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systemd, the modern Linux service and resource manager Alison - - PowerPoint PPT Presentation

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systemd, the modern Linux service and resource manager Alison Chaiken Sept. 8, 2015 mentor.com/automo tive Android is a trademark of Google Inc. Use of this trademark is subject to Google Permissions. Linux is the registered trademark of

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Android is a trademark of Google Inc. Use of this trademark is subject to Google Permissions. Linux is the registered trademark of Linus T

  • rvalds in the U.S. and other countries.

Qt is a registered trade mark of Digia Plc and/or its subsidiaries. All other trademarks mentioned in this document are trademarks of their respective owners.

mentor.com/automo tive

Alison Chaiken

  • Sept. 8, 2015

systemd, the modern Linux service and resource manager

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Philosophy of systemd

  • Extract duplicate functionality from daemons and

move it to systemd core or kernel.

  • Replace /etc scripts with declarative config files.
  • Expose newer kernel APIs to userspace via a simple

interface.

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systemd is:

  • modular;
  • asynchronous and concurrent;
  • described by declarative sets of

properties;

  • bundled with analysis tools and tests;
  • supplied with a fully language-agnostic

API.

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init.d scripts ⇒ systemd unit properties

  • Unit's action and parameters: ExecStart=
  • Dependencies: Before=, After=, Requires=,

Confmicts= and Wants=.

  • Default dependencies:

– Requires= and After= on basic.target; – Confmicts= and Before= on

shutdown.target.

  • T

ypes of unit fjles: service, socket, device, mount, scope, slice, automount, swap, target, path, timer, snapshot

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Example: Automotive Message Broker

From /lib/systemd/system/ambd.service:

# ambd systemd service unit fjle [Unit] Description=Automotive Message Broker After=syslog.target [Service] T ype=dbus BusName=org.automotive.message.broker ExecStart=/usr/bin/ambd [Install] WantedBy=multi-user.target

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Example: Make the gdp-hmi-controller only start when weston is ready

From: Jonathan Maw <jonathan.maw@codethink.co.uk> [ . . . ]

  • -- /dev/null

+++ b/recipes-demo-hmi/genivi-demo-platform-hmi/gdp-hmi- launcher2/StartLauncher.path +[Unit] +Description=GENIVI Start Launcher when weston is ready +Requires=weston.service +After=weston.service +[Path] +PathExists=/var/run/user/0/wayland-0

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sysVinit runlevels ≈ systemd targets

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  • Targets are synchronization points.
  • Check /lib/systemd/system/runlevel?.target symlinks:

– multi-user.target (runlevel 3) – graphical.target (runlevel 5)

  • Select boot-target :

– via /etc/systemd/system/default.target symlink; – appending number or systemd.unit=<target> to bootargs.

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Illustration: systemd-bootchart and custom targets

Courtesy Marko Hoyer, ADIT.

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Custom T argets in GENIVI's Lifecycle Management

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LUC = Last User Context

Node Startup Controller

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  • Organized into system and user units
  • /lib/systemd/system: systemd upstream defaults for system-

wide services

  • /etc/systemd/system: local customizations by override and

extension

  • /lib/systemd/user: systemd's upstream defaults for per-user

services

  • $HOME/.local/share/systemd/user for user-installed units
  • 'drop-ins' are run-time extensions

Hierarchy of unit fjles for system and user sessions

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Illustration:Tizen Multi-user system

Source: Dominig ar Foll, “Tizen 3 IVI Architecture Multi User App FW”, FOSDEM 2014

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Tizen Login Manager and User Sessions

Source: Dominig ar Foll, “Tizen 3 IVI Architecture Multi User App FW”, FOSDEM 2014

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using the systemd journal

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  • Easily pushed to a remote.
  • Can be cryptographically 'sealed'.
  • Configurable max size and rotation.
  • Simple log-reading tools are scriptable:

journalctl -xn journalctl -p err journalctl -u cron journalctl -o json-pretty systemctl status systemctl is-failed bluetooth systemctl --failed

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Both systemd journal and DLT:

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  • are modular and extensible.
  • support pushing data to AF_INET socket.
  • can share data with legacy syslog.
  • natively output binary formats.

→ Linking systemd and DLT involves:

–

translating binary formats;

–

handshaking;

–

synchronization.

  • Performed by remote?
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simplifjes access to kernel's security, resource and watchdog controls

  • Including Capabilities, Watchdog, Cgroups and

kdbus (still a 'coming attraction')

  • Kernel features confjgurable via simple ASCII
  • ptions in unit fjles.
  • Encourages creation of system policies via unit

templates.

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granular resource control: systemd and cgroups

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  • cgroups: a kernel-level mechanism for allocating

storage, memory, CPU and network.

  • slices are groups of daemons whose resources are

managed jointly.

  • systemd scopes are resultant groups of user

processes.

  • Can set BlockIOWeight, IOSchedulingPriority,

OOMScoreAdjust, CPUShares, MemoryLimit … Tomorrow: “An introduction to Control Groups”

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systemd and security: granular encapsulation via kernel's capabilities

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  • CapabilityBoundingSet
  • PrivateTmp, PrivateDevices, PrivateNetwork
  • JoinNamespaces
  • ProtectSystem (/usr and /etc), ProtectHome
  • ReadOnlyDirectories, InaccessibleDirectories
  • systemd-nspawn: systemd's native containers
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systemd's watchdog support

  • Provides simple confjguration of soft or hard

watchdogs.

  • RuntimeWatchdogSec sets a timer for petting the

dog.

  • ShutdownWatchdogSec sets a timer to force

reboot if shutdown hangs.

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Summary

  • Adaptation to systemd requires considerable

thought.

  • Uniform dependency language is attractive.
  • Managing resources, security and and watchdogs

is potentially simplifjed.

  • Backwards compatibility eases transition, but

project moves quickly.

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  • Man pages are part of systemd git repo.
  • freedesktop.org: systemd mailing list archives and wiki
  • Poettering's 0pointer.de blog
  • ➟At wayback machine: “Booting up” articles
  • Neil Brown series at LWN
  • ➟Fedora's SysVinit to systemd cheatsheet
  • Poettering's 'What's new' talk from FOSDEM 2015
  • Josh Triplett's Debconf talk video
  • Linux Action Show interviews with Mark Shuttleworth and

Lennart Poettering

  • A bunch of videos and slides linked at my website

Resources

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resource utilization of systemd itself

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  • systemd-211 in Poky includes 17 packages = 8 MB.
  • systemd-219 builds 90 MB of executables (not all needed).
  • minimal build = systemd, udevd and journald.
  • Memory (RSS) of fully featured build: ≈9 MB; minimum build ≈5 MB.
  • Features added/removed via './configure'.