Linux Cheat Sheet

This is my personal Linux cheat sheet, for when I don't feel like reading man pages. Use it at your own discretion!

Computer Information:

List hardware specifics

• nproc Number of processors
• lscpu CPU info
• lshw Overall hardware info, run as root user
• lspci PCI bus
• lsusb USB controllers
• lsblk Block devices

Distribution Information:

Distribution release file(s)
cat /etc/*-release

On a GNU systemd based system, use the hostnamectl command

User Management

Add a user in the sudo group with a home directory useradd name --comment "Full Name" --groups sudo --create-home --user-group

dd (data define)

Data define, or convert and copy a file
dd bs=## if=PATH/INFILE of=PATH/OUTFILE status=progress

Write an image to disk
dd bs=4M if=PATH/FILE.iso of=/dev/DISK status=progress oflag=sync

Back up a disk as an image file
dd if=/dev/DISK conv=sync,noerror bs=64K | gzip -c > /PATH/FILE.img.gz

fdisk (fixed disks)

List disk info
fdisk -l

Manipulate disk partition table
fdisk /PATH/TO/DISK

Use a curses based textual user interface
cfdisk

SMART Disk Monitoring

Check if disk is SMART capable smartctl --info /dev/dsk

Read error log smartctl --log=error /dev/dsk

Test hard disk smartctl --test=short /dev/dsk smartctl --test=long /dev/dsk

Miscellaneous Disk Management

List and modify partitions
parted

Output block device attributes
blkid

Make and format a file system
mkfs.<format> /PATH/TO/PARTITION

Kernel:

Get kernel name, version and machine hardware
uname -mrs

Output info directly from file containing kernel version
cat /proc/version

LUKS (Linux Unified Key Setup)

Encrypt a partition verbosely and verify the passphrase
cryptsetup -y -v luksformat /dev/part

List info for LUKS partition, including key slots
cryptsetup luksDump /dev/part

Modify or add a passphrase

• cryptsetup luksAddKey /dev/part
• cryptsetup luksChangeKey /dev/part -s i
• cryptsetup luksRemoveKey /dev/part

Remove the ith passphrase
cryptsetup luksKillSlot /dev/part i

Open or close LUKS partition with "target" as name

• cryptsetup luksOpen /dev/part <target>
• cryptsetup luksClose <target>

ssh

Establish an SSH tunnel for VNC connection
ssh -L PORT:127.0.0.1:PORT -C -N -l USER@REMOTE REMOTE

scp

Copy a file from remote to local
scp username@remote:file.txt /local/directory/

Copy a file from local to remote
scp file.txt username@remote:/remote/directory/

swap (chmod to 600)

Disable swap on all swap devices
swapoff -a

Set a file as Linux swap area
mkswap /SWAP/PATH

Enable swap on a file
swapon /SWAP/PATH

Check if swap is active
swapon --show

Check swap niceness between 0-100, Lower values correspond with less use
/proc/sys/vm/swappiness

Assign swap niceness, as described above
sysctl vm.swappiness=100

Syncthing

Set up Syncthing as a system service
systemctl enable syncthing@user.service

Read Syncthing logs
journalctl -e -u syncthing@user.service

Use the web GUI at localhost:8384

systemd

List all running services: systemctl

Configure services in real time

• systemctl start foo.service
• systemctl stop foo.service
• systemctl restart foo.service
• systemctl status foo.service

Configure services at boot time

• systemctl enable foo.service
• systemctl disable foo.service

List all services
systemctl list-unit-files

VirtualBox

List all virtual machines
VBoxManage list vms

List running virtual machines
VboxManage list runningvms

Modify a specific machine
VboxManage modifyvm VM <option1> <arg1> ... <optionn> <argn>

Miscellaneous

Display file or file system status
stat <option> <file>

List directories and their size
du -h --max-depth=1 | sort -hr

Kill the front process
ctrl + alt + *

Switch to virtual console
ctrl + alt + Fkey

Recall previous argument
alt + .

List packages with installation timestamps
grep installed /var/log/dpkg.log

Reconfigure timezone data
dpkg-reconfigure tzdata

Reboot Even If System Utterly Broken

• Alt+SysRq+R Switch keyboard to raw input mode
• Alt+SysRq+E Send SIGTERM signal to all processes
• Alt+SysRq+I Send SIGKILL signal to all processes
• Alt+SysRq+S Sync all file systems to prevent data loss
• Alt+SysRq+U Remount file systems as read-only
• Alt+SysRq+B Forcefully reboot

Archiving Files

Create an encrypted 7zip file with encrypted metadata
7z a -p -mhe=on FILE.7z PATH

Decrypt the same 7zip file
7z x FILE.7z

Create an encrypted tarball with GPG
tar -cvzf - FILE | gpg -c > FILE.tar.gz.gpg

Decrypt an encrypted tarball with GPG
gpg -d FILE.tar.gz.gpg | tar -xvzf -

Battery and Power

Get power sources upower -e

Get power source information upower -i <source>

Battery metrics, including thermals acpi --verbose

Wireguard

Generate key pairs

umask 077  # This makes sure credentials don't leak in a race condition
wg genkey | tee privatekey | wg pubkey > publickey

Configuration files in /etc/wireguard/wgX.conf

Server:

[Interface]
Address = x.x.x.1
PrivateKey = <server's privatekey>
ListenPort = 51820

[Peer]
PublicKey = <client's publickey>
AllowedIPs = x.x.x.2/32

Client:

[Interface]
Address = x.x.x.2
PrivateKey = <client's privatekey>
ListenPort = 21841

[Peer]
PublicKey = <server's publickey>
Endpoint = <server's ip>:51820
AllowedIPs = x.x.x.0/24,<server LAN subnet>

# This is for if you're behind a NAT and
# want the connection to be kept alive.
PersistentKeepalive = 25

Quick up/down over interface:

wg-quick up wg0
wg-quick down wg0

Forward server LAN over iptables:

Add the following at the end of the [Interface] section in the server config file.

PostUp   = iptables -A FORWARD -i %i -j ACCEPT; iptables -A FORWARD -o %i -j ACCEPT; iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
PostDown = iptables -D FORWARD -i %i -j ACCEPT; iptables -D FORWARD -o %i -j ACCEPT; iptables -t nat -D POSTROUTING -o eth0 -j MASQUERADE

Run as a service on client

sudo chown -R root:root /etc/wireguard/
sudo chmod -R og-rwx /etc/wireguard/*
sudo systemctl enable wg-quick@wg0.service
sudo systemctl start wg-quick@wg0.service