Adding upstream version 252.22.upstream/252.22upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 471 insertions, 0 deletions

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+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="sd_notify"
+  xmlns:xi="http://www.w3.org/2001/XInclude">
+
+  <refentryinfo>
+    <title>sd_notify</title>
+    <productname>systemd</productname>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>sd_notify</refentrytitle>
+    <manvolnum>3</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>sd_notify</refname>
+    <refname>sd_notifyf</refname>
+    <refname>sd_pid_notify</refname>
+    <refname>sd_pid_notifyf</refname>
+    <refname>sd_pid_notify_with_fds</refname>
+    <refname>sd_notify_barrier</refname>
+    <refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <funcsynopsis>
+      <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
+
+      <funcprototype>
+        <funcdef>int <function>sd_notify</function></funcdef>
+        <paramdef>int <parameter>unset_environment</parameter></paramdef>
+        <paramdef>const char *<parameter>state</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_notifyf</function></funcdef>
+        <paramdef>int <parameter>unset_environment</parameter></paramdef>
+        <paramdef>const char *<parameter>format</parameter></paramdef>
+        <paramdef>…</paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_pid_notify</function></funcdef>
+        <paramdef>pid_t <parameter>pid</parameter></paramdef>
+        <paramdef>int <parameter>unset_environment</parameter></paramdef>
+        <paramdef>const char *<parameter>state</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_pid_notifyf</function></funcdef>
+        <paramdef>pid_t <parameter>pid</parameter></paramdef>
+        <paramdef>int <parameter>unset_environment</parameter></paramdef>
+        <paramdef>const char *<parameter>format</parameter></paramdef>
+        <paramdef>…</paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_pid_notify_with_fds</function></funcdef>
+        <paramdef>pid_t <parameter>pid</parameter></paramdef>
+        <paramdef>int <parameter>unset_environment</parameter></paramdef>
+        <paramdef>const char *<parameter>state</parameter></paramdef>
+        <paramdef>const int *<parameter>fds</parameter></paramdef>
+        <paramdef>unsigned <parameter>n_fds</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_notify_barrier</function></funcdef>
+        <paramdef>int <parameter>unset_environment</parameter></paramdef>
+        <paramdef>uint64_t <parameter>timeout</parameter></paramdef>
+      </funcprototype>
+    </funcsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+    <para><function>sd_notify()</function> may be called by a service
+    to notify the service manager about state changes. It can be used
+    to send arbitrary information, encoded in an
+    environment-block-like string. Most importantly, it can be used for
+    start-up completion notification.</para>
+
+    <para>If the <parameter>unset_environment</parameter> parameter is
+    non-zero, <function>sd_notify()</function> will unset the
+    <varname>$NOTIFY_SOCKET</varname> environment variable before
+    returning (regardless of whether the function call itself
+    succeeded or not). Further calls to
+    <function>sd_notify()</function> will then fail, but the variable
+    is no longer inherited by child processes.</para>
+
+    <para>The <parameter>state</parameter> parameter should contain a
+    newline-separated list of variable assignments, similar in style
+    to an environment block. A trailing newline is implied if none is
+    specified. The string may contain any kind of variable
+    assignments, but the following shall be considered
+    well-known:</para>
+
+    <variablelist>
+      <varlistentry>
+        <term>READY=1</term>
+
+        <listitem><para>Tells the service manager that service startup is finished, or the service finished loading its
+        configuration. This is only used by systemd if the service definition file has <varname>Type=notify</varname>
+        set. Since there is little value in signaling non-readiness, the only value services should send is
+        <literal>READY=1</literal> (i.e.  <literal>READY=0</literal> is not defined).</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>RELOADING=1</term>
+
+        <listitem><para>Tells the service manager that the service is
+        reloading its configuration. This is useful to allow the
+        service manager to track the service's internal state, and
+        present it to the user. Note that a service that sends this
+        notification must also send a <literal>READY=1</literal>
+        notification when it completed reloading its
+        configuration. Reloads are propagated in the same way as they
+        are when initiated by the user.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>STOPPING=1</term>
+
+        <listitem><para>Tells the service manager that the service is
+        beginning its shutdown. This is useful to allow the service
+        manager to track the service's internal state, and present it
+        to the user.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>STATUS=…</term>
+
+        <listitem><para>Passes a single-line UTF-8 status string back
+        to the service manager that describes the service state. This
+        is free-form and can be used for various purposes: general
+        state feedback, fsck-like programs could pass completion
+        percentages and failing programs could pass a human-readable
+        error message. Example: <literal>STATUS=Completed 66% of file
+        system check…</literal></para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>ERRNO=…</term>
+
+        <listitem><para>If a service fails, the errno-style error
+        code, formatted as string. Example: <literal>ERRNO=2</literal>
+        for ENOENT.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>BUSERROR=…</term>
+
+        <listitem><para>If a service fails, the D-Bus error-style
+        error code. Example:
+        <literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>MAINPID=…</term>
+
+        <listitem><para>The main process ID (PID) of the service, in
+        case the service manager did not fork off the process itself.
+        Example: <literal>MAINPID=4711</literal></para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>WATCHDOG=1</term>
+
+        <listitem><para>Tells the service manager to update the
+        watchdog timestamp. This is the keep-alive ping that services
+        need to issue in regular intervals if
+        <varname>WatchdogSec=</varname> is enabled for it. See
+        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        for information how to enable this functionality and
+        <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+        for the details of how the service can check whether the
+        watchdog is enabled. </para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>WATCHDOG=trigger</term>
+
+        <listitem><para>Tells the service manager that the service detected an internal error that should be handled by
+        the configured watchdog options. This will trigger the same behaviour as if <varname>WatchdogSec=</varname> is
+        enabled and the service did not send <literal>WATCHDOG=1</literal> in time. Note that
+        <varname>WatchdogSec=</varname> does not need to be enabled for <literal>WATCHDOG=trigger</literal> to trigger
+        the watchdog action. See
+        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
+        information about the watchdog behavior. </para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>WATCHDOG_USEC=…</term>
+
+        <listitem><para>Reset <varname>watchdog_usec</varname> value during runtime.
+        Notice that this is not available when using <function>sd_event_set_watchdog()</function>
+        or <function>sd_watchdog_enabled()</function>.
+        Example : <literal>WATCHDOG_USEC=20000000</literal></para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>EXTEND_TIMEOUT_USEC=…</term>
+
+        <listitem><para>Tells the service manager to extend the startup, runtime or shutdown service timeout
+        corresponding the current state. The value specified is a time in microseconds during which the service must
+        send a new message. A service timeout will occur if the message isn't received, but only if the runtime of the
+        current state is beyond the original maximum times of <varname>TimeoutStartSec=</varname>, <varname>RuntimeMaxSec=</varname>,
+        and <varname>TimeoutStopSec=</varname>.
+        See <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        for effects on the service timeouts.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>FDSTORE=1</term>
+
+        <listitem><para>Stores additional file descriptors in the service manager. File descriptors sent this way will
+        be maintained per-service by the service manager and will later be handed back using the usual file descriptor
+        passing logic at the next invocation of the service (e.g. when it is restarted), see
+        <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.  This is
+        useful for implementing services that can restart after an explicit request or a crash without losing
+        state. Any open sockets and other file descriptors which should not be closed during the restart may be stored
+        this way. Application state can either be serialized to a file in <filename>/run/</filename>, or better, stored
+        in a <citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> memory
+        file descriptor. Note that the service manager will accept messages for a service only if its
+        <varname>FileDescriptorStoreMax=</varname> setting is non-zero (defaults to zero, see
+        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>). If
+        <varname>FDPOLL=0</varname> is not set and the file descriptors sent are pollable (see
+        <citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), then any
+        <constant>EPOLLHUP</constant> or <constant>EPOLLERR</constant> event seen on them will result in their
+        automatic removal from the store. Multiple arrays of file descriptors may be sent in separate messages, in
+        which case the arrays are combined. Note that the service manager removes duplicate (pointing to the same
+        object) file descriptors before passing them to the service. When a service is stopped, its file descriptor
+        store is discarded and all file descriptors in it are closed. Use <function>sd_pid_notify_with_fds()</function>
+        to send messages with <literal>FDSTORE=1</literal>, see below.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>FDSTOREREMOVE=1</term>
+
+        <listitem><para>Removes file descriptors from the file descriptor store. This field needs to be combined with
+        <varname>FDNAME=</varname> to specify the name of the file descriptors to remove.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>FDNAME=…</term>
+
+        <listitem><para>When used in combination with <varname>FDSTORE=1</varname>, specifies a name for the submitted
+        file descriptors. When used with <varname>FDSTOREREMOVE=1</varname>, specifies the name for the file
+        descriptors to remove. This name is passed to the service during activation, and may be queried using
+        <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>. File
+        descriptors submitted without this field set, will implicitly get the name <literal>stored</literal>
+        assigned. Note that, if multiple file descriptors are submitted at once, the specified name will be assigned to
+        all of them. In order to assign different names to submitted file descriptors, submit them in separate
+        invocations of <function>sd_pid_notify_with_fds()</function>. The name may consist of arbitrary ASCII
+        characters except control characters or <literal>:</literal>. It may not be longer than 255 characters. If a
+        submitted name does not follow these restrictions, it is ignored.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>FDPOLL=0</term>
+
+        <listitem><para>When used in combination with <varname>FDSTORE=1</varname>, disables polling of the stored
+        file descriptors regardless of whether or not they are pollable. As this option disables automatic cleanup
+        of the stored file descriptors on EPOLLERR and EPOLLHUP, care must be taken to ensure proper manual cleanup.
+        Use of this option is not generally recommended except for when automatic cleanup has unwanted behavior such
+        as prematurely discarding file descriptors from the store.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>BARRIER=1</term>
+
+        <listitem><para>Tells the service manager that the client is explicitly requesting synchronization by
+        means of closing the file descriptor sent with this command. The service manager guarantees that the
+        processing of a <varname>BARRIER=1</varname> command will only happen after all previous notification
+        messages sent before this command have been processed. Hence, this command accompanied with a single
+        file descriptor can be used to synchronize against reception of all previous status messages. Note
+        that this command cannot be mixed with other notifications, and has to be sent in a separate message
+        to the service manager, otherwise all assignments will be ignored. Note that sending 0 or more than 1
+        file descriptor with this command is a violation of the protocol.</para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <para>It is recommended to prefix variable names that are not
+    listed above with <varname>X_</varname> to avoid namespace
+    clashes.</para>
+
+    <para>Note that systemd will accept status data sent from a
+    service only if the <varname>NotifyAccess=</varname> option is
+    correctly set in the service definition file. See
+    <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for details.</para>
+
+    <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
+    the sending process is still around at the time PID 1 processes the message, or if the sending process is
+    explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
+    off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
+    <varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
+    <function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
+    attribute the message to the unit, and thus will ignore it, even if
+    <varname>NotifyAccess=</varname><option>all</option> is set for it.</para>
+
+    <para>Hence, to eliminate all race conditions involving lookup of the client's unit and attribution of notifications
+    to units correctly, <function>sd_notify_barrier()</function> may be used. This call acts as a synchronization point
+    and ensures all notifications sent before this call have been picked up by the service manager when it returns
+    successfully. Use of <function>sd_notify_barrier()</function> is needed for clients which are not invoked by the
+    service manager, otherwise this synchronization mechanism is unnecessary for attribution of notifications to the
+    unit.</para>
+
+    <para><function>sd_notifyf()</function> is similar to
+    <function>sd_notify()</function> but takes a
+    <function>printf()</function>-like format string plus
+    arguments.</para>
+
+    <para><function>sd_pid_notify()</function> and
+    <function>sd_pid_notifyf()</function> are similar to
+    <function>sd_notify()</function> and
+    <function>sd_notifyf()</function> but take a process ID (PID) to
+    use as originating PID for the message as first argument. This is
+    useful to send notification messages on behalf of other processes,
+    provided the appropriate privileges are available. If the PID
+    argument is specified as 0, the process ID of the calling process
+    is used, in which case the calls are fully equivalent to
+    <function>sd_notify()</function> and
+    <function>sd_notifyf()</function>.</para>
+
+    <para><function>sd_pid_notify_with_fds()</function> is similar to
+    <function>sd_pid_notify()</function> but takes an additional array
+    of file descriptors. These file descriptors are sent along the
+    notification message to the service manager. This is particularly
+    useful for sending <literal>FDSTORE=1</literal> messages, as
+    described above. The additional arguments are a pointer to the
+    file descriptor array plus the number of file descriptors in the
+    array. If the number of file descriptors is passed as 0, the call
+    is fully equivalent to <function>sd_pid_notify()</function>, i.e.
+    no file descriptors are passed. Note that sending file descriptors
+    to the service manager on messages that do not expect them (i.e.
+    without <literal>FDSTORE=1</literal>) they are immediately closed
+    on reception.</para>
+
+    <para><function>sd_notify_barrier()</function> allows the caller to
+    synchronize against reception of previously sent notification messages
+    and uses the <varname>BARRIER=1</varname> command. It takes a relative
+    <varname>timeout</varname> value in microseconds which is passed to
+    <citerefentry><refentrytitle>ppoll</refentrytitle><manvolnum>2</manvolnum>
+    </citerefentry>. A value of UINT64_MAX is interpreted as infinite timeout.
+    </para>
+  </refsect1>
+
+  <refsect1>
+    <title>Return Value</title>
+
+    <para>On failure, these calls return a negative errno-style error code. If <varname>$NOTIFY_SOCKET</varname> was
+    not set and hence no status message could be sent, 0 is returned. If the status was sent, these functions return a
+    positive value. In order to support both service managers that implement this scheme and those which do not, it is
+    generally recommended to ignore the return value of this call. Note that the return value simply indicates whether
+    the notification message was enqueued properly, it does not reflect whether the message could be processed
+    successfully. Specifically, no error is returned when a file descriptor is attempted to be stored using
+    <varname>FDSTORE=1</varname> but the service is not actually configured to permit storing of file descriptors (see
+    above).</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Notes</title>
+
+    <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
+
+    <para>These functions send a single datagram with the
+    state string as payload to the <constant>AF_UNIX</constant> socket
+    referenced in the <varname>$NOTIFY_SOCKET</varname> environment
+    variable. If the first character of
+    <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the
+    string is understood as Linux abstract namespace socket. The
+    datagram is accompanied by the process credentials of the sending
+    service, using SCM_CREDENTIALS.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Environment</title>
+
+    <variablelist class='environment-variables'>
+      <varlistentry>
+        <term><varname>$NOTIFY_SOCKET</varname></term>
+
+        <listitem><para>Set by the service manager for supervised
+        processes for status and start-up completion notification.
+        This environment variable specifies the socket
+        <function>sd_notify()</function> talks to. See above for
+        details.</para></listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Examples</title>
+
+    <example>
+      <title>Start-up Notification</title>
+
+      <para>When a service finished starting up, it might issue the
+      following call to notify the service manager:</para>
+
+      <programlisting>sd_notify(0, "READY=1");</programlisting>
+    </example>
+
+    <example>
+      <title>Extended Start-up Notification</title>
+
+      <para>A service could send the following after completing
+      initialization:</para>
+
+      <programlisting>sd_notifyf(0, "READY=1\n"
+        "STATUS=Processing requests…\n"
+        "MAINPID=%lu",
+        (unsigned long) getpid());</programlisting>
+    </example>
+
+    <example>
+      <title>Error Cause Notification</title>
+
+      <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_r(errnum, (char[1024]){}, 1024),
+        errnum);</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", &amp;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>