# apt autoremove
is configured in siduction to remove the oldest kernel, but leave the next oldest, so you have two kernels available after running the command.
Take a look at /etc/apt/apt.conf.d/01autoremove. You should see this:
APT
{
NeverAutoRemove
{
"^firmware-linux.*";
"^linux-firmware$";
"^linux-image-[a-z0-9]*$";
"^linux-image-[a-z0-9]*-[a-z0-9]*$";
};
VersionedKernelPackages
{
# kernels
"linux-.*";
"kfreebsd-.*";
"gnumach-.*";
# (out-of-tree) modules
".*-modules";
".*-kernel";
};
Never-MarkAuto-Sections
{
"metapackages";
"tasks";
};
Move-Autobit-Sections
{
"oldlibs";
};
};