CMD Survival Guide — reason42/tools

THE HITCHHIKER'S GUIDE
TO THE COMMAND LINE

SURVIVAL EDITION // UBUNTU & POWERSHELL_

"The Guide says there is an art to flying, or rather a knack. The knack lies in learning how to throw yourself at the ground and miss. In much the same way, there is an art to the command line. The knack lies in knowing just enough commands to look like you know what you're doing, while quietly Googling the rest."

— The Hitchhiker's Guide to the Command Line, p.1

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01 THE BASICS

"In the beginning was the command prompt, and the command prompt was with the terminal, and the command prompt was the terminal. All things were made through it, and without it was not any server configured that was configured." The Guide notes that most problems in computing stem from people not knowing where they are. The pwd command exists precisely because of this.

CHECK OS VERSION

lsb_release -a

Also: cat /etc/issue.net for a quicker look.

CHECK OS VERSION

Get-ComputerInfo | Select-Object OsName, OsVersion, OsBuildNumber

Or the classic: winver for a GUI pop-up.

SET HOSTNAME

sudo hostnamectl set-hostname <new-hostname>

Takes effect immediately. Reboot to ensure all services pick it up.

SET HOSTNAME

Rename-Computer -NewName "NewName" -Restart

The -Restart flag applies the change immediately on reboot.

WHERE AM I

pwd

Print working directory. Fundamental. Use it constantly.

WHERE AM I

Get-Location

Alias: pwd also works in PowerShell.

MEMORY USAGE

free -h

The -h flag gives human-readable sizes. Focus on Mem row: total vs available.

MEMORY USAGE

Get-CimInstance Win32_OperatingSystem | Select-Object TotalVisibleMemorySize, FreePhysicalMemory

Values are in KB. Divide by 1MB for GB: | ForEach-Object { [math]::Round($_.FreePhysicalMemory/1MB,2) }

CPU INFO

Full output: lscpu

CPU INFO

Get-CimInstance Win32_Processor | Select-Object Name, NumberOfCores, NumberOfLogicalProcessors

LIVE RESOURCE MONITOR

htop

Install first: sudo apt install htop. The classic top works without install. Press h for help inside either.

LIVE RESOURCE MONITOR

Get-Process | Sort-Object CPU -Descending | Select-Object -First 20 Name, CPU, WorkingSet

For continuous update: wrap in while($true){ cls; ...; Start-Sleep 2 }

02 FILE MANAGEMENT

The Guide describes file management as "the art of knowing where you put things, as opposed to the more common skill of knowing where you lost them." It goes on to note that the rm -rf / command is the digital equivalent of the Ravenous Bugblatter Beast of Traal: it assumes that if you can't see it any more, neither can anyone else.

LIST FILES

ls -lah

-l long format, -a show hidden, -h human-readable sizes.

LIST FILES

Get-ChildItem -Force

Alias: ls or dir. -Force shows hidden files.

COPY FILE

sudo cp /source/file /dest/file

Add -r to copy directories recursively.

COPY FILE

Copy-Item "C:\source\file.txt" -Destination "C:\dest\"

Add -Recurse for directories.

MOVE / RENAME FILE

sudo mv /source/file /destination/

Works for renaming too — just change the destination filename.

MOVE / RENAME FILE

Move-Item "C:\source\file.txt" -Destination "C:\dest\"

Rename: change the destination to a new filename.

DELETE FILE

sudo rm /path/to/file

Directories: rm -r /path/to/dir. There is no undo. The Guide recommends caution.

DELETE FILE

Remove-Item "C:\path\to\file.txt"

Directories: add -Recurse. Add -WhatIf to preview before deleting.

CREATE DIRECTORY

sudo mkdir -p /path/to/new/dir

-p creates parent directories as needed, no error if exists.

CREATE DIRECTORY

New-Item -ItemType Directory -Path "C:\new\folder" -Force

-Force suppresses the error if it already exists.

FIND FILES

find /path -name "*.log" -type f

Search within files: grep -r "search term" /path

FIND FILES

Get-ChildItem -Path "C:\" -Filter "*.log" -Recurse -ErrorAction SilentlyContinue

Search within files: Select-String -Path "*.log" -Pattern "term"

COPY FILE TO REMOTE SERVER

scp /local/file user@host:/remote/path/

Reverse for pulling: put remote path first, local second.

COPY FILE TO REMOTE SERVER

Copy-Item "C:\local\file.txt" -Destination "\\server\share\"

For SSH/SCP: scp works in PowerShell if OpenSSH is installed.

EXTRACT TAR ARCHIVE

sudo tar -jxf /path/file.tar.bz2 --directory /destination/

Flags: -j bz2, -z gzip, -x extract, -f filename. For .gz: replace -j with -z.

EXTRACT ZIP ARCHIVE

Expand-Archive -Path "C:\file.zip" -DestinationPath "C:\dest\"

Create zip: Compress-Archive -Path "C:\folder" -DestinationPath "C:\out.zip"

03 DISK MANAGEMENT

The Guide's entry on disk management runs to several thousand pages and is generally considered one of the most depressing things ever written. The abridged version simply says: "Disks fill up. They always fill up. The only question is whether you notice before or after something important stops working."

CHECK DISK SPACE

df -h

For interactive navigation: sudo ncdu / (install: sudo apt install ncdu)

CHECK DISK SPACE

Get-PSDrive -PSProvider FileSystem | Select-Object Name, @{N='Used(GB)';E={[math]::Round($_.Used/1GB,2)}}, @{N='Free(GB)';E={[math]::Round($_.Free/1GB,2)}}

LIST BLOCK DEVICES / DISKS

lsblk

For detailed partition info: sudo fdisk -l

LIST DISKS

Get-Disk

Partitions: Get-Partition. Volumes: Get-Volume

MOUNT A DISK

sudo mount /dev/sdb1 /mnt/data

Unmount: sudo umount /mnt/data. Persist across reboots by adding to /etc/fstab.

ASSIGN DRIVE LETTER

Set-Partition -DiskNumber 1 -PartitionNumber 1 -NewDriveLetter E

EXTEND LVM LOGICAL VOLUME

sudo lvextend -L +10G /dev/ubuntu-vg/ubuntu-lv sudo resize2fs /dev/ubuntu-vg/ubuntu-lv

Check current state first: sudo vgdisplay and sudo lvdisplay

EXTEND PARTITION

$part = Get-Partition -DriveLetter C $max = ($part | Get-PartitionSupportedSize).SizeMax Resize-Partition -DriveLetter C -Size $max

Extends to maximum available space. Check disk has unallocated space first.

FORMAT PARTITION

sudo mkfs.ext4 /dev/sdb1

Other formats: mkfs.xfs, mkfs.fat. This destroys all data on the partition.

FORMAT PARTITION

Format-Volume -DriveLetter E -FileSystem NTFS -NewFileSystemLabel "DataDrive" -Confirm:$false

FileSystem options: NTFS, FAT32, exFAT, ReFS.

04 NETWORKING

"The Internet," the Guide notes, "is very large and very complicated and most of it doesn't work properly most of the time. The rest of it works perfectly but nobody can remember the commands. This section is for the latter group."

SHOW NETWORK INTERFACES

ip addr show

Short form: ip a. Legacy: ifconfig (install: sudo apt install net-tools)

SHOW NETWORK INTERFACES

Get-NetIPAddress | Select-Object InterfaceAlias, IPAddress, PrefixLength, AddressFamily

All adapters: Get-NetAdapter

TEST CONNECTIVITY

ping -c 4 8.8.8.8

-c 4 sends 4 packets then stops. Without it, pings forever. Ctrl+C to quit.

TEST CONNECTIVITY

Test-NetConnection -ComputerName 8.8.8.8 -InformationLevel Detailed

Test specific port: add -Port 443. Classic ping: ping hostname also works.

CHECK OPEN PORTS

ss -tulnp

Flags: -t TCP, -u UDP, -l listening, -n numeric, -p show process. Legacy: netstat -tulnp

CHECK OPEN PORTS

Get-NetTCPConnection -State Listen | Select-Object LocalAddress, LocalPort, OwningProcess | Sort-Object LocalPort

Map PIDs to process names: Get-Process -Id (Get-NetTCPConnection -State Listen).OwningProcess

ROUTING TABLE

ip route show

Default gateway is the default via line.

ROUTING TABLE

Get-NetRoute | Where-Object DestinationPrefix -eq '0.0.0.0/0'

Full table: Get-NetRoute

DNS LOOKUP

dig example.com

Quick: nslookup example.com. Reverse lookup: dig -x 8.8.8.8

DNS LOOKUP

Resolve-DnsName example.com

Specific record type: Resolve-DnsName example.com -Type MX

TRACE NETWORK PATH

traceroute 8.8.8.8

Install if missing: sudo apt install traceroute. MTR combines ping+traceroute: mtr 8.8.8.8

TRACE NETWORK PATH

Test-NetConnection 8.8.8.8 -TraceRoute

Classic: tracert 8.8.8.8 also works in PowerShell.

05 PROCESSES & SERVICES

The Guide observes that processes are like houseguests: they arrive unannounced, consume your resources, occasionally crash the party, and are very difficult to remove once established. The kill command exists for this reason. Its name is, the Guide notes, admirably honest.

LIST RUNNING PROCESSES

ps aux

Filter by name: ps aux | grep nginx

LIST RUNNING PROCESSES

Get-Process | Sort-Object CPU -Descending

Filter: Get-Process -Name chrome

KILL A PROCESS

kill PID

Find PID first: pgrep processname. Force kill: kill -9 PID. By name: pkill name

KILL A PROCESS

Stop-Process -Name "chrome" -Force

By PID: Stop-Process -Id 1234 -Force

LIST SERVICES

systemctl list-units --type=service --state=running

Failed services: systemctl list-units --state=failed

LIST SERVICES

Get-Service | Where-Object Status -eq 'Running'

All services: Get-Service

START / STOP / RESTART SERVICE

sudo systemctl start nginx sudo systemctl stop nginx sudo systemctl restart nginx sudo systemctl status nginx

Enable at boot: sudo systemctl enable nginx

START / STOP / RESTART SERVICE

Start-Service -Name "wuauserv" Stop-Service -Name "wuauserv" Restart-Service -Name "wuauserv"

Set startup type: Set-Service -Name "wuauserv" -StartupType Automatic

SCHEDULE A TASK (CRON)

crontab -e

Format: MIN HOUR DAY MON DOW command. Example — run daily at 2am: 0 2 * * * /path/script.sh

SCHEDULE A TASK

$action = New-ScheduledTaskAction -Execute "powershell.exe" -Argument "C:\script.ps1" $trigger = New-ScheduledTaskTrigger -Daily -At "02:00" Register-ScheduledTask -Action $action -Trigger $trigger -TaskName "MyTask"

06 USER MANAGEMENT

"The concept of user accounts," the Guide explains, "was invented to give system administrators something to blame when things go wrong. Before user accounts, it was always the computer's fault. Now it is always the user's. This represents significant progress."

ADD USER

sudo adduser username

Follows interactive prompts. useradd is the lower-level version — less friendly, more scriptable.

ADD LOCAL USER

$pass = ConvertTo-SecureString "P@ssw0rd" -AsPlainText -Force New-LocalUser -Name "username" -Password $pass -FullName "Full Name"

Add to group: Add-LocalGroupMember -Group "Administrators" -Member "username"

CHANGE USER PASSWORD

sudo passwd username

Omit username to change your own password.

CHANGE USER PASSWORD

$pass = ConvertTo-SecureString "NewP@ss" -AsPlainText -Force Set-LocalUser -Name "username" -Password $pass

GRANT SUDO PRIVILEGES

sudo usermod -aG sudo username

Verify group membership: groups username

ADD USER TO ADMIN GROUP

Add-LocalGroupMember -Group "Administrators" -Member "username"

WHO IS LOGGED IN

Also: who or last for login history.

WHO IS LOGGED IN

Get-CimInstance Win32_LoggedOnUser | Select-Object -ExpandProperty Antecedent

Remote sessions: query session /server:hostname

07 FIREWALL

"A firewall," says the Guide, "is a system for ensuring that the right people cannot get in and the wrong people cannot get out. In practice, it mainly ensures that legitimate administrators cannot remember which rules they set, or why, or when." The Guide recommends writing things down. Nobody ever does.

UFW STATUS & ENABLE

sudo ufw status verbose sudo ufw enable

Always allow SSH before enabling: sudo ufw allow ssh. Disable: sudo ufw disable

FIREWALL STATUS

Get-NetFirewallProfile | Select-Object Name, Enabled

Enable all profiles: Set-NetFirewallProfile -All -Enabled True

ALLOW PORT

sudo ufw allow 443/tcp sudo ufw allow from 192.168.1.0/24 to any port 22

Deny: replace allow with deny. List rules with numbers: sudo ufw status numbered

ALLOW PORT

New-NetFirewallRule -DisplayName "Allow HTTPS" -Direction Inbound -Protocol TCP -LocalPort 443 -Action Allow

Remove rule: Remove-NetFirewallRule -DisplayName "Allow HTTPS"

LIST IPTABLES RULES

sudo iptables -L -n -v --line-numbers

Save rules: sudo iptables-save > /etc/iptables/rules.v4

LIST FIREWALL RULES

Get-NetFirewallRule | Where-Object Enabled -eq 'True' | Select-Object DisplayName, Direction, Action | Sort-Object Direction

08 PACKAGE MANAGEMENT

Installing software, the Guide notes, has historically been one of the most dangerous activities available to humans with access to a terminal. Modern package managers have made it considerably safer, though they retain a certain talent for installing seventeen things you didn't ask for alongside the one thing you did.

UPDATE PACKAGE LIST & UPGRADE

sudo apt update && sudo apt upgrade -y

apt update refreshes the package index. apt upgrade installs updates. Always run update before upgrade.

UPDATE PACKAGES

winget upgrade --all

PowerShell modules: Update-Module. Windows Update: Install-Module PSWindowsUpdate; Get-WindowsUpdate -Install

INSTALL PACKAGE

sudo apt install package-name

Install .deb file: sudo dpkg -i file.deb. Search: apt search term

INSTALL PACKAGE

winget install package-name

PowerShell module: Install-Module ModuleName -Scope CurrentUser. Search: winget search term

REMOVE PACKAGE

sudo apt remove package-name sudo apt purge package-name

remove keeps config files. purge removes everything. Clean up orphans: sudo apt autoremove

REMOVE PACKAGE

winget uninstall package-name

Module: Uninstall-Module ModuleName

> Commands verified for Ubuntu 20.04+ and PowerShell 7+.
> Always test in a non-production environment. The Guide accepts no liability for data loss, existential crises, or rogue processes.
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