man: de-emphasize *_get_session()

Explanation:

"Please note the login session may be limited to a stub
 process or two.  User processes may instead be started from their
 systemd user manager, e.g. GUI applications started using DBus
 activation, as well as service processes which are shared between
 multiple logins of the same user."

The most glaring example being when you run commands from gnome-terminal,
or as you see nowadays, "gnome-terminal-server".

*_get_session() is still currently used (directly or indirectly) by Xorg,
Weston etc. running within the session scope.  That setup is perfectly
functional, although code will be more generally useful if it is able to
run outside the session scope.[1]

[1] https://wiki.archlinux.org/index.php/Systemd/User#Xorg_as_a_systemd_user_service

Re-order the man pages a bit at the same time.  This is to avoid having the
first and titular entry introduce the session concept, and then immediately
try and persuade you not to use it :).

1 files changed, 361 insertions, 0 deletions

diff --git a/man/sd_pid_get_owner_uid.xml b/man/sd_pid_get_owner_uid.xml
new file mode 100644
index 0000000000..5a2a07d096
--- /dev/null
+++ b/man/sd_pid_get_owner_uid.xml
@@ -0,0 +1,361 @@
+<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+  This file is part of systemd.
+
+  Copyright 2010 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="sd_pid_get_owner_uid" conditional='HAVE_PAM'>
+
+  <refentryinfo>
+    <title>sd_pid_get_owner_uid</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_owner_uid</refentrytitle>
+    <manvolnum>3</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>sd_pid_get_owner_uid</refname>
+    <refname>sd_pid_get_session</refname>
+    <refname>sd_pid_get_user_unit</refname>
+    <refname>sd_pid_get_unit</refname>
+    <refname>sd_pid_get_machine_name</refname>
+    <refname>sd_pid_get_slice</refname>
+    <refname>sd_pid_get_user_slice</refname>
+    <refname>sd_pid_get_cgroup</refname>
+    <refname>sd_peer_get_owner_uid</refname>
+    <refname>sd_peer_get_session</refname>
+    <refname>sd_peer_get_user_unit</refname>
+    <refname>sd_peer_get_unit</refname>
+    <refname>sd_peer_get_machine_name</refname>
+    <refname>sd_peer_get_slice</refname>
+    <refname>sd_peer_get_user_slice</refname>
+    <refname>sd_peer_get_cgroup</refname>
+    <refpurpose>Determine the owner uid of the user unit or session,
+    or the session, user unit, system unit, container/VM or slice that
+    a specific PID or socket peer belongs to.</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <funcsynopsis>
+      <funcsynopsisinfo>#include &lt;systemd/sd-login.h&gt;</funcsynopsisinfo>
+
+      <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>
+
+      <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_user_unit</function></funcdef>
+        <paramdef>pid_t <parameter>pid</parameter></paramdef>
+        <paramdef>char **<parameter>unit</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_machine_name</function></funcdef>
+        <paramdef>pid_t <parameter>pid</parameter></paramdef>
+        <paramdef>char **<parameter>name</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_pid_get_slice</function></funcdef>
+        <paramdef>pid_t <parameter>pid</parameter></paramdef>
+        <paramdef>char **<parameter>slice</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_pid_get_user_slice</function></funcdef>
+        <paramdef>pid_t <parameter>pid</parameter></paramdef>
+        <paramdef>char **<parameter>slice</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_pid_get_cgroup</function></funcdef>
+        <paramdef>pid_t <parameter>pid</parameter></paramdef>
+        <paramdef>char **<parameter>cgroup</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_peer_get_owner_uid</function></funcdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+        <paramdef>uid_t *<parameter>uid</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_peer_get_session</function></funcdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+        <paramdef>char **<parameter>session</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_peer_get_user_unit</function></funcdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+        <paramdef>char **<parameter>unit</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_peer_get_unit</function></funcdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+        <paramdef>char **<parameter>unit</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_peer_get_machine_name</function></funcdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+        <paramdef>char **<parameter>name</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_peer_get_slice</function></funcdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+        <paramdef>char **<parameter>slice</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_peer_get_user_slice</function></funcdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+        <paramdef>char **<parameter>slice</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_peer_get_cgroup</function></funcdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+        <paramdef>char **<parameter>cgroup</parameter></paramdef>
+      </funcprototype>
+    </funcsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para><function>sd_pid_get_owner_uid()</function> may be used to
+    determine the Unix UID (user identifier) which owns the login
+    session or systemd user unit of a process identified by the
+    specified PID. For processes which are not part of a login session
+    and not managed by a user manager, this function will fail with
+    <constant>-ENODATA</constant>.</para>
+
+    <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. Please
+    note the login session may be limited to a stub process or two.
+    User processes may instead be started from their systemd user
+    manager, e.g. GUI applications started using DBus activation, as
+    well as service processes which are shared between multiple logins
+    of the same user. For processes which are not part of a login
+    session, this function will fail with <constant>-ENODATA</constant>.
+    The returned string needs to be freed with the libc <citerefentry
+    project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    call after use.</para>
+
+    <para><function>sd_pid_get_user_unit()</function> may be used to
+    determine the systemd user unit (i.e. user service or scope unit)
+    identifier of a process identified by the specified PID. The
+    unit name is a short string, suitable for usage in file system
+    paths. For processes which are not managed by a user manager, this
+    function will fail with <constant>-ENODATA</constant>. The
+    returned string needs to be freed with the libc <citerefentry
+    project='man-pages'><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 system unit (i.e. system service or scope
+    unit) identifier of a process identified by the specified PID. The
+    unit name is a short string, suitable for usage in file system
+    paths.  Note that not all processes are part of a system
+    unit/service. For processes not being part of a systemd system
+    unit, this function will fail with <constant>-ENODATA</constant>.
+    (More specifically, this call will not work for kernel threads.)
+    The returned string needs to be freed with the libc <citerefentry
+    project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    call after use.</para>
+
+    <para><function>sd_pid_get_machine_name()</function> may be used
+    to determine the name of the VM or container is a member of. The
+    machine name is a short string, suitable for usage in file system
+    paths. The returned string needs to be freed with the libc
+    <citerefentry
+    project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    call after use. For processes not part of a VM or container, this
+    function fails with <constant>-ENODATA</constant>.</para>
+
+    <para><function>sd_pid_get_slice()</function> may be used to
+    determine the slice unit the process is a member of. See
+    <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for details about slices. The returned string needs to be freed
+    with the libc
+    <citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    call after use.</para>
+
+    <para>Similarly, <function>sd_pid_get_user_slice()</function>
+    returns the user slice (as managed by the user's systemd instance)
+    of a process.</para>
+
+    <para><function>sd_pid_get_cgroup()</function> returns the control
+    group path of the specified process, relative to the root of the
+    hierarchy. Returns the path without trailing slash, except for
+    processes located in the root control group, where "/" is
+    returned. To find the actual control group path in the file system,
+    the returned path needs to be prefixed with
+    <filename>/sys/fs/cgroup/</filename> (if the unified control group
+    setup is used), or
+    <filename>/sys/fs/cgroup/<replaceable>HIERARCHY</replaceable>/</filename>
+    (if the legacy multi-hierarchy control group setup is used).</para>
+
+    <para>If the <varname>pid</varname> parameter of any of these
+    functions is passed as 0, the operation is executed for the
+    calling process.</para>
+
+    <para>The <function>sd_peer_get_owner_uid()</function>,
+    <function>sd_peer_get_session()</function>,
+    <function>sd_peer_get_user_unit()</function>,
+    <function>sd_peer_get_unit()</function>,
+    <function>sd_peer_get_machine_name()</function>,
+    <function>sd_peer_get_slice()</function>,
+    <function>sd_peer_get_user_slice()</function> and
+    <function>sd_peer_get_cgroup()</function> calls operate similar to
+    their PID counterparts, but operate on a connected AF_UNIX socket
+    and retrieve information about the connected peer process. Note
+    that these fields are retrieved via <filename>/proc</filename>,
+    and hence are not suitable for authorization purposes, as they are
+    subject to races.</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>Errors</title>
+
+    <para>Returned errors may indicate the following problems:</para>
+
+    <variablelist>
+
+      <varlistentry>
+        <term><constant>-ESRCH</constant></term>
+
+        <listitem><para>The specified PID does not refer to a running
+        process.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>-EBADF</constant></term>
+
+        <listitem><para>The specified socket file descriptor was
+        invalid.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>-ENODATA</constant></term>
+
+        <listitem><para>The given field is not specified for the described
+        process or peer.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>-EINVAL</constant></term>
+
+        <listitem><para>An input parameter was invalid (out of range,
+        or NULL, where that is not accepted).</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>-ENOMEM</constant></term>
+
+        <listitem><para>Memory allocation failed.</para></listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Notes</title>
+
+    <para>The <function>sd_pid_get_session()</function>,
+    <function>sd_pid_get_unit()</function>,
+    <function>sd_pid_get_user_unit()</function>,
+    <function>sd_pid_get_owner_uid()</function>,
+    <function>sd_pid_get_machine_name()</function>,
+    <function>sd_pid_get_slice()</function>,
+    <function>sd_pid_get_user_slice()</function>,
+    <function>sd_peer_get_session()</function>,
+    <function>sd_peer_get_unit()</function>,
+    <function>sd_peer_get_user_unit()</function>,
+    <function>sd_peer_get_owner_uid()</function>,
+    <function>sd_peer_get_machine_name()</function>,
+    <function>sd_peer_get_slice()</function> and
+    <function>sd_peer_get_user_slice()</function> interfaces are
+    available as a shared library, which can be compiled and linked to
+    with the <constant>libsystemd</constant> <citerefentry
+    project='die-net'><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>,
+      <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+
+</refentry>