101 lines
4.4 KiB
Plaintext
101 lines
4.4 KiB
Plaintext
vsntp README
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See INSTALL for details on how to install and run vsntp.
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Obtaining the Newest Information
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vsntp's official website is at...
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vsntp project on GitHub: https://github.com/imacat/vsntp
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vsntp project on SourceForge: https://sf.net/p/vsntp
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You can always download the newest version of vsntp from...
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vsntp download on SourceForge: https://sourceforge.net/projects/vsntp/files
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Tavern IMACAT's FTP directory: https://ftp.imacat.idv.tw/pub/vsntp/
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imacat's PGP public key is at...
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Tavern IMACAT's: https://www.imacat.idv.tw/me/pgpkey.asc
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Introduction:
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vsntp is an SNTP client daemon for machines without a sane system
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time. The word "vsntp" stands for "SNTP for Virtual PC". It was
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originally designed for my GNU/Linux server running on Connectix
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Virtual PC. It runs according to RFC 1769 SNTP, connecting the NTP
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server on UDP port 123.
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Without Virtual PC Additions, the system time on Virtual PC is
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completely insane. It's RTC (Real Time Clock, or CMOS time, or
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hardware clock) is software emulated, which does not seems to be
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running. The GNU/Linux kernel hardly maintains a system time itself.
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With smooth run it goes 4 seconds ahead per minute, which is nearly
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1.5 hours per day. That is insane. You can even tell it with your
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eyes.
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David L. Mills' ntp does not work here. It uses a method that
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learns the clock frequency drift first, and adjust the kernel clock
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with adjtimex() so that time adjustment goes smoothly, from the point
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of view of system and applications. This assumes an existing fix-
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speed system clock. But this is not the case of Virtual PC. The
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system clock on Virtual PC is software emulated. It can be faster
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or slower now and then, depending on the load of the hosting machine.
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There is no fixed clock speed. The frequency drift does not exist,
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then. It dooms to fail to measure it.
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There is an sntp client that comes with David L. Mills' ntp
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package. It is suggested to be run from crontab. But crontab runs
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by minutes, and Virtual PC goes 4 seconds ahead per minute. Rolling
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back 4 seconds every minute is insane for most applications. It also
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increases system load heavily to run one instance per minute.
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vsntp is a workaround on this. It runs as a daemon to eliminates
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the additional system load on every synchronization. It uses
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settimeofday() to synchronize the time. It synchronizes the time
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with an arbitrary interval, so that time can be accurate within a
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second.
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There are some defects. Synchronizing the time too often
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introduces heavy network load. It introduces heavy load on the
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target NTP server, too. You should have a working NTP server nearby
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that is owned by you. Also, since settimeofday() is called so often,
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high-accurate time operations like timer, etc., may not run
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correctly.
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vsntp uses sleep() as the synchronization scheduler. Reports show
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that on some systems sleep() may not function normally. If you find
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vsntp stops synchronization after running for some time, that the
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sleep() is not functioning normally on your system, you may want to
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switch to the alarm() scheduler with the "-a" switch.
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If you ever encounter any problem, you may check your syslog.
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vsntp logs detailed debugging information to syslog in log level
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LOG_DEBUG with facility LOG_DAEMON. You may turn it on in your
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/etc/syslog.conf with the following line:
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daemon.debug /var/log/debug
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and check the /var/log/debug file for the debugging message. Remember
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to remove this afterwards, for the amount of the debugging messages
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may be huge and may use up your hard disk in a very short time. To the
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least it may slow down your system for frequent hard disk I/O.
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vsntp was originally written for GNU/Linux. It uses POSIX
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compatible system calls. It should work on any POSIX compatible
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system. But I have yet only tested it on Cygwin. Cygwin is known to
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work. I don't have others to test and run on. Please let me know
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(and submit the patch if needed) if you can port it to other systems.
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I know it does not work on MSWin32, for the way it handles the PID
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file path.
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Please tell me if you have successfully running vsntp on other
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virtual machines, like VMWare.
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Generally, please tell me if you are using vsntp. I would like
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to know that I am really doing some good for the world, *^_^* but not
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having fun myself. :p
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This is my first daemon, my first socket program and my first
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public-released C program. Any comment or suggestion is welcome. ^_*'
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