FreeBSD 7.0 manual page repository

FreeBSD is a free computer operating system based on BSD UNIX originally. Many IT companies, like DeployIS is using it to provide an up-to-date, stable operating system.

adjkerntz - adjust local time CMOS clock to reflect time zone changes and

 

NAME

      adjkerntz - adjust local time CMOS clock to reflect time zone changes and
      keep current timezone offset for the kernel
 

SYNOPSIS

      adjkerntz -i
      adjkerntz -a [-s]
 

DESCRIPTION

      The adjkerntz utility maintains the proper relationship between the ker‐
      nel clock, which is always set to UTC, and the CMOS clock, which may be
      set to local time.  The adjkerntz utility also informs the kernel about
      machine timezone shifts to maintain proper timestamps for local time file
      systems such as the MS-DOS file system.  The main purpose of this thing
      is not general fixing of initially broken MS-DOS file timestamp idea but
      keeping the same timestamps between FreeBSD MS-DOS file system and MS-DOS
      operating system installed on the same machine.  If the file
      /etc/wall_cmos_clock exists, it means that CMOS clock keeps local time
      (MS-DOS and MS-Windows compatible mode).  If that file does not exist, it
      means that the CMOS clock keeps UTC time.  The adjkerntz utility passes
      this state to the machdep.wall_cmos_clock kernel variable.
 
      Adjustments may be needed at system startup and shutdown, and whenever a
      time zone change occurs.  To handle these different situations, adjkerntz
      is invoked in two ways:
 
      -i    This form handles system startups and shutdowns.  The adjkerntz
            utility is invoked with this option from /etc/rc on entry to multi-
            user mode, before any other daemons have been started.  The
            adjkerntz utility puts itself into the background.  Then, for a
            local time CMOS clock, adjkerntz reads the local time from it and
            sets the kernel clock to the corresponding UTC time.  The adjkerntz
            utility also stores the local time zone offset into the
            machdep.adjkerntz kernel variable, for use by subsequent invoca‐
            tions of ’adjkerntz -a’ and by local time file systems.
 
            For a local time CMOS clock ’adjkerntz -i’ pauses, and remains
            inactive as a background daemon until it receives a SIGTERM.  The
            SIGTERM will normally be sent by init(8) when the system leaves
            multi-user mode (usually, because the system is being shut down).
            After receiving the SIGTERM, adjkerntz reads the UTC kernel clock
            and updates the CMOS clock, if necessary, to ensure that it
            reflects the current local time zone.  Then adjkerntz exits.
 
      -a [-s]
            This form is used to update the local time CMOS clock and kernel
            machdep.adjkerntz variable when time zone changes occur, e.g., when
            entering or leaving daylight savings time.  The adjkerntz utility
            uses the kernel clock’s UTC time, the previously stored time zone
            offset, and the changed time zone rule to calculate a new time zone
            offset.  It stores the new offset into the machdep.adjkerntz kernel
            variable, and updates the wall CMOS clock to the new local time.
            If ’adjkerntz -a’ was started at a nonexistent time (during a time‐
            zone change), it exits with a warning diagnostic unless the -s
            option was used, in which case adjkerntz sleeps 30 minutes and
            tries again.
 
            This form should be invoked from root’s crontab(5) every half hour
            between midnight and 5am, when most modern time zone changes occur.
            Warning: do not use the -s option in a crontab(5) command line, or
            multiple ’adjkerntz -a’ instances could conflict with each other.
 
      The adjkerntz utility clears the kernel timezone structure and makes the
      kernel clock run in the UTC time zone.  Super-user privileges are
      required for all operations.
 

ENVIRONMENT

      TZ          Time zone change rule, see tzset(3); not needed when
                  tzsetup(8) or zic(8) is used.
 

FILES

      /etc/localtime        Current zoneinfo file, see tzsetup(8) and zic(8).
      /etc/wall_cmos_clock  Empty file.  Its presence indicates that the
                            machine’s CMOS clock is set to local time, while
                            its absence indicates a UTC CMOS clock.
 

DIAGNOSTICS

      No diagnostics.  If an error occurs, adjkerntz logs an error message via
      syslog(3) and exits with a nonzero return code.
      tzset(3), crontab(5), mount_msdosfs(8), rc(8), sysctl(8), tzsetup(8),
      zic(8)
 

HISTORY

      The adjkerntz utility appeared in FreeBSD 1.0.
 

AUTHORS

      Andrey A. Chernov 〈ache@astral.msk.su〉
 

Sections

Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.