过去几天，我通过 /usr/bin/do-release-upgrade 将我的几个系统从 LTS 12.04 升级到了 16.04.3（先是升级到 14.04，然后是 16.04）。它们之前一直运行良好年其中一个在升级后似乎没问题。另一个在大多数启动过程中最终都以只读根文件系统结束。但偶尔它会正常安装。
我已经运行了 fsck - 文件系统没有问题。我再重复一遍，文件系统本身没有问题。
dmesg 显示与根文件系统 (sda3) 和“mount”相关的这些消息
[ 8.438116] EXT4-fs (sda3): mounting ext3 file system using the ext4 subsystem
[ 8.451426] EXT4-fs (sda3): mounted filesystem with ordered data mode. Opts: (null)
[ 14.143079] systemd[1]: local-fs.target: Found dependency on systemd-remount-fs.service/start
[ 14.143093] systemd[1]: local-fs.target: Breaking ordering cycle by deleting job systemd-remount-fs.service/start <<<<<<<< APPARENTLY A PROBLEM <<<<<<<<<<
[ 14.143096] systemd[1]: systemd-remount-fs.service: Job systemd-remount-fs.service/start deleted to break ordering cycle starting with local-fs.target/start
[ 14.144423] systemd[1]: Set up automount Arbitrary Executable File Formats File System Automount Point.
[ 37.065426] EXT4-fs (sda1): mounting ext3 file system using the ext4 subsystem
[ 37.140357] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null)
/var/log/syslog 显示：
Jan 13 14:06:39 linux4 kernel: [ 554.047976] EXT4-fs (sda3): re-mounted. Opts: (null)
Jan 13 14:09:01 linux4 kernel: [ 8.464055] EXT4-fs (sda3): mounting ext3 file system using the ext4 subsystem
Jan 13 14:09:01 linux4 kernel: [ 8.477996] EXT4-fs (sda3): mounted filesystem with ordered data mode. Opts: (null)
Jan 13 14:09:01 linux4 kernel: [ 21.336148] EXT4-fs (sda3): re-mounted. Opts: errors=remount-ro
Jan 13 14:09:01 linux4 kernel: [ 36.133568] EXT4-fs (sda1): mounting ext3 file system using the ext4 subsystem
Jan 13 14:09:01 linux4 kernel: [ 36.208451] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null)
Jan 13 14:09:01 linux4 systemd[1]: Starting Remount Root and Kernel File Systems...
Jan 13 14:09:01 linux4 systemd[1]: Started Remount Root and Kernel File Systems.
Jan 13 14:09:09 linux4 kernel: [ 52.903086] cgroup: new mount options do not match the existing superblock, will be ignored
Jan 13 14:14:28 linux4 kernel: [ 8.467847] EXT4-fs (sda3): mounting ext3 file system using the ext4 subsystem
Jan 13 14:14:28 linux4 kernel: [ 8.481156] EXT4-fs (sda3): mounted filesystem with ordered data mode. Opts: (null)
Jan 13 14:14:28 linux4 kernel: [ 27.422276] EXT4-fs (sda3): re-mounted. Opts: errors=remount-ro
Jan 13 14:14:28 linux4 systemd[1]: Starting Remount Root and Kernel File Systems...
Jan 13 14:14:28 linux4 kernel: [ 42.464741] EXT4-fs (sda1): mounting ext3 file system using the ext4 subsystem
Jan 13 14:14:28 linux4 kernel: [ 42.527596] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null)
Jan 13 14:14:28 linux4 kernel: [ 44.178553] cgroup: new mount options do not match the existing superblock, will be ignored
Jan 13 14:14:28 linux4 systemd[1]: Started Remount Root and Kernel File Systems.
mount 命令显示：
root@linux4:/var/log# mount | grep sda
/dev/sda3 on / type ext3 (ro,relatime,data=ordered)
/dev/sda1 on /boot type ext3 (rw,relatime,data=ordered)
/etc/fstab 如下所示：
（/dev/scd0、/dev/scd1、/dev/fd0 上的注释是为了排除它们的嫌疑。而且，在我进行此更改后的第一次重新启动时，系统正确启动。注释 /dev/sde1 是错误的。Swap 实际上是 /dev/sda2。并且，/ 是 /dev/sda3，/boot 是 sda1。这些注释可以追溯到 Linux 位于机器的第二个磁盘上的时候）。
# /etc/fstab: static file system information.
#
# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc defaults 0 0
# /dev/sdb3
UUID=f5e2f8ee-adac-48ad-8483-e04ae0da9580 / ext3 relatime,errors=remount-ro 0 1
# /dev/sdb1
#UUID=2f2eef15-17d3-4886-9ffa-6666dc8ad8d4 /boot ext3 relatime 0 2
# /dev/sde2
UUID=d6054f01-2d94-4b27-8662-3ba22ab123c9 none swap sw 0 0
# /dev/scd1 /media/cdrom0 udf,iso9660 user,noauto,exec,utf8 0 0
# /dev/scd0 /media/cdrom1 udf,iso9660 user,noauto,exec,utf8 0 0
# /dev/fd0 /media/floppy0 auto rw,user,noauto,exec,utf8 0 0
UUID=2f2eef15-17d3-4886-9ffa-6666dc8ad8d4 /boot ext3 defaults 0 2
内核是：
root@linux4:/var/log# uname -a
Linux linux4 4.4.0-109-generic #132-Ubuntu SMP Tue Jan 9 19:52:07 UTC 2018 i686 i686 i686 GNU/Linux
奇怪的是，我升级的另一个系统运行的内核是 3.13.0-139-generic，而不是 4.4.0-109-generic - 尽管我仅相隔几天就对它们进行了相同的更新过程。我还尝试了内核 4.4.0.104-generic，结果相同。我之前在此系统上运行的内核是 3.2.0-69-generic-pae。
我不知所措。虽然我从 1976 年就开始使用 Unix（不，这不是打字错误），但“systemd”这个东西对我来说完全是新东西。所以，是的，我会研究它，但我希望有人能给我一些建议，告诉我应该从哪里开始研究。
我查看了“根文件系统在一段时间后以只读方式挂载”这个主题，但没有答案，而且这个主题已经有两年了。
我很难不对 systemd 的“美妙”大加赞赏 - 在我工作的许多年里，我们使用这个词来描述一些不必要的复杂和神秘（并且通常根本没有必要）的东西。