commands for linux troubleshooting (draft)

14 June 2016

port

List open ports

sudo netstat -tulpn | grep LISTEN

view port number and mapped service

cat /etc/services
grep -w '80/tcp' /etc/services
grep -w '443/tcp' /etc/services
grep -E -w '22/(tcp|udp)' /etc/services
grep -E -w '2020/(tcp|udp)' /etc/services
cat /etc/services | grep 8080

list the programs that utilize listening ports

# Display a list of ports in use
sudo lsof -nP -iTCP -sTCP:LISTEN

# Check a specific port number is in use
# If the port is free, the command shows no output
sudo lsof -nP -i :8080
sudo lsof -nP -iUDP:53 # to check if the UDP port 53 is open

sudo fuser 9092/tcp
sudo fuser -n tcp 9092

# display the listening ports/sockets by checking the State column
sudo netstat -tunpl
sudo netstat -ant | grep :2181
sudo netstat -peanut | grep ":5140"

kill process on specific port

fuser -k 8080/tcp
kill -9 $(lsof -t -i:8080)

kill -9 $(lsof -t -i:9092)
fuser -k 9092/tcp

connecting to open port

sudo yum install telnet
telnet localhost 8080

scanning port for open port & running services on it

sudo yum install nmap
sudo nmap -sT -O localhost
sudo nmap -sT -O 127.0.0.1 #[ list open TCP ports ]##
sudo nmap -sU -O 192.168.2.254 #[ list open UDP ports ]##
sudo nmap -sTU -O 192.168.2.24

viewing port info using iptables

# list out all of the active iptables rules by specification
sudo iptables -S
# output all of the active iptables rules in a table
sudo iptables -L

Opening a Port on Linux to Allow TCP Connections

# accept all traffic on your loopback interface
sudo iptables -A INPUT -i lo -j ACCEPT
sudo iptables -A OUTPUT -o lo -j ACCEPT

# Allowing All Incoming fluent-bit port (2020)
sudo iptables -A INPUT -p tcp --dport 2020 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
sudo iptables -A OUTPUT -p tcp --sport 2020 -m conntrack --ctstate ESTABLISHED -j ACCEPT

permission

Changing the ownership of all sub-directories

sudo chown -R snikam:snikam ./Prod/

process

process id of running program

ps aux | grep java

kill prcess with given id

ps aux | grep -i firefox | awk {'print $2'} | xargs kill -9

Shutdown/Restart

Restart now

sudo shutdown -r now

shutdown now (immediately)

sudo ?

networking

Assign static ip

Check if it is configured

sudo ifdown eth0

Edit like this (just the important lines):

sudo gedit /etc/network/interfaces

auto eth0
  iface eth0 inet static
  address <static IP address>
  netmask <netmask>
  gateway <default gateway>
  pre-up sleep 2

Activate the new IP

sudo ifup eth0

Python

ModuleNotFoundError: no module named <X> Error

import sys
import os

# add dir to PYTHONPATH
sys.path.append(os.getcwd())

export PYTHONPATH=${PYTHONPATH}:${HOME}/abcPythonModule 

other

vs code - column selction on Mac

Shift + option + Command + Right/Left

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