sd_bus_open_user_with_description(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | REFERENCE OWNERSHIP | RETURN VALUE | NOTES | SEE ALSO | COLOPHON

SD_BUS_DEFAULT(3)              sd_bus_default              SD_BUS_DEFAULT(3)

NAME         top

       sd_bus_default, sd_bus_default_user, sd_bus_default_system,
       sd_bus_open, sd_bus_open_with_description, sd_bus_open_user,
       sd_bus_open_user_with_description, sd_bus_open_system,
       sd_bus_open_system_with_description, sd_bus_open_system_remote,
       sd_bus_open_system_machine - Acquire a connection to a system or user
       bus

SYNOPSIS         top

       #include <systemd/sd-bus.h>

       int sd_bus_default(sd_bus **bus);

       int sd_bus_default_user(sd_bus **bus);

       int sd_bus_default_system(sd_bus **bus);

       int sd_bus_open(sd_bus **bus);

       int sd_bus_open_with_description(sd_bus **bus,
                                        const char *description);

       int sd_bus_open_user(sd_bus **bus);

       int sd_bus_open_user_with_description(sd_bus **bus,
                                             const char *description);

       int sd_bus_open_system(sd_bus **bus);

       int sd_bus_open_system_with_description(sd_bus **bus,
                                               const char *description);

       int sd_bus_open_system_remote(sd_bus **bus, const char *host);

       int sd_bus_open_system_machine(sd_bus **bus, const char *machine);

DESCRIPTION         top

       sd_bus_default() acquires a bus connection object to the user bus
       when invoked in user context, or to the system bus otherwise. The
       connection object is associated with the calling thread. Each time
       the function is invoked from the same thread, the same object is
       returned, but its reference count is increased by one, as long as at
       least one reference is kept. When the last reference to the
       connection is dropped (using the sd_bus_unref(3) call), the
       connection is terminated. Note that the connection is not
       automatically terminated when the associated thread ends. It is
       important to drop the last reference to the bus connection explicitly
       before the thread ends, as otherwise, the connection will leak. Also,
       queued but unread or unwritten messages keep the bus referenced, see
       below.

       sd_bus_default_user() returns a user bus connection object associated
       with the calling thread.  sd_bus_default_system() is similar, but
       connects to the system bus. Note that sd_bus_default() is identical
       to these two calls, depending on the execution context.

       sd_bus_open() creates a new, independent bus connection to the user
       bus when invoked in user context, or the system bus otherwise.
       sd_bus_open_user() is similar, but connects only to the user bus.
       sd_bus_open_system() does the same, but connects to the system bus.
       In contrast to sd_bus_default(), sd_bus_default_user(), and
       sd_bus_default_system(), these calls return new, independent
       connection objects that are not associated with the invoking thread
       and are not shared between multiple invocations. It is recommended to
       share connections per thread to efficiently make use the available
       resources. Thus, it is recommended to use sd_bus_default(),
       sd_bus_default_user() and sd_bus_default_system() to connect to the
       user or system buses.

       sd_bus_open_with_description(), sd_bus_open_user_with_description(),
       and sd_bus_open_system_with_description() are similar to
       sd_bus_open(), sd_bus_open_user(), and sd_bus_open_system(), but
       allow a description string to be set, see sd_bus_set_description(3).
       description may be NULL, in which case this function is equivalent to
       sd_bus_open(). This description string is used in log messages about
       the bus object, and including a "name" for the bus makes them easier
       to understand. Some messages are emitted during bus initialization,
       hence using this function is prefereable to setting the description
       later with sd_bus_open_with_description(). The argument is copied
       internally and will not be referenced after the function returns.

       If the $DBUS_SESSION_BUS_ADDRESS environment variable is set (cf.
       environ(7)), it will be used as the address of the user bus. This
       variable can contain multiple addresses separated by ";". If this
       variable is not set, a suitable default for the default user D-Bus
       instance will be used.

       If the $DBUS_SYSTEM_BUS_ADDRESS environment variable is set, it will
       be used as the address of the system bus. This variable uses the same
       syntax as $DBUS_SESSION_BUS_ADDRESS. If this variable is not set, a
       suitable default for the default system D-Bus instance will be used.

       sd_bus_open_system_remote() connects to the system bus on the
       specified host using ssh(1).  host consists of an optional user name
       followed by the "@" symbol, and the hostname, optionally followed by
       a ":" and a port, optionally followed by a "/" and a machine name. If
       the machine name is given, a connection is created to the system bus
       in the specified container on the remote machine, and otherwise a
       connection to the system bus on the specified host is created.

       Note that entering a container is a privileged operation, and will
       likely only work for the root user on the remote machine.

       sd_bus_open_system_machine() connects to the system bus in the
       specified machine, where machine is the name of a local container.
       See sd_bus_set_address(3) for a description of the address syntax,
       and machinectl(1) for more information about the "machine" concept.
       Note that connections into local containers are only available to
       privileged processes at this time.

       These calls allocate a bus connection object and initiate the
       connection to a well-known bus of some form. An alternative to using
       these high-level calls is to create an unconnected bus object with
       sd_bus_new(3) and to connect it with sd_bus_start(3).

REFERENCE OWNERSHIP         top

       The functions sd_bus_open(), sd_bus_open_user(),
       sd_bus_open_system(), sd_bus_open_system_remote(), and
       sd_bus_open_system_machine() return a new connection object and the
       caller owns the sole reference. When not needed anymore, this
       reference should be destroyed with sd_bus_unref(3).

       The functions sd_bus_default(), sd_bus_default_user() and
       sd_bus_default_system() do not necessarily create a new object, but
       increase the connection reference of an existing connection object by
       one. Use sd_bus_unref(3) to drop the reference.

       Queued but unwritten/unread messages keep a reference to their bus
       connection object. For this reason, even if an application dropped
       all references to a bus connection, it might not get destroyed right
       away. Until all incoming queued messages are read, and until all
       outgoing unwritten messages are written, the bus object will stay
       alive.  sd_bus_flush() may be used to write all outgoing queued
       messages so they drop their references. To flush the unread incoming
       messages, use sd_bus_close(), which will also close the bus
       connection. When using the default bus logic, it is a good idea to
       first invoke sd_bus_flush() followed by sd_bus_close() when a thread
       or process terminates, and thus its bus connection object should be
       freed.

       Normally, slot objects (as created by sd_bus_add_match(3) and similar
       calls) keep a reference to their bus connection object, too. Thus, as
       long as a bus slot object remains referenced its bus object will
       remain allocated too. Optionally, bus slot objects may be placed in
       "floating" mode. When in floating mode the life cycle of the bus slot
       object is bound to the bus object, i.e. when the bus object is freed
       the bus slot object is automatically unreferenced too. The floating
       state of a slot object may be controlled explicitly with
       sd_bus_slot_set_floating(3), though usually floating bus slot objects
       are created by passing NULL as the slot parameter of
       sd_bus_add_match() and related calls, thus indicating that the caller
       is not directly interested in referencing and managing the bus slot
       object.

       The life cycle of the default bus connection should be the
       responsibility of the code that creates/owns the thread the default
       bus connection object is associated with. Library code should neither
       call sd_bus_flush() nor sd_bus_close() on default bus objects unless
       it does so in its own private, self-allocated thread. Library code
       should not use the default bus object in other threads unless it is
       clear that the program using it will life cycle the bus connection
       object and flush and close it before exiting from the thread. In
       libraries where it is not clear that the calling program will life
       cycle the bus connection object, it is hence recommended to use
       sd_bus_open_system() instead of sd_bus_default_system() and related
       calls.

RETURN VALUE         top

       On success, these calls return 0 or a positive integer. On failure,
       these calls return a negative errno-style error code.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           The specified parameters are invalid.

       -ENOMEM
           Memory allocation failed.

       -ESOCKTNOSUPPORT
           The protocol version required to connect to the selected bus is
           not supported.

       In addition, other connection-related errors may be returned. See
       sd_bus_send(3).

NOTES         top

       These APIs are implemented as a shared library, which can be compiled
       and linked to with the libsystemd pkg-config(1) file.

SEE ALSO         top

       systemd(1), sd-bus(3), sd_bus_new(3), sd_bus_ref(3), sd_bus_unref(3),
       sd_bus_close(3), ssh(1), systemd-machined.service(8), machinectl(1)

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have a bug
       report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2020-07-14.  (At that
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systemd 246                                                SD_BUS_DEFAULT(3)

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