I have a default installation of Ubuntu 18.04.5, it comes with Linux Kernel 5.4.0. After that installation I found out I need a specific kernel version: 5.3.0, so I've installed it using apt:
$ sudo apt install linux-image-5.3.0-69-generic linux-headers-5.3.0-69-generic
Now when I choose this kernel over the default on grub menu, I'm unable to see ttyUSB* devices: their driver is missing
$ sudo modprobe usbserial modprobe: FATAL: Module usbserial not found in directory /lib/modules/5.3.0-69-generic
The default installation of 5.4.0 has those drivers, but it seems like if manually installed, the new kernel version doesn't rebuild the modules.
My question is - how do I rebuild this module with this kernel version?
Some interesting thing that I found is that on an unattended-upgrade of the kernel: a minor version advance, dkms seem to do that automatically. This didn't happen for the manual 'apt' that I did:
$ uname -a Linux s8b 5.4.0-65-generic #73~18.04.1-Ubuntu SMP Tue Jan 19 09:02:24 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux $ lsmod | grep ftdi ftdi_sio 61440 0 usbserial 49152 1 ftdi_sio $ locate ftdi_sio /lib/modules/5.4.0-64-generic/kernel/drivers/usb/serial/ftdi_sio.ko /lib/modules/5.4.0-65-generic/kernel/drivers/usb/serial/ftdi_sio.ko