NTP sends a special message to the kernel (using adjtimex), that boils down to: today you will insert a leap second. This isn't the same as clock drift, which g

NTP sends a special message to the kernel (using adjtimex), that boils down to: today you will insert a leap second. This isn't the same as clock drift, which gets smoothed out, it means a minute with a 60th second (in UTC) or with the 59th second happening twice (in POSIX). NTP servers need a leap second table ( http://support.ntp.org/bin/view/Support/ConfiguringNTP#Section_6.14 http://support.ntp.org/bin/view/Support/ConfiguringNTP#Secti.... ), but most other systems only need to know the current delta between POSIX and TAI, and manage without a leap table.