after upgrade to 18.04, boot process is very slow

If you reboot and log in, then run:

dmesg -T | less

You will see times on the left. Look for large gaps (these are the system messages as the OS boots)

Post the few lines before and after the large gaps and we (and you) can investigate.

[Thu Aug 16 05:53:12 2018] logitech-djreceiver 0003:046D:C52B.0003: hiddev0,hidraw0: USB HID v1.11 Device [Logitech USB Receiver] on usb-0000:00:1d.7-1.4/input2
[Thu Aug 16 05:53:12 2018] tsc: Refined TSC clocksource calibration: 2199.973 MHz
[Thu Aug 16 05:53:12 2018] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x1fb6193927f, max_idle_ns: 440795214998 ns
[Thu Aug 16 05:53:12 2018] input: Logitech M325 as /devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1.4/1-1.4:1.2/0003:046D:C52B.0003/0003:046D:400A.0004/input/input3
[Thu Aug 16 05:53:12 2018] logitech-hidpp-device 0003:046D:400A.0004: input,hidraw1: USB HID v1.11 Mouse [Logitech M325] on usb-0000:00:1d.7-1.4:1
[Thu Aug 16 05:53:13 2018] clocksource: Switched to clocksource tsc
[Thu Aug 16 05:53:48 2018] floppy0: probe failed...
[Thu Aug 16 05:53:48 2018] floppy0: probe failed...
[Thu Aug 16 05:53:48 2018] floppy0: probe failed...
[Thu Aug 16 05:53:49 2018] floppy0: probe failed...
[Thu Aug 16 05:53:49 2018] floppy0: probe failed...
[Thu Aug 16 05:53:50 2018] floppy0: probe failed...
[Thu Aug 16 05:53:50 2018] floppy0: probe failed...
[Thu Aug 16 05:53:50 2018] floppy0: probe failed...
[Thu Aug 16 05:53:51 2018] floppy0: probe failed...
[Thu Aug 16 05:53:51 2018] floppy0: probe failed...
[Thu Aug 16 05:53:51 2018] print_req_error: I/O error, dev fd0, sector 0
[Thu Aug 16 05:53:51 2018] floppy: error 10 while reading block 0
[Thu Aug 16 05:53:56 2018] floppy0: probe failed...
[Thu Aug 16 05:53:56 2018] floppy0: probe failed...
[Thu Aug 16 05:53:56 2018] floppy0: probe failed...
[Thu Aug 16 05:53:57 2018] floppy0: probe failed...
[Thu Aug 16 05:53:57 2018] floppy0: probe failed...
[Thu Aug 16 05:53:58 2018] floppy0: probe failed...
[Thu Aug 16 05:53:58 2018] floppy0: probe failed...
[Thu Aug 16 05:53:58 2018] floppy0: probe failed...
[Thu Aug 16 05:53:59 2018] floppy0: probe failed...
[Thu Aug 16 05:53:59 2018] floppy0: probe failed...
[Thu Aug 16 05:53:59 2018] print_req_error: I/O error, dev fd0, sector 0
[Thu Aug 16 05:53:59 2018] floppy: error 10 while reading block 0
[Thu Aug 16 05:54:04 2018] floppy0: probe failed...

In addition, this floppy search goes on until 05:55:22

Thu Aug 16 05:55:21 2018] floppy0: probe failed...
[Thu Aug 16 05:55:21 2018] floppy0: probe failed...
[Thu Aug 16 05:55:21 2018] print_req_error: I/O error, dev fd0, sector 0
[Thu Aug 16 05:55:21 2018] floppy: error 10 while reading block 0
[Thu Aug 16 05:55:21 2018] EXT4-fs (sdb1): mounted filesystem with ordered data mode. Opts: (null)
[Thu Aug 16 05:55:21 2018] ip_tables: (C) 2000-2006 Netfilter Core Team
[Thu Aug 16 05:55:21 2018] systemd[1]: systemd 237 running in system mode. (+PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD -IDN2 +IDN -PCRE2 default-hierarchy=hybrid)
[Thu Aug 16 05:55:21 2018] systemd[1]: Detected architecture x86-64.
[Thu Aug 16 05:55:21 2018] systemd[1]: Set hostname to <seanix>.
[Thu Aug 16 05:55:22 2018] systemd[1]: Reached target User and Group Name Looku

Does the system have a floppy drive or floppy controller?

Yes, all 3 have floppy drives, I disconnected one and the system would not start at all. I figured the problem is with the floppy drives, the boxes are old (hence the floppy drives) but the innards are relatively new.

The system I am writing this on took 2.13 min to get past the floppy.

I mentioned 3 systems, on the one I use for email only, I removed the floppy drive and re installed 18.04 LTS.
On the second I just removed all mention of floppy as well as disconnecting it and the boot process took considerably less than before. 'dmesg -T | less' did not show any gaps. Problem solved.

Thanks for your help