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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

seperate invocations of

<function>sd_pid_notify_with_fds()</function>. The name may

consist of any ASCII characters, 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>Internally, 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>