tickadj - set time-related kernel variables

Last update: May 4, 2022 17:05 UTC (dbea9b7d4)

Synopsis

tickadj [ -Aqs ] [ -a tickadj ] [ -t tick ]

Description

The tickadj program reads, and optionally modifies, several timekeeping-related variables in the running kernel in some machines, via /dev/kmem. The particular variables it is concerned with are tick, which is the number of microseconds added to the system time for a clock interrupt, tickadj, which sets the slew rate and resolution used by the adjtime system call, and dosynctodr, which indicates to the kernels on some machines whether they should internally adjust the system clock to keep it in line with time-of-day clock or not.

Note that this program does NOT work in some kernels, in particular Solaris 2.6 or later. See the report.

By default, with no arguments, tickadj reads the variables of interest in the kernel and displays them. At the same time, it determines an “optimal” value for the value of the tickadj variable if the intent is to run the ntpd Network Time Protocol (NTP) daemon, and prints this as well. Since the operation of tickadj when reading the kernel mimics the operation of similar parts of the ntpd program fairly closely, this can be useful when debugging problems with ntpd.

Note that tickadj should be run with some caution when being used for the first time on different types of machines. The operations which tickadj tries to perform are not guaranteed to work on all Unix machines and may in rare cases cause the kernel to crash.

Command Line Options

-a tickadj: Set the kernel variable tickadj to the value tickadj_specified.
-A: Set the kernel variable tickadj to an internally computed “optimal” value.
-t tick: Set the kernel variable tick to the value tick specified.
-s: Set the kernel variable dosynctodr to zero, which disables the hardware time-of-year clock, a prerequisite for running the ntpd daemon under SunOS4.
-q: Normally, tickadj is quite verbose about what it is doing. The -q flag tells it to shut up about everything except errors.

Files

/vmunix /unix /dev/kmem

Bugs

Fiddling with kernel variables at run time as a part of ordinary operations is a hideous practice which is only necessary to make up for deficiencies in the implementation of adjtime in many kernels and/or brokenness of the system clock in some vendors' kernels. It would be much better if the kernels were fixed and the tickadj program went away.