Red Hat Enterprise Linux 7: Application Compatibility GUIDE

Updated -
Red Hat Enterprise Linux 7:
Application Compatibility Guide
June 2014 Note: this article discusses Application Compatibility for Red Hat Enterprise Linux 7. For Red Hat Enterprise Linux 6 please see the attached PDF file (rhel6_app_compatibility_wp.pdf).

Table of Contents

Executive Summary

This guide is intended to educate independent software vendors (ISVs) and customers on Red Hat's guidelines regarding support of third-party applications across multiple releases of the Red Hat Enterprise Linux platform. ISV and customer applications can reduce or avoid migration issues between major Red Hat® Enterprise Linux® versions by following these guidelines during application development. This document describes the recommended uses of the system application programming (API) and binary interfaces (ABI) that are intended to provide compatibility across Red Hat Enterprise Linux releases. It outlines the tiered framework under which applications are considered compatible or not compatible.

Introduction

These guidelines seek to provide stability for applications when new releases are deployed and therefore focus primarily on forward-compatibility issues. Although backward compatibility is the goal, development of new capabilities sometimes makes that impractical. Hence, the guidelines and published policy may sometimes be overridden by the objective of providing our customers with the most competitive and capable systems possible; situational testing is always recommended.
If clarification of these compatibility guidelines is required, please see the Red Hat Enterprise Linux 7 Developer Guide for additional details, or contact your Red Hat representative.

Terminology

The following are basic terms used in this document:
  • Binary compatibility
    Binary compatibility means applications that are compiled on a combination of Red Hat Enterprise Linux and a particular hardware architecture will load and run similarly across different instances of the operating environment. Application binaries consist of executable files and Dynamic Shared Objects (DSO), and the level of compatibility is defined by a specific application binary interface (ABI).
  • Application programming interface (API)
    An API is an interface implemented by a software program that enables it to interact with other software, including operating system components. The API is enforced at compile time and determines source compatibility, that is, whether application source code will compile similarly across different instances of the operating environment.
  • Application binary interface (ABI)
    An ABI is a set of runtime conventions that interact with a compiled binary representation of a program. ABI is also a superset of the API and describes the low-level interface between an application and the operating environment. It covers details such as:
    • data type, size, and alignment
    • the calling standard, which defines how function arguments are passed and return values retrieved
    • the binary format of object files and program libraries
    • function and / or data symbol names and their versions
      Tools such as the compilers, linkers, runtime libraries, and the operating system itself need to work with the ABI. An ABI operates at runtime.
  • ABI conformance
    A compiler conforms to an ABI if it generates code that follows all of the specifications enumerated by that ABI. A library conforms to an ABI if it is implemented according to that ABI. An application conforms to an ABI if it is built using tools that conform to that ABI and does not contain source code that changes behavior specified by the ABI or that otherwise bypasses the ABI.
  • Core persistent system infrastructure
    The core persistent system infrastructure refers to interfaces and externally available data structures that represent system state or provide a means of communicating with the system (for instance, system calls and header files).
  • Compatibility in a virtualized environment
    Virtual environments emulate bare-metal environments such that unprivileged applications that run on bare-metal environments will run, unmodified, in corresponding virtual environments. Virtual environments present simplified abstracted views of physical resources, so some differences may exist.
  • Packages in Supplementary and Optional repositories
    Packages available in the Red Hat Network (RHN) Supplementary and Optional channels are not part of the product but are made available for convenience or to satisfy build dependencies.
  • Major and minor releases
    A Red Hat major release represents a significant step in the development of a product (wholesale changes are usually reserved for major releases), and is typically designated by a single numeral (e.g., Red Hat Enterprise Linux 7). Minor releases appear more frequently, within the scope of a major release, and generally represent smaller, incremental developmental steps.
  • Red Hat Enterprise Linux Extended Update Support
    Red Hat Enterprise Linux Extended Update Support (EUS) is an optional support offering that allows a customer to standardize on a specific minor release for an extended period of time. Each Red Hat Enterprise Linux 7 EUS stream is available for 24 months from the availability of the minor release.
  • Red Hat Developer Toolset (DTS)
    Red Hat Developer Toolset (DTS) is an offering that provides the latest stable versions of compilers, debuggers, and select open source development tools. This optional offering has an independent life cycle and is not covered by this Application Compatibility document.
  • Red Hat Software Collections (RHSCL)
    Red Hat Software Collections delivers the latest, stable versions of some of the most popular web development languages and open source databases for use with Red Hat Enterprise Linux. This optional offering has an independent life cycle and is not covered by the guidelines described in this Application Compatibility document.
  • RHEL Extras
    The contents of the Extras channel are exempt from Red Hat's policy that commits to binary compatibility. See https://access.redhat.com/site/solutions/5154 for details about this binary compatibility policy.
  • SystemTap Static Probes
    SystemTap static probes are part of the SystemTap profiling and tracing framework. The probes are integrated into key system libraries to support profiling and debugging of applications and libraries. No assurances are made at this time that integrated SystemTap static probes will continue to have the same probe name, probe location, or interpretation or number of arguments.

Scope of Compatibility

Packages in Red Hat Enterprise Linux are classified under one of the following four compatibility levels:
  • Compatibility level 1: APIs and ABIs are stable across three major releases; the release that introduces a new or revised API or ABI, and the two following major releases (n, n+1, n+2). In the case of this document, release n starts with Red Hat Enterprise Linux 7.
    If a change to a library during its life cycle causes an incompatibility with existing compiled code, a separate version of the library will be provided with the older ABI to run the application without modifications.
  • Compatibility level 2: APIs and ABIs are stable within one major release. In the case of this document, the major release is Red Hat Enterprise Linux 7.
  • Compatibility level 3: Reserved for future use.
  • Compatibility level 4: No compatibility is provided. That includes all libraries that the listed package supplies.
For compatibility levels for specific Red Hat Enterprise Linux software packages, please see Appendix A. Compatibility levels for bare-metal configurations apply to virtualized configurations except for any features that directly interact with hardware. Those features directly related to hardware have no API or ABI compatibility level. For example, applications that rely on Graphics Processing Units (GPU) features cannot expect binary compatibility. Red Hat strongly recommends that application developers validate that any behavior they depend on is explicitly defined in formal API documentation to prevent introducing dependencies on unspecified implementation-specific semantics or introducing dependencies on bugs in a particular implementation of an API. For example, new releases of the GNU C library may not be compatible with older releases if an application used an undocumented API or one with undefined behavior.

Guidelines for Preserving Binary Compatibility

Red Hat recommends that application developers adopt the following principles in order to improve binary compatibility: Red Hat recommends that application developers adopt the following principles in order to improve binary compatibility:
  1. Build applications using the published interfaces of a library. Non-published (a.k.a. internal) interfaces are subject to change at any time, which can cause instability in the dependent application if improperly linked. Application developers should validate that any behavior they depend on is described in the published API documentation to prevent introducing dependencies on unspecified implementation-specific semantics or introducing dependencies on bugs in a particular implementation of an API. For example, new releases of the GNU C library are not guaranteed to be compatible with older releases if the old behavior was not consistent with a published specification.
  2. Avoid static linking of libraries (C/C++). Static linking causes the executables to have their own version of the library. This increases the chance of an application not running predictably on a later version of the operating system as these library dependencies might have changed along the way. Linking applications dynamically is strongly recommended in order to avoid this problem.
  3. Limit linking applications to the core libraries at compatibility level 1. The core libraries (see Appendix A) are intended to preserve binary compatibility across three consecutive major releases.
  4. Provide compatibility libraries for applications that have been built with libraries that are not at the desired compatibility level, provided the bundled libraries themselves only use the interfaces provided by the core libraries.
  5. Package applications using the RPM mechanism. RPM provides a software-packaging mechanism that includes detailed specification of application dependencies. When creating RPMs, the following should be kept in mind:
    (a) Avoid using RPM triggers whenever possible.
    (b) Explicitly state all required runtime and build dependencies using the appropriate RPM syntax.
    (c) Do not modify, replace, or recompile files managed by Red Hat-provided RPM packages. Doing so may lead to unpredictable behavior.
    (d) When considering dependencies, do not assume that all possible packages will be installed on every Red Hat Enterprise Linux system. The default installed packages may change between major releases, between product variants of the same version, and on a customer’s system. For instance, the Workstation product will have a different installed package set than the Server product. Rarely, and due to extenuating circumstances, packages might be removed between minor releases but Red Hat will provide notification if this occurs.
  6. Follow the Filesystem Hierarchy Standard (FHS) version 2.3 when installing programs. Third-party software should be installed to the '/opt' subdirectory. More information on the FHS is available at:
    http://www.pathname.com/fhs/.
  7. Applications should be built against libraries that correspond to the native hardware environment rather than a compatibility layer on top of the hardware. This is because the compatibility userspace contains a subset of system libraries as compared to the native userspace.
  8. Do not design applications that rely on configuration files used by system packages. These files can change between major releases unless the upstream community is explicitly committed to preserving them.
  9. If you require functionality from a package that is currently at a lower compatibility level than you wish, please contact Red Hat for review.
Note: During the life cycle of a major release, Red Hat makes commercially reasonable efforts to maintain binary compatibility for the core runtime environment across all minor releases and errata advisories. If necessary, Red Hat may make exceptions to this compatibility goal for critical impact security or other significant issues. Furthermore, as described above and in Appendix A, major releases of Red Hat Enterprise Linux contain a limited set of backward-compatible libraries included in previous major releases to allow for the easy migration of applications. Typically, Red Hat applies changes in such a way as to minimize the amount of change and to maintain binary compatibility. Exceptions may apply for controlled package re-bases under certain circumstances.

Appendix A: Compatibility Levels for Specific Packages and Libraries

Compatibility level 1: APIs and ABIs are stable across three major releases (starting with RHEL 7)

- - - -
alsa-lib krb5-libs libtbbmalloc.so mesa-libGL
elfutils-libelf libgcc libtbb.so mesa-libGLU
glibc libgfortran libusb motif
glibc-utils libgomp libvirt-client pam
gtk2 libstdc++ libxml2 SDL
hesiod libtbbmalloc_proxy.so libxslt

Compatibility level 2: APIs and ABIs are stable within one major release (RHEL 7)

- - - -
atk kdenetwork libXt
audit-libs kdepim libXtst
audit-libs-python kdepimlibs libX11
boost-date-time kdepim-libs mariadb-libs
boost-filesystem kdepimlibs-akonadi ncurses-libs
boost-graph kdesdk net-snmp-libs
boost-iostreams kdesdk-devel net-snmp-perl
boost-math kdesdk-kmtrace-libs net-snmp-python
boost-program-options kdesdk-kompare nss
boost-python kde-workspace nss-sysinit
boost-regex kde-workspace-libs numactl
boost-serialization libacl pango
boost-signals libaio papi [4]
boost-system libatomic pcre
boost-test libattr perl
boost-thread libblkid perl-Digest-SHA
boost-wave libcanberra perl-libs
bzip2-libs libcanberra-gtk2 perl-Time-Piece
cairo libcanberra-gtk3 phonon-backend-gstream
c-ares libcap-ng polkit
clutter libcurl popt
corosynclib libdb postgresql-libs
cups-libs libdb-cxx pulseaudio-libs
cyrus-sasl-gssapi libgudev1 pulseaudio-libs-glib2
cyrus-sasl-lib libhugetlbfs PyQt4
cyrus-sasl-md5 libICE python
dbus-glib libjpeg-turbo python-libs
dbus-libs libnotify p11-kit
ding-libs (srpm) libpfm [2] qt
elfutils-libs libpng qt-mysql
expat librsvg2 qt-odbc
fuse-libs libSM qt-postgresql
GConf2 libsmbclient qt-x11
gdk-pixbuf2 libtalloc qt3
glib2 libtdb qt3-MySQL
gmp libtevent qt3-ODBC
gnome-keyring libtiff qt3-PostgreSQL
gnome-keyring-pam libusb readline
gnutls libuuid realmd
gstreamer-plugins-base libverto ruby
gstreamer1 libwbclient scl-utils
gtk3 libXau sqlite
httpd libXaw startup-notification
java-1.7.0-openjdk [3] libXext systemd-libs
kde-baseapps libXft systemtap [4]
kde-baseapps-libs libXi tcl
kdegraphics libXinerama tcp_wrappers-libs
kdegraphics-libs libXmu tk
kdelibs libXpm unique
kdemultimedia libXrandr xz-libs
kdemultimedia-libs libXrender zlib
openssl

Notes:
[2]: Non-regression on same hardware only; Red Hat is not guaranteeing future hardware support.
[3]: Red Hat will maintain compatibility for OpenJDK based on the Java SE 7 specification guidelines. Red
Hat will defer to the Java SE specification for compatibility between the respective system/default Java
runtime between major versions of RHEL. In most cases, compatibility between major versions of RHEL
can be maintained by using the same version of OpenJDK. If that is not an option due to customer
preference or Java lifecycle limitations, the Java SE specification should be used as guidelines to
determine if applications can be run unmodified between major versions of RHEL.
[4]:Source-level script compatibility

Compability level 3: Reserved for Future Use

(this section intentionally left blank)

Compability level 4: Stability of APIs or ABIs subject to change at Red Hat's discretion

- - - -
adcli iowatcher mariadb-server postgresql-test
binutils (libraries only) junit mesa-dri-driver pulseaudio-libs
dyninst libasan openldap pulseaudio-modu
e2fsprogs-libs libcgroup openslp-server pulseaudio-modu
glade3-libglade libcom_err postgresql-cont pulseaudio-modu
gnome-desktop libdrm postgresql-docs pulseaudio-util
gstreamer libitm postgresql-plpe samba-libs
gstreamer-devel libldb postgresql-plpy tkinter
gstreamer-plugi libss postgresql-pltc valgrind
gvfs libtsan postgresql-serv xfsprogs
nettle
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