tl;dr: Recipe for Nix installation on a non /nix location, which can be shared across multiple users

caveats: Very hacky

requirements: Every one in your group should at least be a member of the same UNIX group.

As a researcher working on software empirical research, one of the pain points in my research is the creation and maintenance of an environment that can be reproduced easily. I would like to be able to switch environments according to which project I am working on, and even experiment on new programs without affecting my old environments.

Further, I would also wish to collaborate with other researchers, and share my resources with them. If I were to set up an environment once in my machine, it is a waste of time and energy to try to do that again on another system or for another user in the same system. These are the constraints that led me to the Nix package manager in the first place. The promises of Nix are an easily reproducible declarative environment, and purity in the environment thus produced.

Unfortunately, while we have little restriction in available space, or computational power, our systems are fairly locked down. There is no chance of getting access to a folder like /nix in all the machines available (i.e. no chance of root access). So a normal /nix install is completely out of question. These systems are also fairly minimal in their installed packages, and gets updated rather infrequently. Hence the set of packages required to make Nix work is larger than what is required for most Nix installations. Hence, my recipe includes more packages than may be strictly necessary at your environment.

There are still some pieces missing, such as sssd support. These are implemented using rather gross hacks. While there does not seem to be any insurmountable reasons for any of the missing pieces, one may be cautioned that it may not be a priority for the Nix developers at this point of time. Also, be warned that when the corresponding bugs get fixed, some of these hacks might break.

Our environment at Oregon State consists of two separate groups of machines. The first ones consists of our personal desktops (fairly week, 4G RAM, and 40G space), and about 15 machines with about 512G RAM in each, and 1000G space under /scratch (No common NFS share). The second ones consist of about 1000 machines in a Univa cluster with varying capabilities. We also have an NFS mount accessible from each machine in the cluster. So I had to build my recipe to be applicable in both kinds of machines. Each user gets a home environment mounted using NFS, that is accessible in both groups of machines.

While Nix wiki details multiple ways to install Nix on non /nix locations, most of them did not work for me. For example, PRoot does not work in the cluster machines, and where it works, it is too slow. The chroot also had problems on cluster. The manual install only works with the below changes. Finally, LDAP is a must have for almost everyone in an academic setting, since we usually have to login to multiple machines. So we really need the glibc hack if we are to use Nix.

## Recipe

• Fork nix-prefix, change any variables you want in Makefile and checkout to a location of your choice (I assume /scratch).
$export base=/scratch$ git clone https://github.com/vrthra/nix-prefix $base/nix-prefix  • Especially verify that you require all packages that are specified in the checked out Makefile. You can change which packages get installed by modifying the$src variable. By default, these packages are built src=nix bzip2 curl sqlite dbi dbd wwwcurl bison flex gcc coreutils. See the *#@ * lines for where they are fetched from.

• Change to the UNIX group that you share with other team members (I assume that myteam is the UNIX group).

$newgrp myteam  • Initiate make (If you have not changed the Makefile, please provide a reasonable value for base while making). Nix will be installed at$base/nix
$make -f etc/Makefile.nix link$ make

• Note that due to 512 we have to modify the Nix packages slightly. We need a non-released version of Nix (see here), which is fetched automatically.

• You will also require to create/update your ~/.nixpkgs/config.nix. If you don’t have one, it can be created automatically by using nixpkgs target. Remember to use base= argument here if you have not changed it in the Makefile. Update your profile ~/.nix-profile and the Nix Packages checkout link at ~/.nix-defexpr/nixpkgs.

$make nixpkgs nixprofile nixconfig  • At the end of these steps, you should have the nix installation under$base/nix, ~/.nix-profile linked to $base/nix/var/nix/profiles/default, and ~/.nixpkgs/config.nix containing entries from nix-prefix/etc/config.nix with BASE replaced with$base.

• Make sure that you can access your nix commands by executing ./bin/nix.sh You should get a prompt nix>.

$./bin/nix.sh nix> nix-env -q nix-1.12.x  • Remember to garbage collect, if you would like some space back. nix> nix-collect-garbage -d nix> nix-collect-garbage -d  • Exit out of the nix> prompt, and you may now safely cleanup $ make clean

• We are almost there. Unfortunately due to 554, LDAP will not work right now. You can check you need to hack to make it work by
$./bin/check-nss.py  If it throws an exception, execute the next command, if not, skip it. • It does not work: we hack it temporarily by installing sssd, which is in PR 14697 right now, and copying over libnss_sss to the glibc plugins folder. WARNING: GROSS HACK If you are a Nix purist, please hold your nose (or help me fix). $ ./bin/update-glibc-hack.sh

• A final issue is that of sharing with others. Due to 324, one cant yet share an installation with the members in the same group. A hack is to update the permissions under $base/nix so that any file that has user write becomes group write. This can be done by below. Remember to do this each time any of the members have added a new package. $ ./bin/update-perms.sh

• Once you have built $base/nix, you can compress it and transport it to other machines with same operating system. After a GC, the size is really small. nix> nix-collect-garbage -d nix> nix-collect-garbage -d  For some reason, I have to do nix-collect-garbage -d two times to actually delete all garbage. Now, Exit out of the shell, and check the size of installation. $ cd $base$ tar -cf nix.tar nix
$gzip nix.tar$ du -ksh nix.tar.gz
36M     nix.tar.gz


The nix.tar.gz can now be copied to other machines to get a base nix package installation. Once you have the nix> prompt in another machine, you could use copy-closure to copy packages back and forth.

• For another user who wants to use the same $base/nix installation in the same machine, login as that user, and cd to directory where you checked out nix-prefix, and invoke targets nixpkgs and nixprofile. These will create the necessary links in their home directory. $ cd $base/nix-prefix$ make nixprofile nixpkgs nixconfig

• Remember that you need at least these environment variables
$export PATH=$HOME/.nix-profile/bin:$PATH$ export NIXDIR=$HOME/.nix-defexpr$ export NIXPKGS=$NIXDIR/nixpkgs/$ export NIX_PATH=$NIXPKGS:nixpkgs=$NIXPKGS

• Also, switch to the correct group as the second user before touching nix.
$newgrp myteam  • Finally, if you update nix as any user, always run update permissions. $ ./bin/update-perms.sh

• The default.nix in the nix-prefix should get you started for an academic research paper using basic IEEE latex style, and R using ggplot and a number of other packages. You can instantiate it using
$mkdir -p .gcroots$ nix-instantiate . --indirect --add-root $.gcroots/default.drv$ nix-shell . --pure --indirect --add-root .gcroots/dep


Which will land you in a nix-shell containing the required tools. The add-root incantations ensure that your environment will not be garbage collected on nix-collect-garbage invocations. The first nix-instantiate ... --add-root ... creates a reference to the derivation of default.nix, and the second nix-shell ... --add-root ... creates references to all the build dependencies.

With this recipe, you should have a shared prefixed nix installation suitable for academic environments under $base/nix. Ping me if you face any troubles, and I will see if I can help. ## Still to be solved. Because we have multiple kinds of environments, all of which mounts the same$HOME, we don’t have a way to switch the directories ~/.nixpkgs/config.nix and ~/.nix-defexpr. There is this issue 817 still open about it, and it seems there was a NIXPKGS_CONFIG variable at one point of time, but seems to have been removed. See 829.

This can be worked around by using some shell scripting to switch the variables. However, it is very error-prone, and does not let you use different environments simultaneously.