forked from lix-project/lix
manual: add apfs volume section
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@ -136,6 +136,109 @@ sudo rm /Library/LaunchDaemons/org.nixos.nix-daemon.plist
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</section>
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<section xml:id="sect-apfs-volume-installation">
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<title>APFS Volume Installation</title>
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<para>
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The root filesystem is read-only as of macOS 10.15 Catalina, all writable
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paths to a separate data volume. This means creating or writing to <filename>/nix</filename>
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is not allowed. While changing the default prefix would be possible, it's
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a very intrusive change that has side effects we want to avoid for now.
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</para>
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<para>
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For common writable locations <literal>firmlinks</literal> where introduced,
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described by Apple as a "bi-directional wormhole" between two filesystems.
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Essentially a bind mount for APFS volumes. However this is (currently) not
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user configurable and only available for paths like <filename>/Users</filename>.
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</para>
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<para>
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For special cases like NFS mount points or package manager roots <link xlink:href="https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man5/synthetic.conf.5.html">synthetic.conf(5)</link>
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provides a mechanism for some limited, user-controlled file-creation at <filename>/</filename>.
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This only applies on a reboot, but <command>apfs.util</command> can be used
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to trigger the creation (not deletion) of new entries.
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</para>
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<screen>
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alice$ /System/Library/Filesystems/apfs.fs/Contents/Resources/apfs.util -B
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</screen>
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<itemizedlist>
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<listitem>
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<para>
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The simplest solution is creating a symlink with <filename>/etc/synthetic.conf</filename>
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to the data volume. (not recommended)
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</para>
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<screen>
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nix /System/Volumes/Data/nix
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</screen>
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<screen>
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alice$ ls -l /
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lrwxr-xr-x 1 root wheel 25 Jan 1 2019 nix -> /System/Volumes/Data/nix
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</screen>
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<para>
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However builds that detect or resolve this symlink will leak the canonical
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location or even fail in certain cases, making this approach undesirable.
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</para>
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</listitem>
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<listitem>
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<para>
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An empty directory can also be created using <filename>/etc/synthetic.conf</filename>,
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this won't be writable but can be used as a mount point. And with
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<literal>APFS</literal> it's relatively easy to create an separate
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volume for nix instead.
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</para>
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<screen>
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nix
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</screen>
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<screen>
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alice$ sudo diskutil apfs addVolume diskX APFS 'Nix Store' -mountpoint /nix
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alice$ mount
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/dev/disk1s6 on /nix (apfs, local, journaled)
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</screen>
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<para>
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This does make the installation more complicated, requiring both
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<filename>/etc/synthetic.conf</filename> as well as <filename>/etc/fstab</filename>
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</para>
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<screen>
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#
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# Warning - this file should only be modified with vifs(8)
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#
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# Failure to do so is unsupported and may be destructive.
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#
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LABEL=Nix\040Store /nix apfs rw
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</screen>
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<para>
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On macOS volumes are also mounted quite late, launchd services or other
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things that start during login will start before our volume is mounted.
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For these cases eg. <command>wait4path</command> must be used for
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things that depend on <filename>/nix</filename>.
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</para>
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<para>
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This new volume also won't be encrypted by default, and enabling is
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only possible interactively?
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</para>
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<screen>
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diskutil apfs enableFileVault /nix -user disk
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</screen>
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</listitem>
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</itemizedlist>
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</section>
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<section xml:id="sect-nix-install-pinned-version-url">
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<title>Installing a pinned Nix version from a URL</title>
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