systemd/man/sd_pid_get_session.xml

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        "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

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<refentry id="sd_pid_get_session">

        <refentryinfo>
                <title>sd_pid_get_session</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_pid_get_session</refentrytitle>
                <manvolnum>3</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>sd_pid_get_session</refname>
                <refname>sd_pid_get_unit</refname>
                <refname>sd_pid_get_owner_uid</refname>
                <refpurpose>Determine session, service or owner of a session of a specific PID</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <funcsynopsis>
                        <funcsynopsisinfo>#include &lt;systemd/sd-login.h&gt;</funcsynopsisinfo>

                        <funcprototype>
                                <funcdef>int <function>sd_pid_get_session</function></funcdef>
                                <paramdef>pid_t <parameter>pid</parameter></paramdef>
                                <paramdef>char** <parameter>session</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_pid_get_unit</function></funcdef>
                                <paramdef>pid_t <parameter>pid</parameter></paramdef>
                                <paramdef>char** <parameter>unit</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_pid_get_owner_uid</function></funcdef>
                                <paramdef>pid_t <parameter>pid</parameter></paramdef>
                                <paramdef>uid_t* <parameter>uid</parameter></paramdef>
                        </funcprototype>
                </funcsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para><function>sd_pid_get_session()</function> may be
                used to determine the login session identifier of a
                process identified by the specified process
                identifier. The session identifier is a short string,
                suitable for usage in file system paths. Note that not
                all processes are part of a login session (e.g. system
                service processes, user processes that are shared
                between multiple sessions of the same user, or kernel
                threads). For processes not being part of a login
                session this function will fail. The returned string
                needs to be freed with the libc
                <citerefentry><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                call after use.</para>

                <para><function>sd_pid_get_unit()</function> may be
                used to determine the systemd unit (i.e. system
                service) identifier of a process identified by the
                specified process identifier. The unit name is a short
                string, suitable for usage in file system paths. Note
                that not all processes are part of a unit/service
                (e.g. user processes, or kernel threads). For
                processes not being part of a systemd unit/system
                service this function will fail. The returned string
                needs to be freed with the libc
                <citerefentry><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                call after use.</para>

                <para><function>sd_pid_get_owner_uid()</function> may
                be used to determine the Unix user identifier of the
                owner of the session of a process identified the
                specified PID. Note that this function will succeed
                for user processes which are shared between multiple
                login sessions of the same user, where
                <function>sd_pid_get_session()</function> will
                fail. For processes not being part of a login session
                and not being a shared process of a user this function
                will fail.</para>

                <para>If the <literal>pid</literal> paramater of any
                of these functions is passed as 0 the operation is
                executed for the calling process.</para>
        </refsect1>

        <refsect1>
                <title>Return Value</title>

                <para>On success these calls return 0 or a positive
                integer. On failure, these calls return a negative
                errno-style error code.</para>
        </refsect1>

        <refsect1>
                <title>Notes</title>

                <para>The <function>sd_pid_get_session()</function>,
                <function>sd_pid_get_pid()</function>, and
                <function>sd_pid_get_owner_uid()</function> interfaces
                are available as shared library, which can be compiled
                and linked to with the
                <literal>libsystemd-login</literal>
                <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                file.</para>

                <para>Note that the login session identifier as
                returned by <function>sd_pid_get_session()</function>
                is completely unrelated to the process session
                identifier as returned by
                <citerefentry><refentrytitle>getsid</refentrytitle><manvolnum>2</manvolnum></citerefentry>.</para>
        </refsect1>

        <refsect1>
                <title>See Also</title>

                <para>
                        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd-login</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_session_is_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>getsid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>