rootfs validates if the rootfs is an absolute path and is not a symlink to the container's root filesystem.

rootlessEUIDCheck makes sure that the config can be applied when runc is being executed as a non-root user (euid != 0) in the current user namespace.

scheduler is to validate scheduler configs according to https://man7.org/linux/man-pages/man2/sched_setattr.2.html

sysctl validates that the specified sysctl keys are valid or not. proc/sys isn't completely namespaced and depending on which namespaces are specified

terminate sends a SIGKILL to the forked process for the setns routine then waits to avoid the process becoming a zombie.