Q:

Ubuntu 18.04 the boot process takes very long. How to reduce boot time

I am using Ubuntu 18.04 (Asus_M4A88T-M-USB3 motherboard with AMD Phenom(tm) II X4 945 Processor and 8GB ddr3 RAM) the boot process takes very long compared to 16.04 during boot. How to reduce boot time. Or is it ok for 18.04.
Selected information
dmesg 

_
[    9.108094] lp0: using parport0 (interrupt-driven).
[   18.865467] audit: type=1400 audit(1540755431.877:2): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/usr/bin/man" pid=381 comm="apparmor_parser"
......
......
[   29.966625] IPv6: ADDRCONF(NETDEV_CHANGE): enp2s0: link becomes ready
[   35.808136] rfkill: input handler disabled
[   43.642588] nouveau 0000:01:00.0: Direct firmware load for nouveau/nva8_fuc084 failed with error -2
[   43.642595] nouveau 0000:01:00.0: Direct firmware load for nouveau/nva8_fuc084d failed with error -2
[   43.642597] nouveau 0000:01:00.0: msvld: unable to load firmware data
[   43.642601] nouveau 0000:01:00.0: msvld: init failed, -19

_
systemd-analyzed

_
Startup finished in 5.817s (kernel) + 50.562s (userspace) = 56.380s
graphical.target reached after 42.230s in userspace

_
systemd-analyze blame

26.244s apt-daily.service
20.879s plymouth-quit-wait.service
14.776s dev-sda4.device
13.684s systemd-journal-flush.service
10.644s systemd-modules-load.service
8.845s dev-loop0.device
8.836s dns-clean.service
8.702s apparmor.service
8.661s systemd-udevd.service
8.467s binfmt-support.service
7.784s proc-sys-fs-binfmt_misc.mount
7.714s snap-core-5662.mount
......
......

A:

I tried many things but only after I changed nouveau to nvidia-340 the boot time went down by about half.
dmesg
[    8.073745] systemd-journald        272]: Received request to flush runtime journal from PID 1
[   18.353802] shpchp: Standard Hot Plug PCI Controller Driver version: 0.4
........
........
[   29.241267] resource sanity check: requesting    [mem 0x000c0000-0x000fffff], which spans more than PCI Bus 0000:00         mem 0x000d0000-0x000dffff window]
[   29.241405] caller os_map_kernel_space+0x86/0xb0     [nvidia] mapping multiple BARs
[   29.362723] r8169 0000:02:00.0 enp2s0: link up
[   29.362731] IPv6: ADDRCONF(NETDEV_CHANGE): enp2s0: link becomes ready
[   34.017794] rfkill: input handler disabled
:~$ 

systemd-analyze
Startup finished in 5.138s (kernel) + 27.173s (userspace) = 32.311s
graphical.target reached after 27.164s in userspace

systemd-analyze blame
15.847s systemd-journal-flush.service
11.869s dev-sda4.device
11.011s keyboard-setup.service
10.145s systemd-sysctl.service
8.805s systemd-udevd.service

