我一直在浏览这些论坛，试图弄清楚到底发生了什么。首先：
pc@my_pc: uname -a
Linux my_pc 5.8.0-45-generic #51-Ubuntu SMP Fri Feb 19 13:24:51 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
我的电脑是联想 Legion Y545，正在运行 Ubuntu 20.10 和 Windows 双启动。
今天早上我遇到了启动缓慢的问题。以下是我遇到的情况：
pc@my_pc: systemd-analyze time
Startup finished in 6.568s (firmware) + 4.890s (loader) + 5.536s (kernel) + 2min 31.339s (userspace) = 2min 48.334s
graphical.target reached after 2min 31.330s in userspace
pc@my_pc: systemd-analyze blame
1min 55.831s plymouth-quit-wait.service
26.497s apt-daily-upgrade.service
24.608s man-db.service
17.170s systemd-journal-flush.service
15.791s networkd-dispatcher.service
14.018s dev-sda4.device
13.332s udisks2.service
12.832s snapd.service
11.636s logrotate.service
11.411s accounts-daemon.service
7.947s avahi-daemon.service
7.943s bluetooth.service
7.934s NetworkManager.service
7.893s apache2.service
7.872s polkit.service
7.300s dev-loop5.device
6.689s dev-loop6.device
6.627s dev-loop9.device
6.238s dev-loop12.device
5.895s dev-loop11.device
5.859s dev-loop7.device
5.775s dev-loop4.device
5.755s dev-loop8.device
5.615s fwupd.service
5.603s dev-loop0.device
5.556s dev-loop10.device
5.420s gdm.service
5.413s switcheroo-control.service
5.162s ModemManager.service
5.034s apport.service
4.841s systemd-resolved.service
4.750s grub-common.service
4.540s systemd-logind.service
4.539s thermald.service
4.537s wpa_supplicant.service
4.509s apparmor.service
4.157s dev-loop1.device
4.078s dev-loop2.device
3.920s secureboot-db.service
3.919s rsyslog.service
3.661s e2scrub_reap.service
3.660s gpu-manager.service
3.563s nvidia-persistenced.service
3.562s pppd-dns.service
3.173s upower.service
2.359s systemd-udevd.service
2.084s colord.service
2.073s systemd-rfkill.service
1.486s kerneloops.service
1.255s systemd-random-seed.service
1.169s openvpn.service
1.161s systemd-sysusers.service
pc@my_pc: systemd-analyze critical chain
graphical.target @2min 31.330s
└─multi-user.target @2min 31.330s
└─snapd.service @2min 18.496s +12.832s
└─snap-snapd-11402.mount @1min 54.289s +29ms
└─dev-loop13.device @1min 54.316s +2ms
我的第一个想法是“普利茅斯退出等待服务是罪魁祸首“。根据此链接由于 plymouth-quit-wait.service + ubuntu 18.04 导致启动缓慢的问题但事实并非如此。我的第二个想法是，通过查看关键链输出，我可以看到发生了什么。我看到 dev-loop13.device 似乎花费了很多时间。然而，在 blame 输出中，dev-loop13.device 只占用了 2ms 的时间。Snapd 服务也存在同样的差异。
最后我使用 plymouth-quit-wait.service 作为 critical-chain 的参数。下面是我得到的结果
pc@my_pc: systemd-analyze critical-chain plymouth-quit-wait.service
The time when unit became active or started is printed after the "@" character.
The time the unit took to start is printed after the "+" character.
plymouth-quit-wait.service +1min 55.831s
└─systemd-user-sessions.service @32.380s +212ms
└─network.target @31.581s
└─NetworkManager.service @23.646s +7.934s
└─dbus.service @23.638s
└─basic.target @23.589s
└─sockets.target @23.588s
└─snapd.socket @23.584s +2ms
└─sysinit.target @23.439s
└─systemd-timesyncd.service @23.243s +195ms
└─systemd-tmpfiles-setup.service @22.130s +1.066s
└─systemd-journal-flush.service @4.959s +17.170s
└─systemd-journald.service @4.224s +734ms
└─systemd-journald.socket @4.209s
└─system.slice @3.295s
└─-.slice @3.295s
不用说，我有点迷茫了。这里的其他帖子有更具体的问题，问题从错误消息中或多或少可以清楚看出。我不确定如何解释我的消息。问题到底是什么？我该如何解决？有什么建议吗？