--- name: "sd_bus_message_new_method_call" section: "3" platform: "linux" package: "systemd-libs" version: "262.1-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/sd_bus_message_new_method_call" --- # sd\_bus\_message\_new\_method\_call(3) Create a method call message ## NAME sd\_bus\_message\_new\_method\_call, sd\_bus\_message\_new\_method\_return - Create a method call message ## SYNOPSIS ``` #include ``` **int sd\_bus\_message\_new\_method\_call(sd\_bus \****bus***, sd\_bus\_message \*\****m***, const char \****destination***, const char \****path***, const char \****interface***, const char \****member***);** **int sd\_bus\_message\_new\_method\_return(sd\_bus\_message \****call***, sd\_bus\_message \*\****m***);** ## DESCRIPTION The **sd\_bus\_message\_new\_method\_call()** function creates a new bus message object that encapsulates a D-Bus method call, and returns it in the *m* output parameter. The call will be made on the destination *destination*, path *path*, on the interface *interface*, member *member*. Briefly, the *destination* is a dot-separated name that identifies a service connected to the bus. The *path* is a slash-separated identifier of an object within the destination that resembles a file system path. The meaning of this path is defined by the destination. The *interface* is a dot-separated name that resembles a Java interface name that identifies a group of methods and signals supported by the object identified by path. Methods and signals are collectively called *members* and are identified by a simple name composed of ASCII letters, numbers, and underscores. See the **D-Bus Tutorial**\[1\] for an in-depth explanation. The *destination* parameter may be **NULL**. The *interface* parameter may be **NULL**, if the destination has only a single member with the given name and there is no ambiguity if the interface name is omitted. Note that this is a low level interface. See [**sd\_bus\_call\_method**(3)](/sd_bus_call_method/3.md) for a more convenient way of calling D-Bus methods. The **sd\_bus\_message\_new\_method\_return()** function creates a new bus message object that is a reply to the method call *call* and returns it in the *m* output parameter. The *call* parameter must be a method call message. The sender of *call* is used as the destination. ## RETURN VALUE On success, these functions return a non-negative integer. On failure, they return a negative errno-style error code. ### Errors Returned errors may indicate the following problems: **-EINVAL** The output parameter *m* is **NULL**. The *destination* parameter is non-null and is not a valid D-Bus service name ("org.somewhere.Something"), the *path* parameter is not a valid D-Bus path ("/an/object/path"), the *interface* parameter is non-null and is not a valid D-Bus interface name ("an.interface.name"), or the *member* parameter is not a valid D-Bus member ("Name"). The *call* parameter is not a method call object. **-ENOTCONN** The bus parameter *bus* is **NULL** or the bus is not connected. **-ENOMEM** Memory allocation failed. **-EPERM** The *call* parameter is not sealed. **-EOPNOTSUPP** The *call* message does not have a cookie. ## NOTES Functions described here are available as a shared library, which can be compiled against and linked to with the **libsystemd** [**pkg-config**(1)](/pkg-config/1.md) file. All functions listed here are thread-agnostic and only a single thread may operate on a given object at any given time. Different threads may access the same object at different times. Multiple independent objects may be used from different threads in parallel. The code described here uses [**getenv**(3)](/getenv/3.md), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call [**setenv**(3)](/setenv/3.md) from a parallel thread. It is recommended to only do calls to **setenv()** from an early phase of the program when no other threads have been started. ## EXAMPLES **Example 1. Make a call to a D-Bus method that takes a single parameter** ``` /* SPDX-License-Identifier: MIT-0 */ /* This is equivalent to: * busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 \ * org.freedesktop.systemd1.Manager GetUnitByPID $$ * * Compile with 'cc print-unit-path.c -lsystemd' */ #include #include #include #include #include #define _cleanup_(f) __attribute__((cleanup(f))) #define DESTINATION "org.freedesktop.systemd1" #define PATH "/org/freedesktop/systemd1" #define INTERFACE "org.freedesktop.systemd1.Manager" #define MEMBER "GetUnitByPID" static int log_error(int error, const char *message) { fprintf(stderr, "%s: %s\n", message, strerror(-error)); return error; } int main(int argc, char **argv) { _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL; _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL; _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL, *m = NULL; int r; r = sd_bus_open_system(&bus); if (r < 0) return log_error(r, "Failed to acquire bus"); r = sd_bus_message_new_method_call(bus, &m, DESTINATION, PATH, INTERFACE, MEMBER); if (r < 0) return log_error(r, "Failed to create bus message"); r = sd_bus_message_append(m, "u", (unsigned) getpid()); if (r < 0) return log_error(r, "Failed to append to bus message"); r = sd_bus_call(bus, m, -1, &error, &reply); if (r < 0) return log_error(r, MEMBER " call failed"); const char *ans; r = sd_bus_message_read(reply, "o", &ans); if (r < 0) return log_error(r, "Failed to read reply"); printf("Unit path is \"%s\".\n", ans); return 0; } ``` This defines a minimally useful program that will open a connection to the bus, create a message object, send it, wait for the reply, and finally extract and print the answer. It does error handling and proper memory management. ## HISTORY **sd\_bus\_message\_new\_method\_call()** and **sd\_bus\_message\_new\_method\_return()** were added in version 246. ## SEE ALSO [**systemd**(1)](/systemd/1.md), [**sd-bus**(3)](/sd-bus/3.md), [**sd\_bus\_call**(3)](/sd_bus_call/3.md), [**sd\_bus\_call\_method**(3)](/sd_bus_call_method/3.md), [**sd\_bus\_path\_encode**(3)](/sd_bus_path_encode/3.md) ## NOTES - 1\. D-Bus Tutorial https://dbus.freedesktop.org/doc/dbus-tutorial.html#concepts