我最近从 ubuntu 18.04 升级到了 20.04。启动需要很长时间，启动后第一次打开应用程序需要一段时间。18.04 中没有这种情况。以下是 systemd-analyze blame 的输出。
40.177s plymouth-quit-wait.service
13.821s networkd-dispatcher.service
12.331s dev-sda7.device
11.938s snapd.service
10.914s udisks2.service
9.756s apport-autoreport.service
9.003s accounts-daemon.service
6.878s ModemManager.service
5.834s dev-loop9.device
5.799s dev-loop15.device
5.622s avahi-daemon.service
5.620s bluetooth.service
5.533s iio-sensor-proxy.service
5.476s dev-loop4.device
5.452s dev-loop7.device
5.441s dev-loop8.device
5.368s NetworkManager.service
5.357s polkit.service
5.245秒 dev-loop16.device
5.164秒 dev-loop14.device
5.126秒 dev-loop0.device
5.125秒 dev-loop2.device
5.122秒 dev-loop13.device
以下是 systemd-analyze critical-chain 的输出
graphic.target @1min 6.301s └─multi-user.target @1min 6.301s └─networkd-dispatcher.service @20.621s +13.821s └─basic.target @19.895s └─sockets.target @19.895s └─snapd.socket @19.894s +646us └─sysinit.target @19.762s └─systemd-timesyncd.service @19.415s +346ms └─systemd-tmpfiles-setup.service @17.088s +2.324s └─local-fs.target @17.084s └─run-snapd-ns-canonical\x2dlivepatch.mnt.mount @31.721s └─run-snapd-ns.mount @29.157s └─local-fs-pre.target @5.700s └─systemd-tmpfiles-setup-dev.service @4.740s +960ms └─systemd-sysusers.service @3.947s +792ms └─systemd-remount-fs.service @3.604s +136ms └─systemd-journald.socket @3.532s └─-.mount @3.515s └─system.slice @3.515s └─-.slice @3.515s