEvent -FilterHashtable @{LogName='Security'; Id=4625} -MaxEvents 20`	Failed logon events only - faster and more precise than Where-Object filtering
`Test-NetConnection -ComputerName dc01 -Port 443`	Test TCP connectivity to a host/port - modern replacement for telnet port tests
`Invoke-Command -ComputerName srv01,srv02 -ScriptBlock { Get-Service spooler }`	Run commands on one or many remote machines simultaneously over WinRM
`Enter-PSSession -ComputerName srv01`	Interactive remote PowerShell session - like SSH for Windows
`Get-Printer -ComputerName printserver`	List all printers on a print server
`Add-Printer -Name "HP-Floor2" -DriverName "HP Universal" -PortName "IP_10.0.1.50"`	Add a network printer from CLI - no GUI needed
`Install-Module PSWindowsUpdate -Force; Get-WindowsUpdate`	Check pending Windows Updates from PowerShell - requires PSWindowsUpdate module
`Install-WindowsUpdate -AcceptAll -AutoReboot`	Install all available updates and reboot if required (PSWindowsUpdate module)

Windows Networking

Command	Description
`ipconfig /all`	Full adapter info including MAC address, DNS servers, DHCP lease, and gateway
`netstat -ano`	All active TCP/UDP connections with associated PIDs (legacy but universal)
`Get-NetTCPConnection`	Modern netstat equivalent - active TCP connections with state and owning process ID
`Get-DnsClientCache`	View locally cached DNS records - useful for diagnosing stale or poisoned entries
`Get-NetRoute`	Display the full routing table - equivalent to `route print`
`Get-NetAdapter`	List physical and virtual network adapters with link speed and status
`(Invoke-RestMethod ipinfo.io/json).ip`	Retrieve public egress IP address from PowerShell - no browser needed
`Restart-Computer -ComputerName "PC01" -Force`	Remotely restart a machine by name - requires WinRM or admin share access

Windows Storage & Services

Command	Description
`Get-Disk`	List all physical disks with size, partition style (MBR/GPT), and health status
`Get-Volume`	Show all volumes with drive letter, filesystem, total size, and free space
`Get-PhysicalDisk \| select FriendlyName, HealthStatus, OperationalStatus`	SMART-based health status per physical disk - spot failing drives early
`Get-ChildItem C:\Path -Recurse \| Measure-Object -Sum Length`	Calculate total disk usage of a directory tree in bytes
`Get-Service \| Where Status -eq Running`	List only services currently in a Running state
`Get-Service \| where Status -eq 'StartPending'`	Find services stuck in Starting - indicates a hung or deadlocked service
`Restart-Service -Name sshd`	Restart a named service by its service name (not display name)
`Get-CimInstance Win32_Service \| select Name, PathName, StartMode`	Service binary path and start mode - useful for spotting malicious service installs

RAID Types

RAID	Method	Min Disks	Fault Tolerance
RAID 0	Striping	2	None — any disk failure = total loss
RAID 1	Mirroring	2	1 disk failure tolerated
RAID 5	Stripe + parity	3	1 disk failure tolerated
RAID 6	Stripe + dual parity	4	2 disk failures tolerated
RAID 10	Stripe of mirrors	4	1 per mirror pair

Backup Strategy Types

Type	What It Backs Up	Speed	Restore
Full	All data every time	Slowest	Single set — fastest restore
Incremental	Changes since last backup (any)	Fastest	Need all incrementals + last full
Differential	Changes since last full only	Medium	Last full + latest differential
Snapshot	Point-in-time copy (CoW)	Instant	Instant rollback, storage overhead

Active Directory

Command	Description
`Get-ADUser -Identity jsmith -Properties *`	Full user details: last logon, locked status, group membership
`Get-ADUser -Filter {Enabled -eq $true} -Properties LastLogonDate \| Where {$_.LastLogonDate -lt (Get-Date).AddDays(-90)}`	Active accounts with no logon in 90+ days — stale account audit
`Set-ADUser -Identity jsmith -Enabled $false`	Disable a user account
`Unlock-ADAccount -Identity jsmith`	Unlock a locked-out account
`Set-ADAccountPassword -Identity jsmith -Reset -NewPassword (ConvertTo-SecureString "P@ssw0rd!" -AsPlainText -Force)`	Reset a user password from PowerShell
`Get-ADGroupMember -Identity "Domain Admins" -Recursive`	List group members including nested members
`Add-ADGroupMember -Identity "VPN Users" -Members jsmith`	Add a user to a group
`Get-ADComputer -Filter * -Properties LastLogonDate \| Sort LastLogonDate`	All computers sorted by last logon — spot stale machine accounts
`Test-ComputerSecureChannel -Repair`	Fix broken domain trust without removing from domain
`Reset-ComputerMachinePassword`	Fixes "trust relationship failed" — no domain rejoin needed
`gpupdate /force`	Force immediate Group Policy refresh
`gpresult /r`	Show applied GPOs for current user and computer (RSoP)
`dcdiag /test:replications`	Test AD replication health across domain controllers
`repadmin /replsummary`	Replication summary — spot failing DC partners quickly

⑥

Logs & Monitoring

Linux logs · Windows Event IDs · Cron

Linux Log Paths

Path / Command	Contents
`/var/log/auth.log`	SSH logins, sudo, auth failures (Debian/Ubuntu)
`/var/log/secure`	Same as auth.log on RHEL/CentOS
`/var/log/syslog`	General system messages and daemon output
`/var/log/messages`	Kernel + system messages (RHEL/CentOS)
`/var/log/kern.log`	Kernel ring buffer messages
`/var/log/nginx/access.log`	HTTP requests to Nginx web server
`/var/log/nginx/error.log`	Nginx errors and connection issues
`/var/log/apache2/error.log`	Apache web server errors
`/var/log/cron`	Cron job execution history
`journalctl -u nginx`	Systemd journal for a specific service
`journalctl -b -p err`	All errors since last boot (systemd)

Windows Event IDs

Event ID	Log	Meaning
4624	Security	Successful logon
4625	Security	Failed logon attempt
4648	Security	Logon with explicit credentials (runas)
4672	Security	Special privileges assigned to new logon
4688	Security	New process created (process tracking)
4720	Security	User account created
4740	Security	Account locked out
4776	Security	DC validated credentials (NTLM)
7045	System	New service installed on the system
1102	Security	Audit log cleared - investigate immediately

Log Query Tools

Tool / Command	Use
`Event Viewer (eventvwr.msc)`	Windows GUI for all event logs
`Get-WinEvent -LogName Security`	PowerShell security log access
`grep "Failed" /var/log/auth.log`	Filter failed SSH attempts
`last -n 20`	Last 20 logins from /var/log/wtmp
`lastb`	Failed login attempts (/var/log/btmp)

Cron Job Syntax

Field	Range	Example	Meaning
Minute	0-59	`30`	At minute 30
Hour	0-23	`14`	At 14:00 (2pm)
Day/Month	1-31	`1`	On the 1st of month
Month	1-12	`*/3`	Every 3 months
Day/Week	0-7	`1-5`	Mon-Fri (0=7=Sunday)
`*`	any	`*`	Every value in field
`*/n`	step	`*/15`	Every n units
`,`	list	`1,15,30`	At specific values

Cron Expression	Schedule
`0 2 * * *`	Every day at 02:00
`/5 * * *`	Every 5 minutes
`0 0 1 * *`	First day of every month, midnight
`30 8 * * 1-5`	Weekdays at 08:30
`0 /4 * *`	Every 4 hours on the hour
`@reboot /path/script`	Run once at system startup
`0 3 * * 0`	Weekly Sunday at 03:00
`0 12 1 1 *`	Yearly - January 1st at noon

Monitoring Platforms

Tool	Type	Best For
Zabbix	Open source, agent-based	Full infrastructure monitoring - servers, network, VMs, SNMP. Self-hosted, no license cost
PRTG	Commercial, agentless	Windows-centric environments, easy setup, strong network/SNMP monitoring. Licensed by sensor count
Nagios / Icinga	Open source, plugin-based	Highly customisable, large plugin ecosystem. Icinga2 is the modern fork with better config and clustering
Grafana + Prometheus	Open source, metrics stack	Modern cloud-native monitoring - Prometheus scrapes metrics, Grafana visualises. Standard in Kubernetes environments
Datadog	SaaS	Full-stack observability - infrastructure, APM, logs, synthetics. Expensive but minimal setup overhead
Elastic Stack (ELK)	Open source / SaaS	Log aggregation and search at scale - Elasticsearch + Logstash + Kibana. Strong for SIEM use cases
Graylog	Open source / commercial	Centralised log management - easier to operate than ELK for log-focused use cases
Uptime Kuma	Open source, self-hosted	Lightweight uptime/status monitoring with a clean UI - good for small teams or personal use

⑦

Certificates & Firewall

OpenSSL · UFW · iptables

OpenSSL Certificate Commands

Command	Purpose
`openssl x509 -in cert.pem -text -noout`	Inspect cert: expiry, SAN, issuer, subject
`openssl req -new -key key.pem -out csr.pem`	Generate CSR from existing private key
`openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365`	Self-signed cert with new 4096-bit RSA key
`openssl verify -CAfile ca.pem cert.pem`	Verify cert chain against a CA bundle
`openssl s_client -connect host:443`	Test TLS handshake, view cert chain live
`openssl pkcs12 -export -out bundle.pfx`	Export cert + key to PFX/PKCS12 format
`openssl dhparam -out dh.pem 2048`	Generate Diffie-Hellman params for TLS
`certbot renew --dry-run`	Test Let's Encrypt auto-renewal (Certbot)
`certbot certonly --nginx -d example.com`	Issue/renew cert for nginx domain

UFW / iptables Rules

Command	Action
`ufw enable`	Activate UFW firewall
`ufw status verbose`	Show all rules with details
`ufw allow 22/tcp`	Allow SSH (TCP port 22)
`ufw allow from 10.0.0.0/8`	Allow all traffic from subnet
`ufw deny 23`	Block Telnet port
`ufw delete allow 80/tcp`	Remove a specific allow rule
`iptables -L -n -v`	List all iptables rules with packet counts
`iptables -A INPUT -p tcp --dport 443 -j ACCEPT`	Accept HTTPS inbound traffic
`iptables -A INPUT -j DROP`	Drop all other inbound (default deny)
`iptables-save > /etc/iptables.rules`	Persist iptables rules across reboots

⑧

DevOps Tools

Git · Docker · kubectl · IaC

Git

Core Workflow

Command	Description
`git init`	Initialize new local repository
`git remote add origin <url>`	Link local repo to remote
`git status`	Show working tree and staging area status
`git add .`	Stage all changes in current directory
`git commit -m "message"`	Commit staged changes with message
`git log --oneline`	Compact one-line commit history
`git push origin main`	Push local commits to remote

Sync

Command	Description
`git fetch`	Download remote changes without merging
`git pull`	Fetch and merge remote changes
`git pull --rebase`	Fetch and rebase onto remote (cleaner history)

Branching

Command	Description
`git branch`	List local branches
`git branch -av`	List all branches with last commit
`git switch -c new-branch`	Create and switch to new branch
`git switch main`	Switch back to main branch
`git merge feature-branch`	Merge feature branch into current branch
`git branch -d branch-name`	Delete merged branch

Undo

Command	Description
`git restore <file>`	Discard working directory changes to file
`git restore --staged <file>`	Unstage a file (keep working copy)
`git revert <commit>`	Create new commit that undoes a past commit
`git switch --detach <commit>`	Inspect repo at a past commit (read-only)
`git switch main`	Return from detached HEAD to main

Docker

Core Workflow

Command	Description
`docker run -d -p 8080:80 --name web nginx`	Run detached container, map host:container port
`docker ps`	List running containers
`docker ps -a`	List all containers (running + stopped)
`docker stop web`	Gracefully stop container (SIGTERM)
`docker rm web`	Remove stopped container
`docker exec -it web /bin/bash`	Open interactive shell in running container
`docker logs -f web`	Stream live log output from container

Volumes & Ports

Command	Description
`docker run -p 8080:80 nginx`	Map host port 8080 → container port 80
`docker run -v /host:/container nginx`	Bind-mount host directory into container
`docker volume ls`	List all named volumes
`docker volume create data`	Create a named volume
`docker volume prune`	Remove all unused volumes

Docker Compose

Command	Description
`docker compose up -d`	Start all services in docker-compose.yml (detached)
`docker compose down`	Stop and remove containers, networks
`docker compose ps`	List status of compose services
`docker compose logs -f`	Stream logs from all compose services

Images

Command	Description
`docker images`	List locally stored images
`docker pull nginx`	Pull image from Docker Hub
`docker build -t myapp:1 .`	Build image from Dockerfile in current dir
`docker tag myapp:1 myrepo/myapp:latest`	Tag image for registry push
`docker push myrepo/myapp:latest`	Push image to registry
`docker rmi myapp:1`	Delete local image
`docker image prune`	Remove dangling (untagged) images

Troubleshooting

Command	Description
`docker logs -f container`	Stream live logs
`docker exec -it container sh`	Shell into running container (sh fallback)
`docker inspect container`	Full JSON metadata: network, mounts, env
`docker stats`	Live CPU/memory/net/disk usage per container
`docker system df`	Show disk usage by images, containers, volumes
`docker system prune`	Remove all stopped containers, unused images/networks

kubectl ↗ kubernetes.io

Core

Command	Description
`kubectl get pods`	List pods in current namespace
`kubectl get nodes`	List all nodes and their status
`kubectl get all`	List all common resources in namespace
`kubectl describe pod <pod>`	Detailed info: events, limits, conditions
`kubectl logs <pod>`	Print logs from a pod
`kubectl logs -f <pod>`	Stream live logs from a pod
`kubectl exec -it <pod> -- /bin/sh`	Open interactive shell inside pod

Deployments

Command	Description
`kubectl apply -f app.yaml`	Create or update resources from YAML
`kubectl delete -f app.yaml`	Delete resources defined in YAML
`kubectl get deployments`	List deployments in current namespace
`kubectl rollout status deployment/app`	Watch rollout progress
`kubectl rollout restart deployment/app`	Trigger rolling restart (picks up new config/image)

Scaling

Command	Description
`kubectl scale deployment app --replicas=3`	Scale deployment to N replicas

Debugging

Command	Description
`kubectl get events`	Recent cluster events (failures, pulls, restarts)
`kubectl describe pod <pod>`	Events + resource limits + container states
`kubectl top pods`	Live CPU/memory usage per pod

Context

Command	Description
`kubectl config get-contexts`	List all kubeconfig contexts (clusters)
`kubectl config use-context <context>`	Switch active cluster/context

DevOps Tool Landscape

Category	Tools
Containers	Docker, Podman, containerd
Orchestration	Kubernetes, Docker Swarm, Nomad
CI/CD	GitHub Actions, GitLab CI, Jenkins, CircleCI
IaC	Terraform, Pulumi, CloudFormation, Bicep
Config Mgmt	Ansible, Chef, Puppet, SaltStack
Monitoring	Prometheus, Grafana, Datadog, New Relic
Logging	ELK Stack, Loki, Splunk, CloudWatch
Secrets	HashiCorp Vault, AWS Secrets Manager, SOPS

⑨

Networking Deep Dive

DNS resolution · Cables · WiFi 802.11

DNS Resolution - 8-Step Process

Step	Who Acts	What Happens
1	Browser / OS	Check local DNS cache (TTL-based). If hit, done.
2	OS	Check `/etc/hosts` (Linux) or `C:\Windows\System32\drivers\etc\hosts`
3	OS to Resolver	Query sent to configured recursive resolver (ISP or 8.8.8.8)
4	Resolver to Root	Resolver queries a root server (.) - 13 root server clusters
5	Resolver to TLD	Root refers resolver to .com / .org / .io TLD server
6	Resolver to Auth NS	TLD refers resolver to the authoritative nameserver for the domain
7	Auth NS responds	Returns A/AAAA record (the actual IP address)
8	Resolver caches	Stores result per TTL, returns to client. Client caches too.

Cable Types

Cable	Max Speed	Max Length	Notes
Cat5	100 Mbps	100m	Obsolete, avoid for new installs
Cat5e	1 Gbps	100m	Minimum current standard
Cat6	10 Gbps	55m	Common for new installs
Cat6A	10 Gbps	100m	10G at full 100m distance
Cat7	10 Gbps	100m	Shielded, proprietary connectors
Fiber MM	10+ Gbps	2km	Multimode, shorter runs, cheaper
Fiber SM	100+ Gbps	100km	Single-mode, long distance, datacenter
T568B	Std	-	Orange-wh, Orange, Green-wh, Blue… (standard)
T568A	Std	-	Crossover: swap pairs 2 and 3 from T568B

WiFi 802.11 Standards

Standard	Band	Max Speed	Notes
802.11b	2.4 GHz	11 Mbps	Legacy, long range, slow
802.11g	2.4 GHz	54 Mbps	Backward compat with b
802.11n	2.4/5 GHz	600 Mbps	MIMO, dual band - WiFi 4
802.11ac	5 GHz	3.5 Gbps	Wave 2, MU-MIMO - WiFi 5
802.11ax	2.4/5/6 GHz	9.6 Gbps	OFDMA, BSS coloring - WiFi 6/6E
802.11be	2.4/5/6 GHz	46 Gbps	Multi-link operation - WiFi 7

Cloud Service Models

Model	You Manage	Examples
IaaS	OS, runtime, apps, data	AWS EC2, Azure VMs, GCP Compute
PaaS	App and data only	Heroku, Azure App Service, App Engine
SaaS	Nothing (just use it)	Office 365, Salesforce, Gmail
FaaS	Code only	AWS Lambda, Azure Functions, Cloud Run

⑩

Cloud Platforms - AWS & Azure

Core services · IAM · VNet/VPC · Shared responsibility

AWS Core Services

Service	Category	What it Does
`EC2`	Compute	Virtual machines - pay-as-you-go, reserved, or spot pricing
`Lambda`	Compute	Serverless functions - event-driven, pay-per-execution
`ECS / EKS`	Containers	ECS = managed containers; EKS = managed Kubernetes
`S3`	Storage	Object storage - 11-nines durability, unlimited scale
`EBS`	Storage	Block storage volumes attached to EC2 instances
`EFS`	Storage	Managed NFS for Linux - shared across multiple EC2s
`RDS`	Database	Managed SQL DB - MySQL, Postgres, SQL Server, Oracle, Aurora
`DynamoDB`	Database	Fully managed NoSQL - key-value and document model
`VPC`	Networking	Isolated virtual network with subnets, route tables, NACLs, SGs
`Route 53`	Networking	DNS + health checks + routing policies (failover, latency, geo)
`CloudFront`	Networking	CDN with 400+ PoPs, caches S3/EC2 content globally
`IAM`	Security	Users, groups, roles, and policies for access control
`CloudWatch`	Monitoring	Metrics, logs, alarms, dashboards for all AWS services
`CloudFormation`	IaC	Infrastructure as Code using JSON/YAML templates

Azure Core Services

Service	Category	What it Does
Virtual Machines	Compute	IaaS VMs - VM Scale Sets for autoscaling, Availability Zones for HA
App Service	Compute	PaaS web hosting - no OS management, built-in autoscale, deployment slots
Azure Functions	Compute	Serverless event-driven code - pay-per-execution
ACI / AKS	Containers	ACI = serverless containers; AKS = managed Kubernetes cluster
Blob Storage	Storage	Object store - Hot/Cool/Archive tiers, lifecycle management
Azure Disk	Storage	Managed disks: Standard HDD, Standard SSD, Premium SSD
Azure Files	Storage	Managed SMB/NFS file shares - cloud and hybrid use
Azure SQL / Cosmos DB	Database	Managed SQL; Cosmos = multi-model NoSQL (DynamoDB equivalent)
VNet	Networking	Isolated virtual network with subnets, NSGs, route tables, peering
Azure DNS	Networking	Host DNS zones, manage records, private DNS zones for VNets
Azure CDN / Front Door	Networking	CDN delivery + global load balancing with WAF
Azure AD (Entra ID)	Identity	Cloud identity: users, groups, MFA, SSO, Conditional Access
Azure Monitor	Monitoring	Metrics, Log Analytics workspace, alerts, Application Insights
ARM Templates / Bicep	IaC	JSON/Bicep Infrastructure as Code for Azure resources

AWS vs Azure Service Mapping

AWS	Azure	Category
`EC2`	Virtual Machines	Compute
`Lambda`	Azure Functions	Serverless
`ECS / EKS`	ACI / AKS	Containers
`S3`	Blob Storage	Object Store
`EBS`	Azure Disk	Block Storage
`EFS`	Azure Files	File Share
`RDS`	Azure SQL Database	Managed SQL
`DynamoDB`	Cosmos DB	NoSQL DB
`VPC`	VNet	Networking
`Security Groups`	NSG (Network Security Group)	Firewall
`Route 53`	Azure DNS	DNS
`CloudFront`	Azure CDN / Front Door	CDN
`IAM`	Azure AD + RBAC	Identity
`CloudWatch`	Azure Monitor	Monitoring
`CloudFormation`	ARM Templates / Bicep	IaC
`Direct Connect`	ExpressRoute	Private Link
`AWS VPN Gateway`	Azure VPN Gateway	VPN
`AWS Config`	Azure Policy	Compliance

Azure RBAC Built-in Roles

Role	Read	Grant	Create/Del	Scope
Owner	✓	✓	✓	Full control of all resources
Contributor	✓		✓	All actions except access grants
Reader	✓			View only, no changes
User Access Admin	✓	✓		Manage user access only
Global Admin (AAD)	-	-	-	All Azure AD resources
User Admin (AAD)	-	-	-	Users, groups, passwords

AWS vs Azure Pricing

Model	AWS	Azure
Pay-as-you-go	On-Demand	Pay-as-you-go
Reserved (1-3yr)	Reserved Instances	Reserved Instances
Spot / Preemptible	Spot Instances	Spot VMs (up to 90% off)
Savings Plans	Compute Savings Plans	Azure Savings Plan
Ingress	Free	Free
Egress	Charged (per GB)	Charged (per GB out)

Shared Responsibility Model

Layer	On-Premises	IaaS	PaaS	SaaS
Physical DC / Hardware	YOU	Provider	Provider	Provider
Hypervisor / Host OS	YOU	Provider	Provider	Provider
Guest OS / Runtime	YOU	YOU	Provider	Provider
Middleware / Application	YOU	YOU	YOU (app)	Provider
Data / Content	YOU	YOU	YOU	YOU
Network Configuration	YOU	Shared	Shared	Provider
Identities / Accounts	YOU	YOU	YOU	YOU

VNet / VPC Key Concepts

Concept	AWS (VPC)	Azure (VNet)
Address Space	CIDR block (e.g. 10.0.0.0/16)	CIDR block, can add multiple prefixes
Subnets	Public (IGW route) / Private	Any subnet - NSG controls inbound/outbound
Firewall (stateful)	Security Groups (instance level)	Network Security Groups (NSG)
Firewall (stateless)	NACLs (subnet level)	NSG has stateful rules, no separate NACL
Peering	VPC Peering (same/cross-region)	VNet Peering / Global VNet Peering
Private WAN	Direct Connect	ExpressRoute
VPN	AWS VPN Gateway	Azure VPN Gateway
NAT	NAT Gateway (managed, per-AZ)	NAT Gateway (managed)
DNS	Route 53 / VPC DNS (169.254.169.253)	Azure DNS / Private DNS Zones
Flow Logs	VPC Flow Logs to S3/CloudWatch	NSG Flow Logs to Storage/Log Analytics

HA vs Fault Tolerance vs Disaster Recovery

Concept	Goal	Downtime	AWS Example	Azure Example
High Availability	Keep running despite single failures	Minutes (auto-heal)	Multi-AZ RDS, ALB across AZs	Availability Zones, Azure Load Balancer
Fault Tolerance	Zero downtime, no errors, continuous	Near zero	S3 (11-nines), DynamoDB, Global Tables	Cosmos DB, Storage LRS/ZRS/GRS
Disaster Recovery	Restore after regional catastrophe	Hours (RTO goal)	Pilot light, warm standby, multi-region	Azure Site Recovery, geo-replication

RPO (Recovery Point Objective) = max acceptable data loss in time. RTO (Recovery Time Objective) = max acceptable downtime after disaster.

⑫

M365 & Entra ID

Identity · Graph PowerShell · Exchange Online · Intune

Entra ID Core Concepts

Concept	What it Is	Key Notes
Tenant	Your organisation's dedicated Entra ID instance	Identified by a tenant ID (GUID) and domain (contoso.onmicrosoft.com)
User	Person or shared account in the directory	Can be cloud-only or synced from on-prem AD via Entra Connect
Service Principal	Identity for an application or automated process	Like a service account, but for apps - has its own permissions
App Registration	How you register an app to use Entra ID auth	Creates a service principal in your tenant - defines API permissions
Managed Identity	Auto-managed service principal for Azure resources	No credentials to manage - Azure handles rotation. Use this over service accounts for Azure workloads
Entra ID Roles vs Azure RBAC	Two separate role systems	Entra roles control directory objects (users, groups, apps). Azure RBAC controls Azure resources (VMs, storage). Global Admin != Owner
Conditional Access	Policy engine for access decisions	If user + location + device + app + risk = conditions then grant/block/MFA
PIM (Privileged Identity Management)	Just-in-time privileged access	Roles are assigned but not active - user must "activate" with justification and optional approval

Microsoft Graph PowerShell

Replaces the deprecated AzureAD and MSOnline modules. Install: Install-Module Microsoft.Graph -Scope CurrentUser

Command	Description
`Connect-MgGraph -Scopes "User.Read.All","Group.ReadWrite.All"`	Authenticate to Microsoft Graph - specify only the scopes you need
`Get-MgUser -UserId jsmith@contoso.com -Property *`	Full user object including last sign-in, assigned licenses, account status
`Get-MgUser -Filter "accountEnabled eq false"`	All disabled accounts in the tenant
`Update-MgUser -UserId jsmith@contoso.com -AccountEnabled $false`	Disable a user account
`Get-MgGroup -Filter "displayName eq 'VPN Users'"`	Find a group by display name
`Get-MgGroupMember -GroupId <GroupId>`	List all members of a group
`New-MgGroupMember -GroupId <GroupId> -DirectoryObjectId <UserId>`	Add a user to a group
`Get-MgUserAuthenticationMethod -UserId jsmith@contoso.com`	List registered MFA methods for a user
`Get-MgAuditLogSignIn -Filter "userPrincipalName eq 'jsmith@contoso.com'" -Top 20`	Recent sign-in activity for a user including location, device, and result
`Get-MgSubscribedSku`	All M365 license SKUs in the tenant with consumed vs available counts

Entra Connect (AD Sync)

Run on the Entra Connect server. Requires the ADSync module (installed automatically with Entra Connect).

Command	Description
`Start-ADSyncSyncCycle -PolicyType Delta`	Sync only changes since the last cycle - fast, use this for most manual syncs
`Start-ADSyncSyncCycle -PolicyType Initial`	Full sync of all objects - slower, use after major AD changes or connector reconfiguration
`Get-ADSyncScheduler`	Show sync schedule, next run time, and whether sync is enabled
`Set-ADSyncScheduler -SyncCycleEnabled $false`	Pause automatic sync cycles - useful during maintenance or bulk AD changes
`Get-ADSyncConnectorRunStatus`	Check if a sync cycle is currently running before triggering a manual one
`Export-ADSyncToolsHybridAadJoinReport`	Report on Hybrid Azure AD Join status for domain-joined devices

Exchange Online Essentials

Install: Install-Module ExchangeOnlineManagement then Connect-ExchangeOnline

Command	Description
`Get-Mailbox -Identity jsmith`	Mailbox details - type, quota, forwarding, aliases
`Get-Mailbox -RecipientTypeDetails SharedMailbox`	List all shared mailboxes in the org
`Add-MailboxPermission -Identity shared@ -User jsmith -AccessRights FullAccess`	Grant full access to a shared mailbox
`Get-MessageTrace -SenderAddress user@contoso.com -StartDate (Get-Date).AddDays(-2)`	Trace sent mail - check delivery status, routing, spam filtering decisions
`Set-Mailbox -Identity jsmith -ForwardingSmtpAddress "" -DeliverToMailboxAndForward $false`	Remove email forwarding - check all mailboxes for unauthorised forwarding
`Get-Mailbox -ResultSize Unlimited \| Where {$_.ForwardingSmtpAddress -ne $null}`	Audit all mailboxes with forwarding configured - security check

Intune / Endpoint Manager

Concept	Description
Enrollment	How devices join Intune - Autopilot (new devices), MDM enrollment (existing), or BYOD via Company Portal
Compliance Policy	Rules a device must meet (encrypted, PIN, OS version) - non-compliant devices can be blocked by Conditional Access
Configuration Profile	Push settings to devices - WiFi, VPN, certificates, restrictions, BitLocker enforcement
App Protection Policy	MAM - protect org data in apps without full device enrolment (BYOD scenario)
Autopilot	Zero-touch Windows provisioning - device ships to user, they sign in, Intune does the rest
Device Actions	Remote wipe, sync, restart, BitLocker key rotation - available per device in Intune portal
Scope Tags	RBAC for Intune - limit what admins can see and manage to their region or team

⑫

Resources & Tools

Communities · Core tools · Diagnostics

Communities & Learning

Resource	URL / Location	What it Covers
r/sysadmin · r/linux · r/linuxadmin · r/netsec	reddit.com	Community Q&A, incident threads, war stories, tooling discussions
Brutalist Report	brutalist.report	Daily tech & security headlines, aggregated and unformatted
Microsoft Learn	learn.microsoft.com	Free official docs, learning paths, and certifications for Azure, Windows, and M365
O'Reilly Topics	oreilly.com/topics	Broad technical learning - books, videos, courses
Ask Ubuntu	askubuntu.com	Ubuntu-focused Q&A, highly indexed by search engines
DigitalOcean Tutorials	digitalocean.com	Clear, practical guides for Linux, OSS, and infra topics
ServerFault	serverfault.com	Stack Exchange for professional sysadmins and network engineers

Core Tools

Tool	URL / Source	What it Does
MX Toolbox	mxtoolbox.com	DNS, mail, SPF / DMARC / DKIM checks in one place
Sysinternals Suite	learn.microsoft.com	Windows diagnostics & troubleshooting (Process Monitor, Autoruns, TCPView…)
PuTTY	chiark.greenend.org.uk	SSH, Telnet, serial - still essential for Cisco and console work
WinSCP	winscp.net	Fast file transfer over FTP / SFTP / SSH with GUI
Angry IP Scanner	angryip.org	Quick network sweeps - host discovery and port scan
WinDbg	learn.microsoft.com	Windows kernel and crash dump debugging
Wireshark	wireshark.org	Packet capture and deep protocol analysis
Rufus	rufus.ie	Write bootable USB images (ISO to USB) on Windows
Nmap	nmap.org	Network scanning, host discovery, OS fingerprinting, port enumeration
OpenSSL	openssl.org	TLS, certificate generation, cert inspection, and crypto utilities
Git	git-scm.com	Version control for scripts, configs, and infrastructure-as-code
M365 Maps	m365maps.com	Visual map of M365 service dependencies and license feature inclusions
cmd.ms	cmd.ms	Shortcut directory for Microsoft admin portals - cmd.ms/intune, cmd.ms/aad, etc.
Crontab Guru	crontab.guru	Cron expression editor and validator - instant visual feedback
cheat.sh	cheat.sh	Instant CLI cheatsheets from the terminal: `curl cheat.sh/tar`
End-of-Life Info	endoflife.date	Support and EoL timelines for OS, runtimes, databases, and tools

Diagnostics & Security

Tool	URL	What it Does
WhatIsMyIPAddress	whatismyipaddress.com	IP lookup with strong GeoIP resolution - useful for egress verification
Cloudflare Speed Test	speed.cloudflare.com	Clean download / upload / latency test - no ads, no Flash
VirusTotal	virustotal.com	Malware and URL scanning across 60+ antivirus engines simultaneously
ANY.RUN	app.any.run	Interactive sandbox for malware and phishing analysis - watch execution live

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