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[#]: collector: (lujun9972)
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[#]: translator: (geekpi)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (How To Boot Into Rescue Mode Or Emergency Mode In Ubuntu 18.04)
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[#]: via: (https://www.ostechnix.com/how-to-boot-into-rescue-mode-or-emergency-mode-in-ubuntu-18-04/)
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[#]: author: (SK https://www.ostechnix.com/author/sk/)
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How To Boot Into Rescue Mode Or Emergency Mode In Ubuntu 18.04
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======
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As you might already know, **Runlevels** are replaced with **Systemd targets** in many recent Linux distributions like RHEL 7 and Ubuntu 16.04 LTS. For more details about runlevels and systemd target, refer [**this guide**][1]. In this brief tutorial, we are going to see how to boot into **rescue mode** and/or **emergency mode**. This guide is tested in Ubuntu 18.04 LTS, however the steps given below would work on most Linux distributions that uses Systemd as default service manager. Before going further, let me clarify what is rescue mode and emergency mode and what is the purpose of the both modes.
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### What is Rescue mode?
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The **rescue mode** is equivalent to **single user mode** in Linux distributions that uses **SysV** as the default service manager. In rescue mode, all local filesystems will be mounted, only some important services will be started. However, no normal services (E.g network services) won’t be started. The rescue mode is helpful in situations where the system can’t boot normally. Also, we can perform some important rescue operations, such as [**reset root password**][2], in rescue mode.
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### What is Emergency mode?
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In contrast to the rescue mode, nothing is started in the **emergency mode**. No services are started, no mount points mounted, no sockets established, nothing. All you will have is just a **raw shell**. Emergency mode is suitable for debugging purposes.
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### Boot Into Rescue Mode In Ubuntu 18.04 LTS
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Boot your Ubuntu system. When Grub menu appears, choose the first entry and press **e** to edit.
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If you don’t see the Grub menu, just hit ESC key right after the BIOS logo disappears.
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Find the line that starts with word **“linux”** and add the following line at the end of that line (To reach the end, just press **CTRL+e** or use END key or LEFT/RIGHT arrows in your keyboard):
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```
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systemd.unit=rescue.target
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```
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Once you added the above line, just press **CTRL+x** or **F10** to continue to boot into rescue mode. After a few seconds, you will be ended up in the rescue mode (single user mode) as root user. Here is how rescue mode looks like in Ubuntu 18.04 LTS server:
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Next, type the following command to mount root (/) file system into read/write mode.
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```
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mount -n -o remount,rw /
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```
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### Boot Into Emergency Mode
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Booting your Ubuntu into emergency is as same as above method. All you have to do is replace “systemd.unit=rescue.target” with “systemd.unit=emergency.target” when editing grub menu.
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[![emergency mode][3]][4]
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Once you added “systemd.unit=emergency.target”, press **Ctrl+x** or **F10** to continue booting into emergency mode.
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Finally, you can mount root filesystem into read/write mode with command:
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```
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mount -n -o remount,rw /
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```
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### Switch between Rescue to Emergency mode and vice versa
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If you are in rescue mode, you don’t have to edit the grub boot entry as I mentioned above. Instead, just type the following command to switch to emergency mode instantly:
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```
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systemctl emergency
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```
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Similarly, to switch from emergency to rescue mode, type:
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```
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systemctl rescue
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```
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You know now what is rescue and emergency modes and how to boot into those modes in Ubuntu 18.04. Like I already mentioned, the steps provided here will work on many recent Linux versions that uses Systemd.
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And, that’s all for now. Hope this was useful.
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More good stuffs to come. Stay tuned!
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Cheers!
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--------------------------------------------------------------------------------
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via: https://www.ostechnix.com/how-to-boot-into-rescue-mode-or-emergency-mode-in-ubuntu-18-04/
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作者：[SK][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://www.ostechnix.com/author/sk/
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[b]: https://github.com/lujun9972
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[1]: https://www.ostechnix.com/check-runlevel-linux/
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[2]: https://www.ostechnix.com/how-to-reset-or-recover-root-user-password-in-linux/
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[3]: data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7
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[4]: http://www.ostechnix.com/wp-content/uploads/2018/12/emergency-mode.png
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@ -0,0 +1,106 @@
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[#]: collector: (lujun9972)
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[#]: translator: (geekpi)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (How To Boot Into Rescue Mode Or Emergency Mode In Ubuntu 18.04)
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[#]: via: (https://www.ostechnix.com/how-to-boot-into-rescue-mode-or-emergency-mode-in-ubuntu-18-04/)
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[#]: author: (SK https://www.ostechnix.com/author/sk/)
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如何在 Ubuntu 18.04 中启动到救援模式或紧急模式
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======
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正如你可能已经知道的那样，**runlevel** 在许多最近的 Linux 发行版（如 RHEL 7 和 Ubuntu 16.04 LTS）中被 **systemd target** 替换。有关 runlevel 和 systemd target 的更多详细信息，请参阅[**本指南**][1]。在这个简短的教程中，我们将看到如何启动**救援模式**以及**紧急模式**。本指南在 Ubuntu 18.04 LTS 中进行了测试，但是下面给出的步骤适用于大多数使用 systemd 作为默认服务管理器的 Linux 发行版。在进一步讨论之前，让我澄清什么是救援模式和紧急模式以及这两种模式的目的是什么。
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### 什么是救援模式？
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**救援模式**相当于使用 **SysV** 作为默认服务管理器的 Linux 发行版中的 **单用户模式**。在救援模式下，将挂载所有本地文件系统，仅启动一些重要服务。但是，不会启动正常服务（例如网络服务）。救援模式在系统无法正常启动的情况下很有用。此外，我们可以在救援模式下执行一些重要的救援操作，例如[**重置 root 密码**][2]。
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### 什么是紧急模式？
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与救援模式相比，在**紧急模式**中不启动任何东西。没有服务启动、没有挂载点、没有建立套接字，什么也没有。你所拥有的只是一个**原始的 shell**。紧急模式适用于调试目的。
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### 在 Ubuntu 18.04 LTS 中进入救援模式
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启动你的 Ubuntu 系统。出现 Grub 菜单时，选择第一条并按下 **e** 进行编辑。
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如果你没有看到 Grub 菜单，只需在 BIOS logo 消失后立即按下 ESC 键。
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找到以单词 **“linux”** 开头的行，并在该行的末尾添加以下行（要到达末尾，只需按下 **CTRL+e** 或使用 END 键或左右箭头键）：
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```
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systemd.unit=rescue.target
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```
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添加完成后，只需按下 **CTRL+x** 或 **F10** 即可继续启动救援模式。几秒钟后，你将以 root 用户身份进入救援模式（单用户模式）。以下是 Ubuntu 18.04 LTS 服务器版中救援模式的样子：
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接下来，输入以下命令将根 （/） 文件系统挂载成读/写模式。
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```
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mount -n -o remount,rw /
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```
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### 启动到紧急模式
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将 Ubuntu 引导到紧急模式与上述方法相同。你只需在编辑 grub 菜单时将 “systemd.unit=rescue.target” 替换为 “systemd.unit=emergency.target” 即可。
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[![emergency mode][3]][4]
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添加 “systemd.unit=emergency.target” 后，按下 **Ctrl+x** 或 **F10** 继续启动到紧急模式。
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最后，你可以使用以下命令将根文件系统挂载成读/写模式：
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```
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mount -n -o remount,rw /
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```
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### 在救援模式和紧急模式之间切换
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如果你处于救援模式，则不必像上面提到的那样编辑 grub 条目。相反，只需输入以下命令即可立即切换到紧急模式：
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```
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systemctl emergency
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```
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同样，要从紧急模式切换到救援模式，请输入：
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```
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systemctl rescue
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```
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你现在知道了什么是救援模式和紧急模式以及如何在 Ubuntu 18.04 中启动这些模式。就像我已经提到的，这里提供的步骤将适用于许多使用 systemd 的 Linux 版本。
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就是这些了。希望这篇文章有用。
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还有更多好东西。敬请期待！
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干杯！
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--------------------------------------------------------------------------------
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via: https://www.ostechnix.com/how-to-boot-into-rescue-mode-or-emergency-mode-in-ubuntu-18-04/
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作者：[SK][a]
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选题：[lujun9972][b]
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译者：[geekpi](https://github.com/geekpi)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://www.ostechnix.com/author/sk/
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[b]: https://github.com/lujun9972
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[1]: https://www.ostechnix.com/check-runlevel-linux/
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[2]: https://www.ostechnix.com/how-to-reset-or-recover-root-user-password-in-linux/
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[3]: data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7
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[4]: http://www.ostechnix.com/wp-content/uploads/2018/12/emergency-mode.png
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