Notes

I am one of those people who function better by writing things down. One day, I realized that most of my notes don’t have to be private, so here they are - my second brain. Be warned that, if you stumble upon something here that doesn’t make sense to you, it isn’t meant to!

Tailscale inside an unprivileged LXC container on Proxmox

Since I run LXC containers in unprivileged mode, I had to first run the following on Proxmox host. (Without it, Tailscale won’t install): chown 100000:100000 /dev/net/tun Here’s how my container config looks like on the host. root@pve:~# cat /etc/pve/lxc/100.conf # .. bunch of stuff # The following 2 is to allow Tailscale to run on the containers: lxc.cgroup2.devices.allow: c 10:200 rwm lxc.mount.entry: /dev/net/tun dev/net/tun none bind,create=file

Exiftool

Check Exif data on an image: ~/Image-ExifTool-12.40/exiftool -a -G1 -s -time:all filename The following command sorts by year, month, date and camera model name, in that order. Use -o . to move the data to some other directory. Without that, sorting happens in the directory specified at the end of the command (i.e. . below). The -Filename pseudo tag helps you rename the files. (I haven’t done that myself though.) ~/Image-ExifTool-12.40/exiftool -r -P \ '-Directory<$filemodifydate/Others' \ '-Directory<$createdate/Others' \ '-Directory<$datetimeoriginal/Others' \ '-Directory<$filemodifydate/${model;}' \ '-Directory<$createdate/${model;}' \ '-Directory<$datetimeoriginal/${model;}' \ -d '%Y/%m-%B/%d' . Resources: ...

Handle image duplicates

fdupes -rSm Pictures/ # Note: the following removes duplicates, so use with care! fdupes -rSdN Pictures/

OfflineIMAP

Here’s how I setup OfflineIMAP to take regular backups of our Gmail accounts: # Install, on Raspberry Pi. sudo apt install offlineimap3 cat > ~/.offlineimaprc << 'EOF' [general] accounts = foo1, foo2 [Account foo1] localrepository = foo1-local remoterepository = foo1-remote synclabels = yes # This header is where labels go. Usually you will be fine # with default value (X-Keywords), but in case you want it # different, here we go: labelsheader = X-Keywords [Repository foo1-remote] type = Gmail sslcacertfile = OS-DEFAULT remoteuser = [email protected] remotepass = pass1 readonly = True [Repository foo1-local] type = GmailMaildir localfolders = /srv/dev-disk-by-uuid-28fd4901-c675-430d-be16-e1ffddc50727/Backups/Emails/[email protected] [Account foo2] localrepository = foo2-local remoterepository = foo2-remote synclabels = yes # This header is where labels go. Usually you will be fine # with default value (X-Keywords), but in case you want it # different, here we go: labelsheader = X-Keywords [Repository foo2-remote] type = Gmail sslcacertfile = OS-DEFAULT remoteuser = [email protected] remotepass = pass2 readonly = True [Repository foo2-local] type = GmailMaildir localfolders = /srv/dev-disk-by-uuid-28fd4901-c675-430d-be16-e1ffddc50727/Backups/Emails/[email protected] EOF Other resources: ...

Pastebin

Here is my attempt to design a system for a pastebin-like service.

Got Your Backup - Backup Gmail

I use Got Your Back to backup my Gmail emails every night.: I stopped using GYB because the credentials it uses stop working after 7 days for regular Gmail accounts. I switched to OfflineIMAP instead. Here are some helpful commands: # Initial setup. ./bin/gyb/gyb \ --email [email protected] \ --local-folder /srv/dev-disk-by-uuid-28fd4901-c675-430d-be16-e1ffddc50727/Backups/GYB-GMail-Backup/[email protected] \ --action create-project # Quick way to test if everything is setup as expected. ./bin/gyb/gyb \ --email [email protected] \ --local-folder /srv/dev-disk-by-uuid-28fd4901-c675-430d-be16-e1ffddc50727/Backups/GYB-GMail-Backup/[email protected] \ --action estimate # Backup. Omit the last term to backup everything. # The last three parameters are optional to speed things up or make them run in less-memory environments. /home/pi/bin/gyb/gyb \ --email [email protected] \ --local-folder /srv/dev-disk-by-uuid-28fd4901-c675-430d-be16-e1ffddc50727/Backups/GYB-GMail-Backup/[email protected] \ --action backup \ --search "newer_than:7d" \ --memory-limit 100 \ --batch-size 4 Other tools that I checked but didn’t use: ...

Intentionality and awareness

Intentionality - really important. Awareness = paying attention to your surrounding as well. (I guess the default is to have a monologue with yourself about yourself.)

Tiny URL

Here is my attempt to design a system for a tiny URL service.

Near-term plan on system design interview prep

I should practice all the system design questions from that PDF. That includes going through the material once, presenting it to the camera, analyzing the recordings and revising the content after a few days. Should quickly do all of them. The questions shouldn’t be too hard. TBD ETA and I should strive to finish be then. Next step is to do mock interviews. Aim to do both system design and behavioral.

Hash encoding

MD5 hashes and UUIDs are 128 bits. So, if you encode them using hexadecimals, each hex character will encode 4 bits of information, so resultant “string” will be 128/4=32 character/bytes long. If you store UUIDs as string, you need 4 additional characters for the hyphens. If you store them in binary format, you just need 128/8 = 16 bytes because each byte will encode 8 bits of information.