docs/DISTRO_PORTING.md

   1 ---
   2 title: Porting systemd To New Distributions
   3 category: Concepts
   4 layout: default
   5 SPDX-License-Identifier: LGPL-2.1-or-later
   6 ---
   7
   8 # Porting systemd To New Distributions
   9
  10 ## HOWTO
  11
  12 You need to make the follow changes to adapt systemd to your
  13 distribution:
  14
  15 1. Find the right configure parameters for:
  16
  17    * `-Drootprefix=`
  18    * `-Dsysvinit-path=`
  19    * `-Dsysvrcnd-path=`
  20    * `-Drc-local=`
  21    * `-Dloadkeys-path=`
  22    * `-Dsetfont-path=`
  23    * `-Dtty-gid=`
  24    * `-Dntp-servers=`
  25    * `-Ddns-servers=`
  26    * `-Dsupport-url=`
  27
  28 2. Try it out.
  29
  30    Play around (as an ordinary user) with
  31    `/usr/lib/systemd/systemd --test --system` for a test run
  32    of systemd without booting. This will read the unit files and
  33    print the initial transaction it would execute during boot-up.
  34    This will also inform you about ordering loops and suchlike.
  35
  36 ## Compilation options
  37
  38 The default configuration does not enable any optimization or hardening
  39 options. This is suitable for development and testing, but not for end-user
  40 installations.
  41
  42 For deployment, optimization (`-O2` or `-O3` compiler options), link time
  43 optimization (`-Db_lto=true` meson option), and hardening (e.g.
  44 `-D_FORTIFY_SOURCE=2`, `-fstack-protector-strong`, `-fstack-clash-protection`,
  45 `-fcf-protection`, `-pie` compiler options, and `-z relro`, `-z now`,
  46 `--as-needed` linker options) are recommended. The most appropriate set of
  47 options depends on the architecture and distribution specifics so no default is
  48 provided.
  49
  50 ## NTP Pool
  51
  52 By default, systemd-timesyncd uses the Google Public NTP servers
  53 `time[1-4].google.com`, if no other NTP configuration is available.
  54 They serve time that uses a
  55 [leap second smear](https://developers.google.com/time/smear)
  56 and can be up to .5s off from servers that use stepped leap seconds.
  57
  58 If you prefer to use leap second steps, please register your own
  59 vendor pool at ntp.org and make it the built-in default by
  60 passing `-Dntp-servers=` to meson. Registering vendor
  61 pools is [free](http://www.pool.ntp.org/en/vendors.html).
  62
  63 Use `-Dntp-servers=` to direct systemd-timesyncd to different fallback
  64 NTP servers.
  65
  66 ## DNS Servers
  67
  68 By default, systemd-resolved uses Cloudflare and Google Public DNS servers
  69 `1.1.1.1`, `8.8.8.8`, `1.0.0.1`, `8.8.4.4`, `2606:4700:4700::1111`, `2001:4860:4860::8888`, `2606:4700:4700::1001`, `2001:4860:4860::8844`
  70 as fallback, if no other DNS configuration is available.
  71
  72 Use `-Ddns-servers=` to direct systemd-resolved to different fallback
  73 DNS servers.
  74
  75 ## PAM
  76
  77 The default PAM config shipped by systemd is really bare bones.
  78 It does not include many modules your distro might want to enable
  79 to provide a more seamless experience. For example, limits set in
  80 `/etc/security/limits.conf` will not be read unless you load `pam_limits`.
  81 Make sure you add modules your distro expects from user services.
  82
  83 Pass `-Dpamconfdir=no` to meson to avoid installing this file and
  84 instead install your own.
  85
  86 ## Contributing Upstream
  87
  88 We generally do no longer accept distribution-specific patches to
  89 systemd upstream. If you have to make changes to systemd's source code
  90 to make it work on your distribution, unless your code is generic
  91 enough to be generally useful, we are unlikely to merge it. Please
  92 always consider adopting the upstream defaults. If that is not
  93 possible, please maintain the relevant patches downstream.
  94
  95 Thank you for understanding.