first info for the cvmfsexec way

Author: torri

docs/getting_access/non_standard.md

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+# Non-standard ways to use EESSI
+
+In case that an EESSI installation is not possible or desirable, there are a couple of "non-standard" ways to access EESSI.
+
+## Using cvmfsexec
+
+This option relies on the [cvmfsexec package](https://github.com/cvmfs/cvmfsexec) provided by CernVM-FS team. It will allow you to mount cvmfs as an unprivileged user, so no need to have a native cvmfs installation.
+
+### `cvmfsexec_eessi.sh`  wrapper script
+
+
+This wrapper script, `cvmfsexec_eessi.sh`, can be used to run a command in a subshell in which the EESSI CernVM-FS repository (`software.eessi.io`) is mounted via cvmfsexec`.
+
+```bash
+#!/bin/bash
+if [ -d /cvmfs/software.eessi.io ]; then
+    # run command directly, EESSI CernVM-FS repository is already mounted
+    "$@"
+else
+    # run command via in subshell where EESSI CernVM-FS repository is mounted,
+    # via cvmfsexec which is set up in a unique temporary directory
+    orig_workdir=$(pwd)
+    mkdir -p /tmp/$USER
+    tmpdir=$(mktemp -p /tmp/$USER -d)
+    cd $tmpdir
+    git clone https://github.com/cvmfs/cvmfsexec.git > $tmpdir/git_clone.out 2>&1
+    cd cvmfsexec
+    ./makedist default > $tmpdir/cvmfsexec_makedist.out 2>&1
+    cd $orig_workdir
+    $tmpdir/cvmfsexec/cvmfsexec software.eessi.io -- "$@"
+    # cleanup
+    rm -rf $tmpdir
+fi
+
+```
+
+Do make sure that this script is executable:
+
+```bash
+    chmod u+x ~/bin/cvmfsexec_eessi.sh
+```
+
+A simple way to test this script is to use it to inspect the contents of the EESSI repository:
+
+```bash
+    ~/bin/cvmfsexec_eessi.sh ls /cvmfs/software.eessi.io
+```
+
+or to start an interactive shell in which the EESSI repository is mounted:
+
+```bash
+    # Expected output from a machine without a cvmfs installation
+    $ ls /cvmfs
+    ls: cannot access '/cvmfs': No such file or directory
+
+    # Starting interactive shell
+    $ ~/bin/cvmfsexec_eessi.sh /bin/bash -l
+    CernVM-FS: loading Fuse module... done
+    CernVM-FS: mounted cvmfs on /tmp/hvela/tmp.iH6e993Adw/cvmfsexec/dist/cvmfs/cvmfs-config.cern.ch
+    CernVM-FS: loading Fuse module... done
+    CernVM-FS: mounted cvmfs on /tmp/hvela/tmp.iH6e993Adw/cvmfsexec/dist/cvmfs/software.eessi.io
+
+    # Now it's mounted!
+    $ ls /cvmfs/
+    cvmfs-config.cern.ch  software.eessi.io
+
+```
+
+Notice how now that EESSI is mounted, you will need to [set up the environment](https://www.eessi.io/docs/using_eessi/setting_up_environment/) in order to access the software itself.
+
+### `orted`  wrapper script
+
+In order to get multi-node runs of software working without having EESSI available system-wide, we also had to create a small wrapper script for the `orted` command that is used by Open MPI to start processes on remote nodes. This is necessary because `mpirun` launches `orted`, which must be run in an environment in which the EESSI repository is mounted. If not, MPI startup will fail with an error like
+
+```bash
+"error: execve(): orted: No such file or directory".
+```
+
+This wrapper script must be named `orted`, and must be located in a path that is listed in `$PATH`.
+
+We placed it in `~/bin/orted`, and you can add `export PATH=$HOME/bin:$PATH` to your `~/.bashrc` login script.
+
+Contents of ~/bin/orted:
+
+```bash
+#!/bin/bash
+
+# first remove path to this orted wrapper from $PATH, to avoid infinite loop
+orted_wrapper_dir=$(dirname $0)
+export PATH=$(echo $PATH | tr ':' '\n' | grep -v $orted_wrapper_dir | tr '\n' ':')
+
+~/bin/cvmfsexec_eessi.sh orted "$@"
+```
+
+Again, do make sure that also this `orted` wrapper script is executable:
+
+```bash
+chmod u+x ~/bin/orted
+```
+
+If not, you will likely run into an error that starts with:
+
+
+```bash
+An ORTE daemon has unexpectedly failed after launch ...
+```
+
+### Slurm job script
+
+The `cvmfsexec_eessi.sh` can be used insided a Slurm job script inside your HPC system to initialize the EESSI environment in a subshell which the EESSI CernVM-FS repository is mounted. Thus, you will be able to load any module from EESSI you might need.
+
+Example job script:
+
+```bash
+#!/bin/bash
+#SBATCH --ntasks=4
+#SBATCH --ntasks-per-node=2
+#SBATCH --cpus-per-task=1
+#SBATCH --time=5:0:0
+#SBATCH --export=None
+#SBATCH --mem=30000M
+~/bin/cvmfsexec_eessi.sh << EOF
+source /cvmfs/software.eessi.io/versions/2023.06/init/bash
+module load TensorFlow/2.13.0-foss-2023a
+export SLURM_EXPORT_ENV=HOME,PATH,LD_LIBRARY_PATH,PYTHONPATH
+mpirun -np 4 python test.py
+EOF
+
+```
+You can see the original blog post on how they used this solution in Deucalion [here](https://www.eessi.io/docs/blog/2024/06/28/espresso-portable-test-run-eurohpc/#running-espresso-on-deucalion-via-eessi-cvmfsexec).