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Re: [Duplicity-talk] Duplicity, scp, fc5, backend exception problem


From: William Wraith IV
Subject: Re: [Duplicity-talk] Duplicity, scp, fc5, backend exception problem
Date: Mon, 20 Nov 2006 20:40:59 -0500
User-agent: Opera Mail/9.00 (MacIntel)

On Mon, 20 Nov 2006 13:45:40 -0500, Bill Wraith <address@hidden> wrote:

On 11/19/06 10:28 AM, "Bill Wraith" <address@hidden> wrote:

... The errors vary somewhat, but
the basic theme is a backend exception failure which appears to be the
os.system call to scp a file from the repository to local or from local to
repository.
...However, I then tried backing
up to a server on my LAN, which is 100Mbps and still have frequent backend exception errors with scp commands moving a repository file to or from local
tmp file.
In verify mode, the scp also fails.

Any advice on how to resolve this problem or anyone familiar with problems
using duplicity on fc5?

By the way, fc5 was recently updated to kernel 2.6.18 with all updates,
duplicity is v4.2 installed from tar.gz.

I added the following hack to backends.py around line 142, and it seemed to
successfully do a very large verify that has failed consistently in the
past. There was one error message, presumably from a failure that was
retried this time. The hack and the error are listed. Are there parameters in sshd_config on the server or ssh_config on the client that would result in a more forgiving scp/sftp connection, or are there networking parameters
that might make the scp/sftp/sshd communication less likely to fail? This
failure may happen only once in verifying or backing up a 6GB file.

def run_command(self, commandline):
"""Run given commandline with logging and error detection"""
                log.Log("Running '%s'" % commandline, 5)
                if os.system(commandline):
                        if os.system(commandline):
raise BackendException("Error running '%s'"
% commandline)

(In other words, just try one more time - and added similar retry to the popen method)

The error that showed up once, which was probably what would have failed the
entire backup before was:

ssh_exchange_identification: Connection closed by remote host

As the scp was redone successfully, the verify on a large directory (about
6GB) went on to complete successfully and showed no errors.

Also, does anyone have suggestions for better ways to implement retry attempts for the get,put,list,delete methods in scpBackend, other than what I did above? It solves my problem above, but maybe there is a more sophisticated version someone has
done for the retries or maybe scripts to replace the scp/sftp commands?
It sounded in a previous posting like there was some work on retry in cvs/future versions?
Will this include the scp backend, or is it only being implemented for the
ftp backend? Finally, is there an ftp server for FC5 that anyone would
suggest as easy for a local LAN duplicity repository that would be used
to accept duplicity storage from a few servers internal to my LAN,
if I end up switching to the patched ftp backends.py suggested in previous
postings to this list?

Thanks to the developers of duplicity, by the way. It has been a great tool
for remote backup.

Thanks, Bill Wraith




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