Environment Variables Reference

Complete reference of all environment variables, their types, defaults, and validation rules.

Overview

All environment variables are validated on startup using Zod. Invalid values cause the server to fail with a descriptive error message. None of the variables are strictly required - all have sensible defaults for local development. For Docker deployments, DATA_DIR and UPLOADS_DIR are set automatically in the image.

v2.0.0 Breaking Change

All file-related variables have been renamed with a FILE_ prefix (e.g. MAX_FILE_SIZE -> FILE_MAX_SIZE). Old names are no longer supported. See the migration table below.

Migration from v1.x

Old Name (v1)	New Name (v2)
MAX_FILE_SIZE	FILE_MAX_SIZE
MAX_FILES_PER_UPLOAD	FILE_MAX_FILES_PER_UPLOAD
EXPIRE_OPTIONS_SEC	FILE_EXPIRE_OPTIONS_SEC
DEFAULT_EXPIRE_SEC	FILE_DEFAULT_EXPIRE_SEC
DOWNLOAD_OPTIONS	FILE_DOWNLOAD_OPTIONS
DEFAULT_DOWNLOAD	FILE_DEFAULT_DOWNLOAD
UPLOAD_QUOTA_BYTES	FILE_UPLOAD_QUOTA_BYTES
UPLOAD_QUOTA_WINDOW	FILE_UPLOAD_QUOTA_WINDOW

Variables

PORT

Property	Value
Required	No
Type	Integer
Default	3000
Range	1 - 65535
Description	Server listening port

HOST

Property	Value
Required	No
Type	String
Default	0.0.0.0
Description	Server bind address

BASE_URL

Property	Value
Required	Yes
Type	URL
Default	-
Description	Public URL of the instance. Trailing slashes are stripped automatically.

DATA_DIR

Property	Value
Required	No
Type	String (path)
Default	./data
Description	Directory for the database. The SQLite DB is stored at DATA_DIR/db/skysend.db.

UPLOADS_DIR

Property	Value
Required	No
Type	String (path)
Default	DATA_DIR/uploads
Description	Directory for encrypted upload files. Falls back to DATA_DIR/uploads if not set. In Docker, defaults to /uploads for separate volume mounting.

FILE_MAX_SIZE

Property	Value
Required	No
Type	Byte size string
Default	2GB
Description	Maximum upload size. Supports: B, KB, MB, GB

FILE_MAX_FILES_PER_UPLOAD

Property	Value
Required	No
Type	Integer
Default	32
Range	>= 1
Description	Maximum files per multi-file upload

FILE_EXPIRE_OPTIONS_SEC

Property	Value
Required	No
Type	Comma-separated integers
Default	300,3600,86400,604800
Description	Selectable expiry times in seconds for file uploads

FILE_DEFAULT_EXPIRE_SEC

Property	Value
Required	No
Type	Integer
Default	86400
Validation	Must be one of FILE_EXPIRE_OPTIONS_SEC
Description	Default expiry time for file uploads

FILE_DOWNLOAD_OPTIONS

Property	Value
Required	No
Type	Comma-separated integers
Default	1,2,3,4,5,10,20,50,100
Description	Selectable download limits for file uploads

FILE_DEFAULT_DOWNLOAD

Property	Value
Required	No
Type	Integer
Default	1
Validation	Must be one of FILE_DOWNLOAD_OPTIONS
Description	Default download limit for file uploads

FILE_UPLOAD_QUOTA_BYTES

Property	Value
Required	No
Type	Integer (bytes) or byte size string
Default	0 (disabled)
Description	Maximum upload volume per user per window. 0 disables quotas. Supports raw bytes or units: B, KB, MB, GB

FILE_UPLOAD_QUOTA_WINDOW

Property	Value
Required	No
Type	Integer (seconds)
Default	86400
Description	Quota time window for file upload quotas

FILE_UPLOAD_CONCURRENT_CHUNKS

Property	Value
Required	No
Type	Integer
Default	3
Range	1 - 20
Description	Number of parallel chunk uploads per session. Increase to improve upload speed in Chromium browsers through HTTP/2 reverse proxies. The value is exposed via /api/config and read by the client upload worker

FILE_UPLOAD_SPEED_LIMIT

Property	Value
Required	No
Type	Integer (bytes/s) or byte size string
Default	0 (unlimited)
Description	Maximum upload throughput per session. 0 disables the limit. Supports raw bytes or units: B, KB, MB, GB (e.g. 100MB for 100 MB/s). The server delays chunk responses to enforce the limit

FILE_UPLOAD_WS

Property	Value
Required	No
Type	Boolean
Default	true
Description	Enable the WebSocket upload transport at /api/upload/ws. Clients prefer WebSocket and fall back to HTTP chunked uploads automatically if the handshake fails. Set to false to disable the endpoint entirely

FILE_UPLOAD_WS_MAX_BUFFER

Property	Value
Required	No
Type	Byte size string
Default	16MB
Minimum	1MB
Description	Maximum bytes the server buffers in memory per WebSocket upload session before aborting it with close code 1009. Only relevant when the storage backend falls behind the incoming frame rate

NOTE_MAX_SIZE

Property	Value
Required	No
Type	Byte size string
Default	1MB
Description	Maximum plaintext note size before encryption. Supports: B, KB, MB, GB

NOTE_EXPIRE_OPTIONS_SEC

Property	Value
Required	No
Type	Comma-separated integers
Default	300,3600,86400,604800
Description	Selectable expiry times in seconds for notes

NOTE_DEFAULT_EXPIRE_SEC

Property	Value
Required	No
Type	Integer
Default	86400
Validation	Must be one of NOTE_EXPIRE_OPTIONS_SEC
Description	Default expiry time for notes

NOTE_VIEW_OPTIONS

Property	Value
Required	No
Type	Comma-separated integers
Default	0,1,2,3,5,10,20,50,100
Description	Selectable view limits for notes. 0 means unlimited views (the note expires only by time).

NOTE_DEFAULT_VIEWS

Property	Value
Required	No
Type	Integer
Default	0
Validation	Must be one of NOTE_VIEW_OPTIONS
Description	Default view limit for notes. 0 means unlimited views (expires only by time). 1 means burn-after-reading.

ENABLED_SERVICES

Property	Value
Required	No
Type	Comma-separated list
Default	file,note
Allowed values	file, note
Validation	At least one service must be enabled
Description	Controls which services are available. Set to file for file sharing only, note for notes only, or file,note for both. Disabled services return HTTP 403 and their UI tabs are hidden.

CLEANUP_INTERVAL

Property	Value
Required	No
Type	Integer (seconds)
Default	60
Description	Interval for the automatic cleanup job

CUSTOM_TITLE

Property	Value
Required	No
Type	String
Default	SkySend
Description	Displayed site title

RATE_LIMIT_WINDOW

Property	Value
Required	No
Type	Integer (milliseconds)
Default	60000
Description	Rate limit sliding window size

RATE_LIMIT_MAX

Property	Value
Required	No
Type	Integer
Default	60
Description	Maximum requests per window per IP

TRUST_PROXY

Property	Value
Required	No
Type	Boolean
Default	false
Description	Trust X-Forwarded-For / X-Real-IP headers from reverse proxy

CUSTOM_COLOR

Property	Value
Required	No
Type	Hex color code
Default	- (uses default theme)
Validation	Must match 6 hex digits, e.g. 46c89d (the # prefix is optional)
Description	Primary brand color for the web UI. Overrides the default primary color on buttons, links, icons, and other accented elements.

CUSTOM_LOGO

Property	Value
Required	No
Type	URL or absolute path
Default	- (uses built-in SkySend logo)
Validation	Must be a URL (https://...) or an absolute path (/...)
Description	URL or path to a custom logo image displayed in the web app header and as favicon. For local files, place them in the public/ directory (e.g. public/custom-logo.svg) and reference as /custom-logo.svg.

CUSTOM_PRIVACY

Property	Value
Required	No
Type	URL
Default	- (not shown in footer)
Validation	Must be a valid URL (https://...)
Description	URL to your privacy policy page. When set, a "Privacy Policy" link is displayed in the footer.

CUSTOM_LEGAL

Property	Value
Required	No
Type	URL
Default	- (not shown in footer)
Validation	Must be a valid URL (https://...)
Description	URL to your legal notice / impressum page. When set, a "Legal Notice" link is displayed in the footer.

CUSTOM_LINK_URL

Property	Value
Required	No
Type	URL
Default	- (not shown in footer)
Validation	Must be a valid URL (https://...)
Description	URL for a custom footer link. Must be used together with CUSTOM_LINK_NAME.

CUSTOM_LINK_NAME

Property	Value
Required	No
Type	String
Default	-
Validation	Max 50 characters
Description	Display text for the custom footer link defined by CUSTOM_LINK_URL. Both variables must be set for the link to appear.

STORAGE_BACKEND

Property	Value
Required	No
Type	Enum
Default	filesystem
Allowed values	filesystem, s3
Description	Storage backend for encrypted upload files. filesystem stores files on the local disk. s3 uses S3-compatible object storage with presigned download URLs.

S3_BUCKET

Property	Value
Required	When STORAGE_BACKEND=s3
Type	String
Default	-
Description	S3 bucket name for upload storage

S3_REGION

Property	Value
Required	When STORAGE_BACKEND=s3
Type	String
Default	-
Description	S3 region (e.g. eu-central-1, auto for R2)

S3_ENDPOINT

Property	Value
Required	No (required for non-AWS providers)
Type	URL
Default	- (uses AWS S3 default)
Validation	Must be a valid URL
Description	Custom S3 endpoint for non-AWS providers. Examples: https://<id>.r2.cloudflarestorage.com (R2), https://fsn1.your-objectstorage.com (Hetzner), https://minio.example.com:9000 (MinIO)

S3_ACCESS_KEY

Property	Value
Required	When STORAGE_BACKEND=s3
Type	String
Default	-
Description	S3 access key ID

S3_SECRET_KEY

Property	Value
Required	When STORAGE_BACKEND=s3
Type	String
Default	-
Description	S3 secret access key

S3_FORCE_PATH_STYLE

Property	Value
Required	No
Type	Boolean
Default	false
Description	Use path-style URLs (https://endpoint/bucket/key) instead of virtual-hosted-style (https://bucket.endpoint/key). Required for MinIO, Garage, and some self-hosted S3 providers.

S3_PRESIGNED_EXPIRY

Property	Value
Required	No
Type	Integer (seconds)
Default	300
Description	TTL for presigned download URLs. S3 validates the signature only at the start of the download - a download that starts within the TTL will complete even if it takes longer.

S3_PART_SIZE

Property	Value
Required	No
Type	Byte size (e.g. 25MB, 50MB)
Default	25MB
Minimum	5MB
Maximum	5GB
Description	Size of each S3 multipart upload part. Larger values reduce the number of API round-trips but increase memory usage per upload. The S3 protocol requires at least 5MB per part (except the final part). Increase this if you have high bandwidth and want faster uploads.

S3_CONCURRENCY

Property	Value
Required	No
Type	Integer
Default	4
Range	1-16
Description	Number of S3 multipart upload parts uploaded in parallel. Higher values improve throughput by overlapping network transfers, but increase memory and bandwidth usage. Good starting values: 4 for most setups, 8 for high-bandwidth connections.

PUID

Property	Value
Required	No
Type	Integer
Default	1001
Docker only	Yes
Description	User ID the container process runs as. Handled by the entrypoint script.

PGID

Property	Value
Required	No
Type	Integer
Default	1001
Docker only	Yes
Description	Group ID the container process runs as. Handled by the entrypoint script.

Validation Rules

• ENABLED_SERVICES must contain at least one of file or note
• FILE_DEFAULT_EXPIRE_SEC must be included in FILE_EXPIRE_OPTIONS_SEC (only validated when file service is enabled)
• FILE_DEFAULT_DOWNLOAD must be included in FILE_DOWNLOAD_OPTIONS (only validated when file service is enabled)
• NOTE_DEFAULT_EXPIRE_SEC must be included in NOTE_EXPIRE_OPTIONS_SEC (only validated when note service is enabled)
• NOTE_DEFAULT_VIEWS must be included in NOTE_VIEW_OPTIONS (only validated when note service is enabled)
• When STORAGE_BACKEND=s3, S3_BUCKET, S3_REGION, S3_ACCESS_KEY, and S3_SECRET_KEY are required
• S3_ENDPOINT must be a valid URL when set
• PORT must be between 1 and 65535
• FILE_MAX_SIZE must be a valid byte size string with a recognized unit
• NOTE_MAX_SIZE must be a valid byte size string with a recognized unit
• BASE_URL must be a valid URL
• CUSTOM_COLOR must be a 6-digit hex color code (with or without # prefix)
• CUSTOM_LOGO must be a URL or an absolute path starting with /
• CUSTOM_PRIVACY must be a valid URL
• CUSTOM_LEGAL must be a valid URL
• CUSTOM_LINK_URL must be a valid URL
• CUSTOM_LINK_NAME must be at most 50 characters