systemd-analyze 中的 dev-sda.device 是什么，我可以禁用它吗？

Question

我的笔记本电脑上安装了 Ubuntu 16.04 和 windows。在systemd-analyze blame名为“dev-sda7.device”的服务中花费了太多时间。如何解决这个问题或者我应该禁用它？

的结果 systemd-analyze time

Startup finished in 4.207s (firmware) + 4.576s (loader) + 3.466s (kernel) + 33.899s (userspace) = 46.149s

的结果 systemd-analyze blame

         16.326s dev-sda7.device
         12.859s ufw.service
         11.263s systemd-tmpfiles-setup-dev.service
          7.935s NetworkManager-wait-online.service
          3.203s keyboard-setup.service
          2.736s vboxdrv.service
          2.467s accounts-daemon.service
          2.349s apache2.service
          2.239s NetworkManager.service
          2.163s ModemManager.service
          1.963s lightdm.service
          1.843s nmbd.service
          1.749s samba-ad-dc.service
          1.599s systemd-fsck@dev-disk-by\x2duuid-B053\x2dA56B.service
          1.367s thermald.service
          1.127s polkitd.service
          1.112s systemd-journald.service
          1.066s teamviewerd.service
          1.007s udisks2.service
           975ms apparmor.service
           926ms plymouth-start.service

的结果 cat /etc/fstab

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/sda7 during installation
UUID=493cc833-193e-435d-840a-b862ca367fba /               ext4    errors=remount-ro 0       1
# /boot/efi was on /dev/sda2 during installation
UUID=B053-A56B  /boot/efi       vfat    umask=0077      0       1
# swap was on /dev/sda6 during installation
UUID=a49f56b1-53c3-4eaf-9460-0a221e59957a none            swap    sw              0       0

Answer 1

您不能禁用它，因为它/dev/sda7是安装根分区的位置。在 systemd 中，它在启动时可以处理的所有内容都被制成一个 systemd 单元。然后你可以用它做一些事情（比如在这种情况下跟踪时间，或者依赖它来提供服务）。在设备的情况下，链是这样的：

• 内核加载设备并激活它
• systemd 对此进行监视并为其创建/dev/sdxy节点
• 然后 systemd 激活从生成的各种挂载单元 fstab
• 然后触发等待挂载文件系统的各种其他服务
• 等等

这确实允许您识别磁盘激活缓慢，但除非您可以获得新磁盘，否则您无能为力。

您可以尝试分析关键路径，看看是否还有其他问题可以解决：

systemd-analyze critical-chain [UNIT...]  prints a tree of the
time-critical chain of units (for each of the specified UNITs or for
the default target otherwise). The time after the unit is active or
started is printed after the "@" character. The time the unit takes to
start is printed after the "+" character. Note that the output might be
misleading as the initialization of one service might depend on socket
activation and because of the parallel execution of units.

例子：

graphical.target @10.868s
??multi-user.target @10.868s
  ??squid-deb-proxy.service @10.816s +51ms
    ??network-online.target @10.814s
      ??NetworkManager-wait-online.service @2.419s +8.395s
        ??NetworkManager.service @2.243s +155ms
          ??dbus.service @2.192s
            ??basic.target @2.129s
              ??sockets.target @2.129s
                ??snapd.socket @2.127s +1ms
                  ??sysinit.target @2.127s
                    ??swap.target @2.127s
                      ??dev-disk-by\x2duuid-498d24e5\x2d7755\x2d422f\x2dbe45\x2d1b78d50b44e8.swap @2.119s +7ms
                        ??dev-disk-by\x2duuid-498d24e5\x2d7755\x2d422f\x2dbe45\x2d1b78d50b44e8.device @2.119s

例如，就我而言，网络正在减慢启动速度。