Release Notes for CernVM-FS 2.7.0

CernVM-FS 2.7 is a feature release that comes with performance improvements, new functionality, and bugfixes.

CernVM-FS 2.7 includes support for the new platform EL8 (RHEL8, CentOS8, etc.), Debian 10, and macOS 10.15 “Catalina”. Note that on Catalina, in contrast to previous versions a reboot is required to finalize the installation.

As with previous releases, upgrading should be seamless just by installing the new package from the repository. As usual, we recommend to update only a few worker nodes first and gradually ramp up once the new version proves to work correctly. Please take special care when upgrading a client in NFS mode.

For Stratum 0 servers, all transactions must be closed before upgrading. For Stratum 1 servers, there should be no running snapshots during the upgrade. After the software upgrade, publisher nodes require doing cvmfs_server migrate for each repository.

Fuse 3 Support

This release adds support for libfuse 3 platforms in addition to libfuse 2. The libfuse libraries are part of the system’s fuse package. The libfuse libraries take care of the low-level communication with the Fuse kernel module. The libfuse 3 libraries provide new features and performance improvements; they can be installed side-by-side with the libfuse 2 libraries. If libfuse 3 is available and the cvmfs-fuse3 package is installed, the CernVM-FS client will automatically use libfuse 3, otherwise it falls back to libfuse 2. A libfuse version can be enforced by setting the libfuse=[2,3] mount option.

For the EL6 and EL7 platforms, libfuse 3 libraries are provided in the fuse3-libs package through EPEL.

Pre-mounted Repository

This release adds support for “pre-mounted” repositories. Mounting a CernVM-FS repository involves calling the mount() system call on /dev/fuse. This is usually done by the fusermount utility, which is part of the fuse system package. As of libfuse 3, the task of mounting /dev/fuse can be offloaded to an external, custom utility. Such an external executable “pre-mounts” the repository and allows for easier integration in special environments. This functionality has been integrated with Singularity 3.4. See Pre-mounting for more details.


This release adds support for storing and enforcing POSIX ACLs. In order to store ACLs during publication, simply enable extended attributes by setting CVMFS_INCLUDE_XATTRS=true in the repository’s server.conf configuration file. In order to enforce ACLs on the client side, set CVMFS_ENFORCE_ACLS=true in the client configuration. Enforcing POSIX ACLs requires libfuse 3 on the client node. If only libfuse 2 is available, the client will refuse to mount with enforced ACLs.

Note that enforcing ACLs usually only makes sense in concert with a secure distribution infrastructure (see Large-Scale Data, Authorization Helpers).

Client Performance Instrumentation

The CernVM-FS client can now record a histogram of wall-clock time spent in the different Fuse callback routines (CVM-1770). Recording is enabled by setting the client configuration variable CVMFS_INSTRUMENT_FUSE=true. The time distribution histograms are displayed in the cvmfs_talk internal affairs command.

Bug Fixes

  • Client: fix stale negative entries in active cache eviction (CVM-1759)
  • Client: fix potentially incomplete parsing of /etc/hosts
  • Client: fix potential file descriptor mix-up of external cache manager after reload
  • Client: fix repository updates on shared, writable alien cache (CVM-1803)
  • Client: fix missing package dependency on Debian 9 and Ubuntu 18.04 (CVM-1789)
  • Client: fix spurious error message when starting external cache manager
  • Client: fix spurious error message with auto;DIRECT if proxy auto discovery returns an empty list (CVM-1818)
  • Client, macOS >= 10.15: set default mount point to /Users/Shared/cvmfs with a firm link from /cvmfs to the new destination (CVM-1813)
  • Server: fix publish statistics for several corner cases (CVM-1716 - CVM-1720)
  • Server, gateway: fix clashing generic tags for short transactions (CVM-1735)
  • Server, DUCC: use relative symbolic links (CVM-1817)

Other Improvements

  • Client: enable default config repository on Debian stretch and newer (CVM-1794)
  • Client: add new magic extended attribute repo_counters (CVM-1733)
  • Client: add new magic extended attribute repo_metainfo (CVM-1499)
  • Client: enforce CVMFS_NFILES parameter only when mounting through mount helper
  • Client: add support for CVMFS_LIBRARY_PATH environment variable in order to facilitate standalone deployment
  • Server: add support for extended attributes on directories
  • Server: add filestats command to cvmfs_swissknife (CVM-1756)
  • Server: add list_reflog command to cvmfs_swissknife (CVM-1756)