What command checks the Linux kernel version on a system?

The command that checks the Linux kernel version on a system is "uname -r." This command specifically returns the version of the kernel currently running on the system. The "uname" utility is used to display system information, and the "-r" option stands for "release," which provides the kernel version information.

In contrast, the command "kernel -v" is not a valid command in Linux and would not yield any useful output. The "lsb_release -a" command is used to show distribution-specific information, like the distribution name, version, and codename, but it does not provide kernel version details. Lastly, "cat /etc/os-release" displays information about the operating system but, like the previous command, does not provide the specific kernel version. Therefore, "uname -r" is the precise command needed to retrieve the version of the Linux kernel.