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470 lines
23 KiB
XML
470 lines
23 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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<refentry id="sd_notify"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_notify</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_notify</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_notify</refname>
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<refname>sd_notifyf</refname>
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<refname>sd_pid_notify</refname>
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<refname>sd_pid_notifyf</refname>
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<refname>sd_pid_notify_with_fds</refname>
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<refname>sd_notify_barrier</refname>
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<refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_notify</function></funcdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>const char *<parameter>state</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_notifyf</function></funcdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>const char *<parameter>format</parameter></paramdef>
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<paramdef>…</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_pid_notify</function></funcdef>
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<paramdef>pid_t <parameter>pid</parameter></paramdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>const char *<parameter>state</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_pid_notifyf</function></funcdef>
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<paramdef>pid_t <parameter>pid</parameter></paramdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>const char *<parameter>format</parameter></paramdef>
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<paramdef>…</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_pid_notify_with_fds</function></funcdef>
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<paramdef>pid_t <parameter>pid</parameter></paramdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>const char *<parameter>state</parameter></paramdef>
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<paramdef>const int *<parameter>fds</parameter></paramdef>
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<paramdef>unsigned <parameter>n_fds</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_notify_barrier</function></funcdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>uint64_t <parameter>timeout</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_notify()</function> may be called by a service
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to notify the service manager about state changes. It can be used
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to send arbitrary information, encoded in an
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environment-block-like string. Most importantly, it can be used for
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start-up completion notification.</para>
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<para>If the <parameter>unset_environment</parameter> parameter is
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non-zero, <function>sd_notify()</function> will unset the
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<varname>$NOTIFY_SOCKET</varname> environment variable before
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returning (regardless of whether the function call itself
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succeeded or not). Further calls to
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<function>sd_notify()</function> will then fail, but the variable
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is no longer inherited by child processes.</para>
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<para>The <parameter>state</parameter> parameter should contain a
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newline-separated list of variable assignments, similar in style
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to an environment block. A trailing newline is implied if none is
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specified. The string may contain any kind of variable
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assignments, but the following shall be considered
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well-known:</para>
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<variablelist>
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<varlistentry>
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<term>READY=1</term>
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<listitem><para>Tells the service manager that service startup is finished, or the service finished loading its
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configuration. This is only used by systemd if the service definition file has <varname>Type=notify</varname>
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set. Since there is little value in signaling non-readiness, the only value services should send is
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<literal>READY=1</literal> (i.e. <literal>READY=0</literal> is not defined).</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>RELOADING=1</term>
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<listitem><para>Tells the service manager that the service is
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reloading its configuration. This is useful to allow the
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service manager to track the service's internal state, and
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present it to the user. Note that a service that sends this
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notification must also send a <literal>READY=1</literal>
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notification when it completed reloading its
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configuration. Reloads are propagated in the same way as they
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are when initiated by the user.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>STOPPING=1</term>
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<listitem><para>Tells the service manager that the service is
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beginning its shutdown. This is useful to allow the service
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manager to track the service's internal state, and present it
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to the user.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>STATUS=…</term>
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<listitem><para>Passes a single-line UTF-8 status string back
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to the service manager that describes the service state. This
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is free-form and can be used for various purposes: general
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state feedback, fsck-like programs could pass completion
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percentages and failing programs could pass a human-readable
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error message. Example: <literal>STATUS=Completed 66% of file
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system check…</literal></para></listitem>
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</varlistentry>
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<varlistentry>
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<term>ERRNO=…</term>
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<listitem><para>If a service fails, the errno-style error
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code, formatted as string. Example: <literal>ERRNO=2</literal>
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for ENOENT.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>BUSERROR=…</term>
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<listitem><para>If a service fails, the D-Bus error-style
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error code. Example:
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<literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
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</varlistentry>
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<varlistentry>
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<term>MAINPID=…</term>
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<listitem><para>The main process ID (PID) of the service, in
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case the service manager did not fork off the process itself.
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Example: <literal>MAINPID=4711</literal></para></listitem>
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</varlistentry>
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<varlistentry>
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<term>WATCHDOG=1</term>
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<listitem><para>Tells the service manager to update the
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watchdog timestamp. This is the keep-alive ping that services
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need to issue in regular intervals if
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<varname>WatchdogSec=</varname> is enabled for it. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for information how to enable this functionality and
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<citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for the details of how the service can check whether the
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watchdog is enabled. </para></listitem>
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</varlistentry>
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<varlistentry>
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<term>WATCHDOG=trigger</term>
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<listitem><para>Tells the service manager that the service detected an internal error that should be handled by
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the configured watchdog options. This will trigger the same behaviour as if <varname>WatchdogSec=</varname> is
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enabled and the service did not send <literal>WATCHDOG=1</literal> in time. Note that
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<varname>WatchdogSec=</varname> does not need to be enabled for <literal>WATCHDOG=trigger</literal> to trigger
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the watchdog action. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
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information about the watchdog behavior. </para></listitem>
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</varlistentry>
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<varlistentry>
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<term>WATCHDOG_USEC=…</term>
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<listitem><para>Reset <varname>watchdog_usec</varname> value during runtime.
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Notice that this is not available when using <function>sd_event_set_watchdog()</function>
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or <function>sd_watchdog_enabled()</function>.
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Example : <literal>WATCHDOG_USEC=20000000</literal></para></listitem>
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</varlistentry>
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<varlistentry>
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<term>EXTEND_TIMEOUT_USEC=…</term>
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<listitem><para>Tells the service manager to extend the startup, runtime or shutdown service timeout
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corresponding the current state. The value specified is a time in microseconds during which the service must
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send a new message. A service timeout will occur if the message isn't received, but only if the runtime of the
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current state is beyond the original maximum times of <varname>TimeoutStartSec=</varname>, <varname>RuntimeMaxSec=</varname>,
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and <varname>TimeoutStopSec=</varname>.
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See <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for effects on the service timeouts.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>FDSTORE=1</term>
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<listitem><para>Stores additional file descriptors in the service manager. File descriptors sent this way will
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be maintained per-service by the service manager and will later be handed back using the usual file descriptor
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passing logic at the next invocation of the service, see
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<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This is
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useful for implementing services that can restart after an explicit request or a crash without losing
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state. Any open sockets and other file descriptors which should not be closed during the restart may be stored
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this way. Application state can either be serialized to a file in <filename>/run</filename>, or better, stored
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in a <citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> memory
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file descriptor. Note that the service manager will accept messages for a service only if its
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<varname>FileDescriptorStoreMax=</varname> setting is non-zero (defaults to zero, see
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>). If
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<varname>FDPOLL=0</varname> is not set and the file descriptors sent are pollable (see
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<citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), then any
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<constant>EPOLLHUP</constant> or <constant>EPOLLERR</constant> event seen on them will result in their
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automatic removal from the store. Multiple arrays of file descriptors may be sent in separate messages, in
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which case the arrays are combined. Note that the service manager removes duplicate (pointing to the same
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object) file descriptors before passing them to the service. Use <function>sd_pid_notify_with_fds()</function>
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to send messages with <literal>FDSTORE=1</literal>, see below.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>FDSTOREREMOVE=1</term>
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<listitem><para>Removes file descriptors from the file descriptor store. This field needs to be combined with
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<varname>FDNAME=</varname> to specify the name of the file descriptors to remove.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>FDNAME=…</term>
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<listitem><para>When used in combination with <varname>FDSTORE=1</varname>, specifies a name for the submitted
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file descriptors. When used with <varname>FDSTOREREMOVE=1</varname>, specifies the name for the file
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descriptors to remove. This name is passed to the service during activation, and may be queried using
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<citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>. File
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descriptors submitted without this field set, will implicitly get the name <literal>stored</literal>
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assigned. Note that, if multiple file descriptors are submitted at once, the specified name will be assigned to
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all of them. In order to assign different names to submitted file descriptors, submit them in separate
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invocations of <function>sd_pid_notify_with_fds()</function>. The name may consist of arbitrary ASCII
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characters except control characters or <literal>:</literal>. It may not be longer than 255 characters. If a
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submitted name does not follow these restrictions, it is ignored.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>FDPOLL=0</term>
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<listitem><para>When used in combination with <varname>FDSTORE=1</varname>, disables polling of the stored
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file descriptors regardless of whether or not they are pollable. As this option disables automatic cleanup
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of the stored file descriptors on EPOLLERR and EPOLLHUP, care must be taken to ensure proper manual cleanup.
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Use of this option is not generally recommended except for when automatic cleanup has unwanted behavior such
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as prematurely discarding file descriptors from the store.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>BARRIER=1</term>
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<listitem><para>Tells the service manager that the client is explicitly requesting synchronization by means of
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closing the file descriptor sent with this command. The service manager guarantees that the processing of a <varname>
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BARRIER=1</varname> command will only happen after all previous notification messages sent before this command
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have been processed. Hence, this command accompanied with a single file descriptor can be used to synchronize
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against reception of all previous status messages. Note that this command cannot be mixed with other notifications,
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and has to be sent in a separate message to the service manager, otherwise all assignments will be ignored. Note that
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sending 0 or more than 1 file descriptor with this command is a violation of the protocol.</para></listitem>
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</varlistentry>
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</variablelist>
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<para>It is recommended to prefix variable names that are not
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listed above with <varname>X_</varname> to avoid namespace
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clashes.</para>
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<para>Note that systemd will accept status data sent from a
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service only if the <varname>NotifyAccess=</varname> option is
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correctly set in the service definition file. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details.</para>
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<para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
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the sending process is still around at the time PID 1 processes the message, or if the sending process is
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explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
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off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
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<varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
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<function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
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attribute the message to the unit, and thus will ignore it, even if
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<varname>NotifyAccess=</varname><option>all</option> is set for it.</para>
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<para>Hence, to eliminate all race conditions involving lookup of the client's unit and attribution of notifications
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to units correctly, <function>sd_notify_barrier()</function> may be used. This call acts as a synchronization point
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and ensures all notifications sent before this call have been picked up by the service manager when it returns
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successfully. Use of <function>sd_notify_barrier()</function> is needed for clients which are not invoked by the
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service manager, otherwise this synchronization mechanism is unnecessary for attribution of notifications to the
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unit.</para>
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<para><function>sd_notifyf()</function> is similar to
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<function>sd_notify()</function> but takes a
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<function>printf()</function>-like format string plus
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arguments.</para>
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<para><function>sd_pid_notify()</function> and
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<function>sd_pid_notifyf()</function> are similar to
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<function>sd_notify()</function> and
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<function>sd_notifyf()</function> but take a process ID (PID) to
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use as originating PID for the message as first argument. This is
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useful to send notification messages on behalf of other processes,
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provided the appropriate privileges are available. If the PID
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argument is specified as 0, the process ID of the calling process
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is used, in which case the calls are fully equivalent to
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<function>sd_notify()</function> and
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<function>sd_notifyf()</function>.</para>
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<para><function>sd_pid_notify_with_fds()</function> is similar to
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<function>sd_pid_notify()</function> but takes an additional array
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of file descriptors. These file descriptors are sent along the
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notification message to the service manager. This is particularly
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useful for sending <literal>FDSTORE=1</literal> messages, as
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described above. The additional arguments are a pointer to the
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file descriptor array plus the number of file descriptors in the
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array. If the number of file descriptors is passed as 0, the call
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is fully equivalent to <function>sd_pid_notify()</function>, i.e.
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no file descriptors are passed. Note that sending file descriptors
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to the service manager on messages that do not expect them (i.e.
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without <literal>FDSTORE=1</literal>) they are immediately closed
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on reception.</para>
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<para><function>sd_notify_barrier()</function> allows the caller to
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synchronize against reception of previously sent notification messages
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and uses the <literal>BARRIER=1</literal> command. It takes a relative
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<varname>timeout</varname> value in microseconds which is passed to
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<citerefentry><refentrytitle>ppoll</refentrytitle><manvolnum>2</manvolnum>
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</citerefentry>. A value of UINT64_MAX is interpreted as infinite timeout.
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</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On failure, these calls return a negative errno-style error code. If <varname>$NOTIFY_SOCKET</varname> was
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not set and hence no status message could be sent, 0 is returned. If the status was sent, these functions return a
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positive value. In order to support both service managers that implement this scheme and those which do not, it is
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generally recommended to ignore the return value of this call. Note that the return value simply indicates whether
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the notification message was enqueued properly, it does not reflect whether the message could be processed
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successfully. Specifically, no error is returned when a file descriptor is attempted to be stored using
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<varname>FDSTORE=1</varname> but the service is not actually configured to permit storing of file descriptors (see
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above).</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
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<para>These functions send a single datagram with the
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state string as payload to the <constant>AF_UNIX</constant> socket
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referenced in the <varname>$NOTIFY_SOCKET</varname> environment
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variable. If the first character of
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<varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the
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string is understood as Linux abstract namespace socket. The
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datagram is accompanied by the process credentials of the sending
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service, using SCM_CREDENTIALS.</para>
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</refsect1>
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<refsect1>
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<title>Environment</title>
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<variablelist class='environment-variables'>
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<varlistentry>
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<term><varname>$NOTIFY_SOCKET</varname></term>
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<listitem><para>Set by the service manager for supervised
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processes for status and start-up completion notification.
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This environment variable specifies the socket
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<function>sd_notify()</function> talks to. See above for
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details.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<example>
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<title>Start-up Notification</title>
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<para>When a service finished starting up, it might issue the
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following call to notify the service manager:</para>
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<programlisting>sd_notify(0, "READY=1");</programlisting>
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</example>
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<example>
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<title>Extended Start-up Notification</title>
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<para>A service could send the following after completing
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initialization:</para>
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<programlisting>sd_notifyf(0, "READY=1\n"
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"STATUS=Processing requests…\n"
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"MAINPID=%lu",
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(unsigned long) getpid());</programlisting>
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</example>
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<example>
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<title>Error Cause Notification</title>
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|
|
|
<para>A service could send the following shortly before exiting, on failure:</para>
|
|
|
|
<programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
|
|
"ERRNO=%i",
|
|
strerror(errno),
|
|
errno);</programlisting>
|
|
</example>
|
|
|
|
<example>
|
|
<title>Store a File Descriptor in the Service Manager</title>
|
|
|
|
<para>To store an open file descriptor in the service manager,
|
|
in order to continue operation after a service restart without
|
|
losing state, use <literal>FDSTORE=1</literal>:</para>
|
|
|
|
<programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &fd, 1);</programlisting>
|
|
</example>
|
|
|
|
<example>
|
|
<title>Eliminating race conditions</title>
|
|
|
|
<para>When the client sending the notifications is not spawned
|
|
by the service manager, it may exit too quickly and the service
|
|
manager may fail to attribute them correctly to the unit. To
|
|
prevent such races, use <function>sd_notify_barrier()</function>
|
|
to synchronize against reception of all notifications sent before
|
|
this call is made.</para>
|
|
|
|
<programlisting>sd_notify(0, "READY=1");
|
|
/* set timeout to 5 seconds */
|
|
sd_notify_barrier(0, 5 * 1000000);
|
|
</programlisting>
|
|
</example>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
<para>
|
|
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
</para>
|
|
</refsect1>
|
|
|
|
</refentry>
|