iAnatoly

#!/usr/bin/env python3
#
# Ad-hoc monitoring for time_squeeze changes in /proc/net/softnet_stat .
#
# usage: ./softnetstat.py <refresh_interval_seconds>
#
# see https://blog.packagecloud.io/eng/2016/06/22/monitoring-tuning-linux-networking-stack-receiving-data/
# 
from time import sleep
from datetime import datetime

iAnatoly

# see https://github.com/iovisor/bpftrace/blob/master/docs/tutorial_one_liners.md
# histogram for udp_recvmsg timing
sudo bpftrace -e 'kprobe:udp_recvmsg { @start[tid] = nsecs; } kretprobe:udp_recvmsg /@start[tid]/ { @ns[comm] = hist(nsecs - @start[tid]); delete(@start[tid]); }'
# histogram for retval of udp_recvmsg (which is message size in bytes)
sudo bpftrace -e 'kretprobe:udp_recvmsg { @bytes[comm] = hist(retval); }'

iAnatoly

cat ~/.kube/config | grep client-certificate | sed -e ‘s/    client-certificate-data: //’ | base64 -d | openssl x509 -in - -noout -text

iAnatoly

Motivation

At some point, you might find yourself in need to transfer a file (i.e. a dump of the database, or a backup tarball) quickly over a WAN link. Unfortunately, regular copy speeds are impaired by TCP protocol and latency and speed of light - and link bandwidth has very limited effect on the transfer speeds. However, there is a workaround: one can use UDP-based file transfer (UDT). Here is a proof-of-concept experiment that demonstrates the transfer speed improvement.

Experiment

Create a large file to transfer:

iAnatoly

SSH_ENV="$HOME/.ssh/agent-environment"

function start_agent {
    echo "Initialising new SSH agent..."
    /usr/bin/ssh-agent | sed 's/^echo/#echo/' > "${SSH_ENV}"
    echo succeeded
    chmod 600 "${SSH_ENV}"
    . "${SSH_ENV}" > /dev/null
    /usr/bin/ssh-add;
}

iAnatoly

• iTerm2
• iStat menus
• VS code
• ObjeciveSee: BlockBlock, KnockKnock
• Homebrew: ansible, telegraf, bash5, curl, wget, sqlite, python3, go,
• Commons: Chrome, Chromium, FF, Kindle, VLC

iAnatoly

go install -v github.com/projectdiscovery/dnsx/cmd/dnsx@latest
go install -v github.com/projectdiscovery/subfinder/v2/cmd/subfinder@latest
brew install ipinfo-cli
./go/bin/subfinder -d google.com | ./go/bin/dnsx -resp-only | ipinfo summarize

iAnatoly

https://stackoverflow.com/questions/614795/simulate-delayed-and-dropped-packets-on-linux
https://wiki.linuxfoundation.org/networking/netem

```bash
TARGET1='8.8.8.8'
DEV='eth0'

tc qdisc delete dev $DEV root
tc qdisc add dev $DEV root handle 1: prio

iAnatoly

#!/bin/bash
openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -sha256 -days 365 -nodes

iAnatoly

#!/bin/bash

TARGET_FILE_NUM=$1
CURRENT_FILE_NUM=`ls -l | wc -l`
FILES_TO_GENERATE=$((TARGET_FILE_NUM - CURRENT_FILE_NUM))

if [[ $FILES_TO_GENERATE -lt 0 ]]; then
	echo "We already have $CURRENT_FILE_NUM files, no need to generate more"
	exit
fi