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authorJohn Ericson <John.Ericson@Obsidian.Systems>2021-02-25 20:35:11 +0000
committerJohn Ericson <John.Ericson@Obsidian.Systems>2021-02-25 21:51:05 +0000
commitca0994819d68aee26a2906c37a47ae609ac46c4c (patch)
treec96805c008c22926b1eaadc340a99323d53be532 /src/nix/why-depends.md
parent10e81bf871551901ff0383bdede0f79325e93867 (diff)
parentc189031e8be0530d73a817571ad7f81ad5eedce6 (diff)
Merge remote-tracking branch 'upstream/master' into path-info
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+R""(
+
+# Examples
+
+* Show one path through the dependency graph leading from Hello to
+ Glibc:
+
+ ```console
+ # nix why-depends nixpkgs#hello nixpkgs#glibc
+ /nix/store/v5sv61sszx301i0x6xysaqzla09nksnd-hello-2.10
+ └───bin/hello: …...................../nix/store/9l06v7fc38c1x3r2iydl15ksgz0ysb82-glibc-2.32/lib/ld-linux-x86-64.…
+ → /nix/store/9l06v7fc38c1x3r2iydl15ksgz0ysb82-glibc-2.32
+ ```
+
+* Show all files and paths in the dependency graph leading from
+ Thunderbird to libX11:
+
+ ```console
+ # nix why-depends --all nixpkgs#thunderbird nixpkgs#xorg.libX11
+ /nix/store/qfc8729nzpdln1h0hvi1ziclsl3m84sr-thunderbird-78.5.1
+ ├───lib/thunderbird/libxul.so: …6wrw-libxcb-1.14/lib:/nix/store/adzfjjh8w25vdr0xdx9x16ah4f5rqrw5-libX11-1.7.0/lib:/nix/store/ssf…
+ │ → /nix/store/adzfjjh8w25vdr0xdx9x16ah4f5rqrw5-libX11-1.7.0
+ ├───lib/thunderbird/libxul.so: …pxyc-libXt-1.2.0/lib:/nix/store/1qj29ipxl2fyi2b13l39hdircq17gnk0-libXdamage-1.1.5/lib:/nix/store…
+ │ → /nix/store/1qj29ipxl2fyi2b13l39hdircq17gnk0-libXdamage-1.1.5
+ │ ├───lib/libXdamage.so.1.1.0: …-libXfixes-5.0.3/lib:/nix/store/adzfjjh8w25vdr0xdx9x16ah4f5rqrw5-libX11-1.7.0/lib:/nix/store/9l0…
+ │ │ → /nix/store/adzfjjh8w25vdr0xdx9x16ah4f5rqrw5-libX11-1.7.0
+ …
+ ```
+
+* Show why Glibc depends on itself:
+
+ ```console
+ # nix why-depends nixpkgs#glibc nixpkgs#glibc
+ /nix/store/9df65igwjmf2wbw0gbrrgair6piqjgmi-glibc-2.31
+ └───lib/ld-2.31.so: …che Do not use /nix/store/9df65igwjmf2wbw0gbrrgair6piqjgmi-glibc-2.31/etc/ld.so.cache. --…
+ → /nix/store/9df65igwjmf2wbw0gbrrgair6piqjgmi-glibc-2.31
+ ```
+
+* Show why Geeqie has a build-time dependency on `systemd`:
+
+ ```console
+ # nix why-depends --derivation nixpkgs#geeqie nixpkgs#systemd
+ /nix/store/drrpq2fqlrbj98bmazrnww7hm1in3wgj-geeqie-1.4.drv
+ └───/: …atch.drv",["out"]),("/nix/store/qzh8dyq3lfbk3i1acbp7x9wh3il2imiv-gtk+3-3.24.21.drv",["dev"]),("/…
+ → /nix/store/qzh8dyq3lfbk3i1acbp7x9wh3il2imiv-gtk+3-3.24.21.drv
+ └───/: …16.0.drv",["dev"]),("/nix/store/8kp79fyslf3z4m3dpvlh6w46iaadz5c2-cups-2.3.3.drv",["dev"]),("/nix…
+ → /nix/store/8kp79fyslf3z4m3dpvlh6w46iaadz5c2-cups-2.3.3.drv
+ └───/: ….3.1.drv",["out"]),("/nix/store/yd3ihapyi5wbz1kjacq9dbkaq5v5hqjg-systemd-246.4.drv",["dev"]),("/…
+ → /nix/store/yd3ihapyi5wbz1kjacq9dbkaq5v5hqjg-systemd-246.4.drv
+ ```
+
+# Description
+
+Nix automatically determines potential runtime dependencies between
+store paths by scanning for the *hash parts* of store paths. For
+instance, if there exists a store path
+`/nix/store/9df65igwjmf2wbw0gbrrgair6piqjgmi-glibc-2.31`, and a file
+inside another store path contains the string `9df65igw…`, then the
+latter store path *refers* to the former, and thus might need it at
+runtime. Nix always maintains the existence of the transitive closure
+of a store path under the references relationship; it is therefore not
+possible to install a store path without having all of its references
+present.
+
+Sometimes Nix packages end up with unexpected runtime dependencies;
+for instance, a reference to a compiler might accidentally end up in a
+binary, causing the former to be in the latter's closure. This kind of
+*closure size bloat* is undesirable.
+
+`nix why-depends` allows you to diagnose the cause of such issues. It
+shows why the store path *package* depends on the store path
+*dependency*, by showing a shortest sequence in the references graph
+from the former to the latter. Also, for each node along this path, it
+shows a file fragment containing a reference to the next store path in
+the sequence.
+
+To show why derivation *package* has a build-time rather than runtime
+dependency on derivation *dependency*, use `--derivation`.
+
+)""