KUbuntu 20.04.02 install on SSD stuck at Ubiquity screen "Saving installed packages.."

Question

I booted in UEFI mode from a ventoy usb pendrive where I stored the iso image of "kubuntu-20.04.2.0-desktop-amd64.iso".

I checked "Download updates before install" and used manual the following partitioning scheme :

$ sudo gdisk /dev/sda -l
GPT fdisk (gdisk) version 1.0.5

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.
Disk /dev/sda: 250069680 sectors, 119.2 GiB
Model: SAMSUNG SSD PM83
Sector size (logical/physical): 512/512 bytes
Disk identifier (GUID): 57F4500A-2DD6-47A5-B1A3-59FC0D2A7AB1
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 250069646
Partitions will be aligned on 2048-sector boundaries
Total free space is 2014 sectors (1007.0 KiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048          526335   256.0 MiB   EF00  EFI system partition
   2          526336       250069646   119.0 GiB   8E00  Linux LVM
$ sudo pvs
  PV         VG                         Fmt  Attr PSize    PFree
  /dev/sda2  VG_SAMSUNG_SSD_PM830_128GB lvm2 a--  <118.99g 5.00g
$ sudo vgs
  VG                         #PV #LV #SN Attr   VSize    VFree
  VG_SAMSUNG_SSD_PM830_128GB   1  11   0 wz--n- <118.99g 5.00g
$ sudo lvs
  LV               VG                         Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  LV_boot          VG_SAMSUNG_SSD_PM830_128GB -wi-a-----   2.50g                                                    
  LV_home          VG_SAMSUNG_SSD_PM830_128GB -wi-a----- <48.89g                                                    
  LV_opt           VG_SAMSUNG_SSD_PM830_128GB -wi-a-----   5.00g                                                    
  LV_root          VG_SAMSUNG_SSD_PM830_128GB -wi-ao----   5.60g                                                    
  LV_usr           VG_SAMSUNG_SSD_PM830_128GB -wi-a-----  15.00g                                                    
  LV_usr_local     VG_SAMSUNG_SSD_PM830_128GB -wi-a-----   5.00g                                                    
  LV_var           VG_SAMSUNG_SSD_PM830_128GB -wi-a-----   5.00g                                                    
  LV_var_cache     VG_SAMSUNG_SSD_PM830_128GB -wi-a-----   5.00g                                                    
  LV_var_lib_snapd VG_SAMSUNG_SSD_PM830_128GB -wi-a-----  10.00g                                                    
  LV_var_mail      VG_SAMSUNG_SSD_PM830_128GB -wi-a-----  10.00g                                                    
  LV_var_tmp       VG_SAMSUNG_SSD_PM830_128GB -wi-a-----   2.00g                                                    

I didn't create a /tmp LV because I believe the installer would create one in RAM knowing I'm using a SSD.

There is no "Back" button on the "Saving installed packages" Ubiquity screen :

$ pstree -a $(pgrep ubiquity) 
ubiquity /usr/lib/ubiquity/bin/ubiquity kde_ui
  ├─debconf-communi -w /usr/bin/debconf-communicate -fnoninteractive ubiquity
  ├─debconf-communi -w /usr/bin/debconf-communicate -fnoninteractive ubiquity
  └─8*[{ubiquity}]

Can you help me ?

Answer 1

After having unchecked "Download updates before install", the installation went fine.

BTW : The installation of Ubuntu on a SSD using Ubiquity didn't create a separate /tmp filesystem, therefore I added the following line in my /etc/fstab :

tmpfs /tmp tmpfs rw,nosuid,nodev,size=15%