Background 背景

1. Package systems versus image systems
   包系统与镜像系统
   1. Package system benefits and drawbacks
      包系统的优缺点
   2. Image benefits and drawbacks
      镜像的优缺点
2. How rpm-ostree provides a middle ground
   rpm-ostree 如何提供一个折中方案

Package systems versus image systems
软件包系统与镜像系统

Broadly speaking, software update systems for operating systems tend to fall cleanly into one of two camps: package-based or image-based.
广义上说，操作系统的软件更新系统往往可以清晰地分为两大阵营：基于软件包或基于镜像。

Package system benefits and drawbacks
软件包系统的优势和缺点

Benefits: 优势：

• Highly dynamic, fast access to wide array of software
  高度动态，快速访问各种软件
• State management in /etc and /var is well understood
  /etc 和 /var 中的状态管理被充分理解
• Can swap between major/minor system states (apt-get upgrade is similar to apt-get dist-upgrade)
  可以在主要/次要系统状态之间切换（ apt-get upgrade 类似于 apt-get dist-upgrade ）
• Generally supports any filesystem or partition layout
  通常支持任何文件系统或分区布局

Drawbacks: 缺点：

• As package set grows, testing becomes combinatorially more expensive
  随着软件包集的增长，测试变得组合更加昂贵
• Live system mutation, no rollbacks
  实时系统变异，无法回滚

Image benefits and drawbacks
图像的好处和缺点

Benefits: 好处：

• Ensures all users are running a known state
  确保所有用户运行在已知状态
• Rollback supported 支持回滚
• Easier to verify system integrity
  更容易验证系统完整性

Drawbacks: 缺点:

• Many image systems have a read-only /etc, and writable partitions elsewhere
  许多图像系统具有一个只读 /etc ，其他地方有可写分区
• Must reboot for updates 必须重新启动以进行更新
• Usually operate at block level, so require fixed partition layout and filesystem
  通常在块级别运行，因此需要固定的分区布局和文件系统
• Many use a “dual root” mode which wastes space and is inflexible
  许多使用“双根”模式，浪费空间且不灵活
• Often paired with a separate application mechanism, but misses out on things that aren’t apps
  通常与单独的应用机制配对，但会错过不是应用程序的东西
• Administrators still need to know content inside
  管理员仍然需要了解内容内部

How rpm-ostree provides a middle ground
rpm-ostree 如何提供一个折中方案

rpm-ostree in its default mode feels more like image replication, but the underlying architecture allows a lot of package-like flexibility.
在其默认模式下，rpm-ostree 更像是镜像复制，但底层架构允许很多类似软件包的灵活性。

In this default mode, packages are composed on a server, and clients can replicate that state reliably. For example, if one adds a package on the compose server, clients get it. If one removes a package, it’s also removed when clients upgrade.
在这种默认模式下，软件包在服务器上组合，客户端可以可靠地复制该状态。例如，如果在组合服务器上添加一个软件包，客户端会得到它。如果删除一个软件包，当客户端升级时也会被移除。

One simple mental model for rpm-ostree is: imagine taking a set of packages on the server side, install them to a chroot, then doing git commit on the result. And imagine clients just git pull -r from that. What OSTree adds to this picture is support for file uid/gid, extended attributes, handling of bootloader configuration, and merges of /etc.
一个简单的 rpm-ostree 的心智模型是：想象将一组软件包安装到 chroot 中，然后对结果执行 git commit 。想象客户端只是从中 git pull -r 。OSTree 在这个图景中添加的功能包括对文件 uid/gid、扩展属性、处理引导加载程序配置以及 /etc 的支持。

To emphasize, replication is at a filesystem level - that means things like SELinux labels and uid/gid mappings are assigned on the server side.
强调一下，复制是在文件系统级别进行的 - 这意味着像 SELinux 标签和 uid/gid 映射这样的东西是在服务器端分配的。

On the other hand, rpm-ostree works on top of any Unix filesystem. It will not interfere with any filesystem or block-level snapshots or backups such as LVM or BTRFS.
另一方面，rpm-ostree 可以在任何 Unix 文件系统上运行。它不会干扰任何文件系统或块级快照或备份，比如 LVM 或 BTRFS。