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croc
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About

croc is a tool that allows any two computers to simply and securely transfer files and folders. AFAIK, croc is the only CLI file-transfer tool that does all of the following:

  • Allows any two computers to transfer data (using a relay)
  • Provides end-to-end encryption (using PAKE)
  • Enables easy cross-platform transfers (Windows, Linux, Mac)
  • Allows multiple file transfers
  • Allows resuming transfers that are interrupted
  • No need for local server or port-forwarding
  • IPv6-first with IPv4 fallback
  • Can use a proxy, like Tor

For more information about croc, see my blog post or read a recent interview I did.

Example

Install

You can download the latest release for your system, or install a release from the command-line:

curl https://getcroc.schollz.com | bash

On macOS

Using Homebrew:

brew install croc

Using MacPorts:

sudo port selfupdate
sudo port install croc

On Windows

You can install the latest release with Scoop, Chocolatey, or Winget:

scoop install croc
choco install croc
winget install schollz.croc

Using nix-env

You can install the latest release with Nix:

nix-env -i croc

On NixOS

You can add this to your configuration.nix:

environment.systemPackages = [
  pkgs.croc
];

On Alpine Linux

First, install dependencies:

apk add bash coreutils
wget -qO- https://getcroc.schollz.com | bash

On Arch Linux

Install with pacman:

pacman -S croc

On Fedora

Install with dnf:

dnf install croc

On Gentoo

Install with portage:

emerge net-misc/croc

On Termux

Install with pkg:

pkg install croc

On FreeBSD

Install with pkg:

pkg install croc

On Linux, macOS, and Windows via Conda

You can install from conda-forge globally with pixi:

pixi global install croc

Or install into a particular environment with conda:

conda install --channel conda-forge croc

On Linux, macOS via Docker

Add the following one-liner function to your ~/.profile (works with any POSIX-compliant shell):

croc() { [ $# -eq 0 ] && set -- ""; mkdir -p "$HOME/.config/croc"; docker run --rm -it --user "$(id -u):$(id -g)" -v "$(pwd):/c" -v "$HOME/.config/croc:/.config/croc" -w /c -e CROC_SECRET docker.io/schollz/croc "$@"; }

You can also just paste it in the terminal for current session. On first run Docker will pull the image. croc via Docker will only work within the current directory and its subdirectories.

Build from Source

If you prefer, you can install Go and build from source (requires Go 1.22+):

go install github.com/schollz/croc/v10@latest

On Android

There is a 3rd-party F-Droid app available to download.

Usage

To send a file, simply do:

$ croc send [file(s)-or-folder]
Sending 'file-or-folder' (X MB)
Code is: code-phrase

Then, to receive the file (or folder) on another computer, run:

croc code-phrase

The code phrase is used to establish password-authenticated key agreement (PAKE) which generates a secret key for the sender and recipient to use for end-to-end encryption.

Customizations & Options

Using croc on Linux or macOS

On Linux and macOS, the sending and receiving process is slightly different to avoid leaking the secret via the process name. You will need to run croc with the secret as an environment variable. For example, to receive with the secret ***:

CROC_SECRET=*** croc

For single-user systems, the default behavior can be permanently enabled by running:

croc --classic

Custom Code Phrase

You can send with your own code phrase (must be more than 6 characters):

croc send --code [code-phrase] [file(s)-or-folder]

Allow Overwriting Without Prompt

To automatically overwrite files without prompting, use the --overwrite flag:

croc --yes --overwrite <code>

Excluding Folders

To exclude folders from being sent, use the --exclude flag with comma-delimited exclusions:

croc send --exclude "node_modules,.venv" [folder]

Use Pipes - stdin and stdout

You can pipe to croc:

cat [filename] | croc send

To receive the file to stdout, you can use:

croc --yes [code-phrase] > out

Send Text

To send URLs or short text, use:

croc send --text "hello world"

Send Multiple Files

You can send multiple files directly by listing the files and/or folders:

croc send [file1] [file2] [file3] [folder1] [folder2]

Show QR Code

To show QR code (for mobile devices), use:

croc send --qr [file(s)-or-folder]

Use a Proxy

You can send files via a proxy by adding --socks5:

croc --socks5 "127.0.0.1:9050" send SOMEFILE

Change Encryption Curve

To choose a different elliptic curve for encryption, use the --curve flag:

croc --curve p521 <codephrase>

Change Hash Algorithm

For faster hashing, use the imohash algorithm:

croc send --hash imohash SOMEFILE

Clipboard Options

By default, the code phrase is copied to your clipboard. To disable this:

croc --disable-clipboard send [filename]

To copy the full command with the secret as an environment variable (useful on Linux/macOS):

croc --extended-clipboard send [filename]

This copies the full command like CROC_SECRET="code-phrase" croc (including any relay/pass flags).

Quiet Mode

To suppress all output (useful for scripts and automation):

croc --quiet send [filename]

Self-host Relay

You can run your own relay:

croc relay

By default, it uses TCP ports 9009-9013. You can customize the ports (e.g., croc relay --ports 1111,1112), but at least 2 ports are required.

To send files using your relay:

croc --relay "myrelay.example.com:9009" send [filename]

Federated Relay Pool (Main + Community Nodes)

You can run a pool-based relay network where:

  • a main node provides relay discovery APIs,
  • community relay nodes register themselves,
  • senders and receivers automatically discover relays from the pool.

Pool endpoints:

  • POST /register
  • POST /heartbeat
  • POST /relays

There are two common deployment types.

Type 1: Public Pool (Built-in Defaults)

Built-in defaults:

  • Pool URL: http://croc.schollz.com:9000
  • Relay password default: pass123

Use these commands:

# Community relay node joins default public pool
# Note: for relay node mode, place flags before the trailing "node" argument
croc relay node

# Sender (default pool is used automatically)
croc send log.txt

# Receiver (default pool is used automatically)
croc RELAYID-PIN-WORD-WORD-WORD
Type 2: Custom Pool

Use these commands:

# 1) Start main node (pool API)
croc relay main --listen 0.0.0.0:9000

# 2) Start a community relay node and register to the pool
# Note: for relay node mode, place flags before the trailing "node" argument
croc relay --pool http://POOL_IP:9000 --pass YOUR_POOL_PASS --ports 9009,9010,9011,9012,9013 node

# 3) Sender uses pool discovery
croc --pool http://POOL_IP:9000 send log.txt

# 4) Receiver uses the transfer code from sender
croc --pool http://POOL_IP:9000 RELAYID-PIN-WORD-WORD-WORD

Example transfer code format:

12ca-1571-friday-brown-fluid

Notes:

  • If --pool is omitted, croc uses the built-in default pool URL.
  • If pool discovery fails, croc falls back to legacy relay behavior.
  • Legacy direct relay mode with --relay continues to work unchanged.

Self-host Relay with Docker

You can also run a relay with Docker:

docker run -d -p 9009-9013:9009-9013 -e CROC_PASS='YOURPASSWORD' docker.io/schollz/croc

To send files using your custom relay:

croc --pass YOURPASSWORD --relay "myreal.example.com:9009" send [filename]

Acknowledgements

croc has evolved through many iterations, and I am thankful for the contributions! Special thanks to:

And many more!