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diff --git a/man/sd_notify.xml b/man/sd_notify.xml new file mode 100644 index 0000000..7c32a22 --- /dev/null +++ b/man/sd_notify.xml @@ -0,0 +1,589 @@ +<?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_pid_notifyf_with_fds</refname> + <refname>sd_notify_barrier</refname> + <refname>sd_pid_notify_barrier</refname> + <refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose> + </refnamediv> + + <refsynopsisdiv> + <funcsynopsis> + <funcsynopsisinfo>#include <systemd/sd-daemon.h></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_pid_notifyf_with_fds</function></funcdef> + <paramdef>pid_t <parameter>pid</parameter></paramdef> + <paramdef>int <parameter>unset_environment</parameter></paramdef> + <paramdef>const int *<parameter>fds</parameter></paramdef> + <paramdef>size_t <parameter>n_fds</parameter></paramdef> + <paramdef>const char *<parameter>format</parameter></paramdef> + <paramdef>…</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> + + <funcprototype> + <funcdef>int <function>sd_pid_notify_barrier</function></funcdef> + <paramdef>pid_t <parameter>pid</parameter></paramdef> + <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 or reload completion notifications.</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, and 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 see the next section + for a list of assignments understood by the service manager.</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 file descriptors sent to the service manager on a message without <literal>FDSTORE=1</literal> are + immediately closed on reception.</para> + + <para><function>sd_pid_notifyf_with_fds()</function> is a combination of + <function>sd_pid_notify_with_fds()</function> and <function>sd_notifyf()</function>, i.e. it accepts both + a PID and a set of file descriptors as input, and processes a format string to generate the state + string.</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> + + <para><function>sd_pid_notify_barrier()</function> is just like <function>sd_notify_barrier()</function>, + but allows specifying the originating PID for the notification message.</para> + </refsect1> + + <refsect1> + <title>Well-known assignments</title> + + <para>The following assignments have a defined meaning:</para> + + <variablelist> + <varlistentry> + <term>READY=1</term> + + <listitem><para>Tells the service manager that service startup is finished, or the service finished + re-loading its configuration. This is only used by systemd if the service definition file has + <varname>Type=notify</varname> or <varname>Type=notify-reload</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 beginning to reload 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 the + service manager is notified about with this mechanisms are propagated in the same way as they are + when originally initiated through the service manager. This message is particularly relevant for + <varname>Type=notify-reload</varname> services, to inform the service manager that the request to + reload the service has been received and is now being processed.</para> + + <xi:include href="version-info.xml" xpointer="v217"/></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> + + <xi:include href="version-info.xml" xpointer="v217"/></listitem> + </varlistentry> + + <varlistentry> + <term>MONOTONIC_USEC=…</term> + + <listitem><para>A field carrying the monotonic timestamp (as per + <constant>CLOCK_MONOTONIC</constant>) formatted in decimal in μs, when the notification message was + generated by the client. This is typically used in combination with <literal>RELOADING=1</literal>, + to allow the service manager to properly synchronize reload cycles. See + <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> + for details, specifically <literal>Type=notify-reload</literal>.</para> + + <xi:include href="version-info.xml" xpointer="v253"/></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> + + <xi:include href="version-info.xml" xpointer="v233"/></listitem> + </varlistentry> + + <varlistentry> + <term>NOTIFYACCESS=…</term> + + <listitem><para>Reset the access to the service status notification socket during runtime, overriding + <varname>NotifyAccess=</varname> setting in the service unit file. See + <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> + for details, specifically <literal>NotifyAccess=</literal> for a list of accepted values. + </para> + + <xi:include href="version-info.xml" xpointer="v254"/></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> + + <xi:include href="version-info.xml" xpointer="v233"/></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>. Note that this assignment is + currently not used by <command>systemd</command>.</para> + + <xi:include href="version-info.xml" xpointer="v233"/></listitem> + </varlistentry> + + <varlistentry> + <term>EXIT_STATUS=…</term> + + <listitem><para>The exit status of a service or the manager itself. Note that + <command>systemd</command> currently does not consume this value when sent by services, so this + assignment is only informational. The manager will send this notification to <emphasis>its</emphasis> + notification socket, which may be used to to collect an exit status from the system (a container or + VM) as it shuts down. For example, + <citerefentry project='debian'><refentrytitle>mkosi</refentrytitle><manvolnum>1</manvolnum></citerefentry> + makes use of this. The value to return may be set via the + <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> + <command>exit</command> verb.</para> + + <xi:include href="version-info.xml" xpointer="v254"/></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> + + <xi:include href="version-info.xml" xpointer="v233"/></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> + + <xi:include href="version-info.xml" xpointer="v243"/></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> + + <xi:include href="version-info.xml" xpointer="v233"/></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> + + <xi:include href="version-info.xml" xpointer="v236"/></listitem> + </varlistentry> + + <varlistentry> + <term>FDSTORE=1</term> + + <listitem><para>Store file descriptors in the service manager. File descriptors sent this way will be + held for the service by the service manager and will later be handed back using the usual file + descriptor passing logic at the next start or restart of the service, see + <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>. + Any open sockets and other file descriptors which should not be closed during a restart may be stored + this way. When a service is stopped, its file descriptor store is discarded and all file descriptors + in it are closed, except when overridden with <varname>FileDescriptorStorePreserve=</varname>, see + <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>. + </para> + + <para>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>). + The service manager will set the <varname>$FDSTORE</varname> environment variable for services that + have the file descriptor store enabled, see + <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>. + </para> + + <para>If <varname>FDPOLL=0</varname> is not set and the file descriptors 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.</para> + + <para>Multiple sets of file descriptors may be sent in separate messages, in which case the sets are + combined. The service manager removes duplicate file descriptors (those pointing to the same object) + before passing them to the service.</para> + + <para>This functionality should be used to implement services that can restart after an explicit + request or a crash without losing state. 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. Use <function>sd_pid_notify_with_fds()</function> to send messages with + <literal>FDSTORE=1</literal>. It is recommended to combine <varname>FDSTORE=</varname> with + <varname>FDNAME=</varname> to make it easier to manage the stored file descriptors.</para> + + <para>For further information on the file descriptor store see the <ulink + url="https://systemd.io/FILE_DESCRIPTOR_STORE">File Descriptor Store</ulink> overview.</para> + + <xi:include href="version-info.xml" xpointer="v219"/></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> + + <xi:include href="version-info.xml" xpointer="v236"/></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 will be called <literal>stored</literal>.</para> + + <para>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> + + <para>Note that if multiple file descriptors are submitted in a single message, the specified name + will be used for all of them. In order to assign different names to submitted file descriptors, + submit them in separate messages.</para> + + <xi:include href="version-info.xml" xpointer="v233"/></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> + + <xi:include href="version-info.xml" xpointer="v246"/></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> + + <xi:include href="version-info.xml" xpointer="v246"/></listitem> + </varlistentry> + </variablelist> + + <para>The notification messages sent by services are interpreted by the service manager. Unknown + assignments may be logged, but are otherwise ignored. Thus, it is not useful to send assignments which + are not in this list. The service manager also sends some messages to <emphasis>its</emphasis> + notification socket, which are then consumed by the machine or container manager.</para> + </refsect1> + + <refsect1> + <title>Return Value</title> + + <para>On failure, these calls return a negative errno-style error code. If + <varname>$NOTIFY_SOCKET</varname> was not set and hence no status message could be sent, 0 is + returned. If the status was sent, these functions return a positive value. In order to support both + service managers that implement this scheme and those which do not, it is generally recommended to ignore + the return value of this call. Note that the return value simply indicates whether the notification + message was enqueued properly, it does not reflect whether the message could be processed + successfully. Specifically, no error is returned when a file descriptor is attempted to be stored using + <varname>FDSTORE=1</varname> but the service is not actually configured to permit storing of file + descriptors (see above).</para> + </refsect1> + + <refsect1> + <title>Notes</title> + + <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/> + <xi:include href="threads-aware.xml" xpointer="getenv"/> + + <para>These functions send a single datagram with the state string as payload to the socket referenced in + the <varname>$NOTIFY_SOCKET</varname> environment variable. If the first character of + <varname>$NOTIFY_SOCKET</varname> is <literal>/</literal> or <literal>@</literal>, the string is + understood as an <constant>AF_UNIX</constant> or Linux abstract namespace socket (respectively), and in + both cases the datagram is accompanied by the process credentials of the sending service, using + SCM_CREDENTIALS. If the string starts with <literal>vsock:</literal> then the string is understood as an + <constant>AF_VSOCK</constant> address, which is useful for hypervisors/VMMs or other processes on the + host to receive a notification when a virtual machine has finished booting. Note that in case the + hypervisor does not support <constant>SOCK_DGRAM</constant> over <constant>AF_VSOCK</constant>, + <constant>SOCK_SEQPACKET</constant> will be used instead. The address should be in the form: + <literal>vsock:CID:PORT</literal>. Note that unlike other uses of vsock, the CID is mandatory and cannot + be <literal>VMADDR_CID_ANY</literal>. Note that PID1 will send the VSOCK packets from a privileged port + (i.e.: lower than 1024), as an attempt to address concerns that unprivileged processes in the guest might + try to send malicious notifications to the host, driving it to make destructive decisions based on + them.</para> + </refsect1> + + <refsect1> + <title>Environment</title> + + <variablelist class='environment-variables'> + <varlistentry> + <term><varname>$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", &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>History</title> + <para><function>sd_pid_notify()</function>, + <function>sd_pid_notifyf()</function>, and + <function>sd_pid_notify_with_fds()</function> were added in version 219.</para> + <para><function>sd_notify_barrier()</function> was added in version 246.</para> + <para><function>sd_pid_notifyf_with_fds()</function> and + <function>sd_pid_notify_barrier()</function> were added in version 254.</para> + </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> |