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89 lines
3.4 KiB
Text
89 lines
3.4 KiB
Text
Setting up and running Nix UML ("nixu")
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It is possible to run Nix inside a User Mode Linux environment (UML). The Nix
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expressions for this can be found at
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https://svn.cs.uu.nl:12443/repos/trace/nixu/.
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Installation on SuSE Linux 9
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Download the latest nixpkgs collection and checkout the nixu trunk with
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subversion. Install the uml and uml-utilities packages with Nix and run the
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"make-disk.sh" script which can be found in nixu. After it has built
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everything (or downloaded everything from the nixpkgs cache which can be
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used with nix-pull) you can use the "run.sh" script to start the UML.
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Installation on Fedora Core 1
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Installing the Nix UML on Fedora Core 1 is a bit tricky. Nix relies on
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Berkeley DB and there are issues with Berkeley DB and NPTL kernels (New POSIX
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Thread Library) on Red Hat based systems. Since the system we build inside
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UML does not use NPTL we cannot use the Nix we use on the host system to
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fill the disk once we've booted our the kernel of our UML.
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The solution is as follows:
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- install all packages via the nix-pull mechanisms with the MANIFEST from
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the official nix-pkgs site to avoid that impure builds link against the
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NPTL glibc on the host system.
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- install Nix in Nix
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- in the nixu scripts edit make-disk.sh and fill-disk.sh.
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In make-disk.sh prefix all nix-* commands with the absolute path to the
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host-Nix installation bin directory (for example: /nix/bin). In
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fill-disk.sh replace all /nix/bin paths with a relative path to the Nix
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installed with Nix (for example: /usr/home/nix/.nix-profile/bin).
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This should fix the installation problems and the Nix UML should boot
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flawlessly.
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Nix UML and 2.6 kernel
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Installing the current Nix UML packages with a 2.4 kernel on a 2.6
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kernel based host system will most likely fail. Linux kernel 2.6 uses NPTL
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by default, but UML itself seems to be broken somewhat so halfway the system
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seems to hang.
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Installing a 2.6 based UML with Nix is not trivial and is not advised.
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Using the Nix UML
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By default, the Nix UML comes with very little configuration. Apart from the
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networking information and mount information, there is nothing. One of the
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first things to do is to add user and group information, otherwise a lot
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of tools won't work. There are empty passwd, shadow and group files. Due
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to some limitations in Nix it is only possible to modify the password file
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as root.
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- add a root user:
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useradd root
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- edit /etc/passwd and change the UID to 0 ("vim" is provided)
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- add a root group:
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groupadd root
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Adding packages to the UML Nix installation
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Packages can be added the the Nix UML installation by editing a few files.
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The first file packages should be added to is 'pkgs.nix'. The other files
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that should be edited all reside in the "boot" directory. In default.nix
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the packages should be added as an argument (first line) and given as an
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argument to the builder (line starting with "inherit"). In "builder.sh"
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there is a sed expression which subsitutes all occurences of the names of
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the packages in the files with the right value. If the programs that are
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added need to be added to $PATH the file "env.sh" has to be edited and the
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UML has to be recreated.
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Another option would be to enable networking in the UML and use nix-pull to
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get all the right packages, however this does not work yet out of the box.
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A small trick is to symlink /bin/sh to the current version of "sh":
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# cd /bin
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# ln -s `which sh` sh
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We're looking for a more permanent solution to fix this.
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