Wed Nov 02 2022

• Tun interface
  • for tunneling, operates at layer 3, virtual interface like tap interface
  • OpenVPN in user space - uses tun interface, kernel space (eth interface) at the other end
  • VPN combines tun interfaces on the devices connected to it

Tue Nov 01 2022

• Tap interface

  • Linux bridge - Switch implemented in Linux kernel
    • The virtual ports on Linux bridges are called tap interfaces
  • Virtual machine - has to emulate (virtual) Ethernet interface connected to (virtual) ethernet switch (operates at layer 2)
    • virtual NIC expects an Ethernet frame (but a physical NIC will strip the Ethernet header and pass on the payload). Hence we need a tap interface to pass on the ethernet frame as it is to the virtual NIC.

• Ethernet bridging

  • Combine multiple TAP (virtual) interfaces and physical ethernet interfaces under a single bridge interface

Mon Oct 03 2022

• Lactase persistence - usually in mammals, lactase (enzyme for milk digestion) fades after weaning phase. In humans, a gene that persisted lactase even after weaning was selected for (can eat milk and milk products).
  • Example of niche construction - organisms modify environment to create new evolutionary pressures.
  • Non-persistent individuals can consume milk without ill-effects due to lactic acid gut bacteria. Also, fermented milk products like yoghurt and cheese contain less lactose than raw milk.

Wed Sep 28 2022

• ping and traceroute use ICMP (Internet Control Message Protocol - RFC 792)
  • ICMP is a supporting protocol (used for diagnostics)
• tcpdump -v ip => prints fields in ip header

Tue Sep 13 2022

• Merchants pay a fee to the bank for processing card transactions
• UPI is built on top of IMPS (Instant Mobile Payments System)

Sun Aug 28 2022

• WHERE doesn’t work in aggregated query (HAVING is used)

Tue Jul 26 2022

• GET, POST, PUT etc => HTTP verbs

Wed Jun 15 2022

• awk named after initials of founders - Alfred Ahio, Peter Weinberger and Brian Kernighan

Thu Jun 09 2022

• xargs - template command for multiple arguments (piped from STDIN) example - ls | xargs ls => outputs of first ls are taken as arguments to second ls successively
• locate uses a DB to find files -> fast.
  • DB is usually updated daily by cron job that calls updatedb

Thu May 19 2022

• git bisect - binary search on commit history to find the commit at which something changed (like a bug appearing)
  • https://git-scm.com/docs/git-bisect
  • change to commit in middle -> test code -> git bisect good or git bisect bad -> repeat for either half.

Fri May 06 2022

• https://lwn.net/SubscriberLink/893686/8978976335696804/
  • Python is slow not due to its interpreted nature (only 10% overhead), but due to its dynamic nature.
  • type lookup, dynamic variable lookup, dynamic attributes
  • method call is just attribute lookup with extra step of calling the function => repeatedly making method call inside a loop? Fetch the attribute outside the loop and then call it from there.
• Minifying - removing unnecessary characters like spaces, indents, new lines
• Code splitting
  • different URLs, different code required
  • code splitting is splitting the code into separate chunks required by each entrypoint to reduce the initial load time of pages

Thu May 05 2022

• Modern versions of JavaScript - JSX, TypeScript need to be compiled to JS
• Compiler in Next.js - Rust

Wed Apr 06 2022

• https://www.hackthebox.com/blog/Dirty-Pipe-Explained-CVE-2022-0847
  • Smallest unit of memory that CPU controls - page, usually 4 KB
  • Translation lookaside Buffer (TLB)
    • Memory cache that maps virtual memory to physical memory. Maps pages (vritual) to frames (physical)

Thu Mar 31 2022

• KPI - Key Performance Indicator
  • For startups - KPI to track growth must be revenue for paying customers, usage if otherwise
  • https://kpi.org/KPI-Basics

Sun Mar 27 2022

• SQL JOIN - First cross product (all members of first * all members of second), filtered by WHERE clause

Wed Mar 02 2022

• MX record (Mail Exchange) - DNS record that directs email to mail servers

Tue Mar 01 2022

• Code splitting - each page loads only what’s necessary for that page
• prefetching in production build of Next - Linked page, components loaded before it is clicked.

Sat Feb 12 2022

• ctypes library in Python - can import shared object file (.so) into Python

  from ctypes import CDLL
  libfact = CDLL("./fact.so")
  

• compilation - gcc -shared -o fact.so fact.c

Thu Feb 10 2022

• Macros in rust => metaprogramming. Code that can write other code
  • Processed before compilation (similar to C)
  • Can match certain pattern in Rust code and replace it.

Wed Feb 09 2022

• [rv] = await expression => await is used to wait for a Promise to resol

Sat Feb 05 2022

• https://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art026
  • /usr/include - Contains C header files (among others)
  • ##include </path/to/file.h> => appended to /usr/include`

Thu Feb 03 2022

• getattr() - global method in Python to get method/attribute of an object
  • getattr(object, name, default)
    • object => object of class whose method needs to be returned
    • name => string of attribute/method name
    • default => what to return if not found

Sun Jan 30 2022

• Context menu - menu that opens on right click
• GNU Autotools - build system for Unix
  • ./configure, ./make
• Glib - core application building block for libraries and applications written in C

Mon Jan 10 2022

• Liquor/spirits - has been distilled
  • only last 100 years, we haven’t physiologically or culturally adapted

Thu Jan 06 2022

• Folio number in mutual funds - unique ID like bank account number

Sun Jan 02 2022

• AAAA record - name to IPv6 address.
• A record - name to IPv4 address.
• Pass multiple lines of text to a command - <<, heredoc https://linuxize.com/post/bash-heredoc/

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