September 2022

linux process details in /proc

all process run in /proc

ls /proc

We can see what command is used to run the process

cat /proc/<process_id>/cmdline

process std std error log can be found in

cat /proc/<process_id>/fd/1
cat /proc/<process_id>/fd/2

read std logs of process with pid

Get process id

ps -ef | grep process_name

Go to process root direcotry

#stdout
tail -f /proc/<process_id>/fd/1

#stderror
tail -f /proc/<process_id>/fd/2

Remove weak Ciphers SSL – nginx

GCM is preferred over CBC

Verify with cipher is being used?

nmap --script ssl-enum-ciphers -p 443 example.com

update nginx.conf

ssl_ciphers         HIGH:!aNULL:!MD5!TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256;

https://superuser.com/questions/109213/how-do-i-list-the-ssl-tls-cipher-suites-a-particular-website-offers

https://stackoverflow.com/questions/62900667/aws-alb-prevent-usage-of-tls-ecdhe-rsa-with-aes-128-cbc-sha256

Implement HTTPOnly and Secure Cookie

Added header in nginx.conf

add_header Set-Cookie "Path=/; HttpOnly; Secure";

How to verify?

Developer tool > Application > Storage > Cookies

https://geekflare.com/httponly-secure-cookie-nginx/

Backup and Restore etcd snapshot for Kubernetes

Create a deployment to verify the restore in the end

k create deploy nginx-test --image=nginx

2. Update the cert path as per /etc/kubernetes/mainifest/etcd.yaml

ETCDCTL_API=3 etcdctl --endpoints=https://127.0.0.1:2379 \
--cacert=<trusted-ca-file> \
--cert=<cert-file> --key=<key-file> \
  snapshot save /tmp/etcd.backup

2. Stop kubelet

systemctl stop kubelet

3. Stop kube-api and etcd

mv /etc/kubernetes/manifests/kube-apiserver.yaml /root/
mv /etc/kubernetes/manifests/etcd.yaml /root/

4. Restore the etcd.backup

ETCDCTL_API=3 etcdctl --endpoints 127.0.0.1:2379 snapshot restore etcd.backup

It will create “default.etcd” directory in current directory

[root@lp-k8control-1 etcd]# ls default.etcd/
member

5. Look at /etc/kubernetes/manifests/etcd.yaml etcd-data (/var/lib/etcd) directory path

[root@lp-k8control-1 default.etcd]# ls /var/lib/etcd
member

6. Copy member directory content from default.etcd to /var/lib/etcd

7. Start kube-api and etcd

mv /root/kube-apiserver.yaml /etc/kubernetes/manifests/kube-apiserver.yaml
mv /root/etcd.yaml /etc/kubernetes/manifests/etcd.yaml

8. Restart kubelet service

systemctl restart kubelet

9. Verify if nginx deployment we created in step 1 is restored

k get deploy

Switch relay with Raspberry pi + Arduino Uno

The 5V Relay switch require that i have require around 52mA current to work properly.

Raspberry pi max GPIO current with 5v Relay = ?

Arduino pin 13 current with 5v Relay = 38.5mA

Arduino pin 13 + 12 current with 5v Relay = 45 mA

Arduino pin 13 + 12 + 2 current with 5v Relay = 47.3 mA ( This worked )

So Now i can use Arduino as a switch on/off. Also I needed this switching to be based on some external events. So I used Aurdino Pin 2 as INPUT pin and added one 2.7K ohm resistor to from pin2 to Ground.

int status = 0;

void setup() {
  pinMode(13, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(2, INPUT);
}

void loop() {
  status = digitalRead(2);
  if (status == HIGH) {
    digitalWrite(13, HIGH);
    digitalWrite(12, HIGH);
    digitalWrite(8, HIGH);
  }
  else {
    digitalWrite(13, LOW);
    digitalWrite(12, L0W);
    digitalWrite(8, LOW);
  }
}

Switch ON = 7PM
Switch OFF = 12AM

added Cronjob on Raspberry Pi 4

0 19 * * * /usr/bin/python3.8 /opt/led.py on
0 0 * * * /usr/bin/python3.8 /opt/led.py on

led.py

import RPi.GPIO as GPIO
from time import sleep 
import sys

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
GPIO.setup(21, GPIO.OUT, initial=GPIO.LOW)

if sys.argv[1] == "on":
    GPIO.output(21, GPIO.HIGH)
    #print("on")
    exit()
elif sys.argv[1] == "off":
    GPIO.output(21, GPIO.LOW)
    #print("off")
    exit()