tahoe-lafs/trac-2024-07-25
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add FAQ about backups of root caps 

[Imported from Trac: page FAQ, version 110]
zooko 2014-10-20 18:47:50 +00:00
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FAQ.md

@ -113,7 +113,7 @@ A: The node ID is the secure hash of the SSL public key certificate of the node.
**<a name="Q15_same_file_same_cap">Q15:</a> If upload the same file again and again, Tahoe-LAFS will return the same capability. How does Tahoe-LAFS identify that the client is same, when I upload files mutiple times, is it based on node ID?**
A: For immutable files this is true—the resulting capability will be the same each time you upload the same file contents. The capability is derived from two pieces of information: The content of the file and the "[convergence secret](https://tahoe-lafs.org/trac/tahoe-lafs/wiki/Convergence%20Secret)". By default, the convergence secret is randomly generated by the node when it first starts up, then stored in the node's base directory (`~/.tahoe`) and re-used after that. So the same file content uploaded from the same node will always have the same cap string. Uploading the file from a different node with a different convergence secret would result in a different cap string—and in a second copy of the file's contents stored on the grid. If you want files you upload to converge (also known as "deduplicate") with files uploaded by someone else, just make sure you're using the same convergence secret as they are.
A: For immutable files this is true—the resulting capability will be the same each time you upload the same file contents. The capability is derived from two pieces of information: The content of the file and the "[//trac/tahoe-lafs/wiki/Convergence%20Secret convergence secret]". By default, the convergence secret is randomly generated by the node when it first starts up, then stored in the node's base directory (`~/.tahoe`) and re-used after that. So the same file content uploaded from the same node will always have the same cap string. Uploading the file from a different node with a different convergence secret would result in a different cap string—and in a second copy of the file's contents stored on the grid. If you want files you upload to converge (also known as "deduplicate") with files uploaded by someone else, just make sure you're using the same convergence secret as they are.
**<a name="Q15.1_dedupe_dangers">Q15.1:</a> Isn't deduplication dangerous? Can someone figure out whether or not I have a certain file?**
@ -232,3 +232,7 @@ A: That information is currently broadcast by storage servers and collected by c
'''<a name="Q34_better_logging">Q34:</a> There's not a lot of information in the logs. How can I get more verbose logging?
The default logfiles provided by Tahoe do not provide much information. To really see what's going on, you will need to use the "flogtool" utility to expose detailed logging. For more information, see source:trunk/docs/logging.rst
'''<a name="Q35_backing_up_caps">Q36:</a> How do I backup the decryption key and other information necessary to recover my files?
In Tahoe-LAFS the decryption keys are bundled together with the other information into a short string called a *capability* (see the [//trac/tahoe-lafs/browser/docs/architecture.rst#capabilities architecture document]). To backup your capabilities, we recommend printing two or more copies of them out on a printer and storing the resulting pieces of paper in a safe place.