k2 Client Usage

The k2 command-line client runs on Linux (x86_64 / arm64) and macOS (Intel / Apple Silicon).

If you prefer a graphical interface, the Kaitu desktop client has k2 built in — no separate installation needed.

Installation

curl -fsSL https://dl.k2.52j.me/install.sh | sudo sh -s k2

Verify:

k2 --version

Connecting

Pass the k2v5 URL printed by your server to k2 up:

sudo k2 up k2v5://abc123:tok456@203.0.113.5:443?ech=AEX0...&pin=sha256:...

After connecting, system routing is updated automatically and all traffic flows through the tunnel.

Common Commands

# Connect (TUN mode — requires root)
sudo k2 up k2v5://...

# Connect (proxy mode — no root required)
k2 up --mode proxy k2v5://...

# Check connection status
k2 status

# Disconnect
sudo k2 down

# Show version
k2 --version

# Show help
k2 --help

Connection Modes

TUN Mode (Default)

TUN mode creates a virtual network interface that captures all system traffic, acting as a global proxy. Root privileges are required.

sudo k2 up k2v5://...

Proxy Mode

Proxy mode starts a SOCKS5 proxy at 127.0.0.1:1080 without modifying system routes. Suitable when root access is unavailable or only specific applications need proxying.

k2 up --mode proxy k2v5://...

Configure your system or application to use socks5://127.0.0.1:1080.

Configuration File

For environments where passing a URL is inconvenient, generate a config file:

k2 demo-config > client.yml

Connect using the config file:

sudo k2 up --config client.yml

TLS Fingerprint Selection

k2 supports multiple TLS fingerprints to blend with different browser traffic:

# Chrome (default)
sudo k2 up k2v5://...?fp=chrome

# Firefox
sudo k2 up k2v5://...?fp=firefox

# Safari
sudo k2 up k2v5://...?fp=safari

# Random (rotates fingerprint periodically)
sudo k2 up k2v5://...?fp=random

Status Output

Example k2 status output:

State:     connected
Server:    203.0.113.5:443
Protocol:  k2v5 (QUIC/H3)
Latency:   28ms
Uploaded:  1.2 GB
Downloaded: 8.4 GB
Uptime:    2h 15m

When QUIC is unavailable, the protocol automatically switches to k2v5 (TCP-WS) with no manual intervention needed.

Uninstall

sudo k2 down
sudo rm /usr/local/bin/k2

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Next: Protocol Technical Details to understand how k2v5 works under the hood.