Questions concerning the Linux kernel in Ubuntu. Issues may including upgrading and installing kernels, compiling, patches, and kernel modules.

An operating system kernel is the central part of the operating system, handling all main tasks. It is loaded into a protected area of memory at boot time. Kernel space, where the kernel carries out its tasks, and user space, where everything else happens, are kept separate. The /sys directory contains a virtual filesystem that provides a view of kernel data structures and objects from user space.

The Linux kernel is a monolithic kernel originally developed by Linus Torvalds, who still directs its development. The latest vanilla kernel can be downloaded from kernel.org, and Ubuntu kernels (patched by Ubuntu kernel team) are available from the Ubuntu mainline kernel ppa

The kernel is found in the /boot directory. When a new kernel is installed (for example, as part of a routine update and upgrade procedure) old kernels are not automatically removed, and over time the /boot directory becomes full, and this can cause serious problems if /boot is on a small separate partition. To prevent this, users should periodically run sudo apt autoremove to clean up (actually the initrd.img file for each kernel is larger than the kernel itself, but that is removed along with the kernel by autoremove). It is advisable to keep at least one "spare" older kernel. The user can select which kernel to boot from the GRUB menu. The newest kernel (with the highest release number) is booted by default.

The release number of the running kernel may by checked with the command uname -r

For more details, see the documentation maintained by the Ubuntu Kernel Team.