Chapter 5. Issues to be aware of for stretch

Table of Contents

5.1. Upgrade specific items for stretch
5.1.1. Late mounting of /usr is no longer supported
5.1.2. FTP access to Debian hosted mirrors will be removed
5.1.3. Noteworthy obsolete packages
5.1.4. Things to do post upgrade before rebooting
5.1.5. Executables are now compiled as position independent executables (PIE) by default
5.1.6. Most LSB compatibility packages have been removed
5.2. Limitations in security support
5.2.1. Security status of web browsers
5.2.2. Lack of security support for the ecosystem around libv8 and Node.js
5.3. Package specific issues
5.3.1. Older ciphers and SSH1 protocol disabled in OpenSSH by default
5.3.2. Possible backwards incompatible changes to APT
5.3.3. Desktops will migrate to libinput Xorg driver
5.3.4. Upstart removed
5.3.5. The debhelper tool now generates dbgsym packages by default
5.3.6. OpenSSL related changes
5.3.7. Perl changes that may break third-party software
5.3.8. PostgreSQL PL/Perl incompatibility
5.3.9. net-tools will be deprecated in favor of iproute2
5.3.10. The _netdev mount option is recommended when using AoE (ATA over ethernet) devices
5.3.11. Harmless Unescaped ... in regex is deprecated, ... warnings during upgrade
5.3.12. SELinux policy store migration
5.3.13. iSCSI Enterprise Target no longer supported

Sometimes, changes introduced in a new release have side-effects we cannot reasonably avoid, or they expose bugs somewhere else. This section documents issues we are aware of. Please also read the errata, the relevant packages' documentation, bug reports, and other information mentioned in Section 6.1, “Further reading”.

5.1. Upgrade specific items for stretch

This section covers items related to the upgrade from jessie to stretch.

5.1.1. Late mounting of /usr is no longer supported


This section only applies to systems using a custom kernel, where /usr is on a separate mount point from /. If you use the kernel packages provided by Debian, you are unaffected by this issue.

Mounting of /usr using only tools found in / is no longer supported. This has only worked for a few specific configurations in the past, and now they are explicitly unsupported.

This means that for stretch all systems where /usr is a separate partition need to use an initramfs generator that will mount /usr. All initramfs generators in stretch do so.

5.1.2. FTP access to Debian hosted mirrors will be removed

Debian hosted mirrors will stop providing FTP access. If you have been using the ftp: protocol in your sources.list, please migrate to http:. Please consider the following example for migrating:

deb          stretch         main
deb stretch/updates main

# tor variant (requires apt-transport-tor)
# deb  tor+http://vwakviie2ienjx6t.onion/debian          stretch            main
# deb  tor+http://sgvtcaew4bxjd7ln.onion/debian-security stretch/updates    main

The above examples do not include non-free and contrib. Please remember to include these if you require those components enabled.

For more information, please refer to the announcement: Shutting down public FTP services.

5.1.3. Noteworthy obsolete packages

The following is a list of known and noteworthy obsolete packages (see Section 4.8, “Obsolete packages” for a description).

The list of obsolete packages includes:

  • Most -dbg packages have been removed from the main archive. They have been replaced by -dbgsym packages that are available from the debian-debug archive. Please see Section 2.2.8, “A new archive for debug symbols”.

  • The password managers fpm2 and kedpm are no longer maintained upstream. Please use another password manager like pass, keepassx, or keepass2. Make sure that you extract your passwords from fpm2 and kedpm before removing the packages.

  • The net-tools package is being deprecated in favor of iproute2. See Section 5.3.9, “net-tools will be deprecated in favor of iproute2 or the Debian reference manual for more information.

  • The nagios3 monitoring tools have been removed from stretch. The icinga package is the closest replacement. It reads its configuration files from a different path than nagios did, but is otherwise compatible.

5.1.4. Things to do post upgrade before rebooting

When apt-get dist-upgrade has finished, the formal upgrade is complete. For the upgrade to stretch, there are no special actions needed before performing a reboot.

5.1.5. Executables are now compiled as position independent executables (PIE) by default

By default, the GNU GCC 6 compiler provided by Debian stretch will compile all executables as position independent. This provides a mitigation for an entire class of vulnerabilities.

Unfortunately, the Linux kernel provided in Debian 8 (up to 8.7) has an issue that can cause some programs compiled as position independent executables to crash with a non-descriptive issue like segmentation fault. This issue is solved in the Linux version provided in 8.8 (version 3.16.43 or later) and in the kernel provided in Debian 9 (version 4.9 or later).

We recommend that you upgrade your kernel to a fixed version and then reboot before starting the upgrade to stretch. If you are running the kernel from Debian 8.8 or newer, you are not affected by this issue.

If you are running an affected version of the kernel during the upgrade, we highly recommend that you perform a reboot into the stretch kernel right after the upgrade to avoid hitting this. Behavior changes of PIE for system administrators and developers


This section is mainly intended for developers or system administrators. Desktop users are unlikely to be affected by this section.

The above also leads to some changes that are worth being aware of.

  • The file tool (among others) will classify such binaries as shared object rather than an executable. If you have filters based on binary files, these may need to be updated (e.g. spamfilters).

  • Static libraries being compiled into an executable now also need to be compiled as position independent code. The following error message from the linker is a symptom of this:

    relocation ... against '[SYMBOL]' can not be used when making a shared object; recompile with -fPIC

    Note that even though the error message says -fPIC, it is sufficient to recompile with -fPIE (which is the default in the GCC 6 packages that are part of stretch).

  • Historically, position independent executables have been associated with performance loss on some hardware. Notably the Debian architecture i386 (32-bit Intel machines). While GCC 5 and GCC 6 have greatly improved performance for position independent executables on 32-bit Intel, this optimization may not be applicable to all architectures. Please consider evaluating the performance of your code if you are targeting machine architectures with a very limited number of registers.

5.1.6. Most LSB compatibility packages have been removed

Due to lack of interest and testability, Debian has removed the vast majority of the Linux Standard Base (LSB) compatibility packages.

Debian will still provide a selected few key LSB utilities used internally and externally, such as lsb-release and the sysvinit init functions in lsb-base. Furthermore, Debian is still firmly standing by the Filesystem Hierarchy Standard (FHS) version 2.3 with the minor alterations described in the Debian Policy Manual.

5.2. Limitations in security support

There are some packages where Debian cannot promise to provide minimal backports for security issues. These are covered in the following subsections.

Note that the package debian-security-support helps to track the security support status of installed packages.

5.2.1. Security status of web browsers

Debian 9 includes several browser engines which are affected by a steady stream of security vulnerabilities. The high rate of vulnerabilities and partial lack of upstream support in the form of long term branches make it very difficult to support these browsers with backported security fixes. Additionally, library interdependencies make it impossible to update to newer upstream releases. Therefore, browsers built upon the webkit, qtwebkit and khtml engines are included in stretch, but not covered by security support. These browsers should not be used against untrusted websites.

For general web browser use we recommend Firefox or Chromium.

Chromium - while built upon the Webkit codebase - is a leaf package, which will be kept up-to-date by rebuilding the current Chromium releases for stable. Firefox and Thunderbird will also be kept up-to-date by rebuilding the current ESR releases for stable.

5.2.2. Lack of security support for the ecosystem around libv8 and Node.js

The Node.js platform is built on top of libv8-3.14, which experiences a high volume of security issues, but there are currently no volunteers within the project or the security team sufficiently interested and willing to spend the large amount of time required to stem those incoming issues.

Unfortunately, this means that libv8-3.14, nodejs, and the associated node-* package ecosystem should not currently be used with untrusted content, such as unsanitized data from the Internet.

In addition, these packages will not receive any security updates during the lifetime of the stretch release.

5.3. Package specific issues

In most cases, packages should upgrade smoothly between jessie and stretch. There are a small number of cases where some intervention may be required, either before or during the upgrade; these are detailed below on a per-package basis.

5.3.1. Older ciphers and SSH1 protocol disabled in OpenSSH by default

The OpenSSH 7 release has disabled some older ciphers and the SSH1 protocol by default. Please be careful when upgrading machines where you only have SSH access.

Moreover, the default of the "UseDNS" configuration option has changed from yes to no. This may cause users who use the "from=" functionality in authorized_keys to limit ssh access by host to be locked out, which is especially troublesome if upgrading remotely.

Please refer to the OpenSSH documentation for more information.

5.3.2. Possible backwards incompatible changes to APT

This section covers some of the incompatible changes to APT that may affect your system. APT now fetches files as an unprivileged user (_apt)

APT will now attempt to discard all root privileges before fetching files from mirrors. APT can detect some common cases where this will fail and fall back to fetching things as root with a warning. However, it may fail to detect some exotic setups (e.g. UID-specific firewall rules).

If you experience issues with this feature, please change to the _apt user and check that it:

  • has read access to files in /var/lib/apt/lists and /var/cache/apt/archives.

  • has read access to the APT trust store (/etc/apt/trusted.gpg and /etc/apt/trusted.gpg.d/)

  • can resolve DNS names and download files. Example methods for testing:

    # From the dnsutils package (if using tor, please check with tor-resolve instead).
    $ nslookup >/dev/null || echo "Cannot resolve"
    $ wget -q -O- > /dev/null || echo "Cannot download index page of"

    For DNS issues, please check that /etc/resolv.conf is readable. New APT pinning engine

APT 1.1 introduced a new pinning engine that now matches the description in the manual page.

The old engine assigned one pin priority per package; the new one assigns pin priorities per version. It then picks the version with the highest pin that is not a downgrade or that has a pin > 1000.

This changes the effect of some pins, especially negative ones. Previously, pinning a version to -1 effectively prevented the package from being installed (the package pin was -1); it now only prevents the version of this package from being installed. New requirements for APT repository


This section only applies if you have (or intend to use) third-party repositories enabled or if you maintain an APT repository.

To improve download stability and ensure security of the downloaded content, APT now requires the following from an APT repository:

  • The InRelease file must be available.

  • All metadata must include at least SHA256 checksums of all items. This includes the GPG signature of the InRelease file.

  • Signatures on the InRelease file should be done with a key size of 2048 bits or larger.

If you rely on a third-party repository that cannot comply with the above, please urge them to upgrade their repository. More information about the InRelease file can be found on the Debian Wiki.

5.3.3. Desktops will migrate to libinput Xorg driver


This section is only relevant if you have tweaked or need to change the default Xorg input configuration.

In jessie, the default input driver for Xorg is the evdev driver. In stretch, the default has changed to libinput. If you have Xorg configuration that relies on the evdev driver, you will either have to convert it to the libinput driver or reconfigure your system to use the evdev driver.

The following is an example configuration for libinput to enable the Emulate3Buttons feature.

Section "InputClass"
        Identifier "mouse"
        MatchIsPointer "on"
        Driver "libinput"
        Option "MiddleEmulation" "on"

Insert it into /etc/X11/xorg.conf.d/41-middle-emulation.conf, reboot (or restart your Xserver) and it should now be enabled.

The evdev driver is still available in the xserver-xorg-input-evdev package.

5.3.4. Upstart removed

Due to the lack of upstream maintainers, the Upstart init system has been removed from stretch. If your system relies on this package, you should note that it will not be updated during the lifetime of Debian 9, and starting from Debian 10 (buster), Upstart jobs may be removed from packages.

Please consider switching to a supported init system, like systemd or OpenRC.

5.3.5. The debhelper tool now generates dbgsym packages by default


This section is mainly intended for developers or organizations that build their own debian packages.

The debhelper tool suite will now generate dbgsym packages by default for ELF binaries. If you develop and package binaries, please check that your tooling supports these extra auto-generated packages.

If you use reprepro, you want to upgrade it to at least version 4.17.0. For aptly, you will need at least version 1.0.0, which is unfortunately not available in Debian stretch.

Should your tooling be unable to cope with these gracefully, you can ask debhelper to disable this feature by adding noautodbgsym in the DEB_BUILD_OPTIONS variable of your build service. Please see the dh_strip manpage for more information.

5.3.6. OpenSSL related changes

The openssl application expects option arguments before non-option arguments. For example, this does not work anymore:

openssl dsaparam 2048 -out file

while this still does:

openssl dsaparam -out file 2048

The openssl enc command changed the default digest (used to create the key from passphrase) from MD5 to SHA256. The digest can be specified with the -md option in case old files need to be decrypted with newer OpenSSL (or the other way around).

The 3DES and RC4 ciphers are no longer available for TLS/SSL communication. Servers linked against OpenSSL can't offer them and clients can't connect to servers which offer only those. This means that OpenSSL and Windows XP share no common cipher.

The package libssl-dev provides header files to compile against OpenSSL 1.1.0. The API changed a lot and it is possible that the software won't compile anymore. There is an overview of the changes. If you can't update your software, there is also libssl1.0-dev which provides headers against OpenSSL 1.0.2.

5.3.7. Perl changes that may break third-party software


This section applies to code maintained outside Debian - local, third-party, or legacy Perl scripts and modules.

  • Some modules have been removed from Perl core and are now shipped in separate packages. Notable examples are CGI, available in the libcgi-pm-perl package, and Module::Build, available in the libmodule-build-perl package.

  • The current working directory (.) has been removed from the default list of include directories, @INC. This may affect usage of require(), do(), etc., where the arguments are files in the current directory.

    All perl programs and module shipped by Debian should have been fixed to address any incompatibilities caused by the above; please file bugs if this is not the case. As the change has now been made in perl 5.26.0, third-party software should also start to be fixed. Information about how to fix this issue for developers is provided in the perl 5.26 release notes (see the SECURITY section).

    If needed you can temporarily reinstate . in @INC globally by commenting out the line in /etc/perl/ but you should only do this with a understanding of the potential risks. This workaround will be removed in Debian 10. You can also set the PERL_USE_UNSAFE_INC environment variable in a specific context which will have the same effect.

  • The full list of changes in Perl since the version in Debian 8 is available in perl522delta and perl524delta.

5.3.8. PostgreSQL PL/Perl incompatibility

The PostgreSQL PL/Perl procedural language package in jessie is incompatible with the Perl version in stretch. The postgresql-plperl-9.4 package will be removed during the update, rendering server-side Perl procedures dysfunctional. Upgrading to PostgreSQL 9.6 should be unaffected; the procedures will work in the new PostgreSQL cluster if the postgresql-plperl-9.6 package is installed. If unsure, take a backup of your PostgreSQL 9.4 clusters before upgrading to stretch.

5.3.9. net-tools will be deprecated in favor of iproute2

The net-tools package is no longer part of new installations by default, since its priority has been lowered from important to optional. Users are instead advised to use the modern iproute2 toolset (which has been part of new installs for several releases already). If you still prefer to continue using the net-tools programs you can simply install it via

apt install net-tools


Please keep in mind that net-tools may be uninstalled during the upgrade if it was only installed to satisfy a dependency. If you rely on net-tools, please remember to mark it as a manual installed package before the upgrade via:

apt-mark manual net-tools

Here is a summary of the net-tools commands, together with their iproute2 equivalent:

legacy net-tools commandsiproute2 replacement commands
arpip n (ip neighbor)
ifconfigip a (ip addr), ip link, ip -s (ip -stats)
iptunnelip tunnel
nameifip link
netstatss, ip route (for netstat -r), ip -s link (for netstat -i), ip maddr (for netstat -g)
routeip r (ip route)

5.3.10. The _netdev mount option is recommended when using AoE (ATA over ethernet) devices


This only applies to systems that have ATA over ethernet (AoE) devices mounted. If the system does not mount any network shares, you can safely skip this section.

Due to a cleanup in the handling of network deconfiguration, AoE devices in use are no longer handled as expected during shutdown, possibly resulting in hangs and/or data loss. To mitigate that situation, it is suggested to mount such devices using the _netdev mount option. That option is available when using swap over AoE as well.

5.3.11. Harmless Unescaped ... in regex is deprecated, ... warnings during upgrade

During the upgrade, you may see some warning like:

Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/^(.*?)(\\)?\${ <-- HERE ([^{}]+)}(.*)$/ at /usr/share/perl5/Debconf/ line 72.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/\${ <-- HERE ([^}]+)}/ at /usr/share/perl5/Debconf/ line 30.

These are harmless and happens if perl-base is upgraded before the debconf package.

5.3.12. SELinux policy store migration


This section only applies to system that is using SELinux, which is not enabled by default.

In stretch, the SELinux policy store have moved from /etc/selinux/<policy_name> to /var/lib/selinux/<policy_name>. Furthermore, the format used inside the store has changed.

The policies provided by Debian (from e.g. the selinux-policy-default package) will be migrated automatically. However, system specific policies need to be migrated manually.

The semanage-utils package provides the script /usr/lib/selinux/semanage_migrate_store to do this transition.

5.3.13. iSCSI Enterprise Target no longer supported

The iSCSI Enterprise Target (IET), packaged in the iscsitarget package in previous releases, is no longer in Debian, as it will not work with recent kernel versions, and the project has seen no development activity in recent years.

Users of IET are encouraged to switch to the LIO stack, which is fully supported in Debian stretch. The package targetcli-fb provides the configuration utility for the LIO iSCSI target.

As the LIO stack was developed independently of the IET, the configuration has to be migrated manually.