From 9e9e34ff7f28215fa9a275ae568a42aa0176c2cf Mon Sep 17 00:00:00 2001
From: Ryan Yin <xiaoyin_c@qq.com>
Date: Tue, 5 Mar 2024 14:36:14 +0800
Subject: [PATCH] feat: Why some packages are installed

---
 docs/nixos-with-flakes/other-useful-tips.md    | 13 +++++++++----
 docs/zh/nixos-with-flakes/other-useful-tips.md | 12 ++++++++----
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/docs/nixos-with-flakes/other-useful-tips.md b/docs/nixos-with-flakes/other-useful-tips.md
index 5819fc4..6b3ad1c 100644
--- a/docs/nixos-with-flakes/other-useful-tips.md
+++ b/docs/nixos-with-flakes/other-useful-tips.md
@@ -71,11 +71,16 @@ sudo nix profile wipe-history --older-than 7d --profile /nix/var/nix/profiles/sy
 sudo nix store gc --debug
 ```
 
-Another command that returns all packages installed in the system is:
 
-```shell
-nix-env -qa
-```
+## Why some packages are installed?
+
+To find out why a package is installed, you can use the following command:
+
+1. Enter a shell with `nix-tree` available: `nix shell nixpkgs#nix-tree`
+1. ` nix-store --gc --print-roots | rg -v '/proc/' | rg -Po '(?<= -> ).*' | xargs -o nix-tree`
+1. `/<package-name>` to find the package you want to check.
+1. `w` to show the package is depended by which packages, and the full dependency chain.
+
 
 ## Reducing Disk Usage
 
diff --git a/docs/zh/nixos-with-flakes/other-useful-tips.md b/docs/zh/nixos-with-flakes/other-useful-tips.md
index ee6e61e..52275b4 100644
--- a/docs/zh/nixos-with-flakes/other-useful-tips.md
+++ b/docs/zh/nixos-with-flakes/other-useful-tips.md
@@ -68,11 +68,15 @@ sudo nix profile wipe-history --older-than 7d --profile /nix/var/nix/profiles/sy
 sudo nix store gc --debug
 ```
 
-以及查看系统层面安装的所有软件包（这个貌似只能用 `nix-env`）：
+## 查询为什么某个包被安装了 {#why-some-packages-are-installed}
+
+查询为什么某个包被安装，当前环境中的谁依赖了它:
+
+1. 进入一个带有 `nix-tree` 的 shell：`nix shell nixpkgs#nix-tree`
+1. ` nix-store --gc --print-roots | rg -v '/proc/' | rg -Po '(?<= -> ).*' | xargs -o nix-tree`
+1. `/<package-name>` 以查找到你想查询的包
+1. 输入 `w`，看看谁依赖了它（`why depends`），以及完整的依赖链。
 
-```shell
-nix-env -qa
-```
 
 # 节约存储空间