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I'm using NFS to allow two servers two communicate via simple text files, however sometimes it seems that the server reading the text files to get information is reading incomplete files, and then because of this crashes. Then I go to look at the "incomplete" file that made it crash, and the file is complete. Is it possible that the server reading these files is seeing them before they are complete written by NFS? I use linux's mv to move them from the local machine to NFS only when they are completely written, so there "should" never be an incomplete state on the NFS.

Could this problem have something to do with sync vs async? Right now I'm using async. From my understanding, async just means that you return from the write and your program can continue running, and this write will happen at a later time. Whereas sync means that your process will wait for that write to go through before it moves on. Would changing to sync fix this? Or is there a better way to handle this? I know two servers could communicate via a database, but I'm actually doing this to try to keep database usage down. Thanks!

srchulo
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1 Answers1

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mv across file-systems translates into cp+rm and is certainly not atomic, even without NFS involved. You should first copy the file to a temporary in the target file-system and then rename it to the correct name. For instance, instead of:

$ mv myfile.txt /mnt/targetfs/myfile.txt

do:

$ mv myfile.txt /mnt/targetfs/.myfile.txt.tmp
$ mv /mnt/targetfs/.myfile.txt.tmp /mnt/targetfs/myfile.txt

(This assumes that the process reading the file ignores it while it does not have the correct name.)

jop
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  • sorry, I didn't mention this in my description, but this is Actually what I do already, and I'm still getting the issue. – srchulo Nov 16 '12 at 15:16