This is not a duplicate as suggested above - for why, see the text below.
I have the strange situation that an "old" kernel is running (in fact it is the OLDEST):
uname -r
> 4.13.0-43-generic
Using a command to show available kernels I only see NEWER kernels(!):
sudo dpkg --list 'linux-image*'|awk '{ if ($1=="ii") print $2}'|grep -v `uname -r`
linux-image-4.13.0-45-generic
linux-image-4.15.0-24-generic
linux-image-4.15.0-29-generic
linux-image-4.15.0-30-generic
linux-image-4.15.0-32-generic
linux-image-4.15.0-33-generic
linux-image-4.15.0-34-generic
linux-image-extra-4.13.0-45-generic
It looks as if the system never rebooted to "get to the new kernels" - I see for example that in the root dir:
ls -al
lrwxrwxrwx 1 root root 33 Sep 11 06:02 initrd.img -> boot/initrd.img-4.15.0-34-generic
lrwxrwxrwx 1 root root 33 Sep 11 06:02 initrd.img.old -> boot/initrd.img-4.15.0-33-generic
lrwxrwxrwx 1 root root 30 Sep 11 06:02 vmlinuz -> boot/vmlinuz-4.15.0-34-generic
lrwxrwxrwx 1 root root 30 Sep 11 06:02 vmlinuz.old -> boot/vmlinuz-4.15.0-33-generic
which kind of suggests this to me (I'm not an ubuntu guru)...
This is not a duplicate question but a new question because I have no old kernels to delete. Other answers detail deleting old kernels with version numbers less than the current kernel.
The running kernel is the oldest listed. I was worried about deleting kernels newer than the current kernel - between the current kernel and the newest and the kernel that was wanting to be installed - but blocked because of 100% full boot partition.
All answers using "apt" do not work when the boot partition is 100% full so please ignore them :)
From my original question: So I'm tempted to reboot the machine. But is this dangerous - since the boot partition is 100% full. "Normally" I'd delete old kernels etc. to free up space. What's the best/safest way to proceed here?
I ask because it seems I "should" make some space (see Will ubuntu boot if the /boot partition is full?)... but how in this particular case?
THIS IS HOW I SOLVED the problem:
In the end as apt autoremove etc. do not work in this situation I followed the hints given here:https://gist.github.com/ipbastola/2760cfc28be62a5ee10036851c654600
(See: "Case II: Can't Use apt i.e. /boot is 100% full")
In my case I deleted a newer kernel by hand to release space in /boot in order to be able to proceed:
cd /boot
ls *4.13.0-45*
rm -rf *4.13.0-45*
df -h
sudo apt-get -f install
sudo apt-get autoremove
sudo update-grub
more grub/grub.cfg
reboot
df -h shows boot no longer 100% full
With more grub/grub.cfg you can check if the system is catering for the correct kernels (i.e. whether the update grub worked well)