, LinuxThreads may still be seen on production systems, particularly those using version 2.4 or lower of the Linux kernel, as NPTL requires facilities which were specifically added into the 2.6 version of the kernel for its use.
Although LinuxThreads may still exist on production systems, particularly those running Linux kernel versions 2.4 or earlier, it is mainly due to the fact that NPTL requires features that were introduced in the 2.6 kernel version.