66e411811b
Previously we were testing whether /sys/fs/cgroup/systemd/ was a mount point. This might be problematic however, when the cgroup trees are bind mounted into a container from the host (which should be absolutely valid), which might create the impression that the container was running systemd, but only the host actually is. Replace this by a check for the existance of the directory /run/systemd/system/, which should work unconditionally, since /run can never be a bind mount but *must* be a tmpfs on systemd systems, which is flushed at boots. This means that data in /run always reflects information about the current boot, and only of the local container, which makes it the perfect choice for a check like this. (As side effect this is nice to Ubuntu people who now use logind with the systemd cgroup hierarchy, where the old sd_booted() check misdetects systemd, even though they still run legacy Upstart.)
128 lines
5.3 KiB
XML
128 lines
5.3 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2010 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_booted">
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<refentryinfo>
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<title>sd_booted</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_booted</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_booted</refname>
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<refpurpose>Test whether the system is running the systemd init system</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_booted</function></funcdef>
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<paramdef>void</paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_booted()</function> checks whether
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the system was booted up using the systemd init system.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On failure, this call returns a negative
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errno-style error code. If the system was booted up
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with systemd as init system, this call returns a
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positive return value, zero otherwise.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>This function is provided by the reference
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implementation of APIs for new-style daemons and
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distributed with the systemd package. The algorithm it
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implements is simple, and can easily be reimplemented
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in daemons if it is important to support this
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interface without using the reference
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implementation.</para>
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<para>Internally, this function checks whether the
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directory <filename>/run/systemd/system/</filename>
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exists. A simple check like this can also be
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implemented trivially in shell or any other
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language.</para>
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<para>For details about the algorithm check the
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liberally licensed reference implementation sources:
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<ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c"/>
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and <ulink
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url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
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<para><function>sd_booted()</function> is implemented
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in the reference implementation's
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<filename>sd-daemon.c</filename> and
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<filename>sd-daemon.h</filename> files. These
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interfaces are available as shared library, which can
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be compiled and linked to with the
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<literal>libsystemd-daemon</literal>
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<citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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file. Alternatively, applications consuming these APIs
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may copy the implementation into their source
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tree. For more details about the reference
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implementation see
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<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>If the reference implementation is used as
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drop-in files and -DDISABLE_SYSTEMD is set during
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compilation this function will always return 0 and
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otherwise become a NOP.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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