Useful Commands

This README contains a dump of commands that have helped me greatly, yet somehow, I am never able to recall them and always end up spending 10 minutes Googling for them.

General System/OS

Update Ubuntu dependencies

sudo apt-get update
sudo apt-get dist-upgrade

These two commands above together help to update Ubuntu dependencies.

Get disk usage

sudo du -hsx dir/* | sort -rh | head -n 20

Get a summary of disk usage for files in the given dir, and list the top 20 (arbitrary) of them, with the largest at the top.

Generate a new SSH key

ssh-keygen -t ed25519 -C "your_email@example.com"
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

These three commands above help to generate a new SSH key, based on GitHub's instructions. The commands above are for Linux - there are other commands for Mac and Windows.

Create a new superuser account

adduser username
usermod -aG sudo username
su - username
mkdir ~/.ssh && chmod 700 ~/.ssh
touch ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys

These commands above help to create a new superuser account and set up the SSH keys accordingly.

Flush DNS cache

sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

Flushes the DNS cache on Mac.

Certbot and NGINX

Create a certificate without affecting NGINX

sudo certbot certonly -d example.com --nginx

Creates a certificate but doesn't touch the NGINX default configuration.

Link NGINX `sites-enabled`

sudo ln -s /etc/nginx/sites-available/example.com /etc/nginx/sites-enabled/

Links the certificate in sites-available to sites-enabled.

Manual Renewal of Certificates

sudo certbot certonly --manual -d example.com --preferred-challenges dns

Databases

Vacuum PostgreSQL database

vacuumdb --analyze --verbose dbname

Utility for cleaning a PostgreSQL database, and also generate internal statistics used by the PostgreSQL query optimizer. Read more here.

Node & NPM

Update all dependencies

ncu -u
npm install # or yarn install

Requires npm-check-updates to be installed globally. It upgrades package.json dependencies to the latest versions, ignoring specified versions.

Fix audit vulnerabilities for `yarn`

npx yarn-audit-fix

Will install yarn-audit-fix and run it to fix vulnerabilities detected in the dependencies. Used for yarn projects.

Poetry

List outdated top-level dependencies

poetry show --outdated | grep --file=<(poetry show --tree | grep '^\w' | cut -d' ' -f1 | sed 's/.*/^&\\s/')

Credit goes to @Hultner (see his comment here).

Swift & XCode

Clean pods and caches

rm -rf ~/Library/Caches/CocoaPods Pods ~/Library/Developer/Xcode/DerivedData && pod deintegrate && pod install

Clears all pods and caches and reinstalls them. May need to specify a project for pod deintegrate.

Miscellaneous

Get first page of a PDF file as an image

gs -o output.png -sDEVICE=png256 -dLastPage=1 -r300 -dBackgroundColor=16#ffffff input.pdf

Uses Ghostscript to get an image of the first page of input.pdf. The background colour is filled with white.

Replace word in file names recursively

find . -name "*sql.xz" -exec bash -c ' mv $0 ${0/beyond-server/sparks}' {} \;

zhuhanming/useful-commands