errcodex

apt: Could not get lock /var/lib/dpkg/lock-frontend

Tue, 20 Oct 2026 00:00:00 GMT

apt fails with Could not get lock /var/lib/dpkg/lock-frontend while another apt, dpkg or unattended-upgrades runs. Wait for it; never delete the lock.

apt: E: Unable to locate package

Tue, 20 Oct 2026 00:00:00 GMT

apt install fails with E: Unable to locate package when package lists are outdated, the name is wrong, or the package is in a repository that is not enabled.

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.

Caddy: Caddyfile:2: unrecognized directive

Tue, 20 Oct 2026 00:00:00 GMT

Caddy fails with Caddyfile:N: unrecognized directive for a misspelled directive, a plugin missing from the binary, or a global option inside a site block.

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.

CMake: Could not find a package configuration file provided by "Foo"

Tue, 20 Oct 2026 00:00:00 GMT

find_package(Foo REQUIRED) fails when CMake finds neither FindFoo.cmake nor FooConfig.cmake. Install the dev package, or point CMAKE_PREFIX_PATH at it.

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.

GitHub Actions: Error: Process completed with exit code 1

Tue, 20 Oct 2026 00:00:00 GMT

Process completed with exit code 1 means the last command of a run step failed. Scroll up to the first error in the log; bash -e stops at that command.

GitHub Actions: Resource not accessible by integration (HTTP 403)

Tue, 20 Oct 2026 00:00:00 GMT

A workflow gets 403 Resource not accessible by integration when GITHUB_TOKEN lacks a scope like pull-requests: write, or the run is for a fork pull request.

GitLab CI: This job is stuck because the project doesn't have any runners online assigned to it

Tue, 20 Oct 2026 00:00:00 GMT

GitLab marks a job stuck when no online runner can take it: no runner registered, runners offline or paused, or job tags that match no runner. Find which.

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.

make: Makefile:2: *** missing separator. Stop.

Tue, 20 Oct 2026 00:00:00 GMT

GNU make stops with missing separator when a recipe line starts with spaces instead of a tab. Indent recipes with a real tab, or set .RECIPEPREFIX instead.

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.

nginx: [emerg] host not found in upstream "backend"

Tue, 20 Oct 2026 00:00:00 GMT

nginx fails with host not found in upstream when a proxy_pass or upstream hostname does not resolve at startup, common with Docker service names. Fixes.

nginx: "proxy_pass" cannot have URI part in location given by regular expression

Tue, 20 Oct 2026 00:00:00 GMT

nginx rejects proxy_pass http://host/path/ inside a regex location, named location, if or limit_except. Remove the URI part and change the path with rewrite.

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.

pacman: invalid or corrupted package (PGP signature)

Tue, 20 Oct 2026 00:00:00 GMT

pacman stops with invalid or corrupted package (PGP signature) when archlinux-keyring is older than a packager's key. Update the keyring first, then the system.

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.

PostgreSQL: duplicate key value violates unique constraint

Tue, 20 Oct 2026 00:00:00 GMT

PostgreSQL raises duplicate key value violates unique constraint (SQLSTATE 23505) when a key repeats. Read the DETAIL line, then upsert or reset the sequence.

PostgreSQL: ERROR: relation "users" does not exist

Tue, 20 Oct 2026 00:00:00 GMT

PostgreSQL reports relation does not exist (42P01) when a table is missing, in a schema outside the search_path, or was created with a quoted mixed-case name.

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.

SQLite: database is locked (SQLITE_BUSY)

Tue, 20 Oct 2026 00:00:00 GMT

SQLite returns database is locked (SQLITE_BUSY) when another connection holds a write lock. Fix it with a busy timeout, WAL mode, and short write transactions.

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.

Vim: E37: No write since last change (add ! to override)

Tue, 20 Oct 2026 00:00:00 GMT

Vim shows E37: No write since last change when you quit or open another file with unsaved edits. Save with :wq, discard with :q!, or set the hidden option.

List installed packages with apt and dpkg

Tue, 20 Oct 2026 00:00:00 GMT

List installed packages on Debian and Ubuntu with apt list --installed, show manually installed ones with apt-mark showmanual, and export the list to reuse.

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.

actionlint: lint GitHub Actions workflows before you push

Tue, 20 Oct 2026 00:00:00 GMT

actionlint checks .github/workflows files for syntax errors, bad expressions, untrusted input in run scripts, deprecated commands and outdated actions.

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.

nginx -t: test the configuration before reloading

Tue, 20 Oct 2026 00:00:00 GMT

nginx -t checks the configuration syntax and the files it references without touching the running server; nginx -T also prints the full merged config.

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.

PostgreSQL upsert: INSERT … ON CONFLICT DO UPDATE and MERGE

Tue, 20 Oct 2026 00:00:00 GMT

Insert a row or update it if the key exists with INSERT ... ON CONFLICT (id) DO UPDATE SET col = EXCLUDED.col, skip duplicates with DO NOTHING, or use MERGE.

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.

Vim search and replace: :%s/old/new/g and its flags

Tue, 20 Oct 2026 00:00:00 GMT

Replace text in Vim with :%s/old/new/g; add c to confirm each change and i to ignore case, limit it to a range or a selection, and match whole words only.

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.

caddy fmt --overwrite and --diff: format a Caddyfile

Tue, 20 Oct 2026 00:00:00 GMT

caddy fmt prints a Caddyfile in canonical style with tabs; --overwrite rewrites the file in place, --diff shows the changes, and it exits non-zero if needed.

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.

GitHub Actions shell: bash vs the default: -e and pipefail

Tue, 20 Oct 2026 00:00:00 GMT

Without shell:, Linux run steps use bash -e and miss failures inside pipelines. shell: bash runs bash --noprofile --norc -eo pipefail and catches them.

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.

redis-cli --scan --pattern: list keys without blocking Redis

Tue, 20 Oct 2026 00:00:00 GMT

redis-cli --scan --pattern 'user:*' walks keys with SCAN in small batches instead of KEYS, which blocks the server. Counting, type filters, deleting by pattern.

JavaScript regex flags: g, i, m, s, u, v, y and d

Tue, 20 Oct 2026 00:00:00 GMT

What each JavaScript RegExp flag does: g finds all matches, i ignores case, m works per line, s lets . match newlines, u and v add Unicode, plus y and d.

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.

winget install --silent --accept-package-agreements: unattended installs

Tue, 20 Oct 2026 00:00:00 GMT

Install Windows apps without prompts: winget install --id Git.Git -e --silent --accept-package-agreements --accept-source-agreements in setup scripts.

apt sources in deb822 format: .sources files and Signed-By

Tue, 20 Oct 2026 00:00:00 GMT

Debian 12+ and Ubuntu 24.04 describe apt repositories in .sources files (deb822 format). The Types, URIs, Suites, Components and Signed-By fields explained.

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.

GitHub Actions concurrency: cancel-in-progress for older runs

Tue, 20 Oct 2026 00:00:00 GMT

concurrency with a group per workflow and branch plus cancel-in-progress: true cancels the older run when a new commit is pushed to the same branch or PR.

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.

nginx proxy_pass with and without a trailing slash

Tue, 20 Oct 2026 00:00:00 GMT

proxy_pass http://app without a path forwards the full URI; with a path like http://app/ nginx replaces the matched location prefix. Real requests shown.

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.

SQLite PRAGMA journal_mode=WAL: concurrent readers and a writer

Tue, 20 Oct 2026 00:00:00 GMT

PRAGMA journal_mode=WAL makes SQLite write changes to a -wal file, so readers keep working while one connection writes. It is stored in the database file.

~/.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.

errcodex

apt: Could not get lock /var/lib/dpkg/lock-frontend

apt: E: Unable to locate package

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

bash: command not found (exit status 127)

Caddy: Caddyfile:2: unrecognized directive

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

CMake: Could not find a package configuration file provided by "Foo"

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

GitHub Actions: Error: Process completed with exit code 1

GitHub Actions: Resource not accessible by integration (HTTP 403)

GitLab CI: This job is stuck because the project doesn't have any runners online assigned to it

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

make: Makefile:2: *** missing separator. Stop.

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

nginx: [emerg] host not found in upstream "backend"

nginx: "proxy_pass" cannot have URI part in location given by regular expression

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)

pacman: invalid or corrupted package (PGP signature)

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

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

PostgreSQL: duplicate key value violates unique constraint

PostgreSQL: ERROR: relation "users" does not exist

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.

SQLite: database is locked (SQLITE_BUSY)

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

Vim: E37: No write since last change (add ! to override)

List installed packages with apt and dpkg

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

actionlint: lint GitHub Actions workflows before you push

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

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

nginx -t: test the configuration before reloading

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)

PostgreSQL upsert: INSERT … ON CONFLICT DO UPDATE and MERGE

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

Vim search and replace: :%s/old/new/g and its flags

set -euo pipefail: what each flag does in bash

caddy fmt --overwrite and --diff: format a Caddyfile

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

GitHub Actions shell: bash vs the default: -e and pipefail

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

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.