wol

Wake-on-LAN sender for Windows, Linux, and macOS. Sends a magic packet to one or more MAC addresses over UDP broadcast, waking machines that have WoL enabled in their firmware.

Console application with single-file C17 implementation and no external dependencies.

C was chosen primarily as a fun exercise — I wanted a single-file, minimal-dependency tool for a personal project. Sharing it here in case someone else finds it useful.

Building

Pre-built binaries for Windows (x64), Linux (x86_64, aarch64), and macOS (arm64) are published automatically via GitHub Actions when a version tag is pushed. See the Releases page.

Build scripts are included in the repo for convenient local builds and are also used by GitHub Actions.

For manual build commands and compiler flags, see the header comment in wol.c.

Windows

Requires Visual Studio 2017 or later (or Build Tools for Visual Studio) with the Desktop development with C++ workload.

build.bat          # release build  →  wol.exe
build.bat debug    # debug build    →  wold.exe

If cl.exe is already on PATH (e.g. from a Developer Command Prompt) the script uses it directly; otherwise it locates the toolchain automatically via vswhere.exe.

Linux

Requires a C17-capable compiler (gcc or clang) on PATH.

chmod +x build.sh
./build.sh          # release build  →  wol  (statically linked)
./build.sh debug    # debug build    →  wold

macOS

Requires Xcode Command Line Tools (xcode-select --install).

chmod +x build.sh
./build.sh          # release build  →  wol
./build.sh debug    # debug build    →  wold

Self-test

Debug builds (the debug argument to either build script) define WOL_SELF_TEST, enabling a hidden --self-test flag:

wold --self-test

This runs the built-in unit tests for the MAC, port, and broadcast parsers, and exits 0 on pass, 1 on failure. It is not listed in --help and is not available in release builds.

VSCode

A .vscode directory is included with build tasks and two debug launch configurations for all three platforms. Use Ctrl+Shift+B to build and F5 to build and launch the debugger. Both shortcuts invoke the platform build scripts (build.bat or build.sh). On macOS, the debugger uses lldb instead of gdb.

Select the active configuration from the Run and Debug dropdown:

• Debug wol — launches with no arguments
• Debug self-test — launches with --self-test

Usage

wol [options] <MAC> [<MAC> ...]

Option	Default	Description
-b, --broadcast <addr>	255.255.255.255	Broadcast address: IPv4 or IPv4/prefix CIDR
-p, --port <port>	9	UDP destination port
-f, --file <path>	—	Read MAC addresses from a file
--version	—	Print version and exit
-h, --help	—	Show help text and exit
--	—	End option parsing; remaining arguments are MAC addresses

Option flags are case-insensitive (-B and -b are equivalent).

On Windows, /? is also accepted as a help flag.

Options must precede MAC address arguments. Use -- to end option parsing explicitly when needed.

Broadcast address: The default 255.255.255.255 is the limited broadcast and is not forwarded by routers. For machines on a specific subnet, use the subnet-directed broadcast (e.g. 192.168.1.255), or let wol compute it from any host address on the subnet using CIDR notation (e.g. -b 192.168.1.50/24).

Firewall: The UDP port must be open on the network path to the target. The target machine's own firewall is not a factor — WoL is handled by the NIC before the OS starts.

MAC address formats

All five common formats are accepted, upper- or lowercase:

AA:BB:CC:DD:EE:FF
AA-BB-CC-DD-EE-FF
AA.BB.CC.DD.EE.FF
AABBCCDDEEFF
AABB.CCDD.EEFF

MAC file format

One MAC address per line. Blank lines and lines where # is the first non-whitespace character are ignored. Both Unix (LF) and Windows (CRLF) line endings are handled.

# Server room
AA:BB:CC:DD:EE:FF
11-22-33-44-55-66

# Workstations
AABBCCDDEEFF

Examples

Wake a single machine on the limited broadcast:

wol AA:BB:CC:DD:EE:FF

Wake multiple machines on a specific subnet:

wol -b 192.168.1.255 AA:BB:CC:DD:EE:FF 11-22-33-44-55-66

Wake all machines listed in a file:

wol -f macs.txt -b 192.168.1.255

Mix file and command-line sources:

wol -f macs.txt -b 192.168.1.255 AABB.CCDD.EEFF

Wake machines on a subnet, letting wol compute the broadcast from a host address:

wol -b 192.168.1.50/24 AA:BB:CC:DD:EE:FF

Exit codes

Code	Meaning
0	All magic packets sent successfully
1	One or more packets failed, or invalid input

License

Copyright 2026 Jens Bråkenhielm. Licensed under the MIT License.