systemd/man/sd_notify.xml
2015-12-26 20:37:17 +01:00

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<refentry id="sd_notify"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_notify</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</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>
<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>
</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. This is only used by systemd if the service
definition file has Type=notify 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.</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>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 be passed
again using the usual file descriptor passing logic on the
next invocation of the service (see
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
This is useful for implementing service restart schemes where
services serialize their state to <filename>/run</filename>,
push their file descriptors to the system manager, and are
then restarted, retrieving their state again via socket
passing and <filename>/run</filename>. Note that the service
manager will accept messages for a service only if
<varname>FileDescriptorStoreMax=</varname> is set to non-zero
for it (defaults to zero). See
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details. 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 file
descriptors before passing them to the service. Use
<function>sd_pid_notify_with_fds()</function> to send messages
with <literal>FDSTORE=1</literal>, see
below.</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. 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 any ASCII character, but must not contain 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>
</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><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>
</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 data could be sent, 0 is returned. If the status was
sent, these functions return with a positive return value. In
order to support both, init systems that implement this scheme and
those which do not, it is generally recommended to ignore the
return value of this call.</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(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", &amp;fd, 1);</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>