[tpm] more problems than solutions this week

[Indy Singh]

While we are on this topic.  One issue I have encountered is that of how to 
update a 'live' file on a webserver.  Lets say that we have a large file on 
a webserver 'foo.tar' and I want to replace it with a new version.  If I 
SFTP upload a replacement file then I am never sure if I am going to mess up 
someone that may be half way trough downloading the file.

I just verified that the inode number does not change if I upload a 
replacement file with SFTP. Would I be correct in thinking that any file 
downloads that are occurring concurrently with the upload would be 
corrupted?

Would it be safe to upload the new file as 'new.tar' then use the commands 
'rm foo.tar' followed by 'mv new.tar foo.tar'?  On the assumption that the 
rm command would only unlink the directory entry but any current file 
handles being used to download the file would continue to work.  Any new 
downloads would use the new file.


Indy Singh
IndigoSTAR Software -- www.indigostar.com
-----Original Message----- 
From: arocker at Vex.Net
Sent: Friday, May 04, 2012 2:44 PM
To: TPM
Subject: Re: [tpm] more problems than solutions this week


I see Indy's answered your problem, but just a point on the topic:

> But what I've found is that the inode doesn't change!
> [so I'd assume that the ">" redirection simply rewinds
> the write pointer to offset zero and writes the string
> and then truncates the file at that point.]
>

That's why "sort file > file" (and similar commands) is fatal; it resets
the pointer on the (output) file, then starts trying to read from the
(input) file, whose pointer now says it's at EOF.

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