如何调试引导过程？

Question

断电后，我的服务器(Ubuntu16.04)将无法启动，我不明白为什么它会给我“为维护提供根密码”的消息。

我做了fsck根分区，它是在RW模式下运行的：

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:~# 

日志没有给出任何线索：

 -- 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，一切看起来都很好，只是它被困在了init阶段。

假设一切正常，我如何找出导致维护提示出现的原因？init脚本位于何处，如何使其能够打印调试消息或更详细？

Answer 1

我发现了这个问题，所以我会为那些可能陷入同样困境的人贴出答案。

我在/etc/fstab中有一个/volume，但是这个/volume后来被一个bcache文件系统取代了，从那以后我就再也没有重新启动过。现在，在不干净的关闭之后，当我重新启动时，bcache锁定了这个分区供其使用，init进程无法在/volume挂载点挂载它。我在/etc/fstab中注释了这个分区，就这样了。

要找到这个错误，我必须启动到文本模式(通过删除/etc/defaults/grub中的"splash，find“属性)，因为在图形中，我什么也没看到。