X-Git-Url: http://git.ipfire.org/?a=blobdiff_plain;f=hwclock%2Fhwclock.8;fp=clock%2Fhwclock.8;h=7e4106d453b82e5d8344b7e1107ee943f8cd221b;hb=66ee8158b69525e12060ef558cb5d77feadab1dc;hp=f34bfac0093fe1825acb2d096ea311b3db762f7b;hpb=22853e4a82c6ef7b336527529acb94b14a0b0fd8;p=thirdparty%2Futil-linux.git diff --git a/clock/hwclock.8 b/hwclock/hwclock.8 similarity index 96% rename from clock/hwclock.8 rename to hwclock/hwclock.8 index f34bfac009..7e4106d453 100644 --- a/clock/hwclock.8 +++ b/hwclock/hwclock.8 @@ -33,21 +33,21 @@ Also, equivalent options \-r, \-w, \-s, \-a, \-v, \-u, with the program "clock", while \-h asks for a help message. .SH DESCRIPTION -.I hwclock +.B hwclock is a tool for accessing the Hardware Clock. You can display the current time, set the Hardware Clock to a specified time, set the Hardware Clock to the System Time, and set the System Time from the Hardware Clock. .PP You can also run -.I hwclock +.B hwclock periodically to insert or remove time from the Hardware Clock to compensate for systematic drift (where the clock consistently gains or loses time at a certain rate if left to run). .SH OPTIONS You need exactly one of the following options to tell -.I hwclock +.B hwclock what function to perform: .PP .TP @@ -106,7 +106,7 @@ option for details. .TP .B \-\-version Print the version of -.I hwclock +.B hwclock on Standard Output. .br You need the following option if you specify @@ -116,14 +116,14 @@ option. Otherwise, it is ignored. .B \-\-date=date_string Specifies the time to which to set the Hardware Clock. The value of this option is an argument to the -.I date(1) +.BR date (1) program. For example, .sp .I hwclock --set --date="9/22/96 16:45:05" .sp The argument is in local time, even if you keep your Hardware Clock in Coordinated Universal time. See the -.I \-\-utc +.B \-\-utc option. .TP @@ -146,7 +146,7 @@ Indicates that the Hardware Clock is kept in Coordinated Universal Time or local time, respectively. It is your choice whether to keep your clock in UTC or local time, but nothing in the clock tells which you've chosen. So this option is how you give that information to -.IR hwclock . +.BR hwclock . If you specify the wrong one of these options (or specify neither and take a wrong default), both setting and querying of the Hardware Clock @@ -157,7 +157,7 @@ If you specify neither nor .B \-\-localtime , the default is whichever was specified the last time -.I hwclock +.B hwclock was used to set the clock (i.e. hwclock was successfully run with the .B \-\-set , @@ -172,12 +172,12 @@ exist, the default is local time. .B \-\-directisa is meaningful only on an ISA machine or an Alpha (which implements enough of ISA to be, roughly speaking, an ISA machine for -.IR hwclock 's +.BR hwclock 's purposes). For other machines, it has no effect. This option tells -.I hwclock +.B hwclock to use explicit I/O instructions to access the Hardware Clock. Without this option, -.I hwclock +.B hwclock will try to use the /dev/rtc device (which it assumes to be driven by the rtc device driver). If it is unable to open the device (for read), it will use the explicit I/O instructions anyway. @@ -191,7 +191,7 @@ Award BIOSes made between 4/26/94 and 5/31/95) wherein they are unable to deal with years after 1999. If one attempts to set the year-of-century value to something less than 94 (or 95 in some cases), the value that actually gets set is 94 (or 95). Thus, if you have one of these machines, -.I hwclock +.B hwclock cannot set the year after 1999 and cannot use the value of the clock as the true time in the normal way. @@ -199,7 +199,7 @@ To compensate for this (without your getting a BIOS update, which would definitely be preferable), always use .B \-\-badyear if you have one of these machines. When -.I hwclock +.B hwclock knows it's working with a brain-damaged clock, it ignores the year part of the Hardware Clock value and instead tries to guess the year based on the last calibrated date in the adjtime file, by assuming that that date is @@ -210,7 +210,7 @@ or at least once a year! Though -.I hwclock +.B hwclock ignores the year value when it reads the Hardware Clock, it sets the year value when it sets the clock. It sets it to 1995, 1996, 1997, or 1998, whichever one has the same position in the leap year cycle as @@ -219,7 +219,7 @@ they belong. Again, if you let the Hardware Clock run for more than a year without setting it, this scheme could be defeated and you could end up losing a day. -.I hwclock +.B hwclock warns you that you probably need .B \-\-badyear whenever it finds your Hardware Clock set to 1994 or 1995. @@ -233,16 +233,16 @@ whenever it finds your Hardware Clock set to 1994 or 1995. .TP .B \-\-funky\-toy These options all tell -.I hwclock +.B hwclock what kind of Alpha machine you have. They are invalid if you don't have an Alpha and shouldn't be necessary if you do, because -.I hwclock +.B hwclock should be able to determine by itself what it's running on, at least when .I /proc is mounted. These options make it possible for -.I hwclock +.B hwclock to work even when its environment does not conform to its expectations and thus it cannot accurately determine what sort of system it is running on. If you think @@ -251,9 +251,9 @@ running with the .B \-\-debug option to see what conclusions the program is reaching and how. If you find you need one of these options to make -.I hwclock +.B hwclock work, contact the -.I hwclock +.B hwclock maintainer to see if the program can be improved to detect your system automatically. @@ -280,11 +280,11 @@ Do everything except actually updating the Hardware Clock or anything else. This is useful, especially in conjunction with .B \-\-debug, in learning about -.I hwclock. +.B hwclock. .TP .B \-\-debug Display a lot of information about what -.I hwclock +.B hwclock is doing internally. Some of its function is complex and this output can help you understand how the program works. @@ -308,7 +308,7 @@ ticks, so the clock actually has virtually infinite precision. This clock is commonly called the hardware clock, the real time clock, the RTC, the BIOS clock, and the CMOS clock. Hardware Clock, in its capitalized form, was coined for use by -.I hwclock +.B hwclock because all of the other names are inappropriate to the point of being misleading. .PP @@ -349,7 +349,7 @@ the kernel timezone value. An example is the vfat filesystem. If the kernel timezone value is wrong, the vfat filesystem will report and set the wrong timestamps on files. .PP -.I hwclock +.B hwclock sets the kernel timezone to the value indicated by TZ and/or /usr/local/timezone when you set the System Time using the .B \-\-hctosys @@ -366,7 +366,7 @@ This second field is not used under Linux and is always zero. .SH How hwclock Accesses the Hardware Clock .PP -.I hwclock +.B hwclock Uses many different ways to get and set Hardware Clock values. The most normal way is to do I/O to the device special file /dev/rtc, which is presumed to be driven by the rtc device driver. However, @@ -380,13 +380,13 @@ On older systems, the method of accessing the Hardware Clock depends on the system hardware. .PP On an ISA system, -.I hwclock +.B hwclock can directly access the "CMOS memory" registers that constitute the clock, by doing I/O to Ports 0x70 and 0x71. It does this with actual I/O instructions and consequently can only do it if running with superuser effective userid. (In the case of a Jensen Alpha, there is no way for -.I hwclock +.B hwclock to execute those I/O instructions, and so it uses instead the /dev/port device special file, which provides almost as low-level an interface to the I/O subsystem). @@ -399,17 +399,17 @@ working rtc device drivers available. .PP On an m68k system, -.I hwclock +.B hwclock can access the clock via the console driver, via the device special file /dev/tty1. .PP -.I hwclock +.B hwclock tries to use /dev/rtc. If it is compiled for a kernel that doesn't have that function or it is unable to open /dev/rtc, -.I hwclock +.B hwclock will fall back to another method, if available. On an ISA or Alpha machine, you can force -.I hwclock +.B hwclock to use the direct manipulation of the CMOS registers without even trying .I /dev/rtc by specifying the \-\-directisa option. @@ -420,12 +420,12 @@ by specifying the \-\-directisa option. The Hardware Clock is usually not very accurate. However, much of its inaccuracy is completely predictable - it gains or loses the same amount of time every day. This is called systematic drift. -.IR hwclock 's +.BR hwclock 's "adjust" function lets you make systematic corrections to correct the systematic drift. .PP It works like this: -.I hwclock +.B hwclock keeps a file, .I /etc/adjtime, that keeps some historical information. This is called the adjtime file. @@ -433,27 +433,26 @@ that keeps some historical information. This is called the adjtime file. Suppose you start with no adjtime file. You issue a .I hwclock \-\-set command to set the Hardware Clock to the true current time. -.I Hwclock +.B Hwclock creates the adjtime file and records in it the current time as the last time the clock was calibrated. -5 days -later, the clock has gained 10 seconds, so you issue another +5 days later, the clock has gained 10 seconds, so you issue another .I hwclock \-\-set command to set it back 10 seconds. -.I Hwclock +.B Hwclock updates the adjtime file to show the current time as the last time the clock was calibrated, and records 2 seconds per day as the systematic drift rate. 24 hours go by, and then you issue a .I hwclock \-\-adjust command. -.I Hwclock +.B Hwclock consults the adjtime file and sees that the clock gains 2 seconds per day when left alone and that it has been left alone for exactly one day. So it subtracts 2 seconds from the Hardware Clock. It then records the current time as the last time the clock was adjusted. Another 24 hours goes by and you issue another .I hwclock \-\-adjust. -.I Hwclock +.B Hwclock does the same thing: subtracts 2 seconds and updates the adjtime file with the current time as the last time the clock was adjusted. .PP @@ -462,18 +461,18 @@ Every time you calibrate (set) the clock (using or .I \-\-systohc ), -.I hwclock +.B hwclock recalculates the systematic drift rate based on how long it has been since the last calibration, how long it has been since the last adjustment, what drift rate was assumed in any intervening adjustments, and the amount by which the clock is presently off. .PP A small amount of error creeps in any time -.I hwclock +.B hwclock sets the clock, so it refrains from making an adjustment that would be less than 1 second. Later on, when you request an adjustment again, the accumulated drift will be more than a second and -.I hwclock +.B hwclock will do the adjustment then. .PP It is good to do a @@ -493,7 +492,7 @@ Line 1: 3 numbers, separated by blanks: 1) systematic drift rate in seconds per day, floating point decimal; 2) Resulting number of seconds since 1969 UTC of most recent adjustment or calibration, decimal integer; 3) zero (for compatibility with -.IR clock ) +.BR clock (8)) as a decimal integer. .PP Line 2: 1 number: Resulting number of seconds since 1969 UTC of most @@ -505,13 +504,13 @@ contain a valid time). This is a decimal integer. Line 3: "UTC" or "LOCAL". Tells whether the Hardware Clock is set to Coordinated Universal Time or local time. You can always override this value with options on the -.I hwclock +.B hwclock command line. .PP You can use an adjtime file that was previously used with the -.I clock +.BR clock (8) program with -.I hwclock. +.B hwclock. .SH "Automatic Hardware Clock Synchronization By the Kernel" @@ -552,14 +551,14 @@ minute mode. There is some sort of standard that defines CMOS memory Byte 50 on an ISA machine as an indicator of what century it is. -.I hwclock +.B hwclock does not use or set that byte because there are some machines that don't define the byte that way, and it really isn't necessary anyway, since the year-of-century does a good job of implying which century it is. If you have a bona fide use for a CMOS century byte, contact the -.I hwclock +.B hwclock maintainer; an option may be appropriate. Note that this section is only relevant when you are using the "direct