我已经打电话apt-get purge卸载旧内核了。但是在清除过程中发生了一些错误，导致文件夹被遗留下来。它说该文件夹不是空的，因此无法删除。为了释放磁盘空间，我可以手动删除那些已清除的文件夹吗？
1.1M ./4.15.0-20-generic
60M ./4.15.0-32-generic <-- I've purged this
60M ./4.15.0-30-generic <-- and this
236M ./4.15.0-33-generic <-- this is my current one
我也可以删除其中一些包吗？
un linux-headers-4.15.0-20-generic <none> <none> (no description available)
ii linux-headers-4.15.0-30 4.15.0-30.32 all Header files related to Linux kernel version 4.15.0
ii linux-headers-4.15.0-30-generic 4.15.0-30.32 amd64 Linux kernel headers for version 4.15.0 on 64 bit x86 SMP
ii linux-headers-4.15.0-32 4.15.0-32.35 all Header files related to Linux kernel version 4.15.0
ii linux-headers-4.15.0-32-generic 4.15.0-32.35 amd64 Linux kernel headers for version 4.15.0 on 64 bit x86 SMP
ii linux-headers-4.15.0-33 4.15.0-33.36 all Header files related to Linux kernel version 4.15.0
ii linux-headers-4.15.0-33-generic 4.15.0-33.36 amd64 Linux kernel headers for version 4.15.0 on 64 bit x86 SMP
rc linux-image-4.15.0-20-generic 4.15.0-20.21 amd64 Signed kernel image generic
ii linux-image-4.15.0-33-generic 4.15.0-33.36 amd64 Signed kernel image generic
un linux-image-unsigned-4.15.0-20-generic <none> <none> (no description available)
un linux-image-unsigned-4.15.0-33-generic <none> <none> (no description available)
rc linux-modules-4.15.0-20-generic 4.15.0-20.21 amd64 Linux kernel extra modules for version 4.15.0 on 64 bit x86 SMP
ii linux-modules-4.15.0-30-generic 4.15.0-30.32 amd64 Linux kernel extra modules for version 4.15.0 on 64 bit x86 SMP
ii linux-modules-4.15.0-32-generic 4.15.0-32.35 amd64 Linux kernel extra modules for version 4.15.0 on 64 bit x86 SMP
ii linux-modules-4.15.0-33-generic 4.15.0-33.36 amd64 Linux kernel extra modules for version 4.15.0 on 64 bit x86 SMP
rc linux-modules-extra-4.15.0-20-generic 4.15.0-20.21 amd64 Linux kernel extra modules for version 4.15.0 on 64 bit x86 SMP
ii linux-modules-extra-4.15.0-33-generic