| <?xml version='1.0'?> <!--*-nxml-*--> |
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| Copyright 2010 Lennart Poettering |
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| |
| <refentry id="sd_notify"> |
| |
| <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> |
| <refpurpose>Notify init system about start-up completion and other daemon 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> |
| </funcsynopsis> |
| </refsynopsisdiv> |
| |
| <refsect1> |
| <title>Description</title> |
| <para><function>sd_notify()</function> shall be called |
| by a daemon to notify the init system about status |
| 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 |
| 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 an 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 init system |
| that daemon startup is finished. This |
| is only used by systemd if the service |
| definition file has Type=notify |
| set. The passed argument is a boolean |
| "1" or "0". Since there is little |
| value in signalling non-readiness, the |
| only value daemons should send is |
| "READY=1".</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term>STATUS=...</term> |
| |
| <listitem><para>Passes a single-line |
| status string back to the init system |
| that describes the daemon 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: |
| "STATUS=Completed 66% of file system |
| check..."</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term>ERRNO=...</term> |
| |
| <listitem><para>If a daemon fails, the |
| errno-style error code, formatted as |
| string. Example: "ERRNO=2" for |
| ENOENT.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term>BUSERROR=...</term> |
| |
| <listitem><para>If a daemon fails, the |
| D-Bus error-style error code. Example: |
| "BUSERROR=org.freedesktop.DBus.Error.TimedOut"</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term>MAINPID=...</term> |
| |
| <listitem><para>The main pid of the |
| daemon, in case the init system did |
| not fork off the process |
| itself. Example: |
| "MAINPID=4711"</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term>WATCHDOG=1</term> |
| |
| <listitem><para>Tells systemd to |
| update the watchdog timestamp. |
| Services using this feature should do |
| this in regular intervals. A watchdog |
| framework can use the timestamps to |
| detect failed |
| services.</para></listitem> |
| </varlistentry> |
| </variablelist> |
| |
| <para>It is recommended to prefix variable names that |
| are not shown in the list above with |
| <varname>X_</varname> to avoid namespace |
| clashes.</para> |
| |
| <para>Note that systemd will accept status data sent |
| from a daemon 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> |
| </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 |
| don't, it is generally recommended to ignore the return |
| value of this call.</para> |
| </refsect1> |
| |
| <refsect1> |
| <title>Notes</title> |
| |
| <para>These functions are provided by the reference |
| implementation of APIs for new-style daemons and |
| distributed with the systemd package. The algorithms |
| they implement are simple, and can easily be |
| reimplemented in daemons if it is important to support |
| this interface without using the reference |
| implementation.</para> |
| |
| <para>Internally, these functions send a single |
| datagram with the state string as payload to the |
| AF_UNIX socket referenced in the |
| <varname>$NOTIFY_SOCKET</varname> environment |
| variable. If the first character of |
| <varname>$NOTIFY_SOCKET</varname> is @ the string is |
| understood as Linux abstract namespace socket. The |
| datagram is accompanied by the process credentials of |
| the sending daemon, using SCM_CREDENTIALS.</para> |
| |
| <para>For details about the algorithms check the |
| liberally licensed reference implementation sources: |
| <ulink url="http://cgit.freedesktop.org/systemd/plain/src/sd-daemon.c"/> |
| resp. <ulink |
| url="http://cgit.freedesktop.org/systemd/plain/src/systemd/sd-daemon.h"/></para> |
| |
| <para><function>sd_notify()</function> and |
| <function>sd_notifyf()</function> are implemented in |
| the reference implementation's |
| <filename>sd-daemon.c</filename> and |
| <filename>sd-daemon.h</filename> files. These |
| interfaces are available as shared library, which can |
| be compiled and linked to with the |
| <literal>libsystemd-daemon</literal> |
| <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
| file. Alternatively, applications consuming these APIs |
| may copy the implementation into their source tree. For |
| more details about the reference implementation see |
| <citerefentry><refentrytitle>sd_daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> |
| |
| <para>If the reference implementation is used as |
| drop-in files and -DDISABLE_SYSTEMD is set during |
| compilation these functions will always return 0 and |
| otherwise become a NOP.</para> |
| </refsect1> |
| |
| <refsect1> |
| <title>Environment</title> |
| |
| <variablelist> |
| <varlistentry> |
| <term><varname>$NOTIFY_SOCKET</varname></term> |
| |
| <listitem><para>Set by the init system |
| 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 daemon finished starting up, it |
| might issue the following call to notify |
| the init system:</para> |
| |
| <programlisting>sd_notify(0, "READY=1");</programlisting> |
| </example> |
| |
| <example> |
| <title>Extended Start-up Notification</title> |
| |
| <para>A daemon 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 daemon 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> |
| </refsect1> |
| |
| <refsect1> |
| <title>See Also</title> |
| <para> |
| <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>sd_daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| </para> |
| </refsect1> |
| |
| </refentry> |