I was adding some nfs links to fstab but a stray process filled disk so I lost fstab when trying to save. Am trying to recreate, machine is still live.
Found some helpful links, used blkid and think I have put mount for boot device.
However the main system is on lvm and the UUID for that doesn't seem to match the underlying block devices.
I tried looking at fstab and blkid on another machine and copied fstab (called 360g72.71) which works.
I couldn't figure out how the UUID for the lvm is created from blkid or how else to find it. Edit - I found in /etc/lvm/backup a file which contained that id and have edited this into fstab, basically I concatenated the vg identifier and the ubuntu volume id and removed the '-' in between.
Here is my current fstab with comments showing where I have got to, I think I have solved it but appreciate comments before I try it!
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
#copied from 360g72.71
# <file system> <mount point> <type> <options> <dump> <pass>
# / was on /dev/ubuntu-vg/ubuntu-lv during curtin installation
#/dev/disk/by-id/dm-uuid-LVM-g6G2lkUVsE4qegAqsM1UZGb0i88snEbkffPzeOywoh0vzv6Pc3fAySNjDiVa6ztb / ext4 defaults 0 1
#lvm from 360g72
#ubuntu-vg {
# id = "g6G2lk-UVsE-4qeg-AqsM-1UZG-b0i8-8snEbk"
# pv0 {
# id = "dwf5SW-xDsZ-aRM7-0K6z-iy2a-5PkR-0X0CMR"
# device = "/dev/sda3" # Hint only
# id = "ffPzeO-ywoh-0vzv-6Pc3-fAyS-NjDi-Va6ztb"
#new
#lvm extracts from here /etc/lvm/backup
#vg
#7FHuF7-Wdbd-WZQV-Qrfg-0rZI-MIWN-ux3Scj
#ubuntu
#ENY1Z6-l9ti-zdHj-hjXd-PE1M-PzeQ-YhA4ez
/dev/disk/by-id/dm-uuid-LVM-7FHuF7WdbdWZQVQrfg0rZIMIWNux3ScjENY1Z6l9tizdHjhjXdPE1MPzeQYhA4ez / ext4 defaults 0 1
#blkid from 360g72.71
#/dev/mapper/ubuntu--vg-ubuntu--lv: UUID="045b0ff5-18a4-43f7-906c-e22c53a8b08a" BLOCK_SIZE="4096" TYPE="ext4"
#UUID="kaGiOI-TF2O-GbBt-B1zS-EHRO-IifV-brUmJW": UUID="QuFATb-PqON-3HDt-LdrU-LdGg-uPCA-D7cVKQ" TYPE="LVM2_member"
#UUID="0a166d03-2dae-42b6-b877-6616d3fcd9ff" BLOCK_SIZE="4096": UUID="f1501104-970c-49e8-9e4b-f903dedbf018" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="aa65834e-ec0c-44d0-aae5-7caf363d04dc"
#UUID="pm2Yk5-jfUs-klJj-xwl2-PSbO-XYY3-fiFEmD": UUID="dwf5SW-xDsZ-aRM7-0K6z-iy2a-5PkR-0X0CMR" TYPE="LVM2_member" PARTUUID="4242fec0-5a25-44a8-8e39-0cd9ba9b9c1f"
# /boot was on UUID="0a166d03-2dae-42b6-b877-6616d3fcd9ff" BLOCK_SIZE="4096" during curtin installation
#from 360g72
#/dev/disk/by-uuid/f1501104-970c-49e8-9e4b-f903dedbf018 /boot ext4 defaults 0 1
#
#new
#this blkid output
#/dev/mapper/ubuntu--vg-ubuntu--lv: UUID="4ed86e70-199c-41e8-918d-e200f7e08a63" BLOCK_SIZE="4096" TYPE="ext4"
#UUID="kaGiOI-TF2O-GbBt-B1zS-EHRO-IifV-brUmJW": UUID="kaGiOI-TF2O-GbBt-B1zS-EHRO-IifV-brUmJW" TYPE="LVM2_member"
#UUID="0a166d03-2dae-42b6-b877-6616d3fcd9ff" BLOCK_SIZE="4096": UUID="0a166d03-2dae-42b6-b877-6616d3fcd9ff" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="6b874856-8811-4dce-b578-a8303d6bdfc3"
#UUID="pm2Yk5-jfUs-klJj-xwl2-PSbO-XYY3-fiFEmD": UUID="pm2Yk5-jfUs-klJj-xwl2-PSbO-XYY3-fiFEmD" TYPE="LVM2_member" PARTUUID="8cedc84d-8808-42fb-b1ff-9579c6fd5c77"
#/dev/sda1: PARTUUID="c4569521-c7a0-4b61-8dd8-65dd2c0f8de1"
/dev/disk/by-uuid/0a166d03-2dae-42b6-b877-6616d3fcd9ff /boot ext4 defaults 0 1
#
/swap.img none swap sw 0 0
ipsodell310:/nfs/10T /nfs/10T nfs defaults 0 0
ipsodell310:/nfs/4T /nfs/4T nfs defaults 0 0
truenas:/mnt/Hp40 /nfs/40T nfs defaults 0 0