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howtos:network_services:ntp [2012/09/26 03:34 (UTC)] – [Sources] updated tag mfillpot | howtos:network_services:ntp [2013/03/01 16:36 (UTC)] – Added a short explanation about problems with NFS and NIS when clients are out of sync kikinovak | ||
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* configuring an NTP server on Slackware Linux; | * configuring an NTP server on Slackware Linux; | ||
* synchronizing client PCs with your local NTP server. | * synchronizing client PCs with your local NTP server. | ||
+ | |||
+ | ===== Introduction ===== | ||
+ | |||
+ | When several users manipulate shared data on different client PCs on a network, it's important that these machines are all synchronized. This is especially true if you share files over NFS, or if you use NIS for centralized authentication. You'll get all sorts of weird errors if your clocks are out of sync. Unfortunately, | ||
+ | |||
+ | That's where NTP (//Network Time Protocol//) comes in handy. It allows networked machines to adjust their clocks so as to be perfectly synchronized. A series of public time servers on the Internet allow the reception of the exact time. From this point, we can use NTP in several ways. | ||
+ | |||
+ | * The '' | ||
+ | * This one-time-adjustment isn't sufficient for a server that is supposed to be up 24/7, since its clock will drift away gradually from the exact time. In that case, we have to configure the '' | ||
+ | * The '' | ||
+ | |||
+ | It's considered good practice to use '' | ||
+ | |||
+ | ===== Firewall considerations ===== | ||
+ | |||
+ | The NTP services uses UDP port 123. Open this port if you want to allow remote machines to connect to your NTP server. | ||
===== Synchronize a LAN server or a public root server with an NTP server on the Internet ===== | ===== Synchronize a LAN server or a public root server with an NTP server on the Internet ===== | ||
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< | < | ||
- | # chmod 0755 / | + | # chmod +x / |
</ | </ | ||
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The little '' | The little '' | ||
- | === Synchronizing at boot time === | + | <note tip>The first synchronization can take a few minutes, sometimes up to half an hour.</note> |
- | If instead of using a daemon, all you want to do is to synchronize time once per boot, it is possible to add the command '' | + | |
- | + | ||
- | ~# cat /etc/ | + | |
- | #!/bin/sh | + | |
- | # | + | |
- | # / | + | |
- | # | + | |
- | # Put any local startup commands in here. Also, if you have | + | |
- | # anything that needs to be run at shutdown time you can | + | |
- | # make an / | + | |
- | # commands in there. | + | |
- | . | + | |
- | . | + | |
- | . | + | |
- | ntpd -qg & | + | |
- | <note tip>The first synchronization can take a few minutes, sometimes up to half an hour.</ | ||
===== Synchronize your client PC(s) with your local NTP server ===== | ===== Synchronize your client PC(s) with your local NTP server ===== | ||
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< | < | ||
- | # chmod 0755 / | + | # chmod +x / |
# / | # / | ||
</ | </ | ||
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<note tip> | <note tip> | ||
- | ===== Firewall considerations ===== | + | === Synchronizing at boot time === |
- | The NTP services uses UDP port 123. Open this port if you want to allow remote machines | + | If instead of using a daemon, all you want to do is to synchronize time once per boot, it is possible |
+ | |||
+ | ~# cat / | ||
+ | #!/bin/sh | ||
+ | # | ||
+ | # / | ||
+ | # | ||
+ | # Put any local startup commands in here. Also, if you have | ||
+ | # anything that needs to be run at shutdown time you can | ||
+ | # make an / | ||
+ | # commands in there. | ||
+ | . | ||
+ | . | ||
+ | | ||
+ | ntpd -qg & | ||
====== Sources ====== | ====== Sources ====== | ||
+ | |||
* Originally written by [[wiki: | * Originally written by [[wiki: | ||