Parrot Connector to CernVM-FS

In case you want to access CernVM-FS repositories but the fuse module is not installed neither do you have the permissions to install it yourself, the parrot toolkit provides you a means to “mount” CernVM-FS on Linux in pure user space. Parrot sandboxes your application in a similar way gdb sandboxes your application. But instead of debugging the application, parrot transparently rewrites file system calls and can effectively provide /cvmfs to your application.

This page provides examples on how to start an application in a parrot+cvmfs sandbox. We recommend the precompiled parrot from the cctools 5.4.13 package. At the end of the page, there are instructions on how to compile parrot+cvmfs from sources.


In order to sandbox a command <CMD> with options <OPTIONS> in parrot, we run it as


Make sure the right version of parrot is executed by checking parrot_run -v. In addition to the parrot_run binary you intend to use, there might be one present on the system or in your $PATH environment, which is taken instead.

Export the following environment variables:

export PARROT_CVMFS_REPO="<default-repositories>"
export HTTP_PROXY='<SITE HTTP PROXY>'  # or 'DIRECT;' if not on a cluster or grid site

Test parrot with

parrot_run bash
ls /cvmfs/

Non-Default repositories

Repositories that are not available by default from the builtin <default-repositories> list can be explicitly added to PARROT_CVMFS_REPO. The repository name, a stratum 1 URL, and the public key of the repository need to be provided. The public key should be referenced with its full path. For instance, in order to add and to the list of repositories, we can write

export CERN_S1=""
export DESY_S1=""
export PARROT_CVMFS_REPO="<default-repositories> \${CERN_S1}/,pubkey=/etc/cvmfs/keys/ \${DESY_S1}/,pubkey=/etc/cvmfs/keys/"

given that the repository public keys are in the provided paths.

LHC Experiment Frameworks

The experiment frameworks of the four large LHC experiments are supposed to run with parrot+cvmfs. For a demonstration, you can have a look at the corresponding plugins for the script from the CernVM-FS github space.

Should the symbolic link /cvmfs/ point to one of the directories in /cvmfs/, it is sufficient to set the CMS_LOCAL_SITE environment variable, for instance


If this symlink should point to a directory outside /cvmfs, it is a bit more difficult because symbolic links in a parrot file system cannot point outside its root directory. We can use the --mount option of parrot to redirect this particular symlink to a local path, like

parrot_run --mount=/cvmfs/ <CMD> <OPTIONS>


In case of problems, the debug log can often provide helpful information. In order to activate CernVM-FS specific debug messages, use

parrot_run -d cvmfs <CMD> <OPTIONS>

Cache Location

By default, parrot uses a shared CernVM-FS cache for all parrot instances of the same user stored under /tmp/parrot.. In order to place the CernVM-FS cache into a different directory, use

export PARROT_CVMFS_ALIEN_CACHE=</path/to/cache>

In order to share this directory among multiple users, the users have to belong to the same UNIX group.

Bugs and Problems

For feedback and bug reports, please write to either the cctools mailing list or to the CernVM-FS support.

Compiling from Sources

If you want to compile parrot+cvmfs from sources, please use the libcvmfs-stable git branch from the CernVM-FS github repository. The libcvmfs-stable branch reflects a state between the head of development (devel) and the latest released version (master).

Compile a static libuuid:

./configure --prefix=/tmp/cvmfs/UUID --enable-static --disable-shared
make install

To create libcvmfs.a in /tmp/cvmfs/INSTALLCVMFS, compile and install CernVM-FS with the following commands

  -DUUID_LIBRARY:FILE=/tmp/cvmfs/UUID/lib/libuuid.a \
cd cvmfs && make && make install

For parrot, use the git branch that reflects the latest released version from the cctools github repository. Configure and compile cctools as usual with the ./configure --with-cvmfs-path <CVMFS INSTALL PREFIX>, e.g. ./configure --with-cvmfs-path /tmp/cvmfs/CVMFS.

Note that the cvmfs-devel package contains libcvmfs.h and libcvmfs.a but not necessarily the latest known good version.

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