> ## Documentation Index > Fetch the complete documentation index at: https://docs.specterops.io/llms.txt > Use this file to discover all available pages before exploring further. # Custom Build > Building custom Merlin Agent binaries with specific configurations This section details how to build custom build a Merlin Agent using the Make file. Merlin is distributed with pre-compiled agent binaries for all major platforms in the `data/bin` directory. ## Basic The provided Make file can be used to build a new agent from **source**. It is recommended that you first use `go get github.com/Ne0nd0g/merlin-agent` to pull a copy of the Merlin source code to the host. Move into the Merlin root directory where the Make file is located. * Windows agent: `make windows` * Linux agent: `make linux` * macOS agent: `make darwin` * MIPS agent: `make mips` * ARM agent: `make arm` ## Advanced Use the provided Make file to build a Merlin Agent with hard coded values. This removes the need for an operator to use commandline arguments and allows the Agent to simply be executed. The table below shows configurable compile options View the [Listeners](/cli/listeners) page for additional information on specific listener configurable options. | Option | Description | Notes | | ---------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------- | | ADDR | The interface and port for peer-to-peer agents to bind or connect to | Overrides the `-addr` flag | | AUTH | The method of Agent authentication to the server | Overrides the `-auth` flag | | HEADERS | Comma Separated list of HTTP headers to send with every HTTP request. | Overrides the `-headers` flag | | HOST | HTTP Host header | Overrides the `-host` commandline flag | | HTTPCLIENT | The type of HTTP client (or driver) to use (e.g., go or winhttp) | Overrides the `-http-client` commandline flag | | JA3 | JA3 signature string (not the MD5 hash) | Overrides the `-ja3` commandline flag | | KILLDATE | The date, as a Unix EPOCH timestamp, that the agent will quit running | Overrides the `-killdate` commandline flag | | LISTENER | The UUID of the listener that the peer-to-peer agent is configured to communicate with. | Overrides the `-listener` flag | | RETRY | The maximum amount of failed checkins before the agent will quit running | Overrides the `-maxretry` commandline flag | | PAD | The maximum amount of data that will be randomly selected and appended to every message | Overrides the `-padding` commandline flag | | PARROT | Configure the HTTP client's TLS configuration to match the provided browser string | Overrides the `-parrot` commandline flag | | PROTO | Protocol for the agent to connect with \[https (HTTP/1.1), http (HTTP/1.1 Clear-Text), h2 (HTTP/2), h2c (HTTP/2 Clear-Text), http3 (QUIC or HTTP/3.0)] (default 'h2') | Overrides the `-proto` commandline flag | | PROXY | Hardcoded proxy to use for http/1.1 traffic only that will override host configuration | Overrides the `-proxy` commandline flag | | PSK | Pre-Shared Key used to encrypt initial communications (default "merlin") | Overrides the `-psk` commandline flag | | SECURE | Require TLS certificate validation for HTTP communications | Overrides the `-secure` commandline flag | | SKEW | Amount of skew, or variance, between agent checkins | Overrides the `-skew` commandline flag | | SLEEP | The amount of time the Agent will sleep between checkins Must use golang time notation (e.g., `10s` for ten seconds) | Overrides the `-sleep` command line flag | | TAGS | Comma separated list of Go build tags for compiling the agent | Overrides Go's `-tags` commandline flag | | TRANSFORMS | Ordered CSV of transforms to construct a message with | Overrides the `-transforms` commandline flag | | URL | Full URL for agent to connect to (default "[https://127.0.0.1:443](https://127.0.0.1:443)") | Overrides the `-url` commandline flag | | USERAGENT | The HTTP User-Agent header string that Agent will use while sending traffic | Overrides the `-useragent` commandline flag | An example of creating a new Linux HTTP agent that is using domain fronting through `https://merlin.com/c2endpoint.php` using a PSK of `SecurePassword1`: `make linux URL=https://merlin.com:443/c2endpoint.php HOST=myendpoint.azureedge.net PROTO=https PSK=SecurePassword1` ## Build Tags By default, the Merlin Agent is built with all available features and components compiled in. Build tags can be used to control what features are compiled into the agent to reduce the size of the binary or to restrict the agent's capabilities. When any build tag is included, the agent will ONLY include that feature and nothing else. For example, if ONLY the `http` tag is provided, the SMB, TCP, and UDP clients will not be included. The following build tags are available: | Tag | Description | Notes | | ------ | ------------------------------------- | -------------------------------------------------------------------------------------------- | | http | Include ALL HTTP clients | | | http1 | Include Go's built-in HTTP/1.1 client | Used with the `-proto` flag's `http` & `https` options | | http2 | Include the HTTP/2 client | Used with the `-proto` flag's `http2` & `h2c` options | | http3 | Include the HTTP/3 UDP client | Used with the `-proto` flag's `http3` option | | mythic | Include the Mythic C2 client | Used with the Mythic C2 Framework's [http](https://github.com/MythicC2Profiles/http) profile | | smb | Include the SMB client | Used with the `-proto` flag's `smb-bind` & `smb-reverse` options | | tcp | Include the TCP client | Used with the `-proto` flag's `tcp-bind` & `tcp-reverse` options | | udp | Include the UDP client | Used with the `-proto` flag's `udp-bind` & `udp-reverse` options | ## Windows Agent The Windows Merlin Agent executable is compiled as a GUI application instead of console application. The Merlin Agent does not have a GUI component. The reason this is used is so that the Merlin Agent window disappears after it is executed. This behavior is intentional so that the user will not see the application window. This is done with the LDFLAGS when building the agent using the `-H=windowsgui` option as shown [here](https://golang.org/cmd/link/) This causes problems when a user **WANTS** to see the Merlin Agent verbose or debug output. To view Merlin verbose/debug output, use the Makefile `windows-debug` target (e.g., `make windows-debug`) ## Cross-Compiling The Merlin agent and server can be cross-compiled to any operating system or architecture. A list of golang supported operating systems and architectures can be found here: [https://golang.org/doc/install/source#environment](https://golang.org/doc/install/source#environment) | \$GOOS | \$GOARCH | | --------- | -------- | | android | arm | | darwin | 386 | | darwin | amd64 | | darwin | arm | | darwin | arm64 | | dragonfly | amd64 | | freebsd | 386 | | freebsd | amd64 | | freebsd | arm | | linux | 386 | | linux | amd64 | | linux | arm | | linux | arm64 | | linux | ppc64 | | linux | ppc64le | | linux | mips | | linux | mipsle | | linux | mips64 | | linux | mips64le | | netbsd | 386 | | netbsd | amd64 | | netbsd | arm | | openbsd | 386 | | openbsd | amd64 | | openbsd | arm | | plan9 | 386 | | plan9 | amd64 | | solaris | amd64 | | windows | 386 | | windows | amd64 |