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ctime vs checksum in copies

From: Paul Krizak
Subject: ctime vs checksum in copies
Date: Wed, 30 Nov 2005 13:13:48 -0600
User-agent: Mozilla Thunderbird 1.0.7 (X11/20050923)

I've got a question about what you guys think the best solution is in this situation.

I've got some files that must be customized on a per-host basis, but are based on a common "root" file. My goal is to have the following system:

* When the system is first installed, or if the file on the system is wildly different than the master, a copy: statement pulls down a fresh copy of the file, which an edifiles: stanza corrects for that specific host.

* Later, if the master file changes, the clients should "know" to pull down a new copy of the file, and then perform the same editfiles: stanza again.

Using "checksum" for the copy statement doesn't really work, since once you make a change to the file using editfiles:, the checksums don't match and thus the file gets copied every time. On the upside, you're guaranteed to always have the correct version of the file on the target system.

Using "ctime" for the copy statement *sounds* good, as the copy only happens when the "master" file updates on the server. Where this falls flat, however, is on freshly installed systems, where the ctime of the *incorrect*, freshly-installed file is *later* than the ctime of the "master" file. In this situation, the "master" file is not copied (and I wouldn't expect it to).

I've got several cases in my (very lengthy) cfengine config where I run into this type of issue. For small files, I can put the entire contents of the file into an editfiles: block and avoid using copy: at all. This doesn't work for large files, however, as I don't want a cf.* file to have a 5,000-line config file in it with Append statements.

For large files, I use checksum copies and just accept the fact that they will get copied every time cfagent runs.

I'm looking to improve convergence in my config files...anybody else have clever workarounds for this problem?


Paul Krizak                         5900 E. Ben White Blvd. MS 625
Advanced Micro Devices              Austin, TX  78741
Linux/Unix Systems Engineering      Phone: (512) 602-8775
Microprocessor Solutions Sector

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