man/user__at__.service.xml

<?xml version="1.0"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="user@.service">
  <refentryinfo>
    <title>user@.service</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>user@.service</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>user@.service</refname>
    <refname>user-runtime-dir@.service</refname>
    <refname>systemd-user-runtime-dir</refname>
    <refpurpose>System units to start the user manager</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>user@<replaceable>UID</replaceable>.service</filename></para>
    <para><filename>user-runtime-dir@<replaceable>UID</replaceable>.service</filename></para>
    <para><filename>/usr/lib/systemd/systemd-user-runtime-dir</filename></para>
    <para><filename>user-<replaceable>UID</replaceable>.slice</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>The <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    system manager (PID 1) starts user manager instances as
    <filename>user@<replaceable>UID</replaceable>.service</filename>, with the user's numerical UID used as
    the instance identifier. These instances use the same executable as the system manager, but running in a
    mode where it starts a different set of units. Each <command>systemd --user</command> instance manages a
    hierarchy of units specific to that user. See
    <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> for a
    discussion of units and
    <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry> for a
    list of units that form the basis of the unit hierarchies of system and user units.</para>

    <para><filename>user@<replaceable>UID</replaceable>.service</filename> is accompanied by the
    system unit <filename>user-runtime-dir@<replaceable>UID</replaceable>.service</filename>, which
    creates the user's runtime directory
    <filename>/run/user/<replaceable>UID</replaceable></filename>, and then removes it when this
    unit is stopped. <filename>user-runtime-dir@<replaceable>UID</replaceable>.service</filename>
    executes the <filename>systemd-user-runtime-dir</filename> binary to do the actual work.</para>

    <para>User processes may be started by the <filename>user@.service</filename> instance, in which
    case they will be part of that unit in the system hierarchy. They may also be started elsewhere,
    for example by
    <citerefentry project='die-net'><refentrytitle>sshd</refentrytitle><manvolnum>8</manvolnum></citerefentry> or a
    display manager like <command>gdm</command>, in which case they form a .scope unit (see
    <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
    Both <filename>user@<replaceable>UID</replaceable>.service</filename> and the scope units are
    collected under the <filename>user-<replaceable>UID</replaceable>.slice</filename>.</para>

    <para>Individual <filename>user-<replaceable>UID</replaceable>.slice</filename> slices are
    collected under <filename>user.slice</filename>, see
    <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
    </para>
  </refsect1>

  <refsect1>
    <title>Controlling resources for logged-in users</title>

    <para>Options that control resources available to logged-in users can be configured at a few
    different levels. As described in the previous section, <filename>user.slice</filename> contains
    processes of all users, so any resource limits on that slice apply to all users together. The
    usual way to configure them would be through drop-ins, e.g. <filename
    index="false">/etc/systemd/system/user.slice.d/resources.conf</filename>.
    </para>

    <para>The processes of a single user are collected under
    <filename>user-<replaceable>UID</replaceable>.slice</filename>. Resource limits for that user
    can be configured through drop-ins for that unit, e.g. <filename
    index="false">/etc/systemd/system/user-1000.slice.d/resources.conf</filename>. If the limits
    should apply to all users instead, they may be configured through drop-ins for the truncated
    unit name, <filename>user-.slice</filename>. For example, configuration in <filename
    index="false">/etc/systemd/system/user-.slice.d/resources.conf</filename> is included in all
    <filename>user-<replaceable>UID</replaceable>.slice</filename> units, see
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for a discussion of the drop-in mechanism.</para>

    <para>When a user logs in and a .scope unit is created for the session (see previous section),
    the creation of the scope may be managed through
    <citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
    This PAM module communicates with
    <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    to create the session scope and provide access to hardware resources. Resource limits for the
    scope may be configured through the PAM module configuration, see
    <citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
    Configuring them through the normal unit configuration is also possible, but since
    the name of the slice unit is generally unpredictable, this is less useful.</para>

    <para>In general any resources that apply to units may be set for
    <filename>user@<replaceable>UID</replaceable>.service</filename> and the slice
    units discussed above, see
    <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for an overview.</para>
  </refsect1>

  <refsect1>
    <title>Examples</title>
    <example>
      <title>Hierarchy of control groups with two logged in users</title>

      <programlisting>$ systemd-cgls
Control group /:
-.slice
├─user.slice
│ ├─user-1000.slice
│ │ ├─user@1000.service
│ │ │ ├─pulseaudio.service
│ │ │ │ └─2386 /usr/bin/pulseaudio --daemonize=no
│ │ │ └─gnome-terminal-server.service
│ │ │   └─init.scope
│ │ │     ├─ 4127 /usr/libexec/gnome-terminal-server
│ │ │     └─ 4198 zsh
│ │ …
│ │ └─session-4.scope
│ │   ├─ 1264 gdm-session-worker [pam/gdm-password]
│ │   ├─ 2339 /usr/bin/gnome-shell
│ │   …
│ │ ├─session-19.scope
│ │   ├─6497 sshd: zbyszek [priv]
│ │   ├─6502 sshd: zbyszek@pts/6
│ │   ├─6509 -zsh
│ │   └─6602 systemd-cgls --no-pager
│ …
│ └─user-1001.slice
│   ├─session-20.scope
│   │ ├─6675 sshd: guest [priv]
│   │ ├─6708 sshd: guest@pts/6
│   │ └─6717 -bash
│   └─user@1001.service
│     ├─init.scope
│     │ ├─6680 /usr/lib/systemd/systemd --user
│     │ └─6688 (sd-pam)
│     └─sleep.service
│       └─6706 /usr/bin/sleep 30
…</programlisting>
      <para>User with UID 1000 is logged in using <command>gdm</command> (<filename
      index="false">session-4.scope</filename>) and
      <citerefentry project='die-net'><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>
      (<filename index="false">session-19.scope</filename>), and also has a user manager instance
      running (<filename index="false">user@1000.service</filename>).  User with UID 1001 is logged
      in using <command>ssh</command> (<filename index="false">session-20.scope</filename>) and
      also has a user manager instance running (<filename
      index="false">user@1001.service</filename>).  Those are all (leaf) system units, and form
      part of the slice hierarchy, with <filename index="false">user-1000.slice</filename> and
      <filename index="false">user-1001.slice</filename> below <filename
      index="false">user.slice</filename>.  User units are visible below the
      <filename>user@.service</filename> instances (<filename
      index="false">pulseaudio.service</filename>, <filename
      index="false">gnome-terminal-server.service</filename>, <filename
      index="false">init.scope</filename>, <filename index="false">sleep.service</filename>).
      </para>
    </example>

    <example>
      <title>Default user resource limits</title>

      <programlisting>$ systemctl cat user-1000.slice
# /usr/lib/systemd/system/user-.slice.d/10-defaults.conf
# …
[Unit]
Description=User Slice of UID %j
After=systemd-user-sessions.service

[Slice]
TasksMax=33%</programlisting>
     <para>The <filename>user-<replaceable>UID</replaceable>.slice</filename> units by default don't
     have a unit file. The resource limits are set through a drop-in, which can be easily replaced
     or extended following standard drop-in mechanisms discussed in the first section.</para>
    </example>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    </para>
  </refsect1>
</refentry>