Nix vs. Linux Standard Base: Difference between revisions

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This article is a comparison between the ~~way~~ [[Nix]] ~~install packages to the filesystem hierarchy,~~ and the [https://en.wikipedia.org/wiki/Linux_Standard_Base Linux Standard Base] (LSB) standard ~~which~~ most conventional Linux distributions~~, package managers and installers~~ follow.

This article is a comparison between the [[Nix package manager]] and the [https://en.wikipedia.org/wiki/Linux_Standard_Base Linux Standard Base] (LSB) standard that the package managers of most conventional Linux distributions follow.

== Package Installation ==

In most distributions, ~~asking for a~~ package ~~to be installed, means having all its files available in the root filesystem (~~<code>/{,usr}/{bin,etc,lib~~,sbin~~,...}</code>).

In most distributions, files of an installed package are stored under <code>/{,usr}/{bin,etc,lib,...}</code>.

With Nix, the ~~installed~~ files of a package go into a ''profile'' (as if it was a rootfs), and ~~you~~ can have as many profiles as ~~you~~ want~~. There is the notion of each user having at least one profile, so `~/.nix-profile` points to the last version of the profile the user chose (last generation)~~.

With Nix, the files of a package go into a ''profile'' (as if it was a rootfs), and users can have as many profiles as they want.

By default, the only part of the system made aware of the contents of the user profile is the PATH. The user PATH is set through bashrc to include `~/.nix-profile/bin`. So, by default, installing a Nix package means "having it in the PATH". A simple operation like <code>nix-env -i firefox</code> is meant to update the nix store, then generate a new profile in the store having all the programs ''installed'' plus the new one, and updating the symlink `~/.nix-profile`, so `~/.nix-profile/bin` will contain a symlink to the executable of firefox. Then a user can type <code>firefox</code> and have it running.

By default, the only part of the system made aware of the contents of the user profile is the <code>PATH</code> environment variable. The user <code>PATH</code> is set through bashrc to include <code>~/.nix-profile/bin</code>. So, by default, installing a Nix package means "having it in the PATH". A simple operation like <code>nix-env -i firefox</code> is meant to update the nix store, then generate a new profile in the store having all the programs ''installed'' plus the new one, and updating the symlink <code>~/.nix-profile</code>, so <code>~/.nix-profile/bin</code> will contain a symlink to the executable of firefox. Then a user can type <code>firefox</code> and have it running.

If other kind of files are to be found by programs looking at the usual `<code>/{,usr}/{bin,etc,lib,sbin,...}</code>` locations, other variables may be of help. For example, gcc would welcome <code>CPATH</code> and <code>LIBRARY_PATH</code>. And the dynamic loader will welcome <code>LD_LIBRARY_PATH</code>.

If other kind of files are to be found by programs looking at the usual <code>/{,usr}/{bin,etc,lib,sbin,...}</code> locations, other variables may be of help. For example, gcc would welcome <code>CPATH</code> and <code>LIBRARY_PATH</code>. And the dynamic loader will welcome <code>LD_LIBRARY_PATH</code>.

== Build and install from Source ==

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With Nix, you can install the needed development tools into your profile (gcc-wrapper, gnumake), and the dependencies for the source you want to build (libpng, qt, ...). Once that done, set the environment variables (for gcc): <syntaxhighlight lang="bash" inline>CPATH=~/.nix-profile/include; LIBRARY_PATH=~/.nix-profile/lib; QTDIR=~/nix-profile</syntaxhighlight>... And then you should get your build running. In most LSB distributions, you proceed like the section above to build the program, and then run <code>make install</code> to get it into /usr/local, overwritting any files you had there.

Using Nix, if you built your program like the section above, you may end up having /usr/local files depending on dynamic libraries only present in your profile. That situation may require a <code>LD_LIBRARY_PATH</code> variable, or your ld.so.conf pointing to your profile, but this situation can end in your programs not working if you remove those dependencies from your profile. This would be also a problem in your LSB distribution, if you remove uninstall packages required by programs you put manually in /usr/local.

Using Nix, if you built your program like the section above, you may end up having /usr/local files depending on dynamic libraries only present in your profile. That situation may require a <code>LD_LIBRARY_PATH</code> variable, or your ld.so.conf pointing to your profile, but this situation can end in your programs not working if you remove those dependencies from your profile. This would be also a problem in your LSB distribution, if you remove uninstall packages required by programs you put manually in <code>/usr/local</code>.

Therefore, it is advisable to use Nix not only for acquiring dependencies, but also for managing the build of your package. In fact, creating an ad-hoc Nix package for the software is often easier, because the standard environment in NixPkgs automatically takes care of issues that could arise because of the differences between the Nix and LSB approaches. For example, a well packaged autotools-based project usually builds successfully after specifying its dependencies in Nix, whereas if you would install the dependencies and try to build it yourself, you will have a hard time.

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== Modifying a Package ==

In LSB distributions, ~~after installing a package, you would go to~~ /usr~~/whatever and edit~~ the ~~files you want to change~~.

In LSB distributions, files installed under {{ic|/usr}} can be edited by the user as needed.

~~With~~ Nix~~, any files inside the~~ store (/nix/store~~, where all nix installed files end up; ~/.nix-profile is a symlink to a store path~~), are meant to be read-only~~. That is, nix expects those files~~ only ~~under her control, and it is a requirement to allow rollbacks and reproducibility. Of course the owner of~~ the nix ~~store can change files there, but then you cannot expect rollbacks or reproducibility~~. "nix-store --verify --check-contents~~" will tell you if there are files modified in the store (since the creation~~ of ~~each store path). Although modifying a file in~~ the store ~~seems like an easy quick fix, it should be regarded as bad as modifying the memory of a running process, because it has almost all the analogous downsides~~.

Files in the Nix store ({{ic|/nix/store}}) are meant to be read-only and changes are only done using the {{ic|nix}} commands. {{ic|nix-store --verify --check-contents}} can be used to ensure integrity of the store data.

~~For a discussion of methods to~~ make ~~(durable)~~ changes to Nix packages, see [[Modifying a Package]]

To make changes to Nix packages properly, see [[Modifying a Package]].

== See also ==

@@ Line 1: / Line 1: @@
-This article is a comparison between the way [[Nix]] install packages to the filesystem hierarchy, and the [https://en.wikipedia.org/wiki/Linux_Standard_Base Linux Standard Base] (LSB) standard which most conventional Linux distributions, package managers and installers follow.
+This article is a comparison between the [[Nix package manager]] and the [https://en.wikipedia.org/wiki/Linux_Standard_Base Linux Standard Base] (LSB) standard that the package managers of most conventional Linux distributions follow.
 == Package Installation ==
-In most distributions, asking for a package to be installed, means having all its files available in the root filesystem (<code>/{,usr}/{bin,etc,lib,sbin,...}</code>).
+In most distributions, files of an installed package are stored under <code>/{,usr}/{bin,etc,lib,...}</code>.
-With Nix, the installed files of a package go into a ''profile'' (as if it was a rootfs), and you can have as many profiles as you want. There is the notion of each user having at least one profile, so `~/.nix-profile` points to the last version of the profile the user chose (last generation).
+With Nix, the files of a package go into a ''profile'' (as if it was a rootfs), and users can have as many profiles as they want.
-By default, the only part of the system made aware of the contents of the user profile is the PATH. The user PATH is set through bashrc to include `~/.nix-profile/bin`. So, by default, installing a Nix package means "having it in the PATH". A simple operation like <code>nix-env -i firefox</code> is meant to update the nix store, then generate a new profile in the store having all the programs ''installed'' plus the new one, and updating the symlink `~/.nix-profile`, so `~/.nix-profile/bin` will contain a symlink to the executable of firefox. Then a user can type <code>firefox</code> and have it running.
+By default, the only part of the system made aware of the contents of the user profile is the <code>PATH</code> environment variable. The user <code>PATH</code> is set through bashrc to include <code>~/.nix-profile/bin</code>. So, by default, installing a Nix package means "having it in the PATH". A simple operation like <code>nix-env -i firefox</code> is meant to update the nix store, then generate a new profile in the store having all the programs ''installed'' plus the new one, and updating the symlink <code>~/.nix-profile</code>, so <code>~/.nix-profile/bin</code> will contain a symlink to the executable of firefox. Then a user can type <code>firefox</code> and have it running.
-If other kind of files are to be found by programs looking at the usual `<code>/{,usr}/{bin,etc,lib,sbin,...}</code>` locations, other variables may be of help. For example, gcc would welcome <code>CPATH</code> and <code>LIBRARY_PATH</code>. And the dynamic loader will welcome <code>LD_LIBRARY_PATH</code>.
+If other kind of files are to be found by programs looking at the usual <code>/{,usr}/{bin,etc,lib,sbin,...}</code> locations, other variables may be of help. For example, gcc would welcome <code>CPATH</code> and <code>LIBRARY_PATH</code>. And the dynamic loader will welcome <code>LD_LIBRARY_PATH</code>.
 == Build and install from Source ==
@@ Line 17: / Line 17: @@
 With Nix, you can install the needed development tools into your profile (gcc-wrapper, gnumake), and the dependencies for the source you want to build (libpng, qt, ...). Once that done, set the environment variables (for gcc): <syntaxhighlight lang="bash" inline>CPATH=~/.nix-profile/include; LIBRARY_PATH=~/.nix-profile/lib; QTDIR=~/nix-profile</syntaxhighlight>... And then you should get your build running. In most LSB distributions, you proceed like the section above to build the program, and then run <code>make install</code> to get it into /usr/local, overwritting any files you had there.
-Using Nix, if you built your program like the section above, you may end up having /usr/local files depending on dynamic libraries only present in your profile. That situation may require a <code>LD_LIBRARY_PATH</code> variable, or your ld.so.conf pointing to your profile, but this situation can end in your programs not working if you remove those dependencies from your profile. This would be also a problem in your LSB distribution, if you remove uninstall packages required by programs you put manually in /usr/local.
+Using Nix, if you built your program like the section above, you may end up having /usr/local files depending on dynamic libraries only present in your profile. That situation may require a <code>LD_LIBRARY_PATH</code> variable, or your ld.so.conf pointing to your profile, but this situation can end in your programs not working if you remove those dependencies from your profile. This would be also a problem in your LSB distribution, if you remove uninstall packages required by programs you put manually in <code>/usr/local</code>.
 Therefore, it is advisable to use Nix not only for acquiring dependencies, but also for managing the build of your package. In fact, creating an ad-hoc Nix package for the software is often easier, because the standard environment in NixPkgs automatically takes care of issues that could arise because of the differences between the Nix and LSB approaches. For example, a well packaged autotools-based project usually builds successfully after specifying its dependencies in Nix, whereas if you would install the dependencies and try to build it yourself, you will have a hard time.
@@ Line 31: / Line 31: @@
 == Modifying a Package ==
-In LSB distributions, after installing a package, you would go to /usr/whatever and edit the files you want to change.
+In LSB distributions, files installed under {{ic|/usr}} can be edited by the user as needed.
-With Nix, any files inside the store (/nix/store, where all nix installed files end up; ~/.nix-profile is a symlink to a store path), are meant to be read-only. That is, nix expects those files only under her control, and it is a requirement to allow rollbacks and reproducibility. Of course the owner of the nix store can change files there, but then you cannot expect rollbacks or reproducibility. "nix-store --verify --check-contents" will tell you if there are files modified in the store (since the creation of each store path). Although modifying a file in the store seems like an easy quick fix, it should be regarded as bad as modifying the memory of a running process, because it has almost all the analogous downsides.
+Files in the Nix store ({{ic|/nix/store}}) are meant to be read-only and changes are only done using the {{ic|nix}} commands. {{ic|nix-store --verify --check-contents}} can be used to ensure integrity of the store data.
-For a discussion of methods to make (durable) changes to Nix packages, see [[Modifying a Package]]
+To make changes to Nix packages properly, see [[Modifying a Package]].
 == See also ==