Beyond Linux® From Scratch (System V Edition) - Version 11.3

Chapter 12. System Utilities

elogind-246.10

Introduction to elogind

elogind is the systemd project's "logind", extracted to be a standalone daemon. It integrates with Linux-PAM-1.5.2 to track all the users logged in to a system, and whether they are logged in graphically, on the console, or remotely. Elogind exposes this information via the standard org.freedesktop.login1 D-Bus interface, and also through the file system using systemd's standard /run/systemd layout.

This package is known to build and work properly using an LFS 11.3 platform.

Package Information

elogind Dependencies

Required

dbus-1.14.6

Recommended

Linux-PAM-1.5.2 (required for Xorg), Polkit-122 (runtime), docbook-xml-4.5, docbook-xsl-nons-1.79.2, and libxslt-1.1.37 (all three to build the man pages)

Optional

For the tests: lxml-4.9.2, gobject-introspection-1.74.0, zsh-5.9, Valgrind-3.20.0, audit-userspace, bash-completion, kexec, and SELinux

User Notes: https://wiki.linuxfromscratch.org/blfs/wiki/elogind

Kernel Configuration

Enable the following options in the kernel configuration and recompile the kernel if necessary: 

General setup --->
    [*]     Control Group support                        [CONFIG_CGROUPS]
File systems --->
    [*]     Inotify support for userspace                [CONFIG_INOTIFY_USER]
            Pseudo filesystems --->
                [*]    Tmpfs POSIX Access Control Lists  [CONFIG_TMPFS_POSIX_ACL]

In addition, some tests need the userspace cryptographic kernel API, which is enabled with: 

-*- Cryptographic API --->                               [CONFIG_CRYPTO]
   <M/*> Userspace cryptographic algorithm configuration [CONFIG_CRYPTO_USER]
   <M/*> User-space interface for hash algorithms        [CONFIG_CRYPTO_USER_API_HASH]

Installation of elogind

Install elogind by running the following commands: 

sed -i '/Disable polkit/,+8 d' meson.build &&

sed '/request_name/i\
r = sd_bus_set_exit_on_disconnect(m->bus, true);\
if (r < 0)\
    return log_error_errno(r, "Failed to set exit on disconnect: %m");' \
    -i src/login/logind.c &&

mkdir build &&
cd    build &&

meson --prefix=/usr                        \
      --buildtype=release                  \
      -Dcgroup-controller=elogind          \
      -Ddbuspolicydir=/etc/dbus-1/system.d \
      -Dman=auto                           \
      ..  &&
ninja

To test the results, issue: ninja test. A few tests are skipped if not run with root privileges.

Now, as the root user: 

ninja install                                           &&
ln -sfv  libelogind.pc /usr/lib/pkgconfig/libsystemd.pc &&
ln -sfvn elogind /usr/include/systemd

Command Explanations

sed ... meson.build: This change allows the package to be built without polkit being installed (it is still a runtime dependency) but able to use polkit after that package is installed.

sed ... src/login/logind.c: This change allows the elogind daemon to exit when it is disconnected from dbus (for example when dbus is killed).

-Dcgroup-controller=elogind: This switch ensures that elogind is selected as the cgroup controller, even if booted with another running cgroup controller.

-Ddbuspolicydir=/etc/dbus-1/system.d: This switch sets the location of the D-Bus policy directory.

-Dman=auto: The default value of this switch is false. Setting it to auto allows building and installing the man pages if the recommended dependencies are installed.

-Ddefault-kill-user-processes=false: Determines whether the processes of a user should be killed when the user logs out. The default is true, but this defeats the traditional use of screen or tmux. This can also be changed in the configuration file (see below).

ln -s ...: These commands install symlinks so that software packages can find the systemd-compatible library and headers.

Configuring elogind

Config File

/etc/elogind/logind.conf

Configuration Information

The installed file /etc/elogind/logind.conf contains all the possible options with their defaults, commented out. You may wish to disable automatically killing user processes when the user logs out, by running, as the root user: 

sed -e '/\[Login\]/a KillUserProcesses=no' \
    -i /etc/elogind/logind.conf

Each user will need to register a user session using Linux-PAM at login. The /etc/pam.d/system-session file needs to be modified and a new file must be created in order for elogind to work correctly. Run the following commands as the root user: 

cat >> /etc/pam.d/system-session << "EOF" &&
# Begin elogind addition

session  required    pam_loginuid.so
session  optional    pam_elogind.so

# End elogind addition
EOF
cat > /etc/pam.d/elogind-user << "EOF"
# Begin /etc/pam.d/elogind-user

account  required    pam_access.so
account  include     system-account

session  required    pam_env.so
session  required    pam_limits.so
session  required    pam_unix.so
session  required    pam_loginuid.so
session  optional    pam_keyinit.so force revoke
session  optional    pam_elogind.so

auth     required    pam_deny.so
password required    pam_deny.so

# End /etc/pam.d/elogind-user
EOF

Contents

Installed Programs: busctl, elogind-inhibit, and loginctl
Installed Library: libelogind.so
Installed Directories: /lib/elogind, /etc/elogind, /usr/include/elogind, and /usr/share/doc/elogind-246.10

Short Descriptions

busctl

is used to introspect and monitor the D-Bus bus

elogind-inhibit

is used to execute a program with a shutdown, sleep or idle inhibitor lock taken

loginctl

is used to introspect and control the state of the elogind Login Manager

libelogind.so

is the main elogind utility library