Abstract
The CernVM File System provides the software and container distribution backbone for most High Energy and Nuclear Physics experiments. It is implemented as a file system in user-space (Fuse) module, which permits its execution without any elevated privileges. Yet, mounting the file system in the first place is handled by a privileged suid helper program that is installed by the Fuse package on most systems. The privileged nature of the mount system call is a serious hindrance to running CernVM-FS on opportunistic resource and supercomputers. Fortunately, recent developments in the Linux kernel and in the Fuse user-space libraries enabled fully unprivileged mounting for Fuse file systems (as of RHEL 8), or at least outsourcing the privileged mount system call to a custom, external process. This opens the door to several, very appealing new ways to use CernVM-FS, such as a generally usable “super pilot” consisting of the pilot code bundled with Singularity and CernVM-FS, or the on-demand instantiation of unprivileged, ephemeral containers to publish new CernVM-FS content from anywhere. In this contribution, we discuss the integration of these new Linux features with CernVM-FS and show some of its most promising, new applications.
Highlights
The CernVM File System (CernVM-FS) provides the software and container distribution backbone for most High Energy and Nuclear Physics experiments [1, 2]
We review the current and future state of mounting File System in User Space (Fuse) file systems
We show how the latest Linux and Fuse developments lift restrictions on mounting Fuse file systems and the implications of this development for opportunistic CernVM-FS deployments
Summary
The CernVM File System (CernVM-FS) provides the software and container distribution backbone for most High Energy and Nuclear Physics experiments [1, 2]. Fuse implements a minimal, forwarding kernel-level file system that issues upcalls to a user space Fuse module that in turn implements the actual file system logic. This architecture permits execution of the file system client without any elevated privileges. Other systems deploy “fat containers” that can grow to hundreds of gigabytes and contain a substantial part of all the available experiment software. These approaches tend to be fragile and cumbersome. We show how the latest Linux and Fuse developments lift restrictions on mounting Fuse file systems and the implications of this development for opportunistic CernVM-FS deployments
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