Singularity was updated to version 2.6.0, bringing features, bugfixes and security fixes.

Security issues fixed:

- CVE-2018-12021: Fixed access control on systems supporting overlay file system (boo#1100333).

Highlights of 2.6.0:

- Allow admin to specify a non-standard location for mksquashfs binary at 
  build time with '--with-mksquashfs' option #1662
- '--nv' option will use
  [nvidia-container-cli](https://github.com/NVIDIA/libnvidia-container) if
  installed #1681
- [nvliblist.conf]
  (https://github.com/singularityware/singularity/blob/master/etc/nvliblist.conf)
  now has a section for binaries #1681
- '--nv' can be made default with all action commands in singularity.conf #1681
- '--nv' can be controlled by env vars '$SINGULARITY_NV' and 
  '$SINGULARITY_NV_OFF' #1681
- Restore shim init process for proper signal handling and child reaping when
  container is initiated in its own PID namespace #1221
- Add '-i' option to image.create to specify the inode ratio. #1759
- Bind '/dev/nvidia*' into the container when the '--nv' flag is used in 
  conjuction with the '--contain' flag #1358
- Add '--no-home' option to not mount user $HOME if it is not the $CWD and
  'mount home = yes' is set. #1761
- Added support for OAUTH2 Docker registries like Azure Container Registry
  #1622

Highlights of 2.5.2:

- a new `build` command was added to replace `create` + 
  `bootstrap`
- default image format is squashfs, eliminating the need to 
  specify a size
- a `localimage` can be used as a build base, including ext3, 
  sandbox, and other squashfs images
- singularity hub can now be used as a base with the uri
- Restore docker-extract aufs whiteout handling that implements 
  correct extraction of docker container layers.

Bug fixes:

- Fix 404 when using Arch Linux bootstrap #1731
- Fix environment variables clearing while starting instances #1766
- several more bug fixes, see CHANGELOG.md for details