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Lecture 10: Potpourri

Daemons​

  • processes that runs in the background rather than waiting for a user to launch them and interact with them
  • programs that run as daemon ofthen end with a d, e.g. sshd (SSH daemon), systemd (running and setting up daemon processes)
  • systemctl status to list current runing daemons
  • e.g. managing the network, solving DNS queries or displaying the graphical interface for the system
  • cron: a daemon your system already runs to perform scheduled tasks
    • if need to run some program with a given frequency
    • no need to build a custom daemon

Example: a daemon for running a simple Python app

# /etc/systemd/system/myapp.service
[Unit]
Description=My Custom App
After=network.target

[Service]
User=foo
Group=foo
WorkingDirectory=/home/foo/projects/mydaemon
ExecStart=/usr/bin/local/python3.7 app.py
Restart=on-failure

[Install]
WantedBy=multi-user.target

FUSE (Filesystem in User Space)​

  • UNIX filesystems are traditonally implemented as kernel modules and only the kernel is allowed to perform filesystem calls
  • FUSE allows filesystems to be implemented by a user program
  • Examples:
    • sshfs: open locally remote files/folder through an SSH connection
    • rclone: Mount cloud storage services like Dropbox, GDrive, Amazon S3 or Google Cloud Storage and open data locally

Backups​

  • Any data that you haven’t backed up is data that could be gone at any moment, forever
  • 3-2-1 rule:
    • at least 3 copies of your data
    • 2 copies in different mediums
    • 1 of the copies being offsite
  • Bad solutions:
    • copy of the data on the same disk
    • an external drive in your home
    • synchronization solutions (e.g. Dropbox)
    • disk mirroring solutions (e.g. RAID)
  • Good backups:
    • versioning
    • deduplication
    • security
    • having offline copies of data in the cloud (e.g. email)

APIs​

  • Structured URLs:
    • often rooted at api.service.com
    • path and query parameters indicate what data you want to read or what action you want to perform
  • curl: used to transfer data with URLs
  • OAuth: a way to give you tokens that can "act as you" on a given service
    • some APIs require authentication: secret token to include with the request
  • IFTTT: provides integrations with tons of services, and lets you chain events from them in nearly arbitrary ways

Common command-line flags/patterns​

  • --help: dispaly brief usage instructions
  • --version or -V: print version
  • --verbose or -v: produce more verbose output, e.g. -vvv to get more verbose outout
  • --quiet: only print something on error
  • "dry run": only print what the tools would have done, but do not actually perform the change
  • "interactive" flag: prompt you for each destructive action
  • -r: make destructive tools recursive
  • - in place of a file name: "standard input" (keyboard by default) or "standard output" (terminal screen by default)
  • --: makes a program stop processing flags and options (things starting with -):
    • e.g. remove a file called -r: rm -- -r

Window managers​

  • "floating" window manager
  • "tiling" window manager

VPNs​

  • just a way for you to change your internet service provider as far as the internet is concerned
  • all your traffic will look like it’s coming from the VPN provider instead of your “real” location
  • and the network you are connected to will only see encrypted traffic
  • when you use a VPN, all you are really doing is shifting your trust from you current ISP to the VPN hosting company, whatever your ISP could see, the VPN provider now sees instead
  • much of your traffic, at least of a sensitive nature, is already encrypted through HTTPS or TLS more generally
  • some VPN providers are malicious (or at the very least opportunist), and will log all your traffic, and possibly sell information about it to third parties
  • WireGuard to roll your own VPN

Booting + Live USBs​

Booting:

  • When machine boots up, before the OS is loaded, the BIOS/UEFI initializes the system
  • “Press F9 to configure BIOS. Press F12 to enter boot menu.” during the boot process
  • BIOS menu: configure all sorts of hardware-related settings
  • Boot menu: to boot from an alternate device instead of your hard drive

Live USBs:

  • USB flash drives containing an OS

Docker, Vagrant, VMs, Cloud, OpenStack​

https://missing.csail.mit.edu/2020/potpourri/#docker-vagrant-vms-cloud-openstack