每次我登录 ubuntu 16.04.1 时，桌面左侧栏都会出现两个问号图标，然后几秒后它们就会消失。我该怎么做才能避免这种情况？
运行命令systemd-analyze blame后，输出如下：
380ms dev-sda5.device
265ms alsa-restore.service
247ms systemd-timesyncd.service
137ms snapd.firstboot.service
132ms apparmor.service
125ms ModemManager.service
117ms accounts-daemon.service
114ms systemd-modules-load.service
111ms systemd-fsck@dev-disk-by\x2duuid-A021\x2dDF65.service
88ms systemd-localed.service
88ms systemd-hostnamed.service
83ms systemd-logind.service
82ms grub-common.service
69ms NetworkManager.service
69ms keyboard-setup.service
67ms systemd-journald.service
64ms plymouth-start.service
62ms speech-dispatcher.service
61ms systemd-udevd.service
54ms ondemand.service
53ms systemd-udev-trigger.service
49ms thermald.service
48ms console-setup.service
47ms apport.service
45ms irqbalance.service
43ms systemd-fsck@dev-disk-by\x2duuid-50516ce7\x2d3a77\x2d44fd\x2d90bc\x2d2a69ac4acfac.service
40ms pppd-dns.service
40ms networking.service
37ms home.mount
37ms rsyslog.service
37ms systemd-user-sessions.service
37ms gpu-manager.service
35ms avahi-daemon.service