Unix Tools

🤗 User Management

# Change username
usermod -l new old

📁 File Management

tar -xzvf (uncompress gz)
tar -xjvf (uncompress bz2)

tar -czvf router.apkovl.tar.gz router/ (compress to gz)

When filesystem is mounted under SMB, even root will have trouble settings correct permissions through the sudo command. You can get around this problem by specifying --no-same-owner

tar xzvf stuff.tar.gz --no-same-owner -C /media/dest

💾 Disk Management

df -h # human readable disk usage
fdisk
parted

💻 Hardware Management

lsmod # list loaded kernel modules

# blacklisting kernel modules
vim /etc/modprobe.d/blacklist.conf

# see installed firmware
cd /lib/firmware/*

🌐 LAN Management

# All saved / bootable interfaces
cat /etc/network/interfaces

# Example

auto lo iface lo inet loopback

iface eth0 inet manual

auto-hotplug wlan0 iface wlan0 inet dhcp wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf

# All current available interfaces
ls /sys/class/net

# Probe master mode for interface
iwconfig wlan1 mode master

TIL wtf a subnet mask actually is

Only change within the range of numbers not AND'ed by that value

ip = 192.168.5.255/24 #CIDR Notation

base = 192.168.5.255

subnet-mask = 255.255.255.000
 
     11000000.10101000.00000111.01111111
 AND 11111111.11111111.11111111.00000000
     ———————————————————————————————————
     1100000.00001010.00000111.00000000

Configuring A DHCP Service

sudo apt install isc-dhcp-server
# or
sudo apk add dhcp-server-vanilla dhcp-openrc 

• Modify Interfaces

• Modify dhcpd.conf https://www.cyberciti.biz/faq/debian-ubuntu-linux-setting-wireless-access-point/

https://wiki.alpinelinux.org/wiki/Small_Office_Services#Install_and_Configure_DHCP_and_DNS_services

https://wiki.debian.org/NetworkConfiguration#Manual_config

🌎 WAN Management

SSH Reverse Tunneling

ssh –f –N –T –R 2222:localhost:22 [email protected]

• -f: tells the SSH to background itself after it authenticates, saving you time by not having to run something on the remote server for the tunnel to remain alive.
• -N: if all you need is to create a tunnel without running any remote commands then include this option to save resources.
• -T: useful to disable pseudo-tty allocation, which is fitting if you are not trying to create an interactive shell.

  autossh -M 0 -o "ServerAliveInterval 30" -o "ServerAliveCountMax 3"
  

• autossh for auto reconnect on intervals 

  autossh -M 0 -o "ServerAliveInterval 30" -o "ServerAliveCountMax 3" –f –N –T –R 2222:localhost:22 [email protected]
  

🔑 Auth / Logging

last
> user      pts/4        108.210.178.151  Sun Jan 26 04:05   still 
> logged in
...

vim /var/log/auth.log
> Jan 24 03:07:47 hostname sshd[14435]: Invalid user admin from 141.98.81.37 port 42579
...

cat /etc/passwd # for user lists and shell defaults

🌱 Init Systems

Open RC

• They are finally writing this 👏 - https://wiki.alpinelinux.org/wiki/Writing_Init_Scripts
• https://wiki.gentoo.org/wiki/OpenRC
• https://wiki.alpinelinux.org/wiki/Alpine_Linux_Init_System

Commands

rc-update add <service> <runlevel>
rc-update del <service> <runlevel>
rc-service <service> <start stop restart>
rc-status
rc <runlevel> 

Script Example

• init scripts in /etc/init.d
• update-rc.d does not work fine if there is no specific comment block in the start script that looks like this:
• On Raspbian Buster (v10) #! /bin/sh must appear right before the BEGIN INIT INFO block.

  #!/sbin/openrc-run
  

BEGIN INIT INFO

Provides: reverse-ssh

Required-Start:

Required-Stop:

Default-Start: 2 3 4 5

Default-Stop: 0 1 6

Short-Description: Start reverse ssh at boot time

Description: Start reverse ssh at boot time.

END INIT INFO

. /etc/init.d/functions.sh

depend(){ need sshd }

start() { echo "Opening reverse shell." /usr/bin/autossh -M 0 -o "ServerAliveInterval 30" -o "ServerAliveCountMax 3" -f -N -R 8000:localhost:22 vpn@192.168.0.0 }

### Systemd

#### Commands

sudo service