errcodex

AWS CLI: Unable to locate credentials. You can configure credentials by running aws configure

Tue, 20 Oct 2026 00:00:00 GMT

The AWS CLI prints Unable to locate credentials when no access key, profile, SSO session or role is found. Check what it found with aws configure list.

bash: command not found (exit status 127)

Tue, 20 Oct 2026 00:00:00 GMT

bash prints "command not found" and exits with status 127 when a command is not in PATH, not installed or misspelled. Check with command -v and fix PATH.

Certbot: Problem binding to port 80: Could not bind to IPv4 or IPv6

Tue, 20 Oct 2026 00:00:00 GMT

certbot --standalone fails with Problem binding to port 80 when nginx, Apache or another service already listens there. Use the webroot or nginx plugin instead.

blocked by CORS policy: No 'Access-Control-Allow-Origin' header

Tue, 20 Oct 2026 00:00:00 GMT

The browser blocks a cross-origin response without Access-Control-Allow-Origin. Fix it on the server by sending the header for your origin, or proxy the API.

ImproperlyConfigured: Requested setting …, but settings are not configured

Tue, 20 Oct 2026 00:00:00 GMT

Django raises ImproperlyConfigured when code reads settings before DJANGO_SETTINGS_MODULE is set or settings.configure() runs. Set it, then call django.setup().

Error: getaddrinfo ENOTFOUND (DNS lookup failed)

Tue, 20 Oct 2026 00:00:00 GMT

Node.js throws getaddrinfo ENOTFOUND when DNS cannot resolve the host: a typo, a full URL passed as host, a name only in /etc/hosts, or no working DNS.

Docker Compose: service "web" depends on undefined service "db"

Tue, 20 Oct 2026 00:00:00 GMT

docker compose fails with service "web" depends on undefined service "db" when depends_on names a service missing from the file, the -f list or a profile.

Error: listen EADDRINUSE: address already in use :::3000

Tue, 20 Oct 2026 00:00:00 GMT

Node.js and Express fail with listen EADDRINUSE when another process already uses the port. Find it with lsof, ss or netstat, stop it, or listen on a free port.

ffmpeg: Unknown encoder 'libx264' (Encoder not found)

Tue, 20 Oct 2026 00:00:00 GMT

ffmpeg prints Unknown encoder when the codec name is misspelled or the build lacks that library, such as libx264 or libfdk_aac. List them with -encoders.

libx264: width not divisible by 2 / height not divisible by 2

Tue, 20 Oct 2026 00:00:00 GMT

libx264 rejects odd sizes with yuv420p: width not divisible by 2 (101x101). Scale to even sizes with scale=trunc(iw/2)*2:trunc(ih/2)*2 or use scale=-2:720.

find: paths must precede expression

Tue, 20 Oct 2026 00:00:00 GMT

find reports paths must precede expression when an unquoted glob such as *.txt is expanded by the shell into several file names. Quote it: find . -name '*.txt'.

error: failed to push some refs (rejected, fetch first)

Tue, 20 Oct 2026 00:00:00 GMT

git push is rejected with failed to push some refs when the remote branch has commits you do not have. Pull or fetch and rebase first, then push again safely.

fatal: not a git repository (or any of the parent directories): .git

Tue, 20 Oct 2026 00:00:00 GMT

Git prints not a git repository when the current folder and none of its parents contain a .git directory. cd into the repository, run git init, or set GIT_DIR.

fatal: refusing to merge unrelated histories

Tue, 20 Oct 2026 00:00:00 GMT

Git refuses to merge two branches that share no common commit, for example a new local repo and a remote created with a README. Use --allow-unrelated-histories.

gpg: signing failed: Inappropriate ioctl for device

Tue, 20 Oct 2026 00:00:00 GMT

gpg cannot ask for your passphrase because GPG_TTY is not set, so signing fails with Inappropriate ioctl for device. Export GPG_TTY=$(tty) or use GUI pinentry.

Helm: nil pointer evaluating interface {}.value

Tue, 20 Oct 2026 00:00:00 GMT

helm template and helm install fail with nil pointer evaluating interface {} when a template reads a nested value whose parent key is missing from values.yaml.

ImageMagick: not allowed by the security policy `PDF'

Tue, 20 Oct 2026 00:00:00 GMT

ImageMagick refuses to read or write PDF, PS or EPS when policy.xml disables the Ghostscript coders. Allow the PDF coder in policy.xml for trusted files only.

SyntaxError: Unexpected token '<', "
Tue, 20 Oct 2026 00:00:00 GMT
JSON.parse fails with Unexpected token '<' when the response is an HTML page, usually an error or login page, not JSON. Check the status and content type first.

kubectl: error converting YAML to JSON: mapping values are not allowed in this context

Tue, 20 Oct 2026 00:00:00 GMT

kubectl apply fails with error converting YAML to JSON: mapping values are not allowed in this context when indentation is wrong or a colon is unquoted.

Hydration failed because the server rendered HTML didn't match the client

Tue, 20 Oct 2026 00:00:00 GMT

Next.js and React 19 report Hydration failed when server HTML differs from the first client render: Date.now(), window checks, locale formats, bad nesting.

Error: Cannot find module '…' in Node.js

Tue, 20 Oct 2026 00:00:00 GMT

Node.js throws Cannot find module when require() or import cannot resolve a path or package. Install the package, fix the relative path or add the extension.

npm ERR! code ERESOLVE: unable to resolve dependency tree

Tue, 20 Oct 2026 00:00:00 GMT

npm fails with ERESOLVE when a package's peer dependency conflicts with the version you install. Read Found and Could not resolve, then align the versions.

ValueError: operands could not be broadcast together with shapes

Tue, 20 Oct 2026 00:00:00 GMT

NumPy raises operands could not be broadcast together when array shapes are incompatible. Compare shapes from the right: each pair must be equal or 1.

unable to get local issuer certificate (OpenSSL verify error 20)

Tue, 20 Oct 2026 00:00:00 GMT

OpenSSL error 20, unable to get local issuer certificate, means the issuing CA is missing from the trust store or the chain. Add the CA or intermediate.

SettingWithCopyWarning: A value is trying to be set on a copy of a slice

Tue, 20 Oct 2026 00:00:00 GMT

pandas 2 warns SettingWithCopyWarning when you assign to a filtered DataFrame that may be a copy. Use .loc on the original or .copy(); pandas 3 removed it.

pip error: externally-managed-environment (PEP 668)

Tue, 20 Oct 2026 00:00:00 GMT

pip refuses to install into a system Python marked EXTERNALLY-MANAGED by PEP 668, as on Debian and Ubuntu. Use a venv, pipx or the distro package instead.

ModuleNotFoundError: No module named '…'

Tue, 20 Oct 2026 00:00:00 GMT

Python raises ModuleNotFoundError when the package is not installed for the interpreter that runs your code. Check sys.executable, then install with -m pip.

torch.OutOfMemoryError: CUDA out of memory. Tried to allocate …

Tue, 20 Oct 2026 00:00:00 GMT

PyTorch raises CUDA out of memory when the GPU cannot fit the next allocation. Lower the batch size, use mixed precision, drop references, reduce fragmentation.

Each child in a list should have a unique "key" prop

Tue, 20 Oct 2026 00:00:00 GMT

React warns Each child in a list should have a unique "key" prop when map() returns elements without key. Use a stable id from your data, not the index.

Error: Too many re-renders. React limits the number of renders to prevent an infinite loop.

Tue, 20 Oct 2026 00:00:00 GMT

React throws Too many re-renders when a component sets state during render, often onClick={setCount(1)} instead of onClick={() => setCount(1)}. How to fix it.

sed: -e expression #1, char N: unterminated `s' command

Tue, 20 Oct 2026 00:00:00 GMT

GNU sed reports unterminated `s' command when a substitution misses its final delimiter, often because the pattern or replacement contains an unescaped slash.

Spring Boot: Web server failed to start. Port 8080 was already in use.

Tue, 20 Oct 2026 00:00:00 GMT

Spring Boot stops with Web server failed to start. Port 8080 was already in use. when another process holds the port. Free it or set server.port to a new value.

Permission denied (publickey) with ssh

Tue, 20 Oct 2026 00:00:00 GMT

ssh fails with Permission denied (publickey) when the server accepts only keys and none you offer is authorized. Check the key, the user and file permissions.

Terraform: Reference to undeclared input variable

Tue, 20 Oct 2026 00:00:00 GMT

terraform validate and plan fail with Reference to undeclared input variable when code uses var.name without a variable block in the same module. How to fix it.

Terraform: Error: Unsupported argument. An argument named "x" is not expected here

Tue, 20 Oct 2026 00:00:00 GMT

Terraform fails with Unsupported argument, An argument named "name" is not expected here, when a block sets an attribute its resource or module lacks.

error TS5108: Option 'moduleResolution=node10' has been removed

Tue, 20 Oct 2026 00:00:00 GMT

TypeScript 7 removed moduleResolution node and node10. Use bundler for code built by a bundler, or nodenext with module nodenext for code that Node.js runs.

python manage.py makemigrations and migrate: create and apply migrations

Tue, 20 Oct 2026 00:00:00 GMT

makemigrations turns model changes into migration files and migrate applies them to the database. Preview SQL with sqlmigrate, check state with showmigrations.

ffmpeg: extract audio from a video (with and without re-encoding)

Tue, 20 Oct 2026 00:00:00 GMT

Extract audio with ffmpeg -i input.mp4 -vn -c:a copy audio.m4a without re-encoding, or make an MP3 with -c:a libmp3lame -q:a 2. Check codecs with ffprobe.

git reset --soft HEAD~1: undo the last commit, keep the changes

Tue, 20 Oct 2026 00:00:00 GMT

Undo the last commit and keep its changes staged with git reset --soft HEAD~1. --mixed unstages them, --hard deletes them. Undo a reset with the reflog.

Decode a JWT from the command line (header and payload)

Tue, 20 Oct 2026 00:00:00 GMT

A JWT is three base64url parts joined by dots. Decode the header and payload with Node.js or base64 in one line; decoding is not verifying the signature.

Generate Kubernetes YAML with kubectl create --dry-run=client -o yaml

Tue, 20 Oct 2026 00:00:00 GMT

kubectl create deployment, service, configmap or secret with --dry-run=client -o yaml prints a ready manifest without a cluster. Save it with > file.yaml.

npm install a specific version: npm install package@version

Tue, 20 Oct 2026 00:00:00 GMT

Install an exact version with npm install package@1.2.3, a range with package@^1.2, or a dist-tag with package@next. List published versions with npm view.

openssl req -x509: create a self-signed certificate

Tue, 20 Oct 2026 00:00:00 GMT

Create a self-signed certificate and key in one step with openssl req -x509 -newkey ec -nodes -keyout key.pem -out cert.pem -days 365, plus -subj and SAN.

pandas merge: join DataFrames on a key (inner, left, outer)

Tue, 20 Oct 2026 00:00:00 GMT

pd.merge(left, right, on='id', how='left') joins DataFrames like SQL. how picks inner, left, right, outer or cross; validate= catches duplicated keys.

prettier --write and --check: format files from the command line

Tue, 20 Oct 2026 00:00:00 GMT

Format a project with npx prettier . --write, or fail CI on unformatted files with npx prettier . --check. Configure it with .prettierrc and .prettierignore.

python -m json.tool: pretty-print and validate JSON

Tue, 20 Oct 2026 00:00:00 GMT

Pretty-print or validate JSON from the shell with python -m json.tool (or python -m json on 3.14+). Sort keys, set indent, compact output and read JSON Lines.

tar -xzf: extract a .tar.gz archive

Tue, 20 Oct 2026 00:00:00 GMT

Extract a .tar.gz archive with tar -xzf archive.tar.gz. Use -C to choose the target directory, -t to list contents first and -v to print each extracted file.

terraform fmt -check and -recursive: format HCL files

Tue, 20 Oct 2026 00:00:00 GMT

terraform fmt rewrites .tf files in canonical style; -check only reports unformatted files with a non-zero exit, -diff shows changes, -recursive adds modules.

set -euo pipefail: what each flag does in bash

Tue, 20 Oct 2026 00:00:00 GMT

set -e exits on the first failing command, -u treats unset variables as errors and -o pipefail makes a pipeline fail if any command in it fails. Examples.

curl -k (--insecure): skip TLS certificate verification

Tue, 20 Oct 2026 00:00:00 GMT

curl -k, or --insecure, makes curl accept a TLS certificate it cannot verify, such as a self-signed one. Safer: --cacert for a private CA, or --pinnedpubkey.

eslint --fix: automatically fix lint problems

Tue, 20 Oct 2026 00:00:00 GMT

npx eslint . --fix applies the fixes that rules provide, such as let to const, and reports what it cannot fix. Preview changes first with --fix-dry-run.

uvicorn --reload: auto-restart FastAPI on code changes

Tue, 20 Oct 2026 00:00:00 GMT

uvicorn main:app --reload restarts the server when Python files change; --reload-dir and --reload-include choose what to watch. Use it only in development.

ffmpeg -crf: constant rate factor for x264, x265 and AV1

Tue, 20 Oct 2026 00:00:00 GMT

-crf sets constant quality: lower means better and bigger. libx264 defaults to 23 on a 0 to 51 scale, libx265 to 28. Use it with -preset; sizes measured.

git push --force-with-lease: a safer force push

Tue, 20 Oct 2026 00:00:00 GMT

--force-with-lease overwrites the remote branch only if it still points where your remote-tracking ref says, so commits pushed since your fetch are never lost.

helm --set, --set-string and -f: override chart values

Tue, 20 Oct 2026 00:00:00 GMT

helm --set key=value overrides values.yaml from the command line; nested keys use dots, lists use {a,b}. --set-string forces strings, -f loads a file.

Set-Cookie attributes: SameSite, Secure, HttpOnly, Max-Age

Tue, 20 Oct 2026 00:00:00 GMT

Set-Cookie attributes decide when browsers send a cookie: SameSite controls cross-site requests, None needs Secure, HttpOnly hides it from JavaScript.

npm install --legacy-peer-deps: what it does and when to use it

Tue, 20 Oct 2026 00:00:00 GMT

--legacy-peer-deps makes npm skip installing and checking peer dependencies, as npm 6 did, so ERESOLVE conflicts no longer stop the install. Risks and fixes.

openssl s_client -servername: test TLS with SNI

Tue, 20 Oct 2026 00:00:00 GMT

openssl s_client -connect host:443 -servername host sends SNI so the server returns the right certificate. Add -brief for a summary or -showcerts for the chain.

pandas read_csv low_memory and DtypeWarning: Columns have mixed types

Tue, 20 Oct 2026 00:00:00 GMT

read_csv parses big files in chunks; when chunks infer different types it warns DtypeWarning: Columns have mixed types. Set dtype or use low_memory=False.

terraform plan -out: save a plan and apply exactly that plan

Tue, 20 Oct 2026 00:00:00 GMT

terraform plan -out=tfplan saves the plan to a file; terraform apply tfplan then applies exactly those changes without a prompt. Inspect it with terraform show.

Django ALLOWED_HOSTS: values, wildcards and DisallowedHost errors

Tue, 20 Oct 2026 00:00:00 GMT

ALLOWED_HOSTS lists the host names a Django site may serve. Any other Host header raises DisallowedHost, a 400 error. Use exact names or .example.com.

Compose depends_on condition: service_healthy with a healthcheck

Tue, 20 Oct 2026 00:00:00 GMT

depends_on with condition: service_healthy makes Compose wait until a dependency's healthcheck passes before it starts the services that depend on it.

git config core.autocrlf: true, input or false

Tue, 20 Oct 2026 00:00:00 GMT

core.autocrlf sets line-ending conversion: true gives CRLF on checkout, input turns CRLF into LF on commit, false never converts. Share it via .gitattributes.

Strict-Transport-Security (HSTS): max-age, includeSubDomains, preload

Tue, 20 Oct 2026 00:00:00 GMT

Strict-Transport-Security makes browsers use only HTTPS for max-age seconds. includeSubDomains covers subdomains; preload is a commitment that is hard to undo.

ImageMagick policy.xml: resource limits and coder rules

Tue, 20 Oct 2026 00:00:00 GMT

ImageMagick policy.xml limits memory, disk, image size and allowed formats. The policy domains, raising width or area limits, enabling or blocking coders.

package.json "type": "module": ES modules in Node.js

Tue, 20 Oct 2026 00:00:00 GMT

Setting "type": "module" in package.json makes Node.js load .js files as ES modules: import and export work, require is undefined, and .cjs stays CommonJS.

pandas display options: show all columns and rows (display.max_columns)

Tue, 20 Oct 2026 00:00:00 GMT

pandas truncates wide and long DataFrames when printing. Set display.max_columns and display.max_rows to None to see everything, or use option_context once.

~/.ssh/config: Host, HostName, User, Port and IdentityFile

Tue, 20 Oct 2026 00:00:00 GMT

~/.ssh/config defines per-host SSH settings: an alias with Host, the real name with HostName, plus User, Port and IdentityFile. Check the result with ssh -G.

Terraform variable precedence: tfvars, auto.tfvars, -var and TF_VAR_

Tue, 20 Oct 2026 00:00:00 GMT

Terraform reads variables from TF_VAR_ environment variables, terraform.tfvars, *.auto.tfvars, then -var-file and -var. Later sources win, shown with plans.

tsconfig moduleResolution: bundler, nodenext, node16

Tue, 20 Oct 2026 00:00:00 GMT

moduleResolution tells tsc how to find imports. TypeScript 7 accepts bundler, node16 and nodenext; node10 and classic were removed. Valid pairs with module.

vite.config server.proxy: proxy API calls in the dev server

Tue, 20 Oct 2026 00:00:00 GMT

server.proxy in vite.config.js forwards dev-server requests such as /api to a backend to avoid CORS in development. Targets, rewrite, changeOrigin, ws.

WireGuard AllowedIPs: routing and peer filtering explained

Tue, 20 Oct 2026 00:00:00 GMT

WireGuard AllowedIPs lists the addresses a peer may send from and the routes sent to it. 0.0.0.0/0, ::/0 routes all traffic; a /32 per peer limits it to one IP.

awk cheat sheet: fields, patterns, sums and printf

Tue, 20 Oct 2026 00:00:00 GMT

awk cheat sheet: print fields, change the separator, filter rows by pattern or condition, sum and count columns, use BEGIN and END, printf formats and arrays.

Bash cheat sheet: variables, tests, loops and expansions

Tue, 20 Oct 2026 00:00:00 GMT

Bash cheat sheet with the syntax you use daily: variables, parameter expansion, tests, loops, functions, arrays, redirection and safe script headers on a page.

CSS flexbox cheat sheet: container and item properties

Tue, 20 Oct 2026 00:00:00 GMT

CSS flexbox cheat sheet: display flex, flex-direction, justify-content, align-items, flex-wrap and gap on the container; flex, align-self, order on items.

Django manage.py cheat sheet: project, migrations, users, testing

Tue, 20 Oct 2026 00:00:00 GMT

Django manage.py cheat sheet: startproject and startapp, makemigrations and migrate, createsuperuser, runserver, shell, check, test, collectstatic and dumpdata.

FFmpeg cheat sheet: convert, cut, scale, extract and inspect

Tue, 20 Oct 2026 00:00:00 GMT

FFmpeg cheat sheet: inspect files with ffprobe, change containers, encode H.264, cut without re-encoding, scale, extract audio, make GIFs and thumbnails.

Git cheat sheet: everyday commands

Tue, 20 Oct 2026 00:00:00 GMT

Git cheat sheet: setup, stage and commit, branches with switch, history, undo with restore, reset and revert, stash, remotes, tags and the reflog on one page.

kubectl cheat sheet: everyday Kubernetes commands

Tue, 20 Oct 2026 00:00:00 GMT

kubectl cheat sheet: contexts and namespaces, get and describe, logs and exec, apply and rollout, port-forward, scaling, and manifests with --dry-run=client.

npm cheat sheet: install, run, update, publish

Tue, 20 Oct 2026 00:00:00 GMT

npm cheat sheet: init, install and uninstall, version specifiers, scripts, outdated and update, npm ci for CI, ls and explain, config and cache commands.

OpenSSL cheat sheet: keys, CSRs, certificates and TLS checks

Tue, 20 Oct 2026 00:00:00 GMT

OpenSSL cheat sheet: generate keys and CSRs, inspect certificates, check that key and certificate match, convert PEM, DER and PFX, verify chains and test TLS.

pandas cheat sheet: read, select, filter, group and reshape

Tue, 20 Oct 2026 00:00:00 GMT

pandas cheat sheet: read CSV and Parquet, select with loc and iloc, filter rows, add columns, group and aggregate, pivot, handle missing values and write files.

Terraform cheat sheet: init, plan, apply, state and workspaces

Tue, 20 Oct 2026 00:00:00 GMT

Terraform cheat sheet: init and upgrade, fmt and validate, plan and apply, outputs, state list, mv and rm, import, workspaces, and common language syntax.

YAML cheat sheet: syntax, multiline strings and gotchas

Tue, 20 Oct 2026 00:00:00 GMT

YAML cheat sheet: maps, lists, scalars, block strings with | and >, anchors and aliases, and the YAML 1.1 traps where no becomes false and 012 is octal.

Django 5.2 to 6.1: breaking changes and upgrade notes

Tue, 20 Oct 2026 00:00:00 GMT

Upgrading from Django 5.2 LTS to 6.0 and 6.1: Python 3.12+, BigAutoField by default, https for URLField, CSP and background tasks, and calendar versioning.

docker-compose v1 to docker compose v2: what changed

Tue, 20 Oct 2026 00:00:00 GMT

Compose v2 replaces the Python docker-compose with the docker compose plugin: version is obsolete, container names use hyphens, and v1 is end of life.

Git 2.55 to 2.56: what changed

Tue, 20 Oct 2026 00:00:00 GMT

Git 2.56 makes -h and --help exit with 0 instead of 129, adds git add --resolved, git branch --delete-merged and git refs subcommands, and flags push typos.

ImageMagick 6 to 7: convert becomes magick

Tue, 20 Oct 2026 00:00:00 GMT

ImageMagick 7 replaces convert with magick, runs identify, mogrify and compare as magick subcommands, enables HDRI by default and changes the MagickCore C API.

Node.js 24 to 26: breaking changes and migration

Tue, 20 Oct 2026 00:00:00 GMT

Upgrading from Node.js 24 to 26: Temporal on by default, V8 14.6, Undici 8, fs.F_OK and SlowBuffer removed, legacy _stream modules gone, native addons rebuilt.

OAuth 2.0 to OAuth 2.1: what changes

Tue, 20 Oct 2026 00:00:00 GMT

OAuth 2.1 (draft-ietf-oauth-v2-1-16) requires PKCE, exact redirect URI matching and no tokens in query strings, and drops the implicit and password grants.

OpenSSL 3.x to 4.0: removed features and breaking changes

Tue, 20 Oct 2026 00:00:00 GMT

OpenSSL 4.0 removes engines, SSLv3, the SSLv2 Client Hello and c_rehash, makes ASN1_STRING opaque, adds const to many APIs, and changes hex dump output format.

pandas 2 to 3: Copy-on-Write, the str dtype and other breaking changes

Tue, 20 Oct 2026 00:00:00 GMT

pandas 3.0 makes Copy-on-Write the only mode, infers strings as the new str dtype, drops SettingWithCopyWarning and needs Python 3.11+. Shown side by side.

Python 3.14 to 3.15: what changes and what breaks

Tue, 20 Oct 2026 00:00:00 GMT

Upgrading from Python 3.14 to 3.15: UTF-8 becomes the default encoding, lazy imports and frozendict arrive, and sqlite3, argparse and base64 change behaviour.

OpenSSH 9.9 to 10.x: incompatible changes from 10.0 to 10.6

Tue, 20 Oct 2026 00:00:00 GMT

OpenSSH 10.x: DSA removed and modp DH off by default in sshd (10.0), agent sockets moved to ~/.ssh/agent (10.1), stricter user names on the command line (10.6).

Tailwind CSS v3 to v4: renamed utilities and breaking changes

Tue, 20 Oct 2026 00:00:00 GMT

Tailwind CSS v4 moves config into CSS with @import and @theme, splits the PostCSS plugin and CLI, renames shadow, blur and rounded scales, needs Safari 16.4.

Terraform 1.5 to 1.16: import, removed and check blocks, and what else changed

Tue, 20 Oct 2026 00:00:00 GMT

Config-driven refactoring came after Terraform 1.4: import and check blocks in 1.5, terraform test in 1.6, removed blocks in 1.7, ephemeral values in 1.10.

CSS :has() browser support

Tue, 20 Oct 2026 00:00:00 GMT

CSS :has() works in Chrome and Edge 105+, Safari 15.4+ and Firefox 121+, per MDN browser-compat-data. Feature-detect it with @supports selector(:has(a)).

Python versions supported by each Django version

Tue, 20 Oct 2026 00:00:00 GMT

Python support per Django release: 5.2 LTS runs on Python 3.10 to 3.14; Django 6.0, 6.1 and 6.2 need 3.12 to 3.14, and 6.1.3+ adds 3.15. From the Django FAQ.

Which codec in which container? MP4, WebM, MKV, MOV with FFmpeg

Tue, 20 Oct 2026 00:00:00 GMT

Codec and container compatibility tested with FFmpeg 9: H.264 and AAC fit MP4 and MKV but not WebM, which accepts only VP8, VP9, AV1, Vorbis and Opus.

Git features by version: switch, sparse-checkout, reftable

Tue, 20 Oct 2026 00:00:00 GMT

Which Git version introduced each feature: switch and restore 2.23, sparse-checkout 2.25, SHA-256 2.29, force-if-includes 2.30, zdiff3 2.35, reftable 2.45.

errcodex

AWS CLI: Unable to locate credentials. You can configure credentials by running aws configure

bash: command not found (exit status 127)

Certbot: Problem binding to port 80: Could not bind to IPv4 or IPv6

blocked by CORS policy: No 'Access-Control-Allow-Origin' header

ImproperlyConfigured: Requested setting …, but settings are not configured

Error: getaddrinfo ENOTFOUND (DNS lookup failed)

Docker Compose: service "web" depends on undefined service "db"

Error: listen EADDRINUSE: address already in use :::3000

ffmpeg: Unknown encoder 'libx264' (Encoder not found)

libx264: width not divisible by 2 / height not divisible by 2

find: paths must precede expression

error: failed to push some refs (rejected, fetch first)

fatal: not a git repository (or any of the parent directories): .git

fatal: refusing to merge unrelated histories

gpg: signing failed: Inappropriate ioctl for device

Helm: nil pointer evaluating interface {}.value

ImageMagick: not allowed by the security policy `PDF'

SyntaxError: Unexpected token '<', " Tue, 20 Oct 2026 00:00:00 GMT JSON.parse fails with Unexpected token '<' when the response is an HTML page, usually an error or login page, not JSON. Check the status and content type first.

kubectl: error converting YAML to JSON: mapping values are not allowed in this context

Hydration failed because the server rendered HTML didn't match the client

Error: Cannot find module '…' in Node.js

npm ERR! code ERESOLVE: unable to resolve dependency tree

ValueError: operands could not be broadcast together with shapes

unable to get local issuer certificate (OpenSSL verify error 20)

SettingWithCopyWarning: A value is trying to be set on a copy of a slice

pip error: externally-managed-environment (PEP 668)

ModuleNotFoundError: No module named '…'

torch.OutOfMemoryError: CUDA out of memory. Tried to allocate …

Each child in a list should have a unique "key" prop

Error: Too many re-renders. React limits the number of renders to prevent an infinite loop.

sed: -e expression #1, char N: unterminated `s' command

Spring Boot: Web server failed to start. Port 8080 was already in use.

Permission denied (publickey) with ssh

Terraform: Reference to undeclared input variable

Terraform: Error: Unsupported argument. An argument named "x" is not expected here

error TS5108: Option 'moduleResolution=node10' has been removed

python manage.py makemigrations and migrate: create and apply migrations

ffmpeg: extract audio from a video (with and without re-encoding)

git reset --soft HEAD~1: undo the last commit, keep the changes

Decode a JWT from the command line (header and payload)

Generate Kubernetes YAML with kubectl create --dry-run=client -o yaml

npm install a specific version: npm install package@version

openssl req -x509: create a self-signed certificate

pandas merge: join DataFrames on a key (inner, left, outer)

prettier --write and --check: format files from the command line

python -m json.tool: pretty-print and validate JSON

tar -xzf: extract a .tar.gz archive

terraform fmt -check and -recursive: format HCL files

set -euo pipefail: what each flag does in bash

curl -k (--insecure): skip TLS certificate verification

eslint --fix: automatically fix lint problems

uvicorn --reload: auto-restart FastAPI on code changes

ffmpeg -crf: constant rate factor for x264, x265 and AV1

git push --force-with-lease: a safer force push

helm --set, --set-string and -f: override chart values

Set-Cookie attributes: SameSite, Secure, HttpOnly, Max-Age

npm install --legacy-peer-deps: what it does and when to use it

openssl s_client -servername: test TLS with SNI

pandas read_csv low_memory and DtypeWarning: Columns have mixed types

terraform plan -out: save a plan and apply exactly that plan

Django ALLOWED_HOSTS: values, wildcards and DisallowedHost errors

Compose depends_on condition: service_healthy with a healthcheck

git config core.autocrlf: true, input or false

Strict-Transport-Security (HSTS): max-age, includeSubDomains, preload

ImageMagick policy.xml: resource limits and coder rules

package.json "type": "module": ES modules in Node.js

pandas display options: show all columns and rows (display.max_columns)

~/.ssh/config: Host, HostName, User, Port and IdentityFile

Terraform variable precedence: tfvars, auto.tfvars, -var and TF_VAR_

tsconfig moduleResolution: bundler, nodenext, node16

vite.config server.proxy: proxy API calls in the dev server

WireGuard AllowedIPs: routing and peer filtering explained

awk cheat sheet: fields, patterns, sums and printf

Bash cheat sheet: variables, tests, loops and expansions

CSS flexbox cheat sheet: container and item properties

Django manage.py cheat sheet: project, migrations, users, testing

FFmpeg cheat sheet: convert, cut, scale, extract and inspect

Git cheat sheet: everyday commands

kubectl cheat sheet: everyday Kubernetes commands

SyntaxError: Unexpected token '<', "
Tue, 20 Oct 2026 00:00:00 GMT
JSON.parse fails with Unexpected token '<' when the response is an HTML page, usually an error or login page, not JSON. Check the status and content type first.