我已经花费了大量时间来提高我的启动时间，现在我已经达到了无法超越的界限。
所以，我想到这里来寻求帮助。
systemd 的命令输出：
1）systemd 分析
systemd-analyze
Startup finished in 4.362s (kernel) + 28.046s (userspace) = 32.408s
graphical.target reached after 28.032s in userspace
2）systemd-analyze 指责
systemd-analyze blame
19.562s dev-sda2.device
17.507s systemd-tmpfiles-setup-dev.service
16.429s systemd-sysctl.service
3.079s networkd-dispatcher.service
2.990s NetworkManager.service
1.874s accounts-daemon.service
1.641s udisks2.service
1.540s grub-common.service
1.145s preload.service
1.134s systemd-modules-load.service
1.057s keyboard-setup.service
605ms systemd-journald.service
537ms ufw.service
429ms swapfile.swap
421ms systemd-fsck@dev-disk-by\x2duuid-B07A\x2d539E.service
415ms apparmor.service
402ms systemd-random-seed.service
396ms systemd-logind.service
338ms setvtrgb.service
317ms plymouth-read-write.service
316ms binfmt-support.service
313ms upower.service
306ms systemd-remount-fs.service
3）systemd-analyze 关键链
graphical.target @28.032s
└─multi-user.target @28.030s
└─getty.target @28.028s
└─[email protected] @28.027s
└─system-getty.slice @28.024s
└─setvtrgb.service @27.684s +338ms
└─systemd-user-sessions.service @27.665s +13ms
└─network.target @27.663s
└─NetworkManager.service @24.671s +2.990s
└─dbus.service @24.446s
└─basic.target @24.429s
└─paths.target @24.428s
└─acpid.path @24.426s
└─sysinit.target @24.377s
└─systemd-timesyncd.service @24.149s +226ms
└─systemd-tmpfiles-setup.service @23.859s +241ms
└─local-fs.target @23.847s
└─boot-efi.mount @23.651s +195ms
└─systemd-fsck@dev-disk-by\x2duuid-B07A\x2d539E.service @23.197s +421ms
└─dev-disk-by\x2duuid-B07A\x2d539E.device @23.172s
仅供参考：我有一个硬盘。
有什么建议吗？提前谢谢！
编辑 1：我的系统规格
System: Host: federico-Aspire-E5-573G Kernel: 4.15.0-66-generic x86_64
bits: 64 gcc: 7.4.0
Desktop: LXDE (Openbox 3.6.1) dm: lightdm
Distro: Ubuntu 18.04.3 LTS
Machine: Device: laptop System: Acer product: Aspire E5-573G v: V3.72 serial: N/A
Mobo: Acer model: ZORO_BH v: Type2 - A01 Board Version serial: N/A
UEFI: Insyde v: V1.07 date: 03/17/2015
Battery BAT1: charge: 27.3 Wh 86.0% condition: 31.7/37.0 Wh (86%)
volts: 16.2/14.8
model: SANYO AL15A32 serial: <filter>status: Discharging
CPU: Dual core Intel Core i3-4005U (-MT-MCP-)
arch: Haswell rev.1 cache: 3072 KB
flags: (lm nx sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx) bmips: 6784
clock speeds: min/max: 800/1600 MHz 1: 798 MHz 2: 798 MHz
3: 798 MHz 4: 798 MHz
Graphics: Card-1: Intel Haswell-ULT Integrated Graphics Controller
bus-ID: 00:02.0 chip-ID: 8086:0a16
Card-2: NVIDIA GK208BM [GeForce 920M]
bus-ID: 04:00.0 chip-ID: 10de:1299
Display Server: x11 (X.Org 1.19.6 )
drivers: modesetting (unloaded: fbdev,vesa)
Resolution: [email protected]
OpenGL: renderer: Mesa DRI Intel Haswell Mobile
version: 4.5 Mesa 19.0.8 (compat-v: 3.0) Direct Render: Yes
Audio: Card-1 NVIDIA GK208 HDMI/DP Audio Controller
driver: snd_hda_intel bus-ID: 04:00.1 chip-ID: 10de:0e0f
Card-2 Intel 8 Series HD Audio Controller
driver: snd_hda_intel bus-ID: 00:1b.0 chip-ID: 8086:9c20
Card-3 Intel Haswell-ULT HD Audio Controller
driver: snd_hda_intel bus-ID: 00:03.0 chip-ID: 8086:0a0c
Sound: Advanced Linux Sound Architecture v: k4.15.0-66-generic
Network: Card-1: Realtek RTL8111/8168/8411 PCIE Gigabit Ethernet Controller
driver: r8169 v: 2.3LK-NAPI port: 4000
bus-ID: 02:00.0 chip-ID: 10ec:8168
IF: enp2s0 state: down mac: <filter>
Card-2: Qualcomm Atheros QCA9377 802.11ac Wireless Network Adapter
driver: ath10k_pci bus-ID: 03:00.0 chip-ID: 168c:0042
IF: wlp3s0 state: up mac: <filter>
Drives: HDD Total Size: 500.1GB (11.2% used)
ID-1: /dev/sda model: ST500LT012 size: 500.1GB
serial: <filter> temp: 27C
Partition: ID-1: / size: 457G used: 53G (13%) fs: ext4 dev: /dev/sda2
RAID: System: supported: N/A
No RAID devices: /proc/mdstat, md_mod kernel module present
Unused Devices: none
Sensors: System Temperatures: cpu: 43.0C mobo: N/A
Fan Speeds (in rpm): cpu: N/A
Info: Processes: 168 Uptime: 6 min Memory: 642.8/3865.5MB
Init: systemd v: 237 runlevel: 5 Gcc sys: 7.4.0
Client: Shell (bash 4.4.201 running in x-terminal-emul) inxi: 2.3.56
已采取的措施：
- Swapiness
- 默认 GRUB 时间
- 禁用大多数无用的服务（不是全部，因为有些我不太确定）。
- 删除 grub 中的 Quiet splash 功能
- 普利茅斯蒙面