使用 USB 启动棒安装 Ubuntu 20.04 的最新 LTS 版本后，我的笔记本电脑启动速度与旧 LTS 版本（即 Ubuntu 14.04）相比变慢了。如何提高笔记本电脑的启动速度？笔记本电脑描述 - Dell Inspiron15- 3000 系列 4GB RAM、500GB HDD、Intel Core i3 5005U CPU@2GHzx4、操作系统 64 位（未安装 Windows，只有单个 Ubuntu 操作系统）systemd-analyze 启动在 6.047 秒（固件）+ 5.504 秒（加载程序）+ 3.985 秒（内核）+ 44.256 秒（用户空间）= 59.793 秒 graphic.target 在用户空间中经过 44.174 秒后达到
systemd-analyze blame 22.532s plymouth-quit-wait.service
22.532s plymouth-quit-wait.service
16.554s NetworkManager-wait-online.service
11.533s dev-sda2.device
10.164s systemd-journal-flush.service
10.149s networkd-dispatcher.service
9.503s snapd.service
6.821s accounts-daemon.service
6.380s udisks2.service
6.341s fwupd.service
5.423s NetworkManager.service
4.503s polkit.service
3.821s dev-loop2.device
3.810s dev-loop6.device
3.792s dev-loop3.device
3.785s dev-loop1.device
3.746s dev-loop5.device
3.742s dev-loop4.device
3.725s dev-loop7.device
3.707s dev-loop0.device
3.631s avahi-daemon.service
3.629s bluetooth.service
2.965s gpu-manager.service
2.926s ModemManager.service
systemd-analyze critical-chain graphic.target @44.174s └─multi-user.target @44.174s └─kerneloops.service @38.115s +166ms └─network-online.target @38.096s └─NetworkManager-wait-online.service @21.541s +16.554s └─NetworkManager.service @16.114s +5.423s └─dbus.service @16.111s └─basic.target @15.936s └─sockets.target @15.936s └─snapd.socket @15.934s +1ms └─sysinit.target @15.854s └─snapd.apparmor.service @15.432s +421ms └─apparmor.service @14.237s +1.193s └─local-fs.target @14.236s └─boot-efi.mount @14.191s +44ms └─systemd-fsck@dev-disk-by\x2duuid-1D00\x2d6320.ser> └─dev-disk-by\x2duuid-1D00\x2d6320.device @14.057s 请建议如何加快启动速度。