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RE: ctime vs checksum in copies


From: Nielsen, Steve
Subject: RE: ctime vs checksum in copies
Date: Wed, 30 Nov 2005 14:21:59 -0500

Generally I have this approach:

- copy the template over to a "temp area" (i.e. /var/cfengine/temp)
- do file edits on the temporary copy
- compare the temp copy to the production and copy if changed (using
checksum).

This has worked really well for me.

Steve

-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf
Of Paul Krizak
Sent: Wednesday, November 30, 2005 1:14 PM
To: address@hidden
Subject: ctime vs checksum in copies

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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