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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_VARLINK_SEND(3) sd_varlink_send SD_VARLINK_SEND(3)
sd_varlink_send, sd_varlink_sendb, sd_varlink_sendbo - Enqueues a
Varlink method call, not expecting a reply
#include <systemd/sd-varlink.h>
int sd_varlink_send(sd_varlink *link, const char *method,
sd_json_variant *parameters);
int sd_varlink_sendb(sd_varlink *link, const char *method, ...);
int sd_varlink_sendbo(sd_varlink *link, const char *method, ...);
sd_varlink_send() submits a method call via a Varlink connection.
It takes the Varlink connection object, a method name as string
parameter, and a JSON object containing the parameters to pass as
function parameters. This call is asynchronous: the message will
not be delivered immediately but only once sd_varlink_process(3)
is invoked (which will happen automatically in one of the
following event loop iterations if the Varlink connection is
attached to an even loop).
sd_varlink_sendb() is similar to sd_varlink_send(), but instead of
expecting a fully constructed sd_json_variant object carrying the
parameters, this object is constructed on-the-fly directly from
the parameter list, in a style identical to sd_json_build(3).
sd_varlink_sendbo() is identical to sd_varlink_sendb(), but an
enclosing object is implicitly added, so that the parameter list
is expected to consist of field pairs only. For details about the
expected argument list, see sd_json_buildo(3).
Use sd_varlink_send(), sd_varlink_sendb() and sd_varlink_sendbo()
only if no method call results are required, as they neither
provide return parameters nor success/failure information. Use
sd_varlink_call(3) (and related calls) to submit a method call
synchronously, returning the server's response.
On success, sd_varlink_send(), sd_varlink_sendb() and
sd_varlink_sendbo() return a non-negative integer. On failure,
they return a negative errno-style error code.
Errors
Returned errors may indicate the following problems:
-EINVAL
An argument is invalid.
-ENOMEM
Memory allocation failed.
-ENOTCONN
The Varlink connection object is not connected.
-EBUSY
The Varlink connection object is already used for other
purposes, i.e. executing a method call or similar.
-ENOBUFS
The internal limit of queued messages for the Varlink
connection has been reached. This limit is set very high, and
hitting it typically indicates that the Varlink connection
object is stalled — possibly because sd_varlink_process() has
not been called regularly enough, or because the peer is not
processing any queued messages. This limit is a safety
precaution to ensure a stalled peer will not result in
unbounded memory allocations on the client side.
Functions described here are available as a shared library, which
can be compiled against and linked to with the
libsystemd pkg-config(1) file.
The code described here uses getenv(3), which is declared to be
not multi-thread-safe. This means that the code calling the
functions described here must not call setenv(3) 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.
sd_varlink_send(), sd_varlink_sendb(), sd_varlink_sendbo() were
added in version 257.
systemd(1), sd-varlink(3), sd_varlink_call(3), sd_varlink_build(3)
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 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 SD_VARLINK_SEND(3)
Pages that refer to this page: systemd.directives(7), systemd.index(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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