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如何调试启动过程？

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如何调试启动过程？

断电后我的服务器（Ubuntu 16.04）无法启动，我不明白为什么它会给我“输入 root 密码进​​行维护”的消息。

我做了fsck根分区并且它正在以 RW 模式挂载：

root@dev:~# cat /proc/mounts|grep ' / ' 
/dev/sda1 / ext4 rw,relatime,errors=remount ro,data=ordered 0 0
root@dev:~# 
root@dev:~# touch /works
root@dev:~# rm /works
root@dev:~#

日志没有提供任何线索：

 -- Unit plymouth-read-write.service has begun starting up.
oct 27 19:03:36 dev systemd[1]: Reached target Emergency Mode.
-- Subject: Unit emergency.target has finished start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit emergency.target has finished starting up.
-- 
-- The start-up result is done.
oct 27 19:03:36 dev systemd[1]: Started Stop ureadahead data collection.
-- Subject: Unit ureadahead-stop.service has finished start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ureadahead-stop.service has finished starting up.
-- 
-- The start-up result is done.
oct 27 19:03:36 dev systemd[1]: Started Update UTMP about System Runlevel Changes.
-- Subject: Unit systemd-update-utmp-runlevel.service has finished start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit systemd-update-utmp-runlevel.service has finished starting up.
-- 
-- The start-up result is done.
oct 27 19:03:36 dev systemd[1]: Stopped Read required files in advance.
-- Subject: Unit ureadahead.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ureadahead.service has finished shutting down.
oct 27 19:03:36 dev systemd[1]: Started Tell Plymouth To Write Out Runtime Data.
-- Subject: Unit plymouth-read-write.service has finished start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit plymouth-read-write.service has finished starting up.
--

我可以手动设置以太网接口并启动 SSH 守护进程，我可以登录，一切似乎都很好，除了它卡在阶段init。

如果一切正常，我该如何找出导致维护提示出现的原因？初始化脚本位于哪里以及如何使其能够打印调试消息或更详细？

答案1

我发现了这个问题，因此我将为可能遇到同样问题的人发布答案。

我在 /etc/fstab 中有一个 /volume，但后来这个 /volume 被文件系统替换了bcache，从那以后我就再也没有重启过。现在，在非正常关机后，当我重启时，bcache这个分区被锁定，无法使用，并且 init 进程无法将其挂载到 /volume 挂载点。我在 /etc/fstab 中注释了这个分区，就这样。

为了找到这个错误，我必须启动到文本模式（通过删除中的“splash, quiet”属性/etc/defaults/grub），因为在图形中我什么都看不到。

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