[CentOS] SFTP - stalled - on large files

Jay Leafey jay.leafey at mindless.com
Wed Dec 23 00:41:36 UTC 2009


We had a similar problem copying files between servers on two of our 
campuses via SCP.  After a while the connection just stalled out and 
hung.  The problem turned out to be SCP and SFTP interacting a bug in 
the SACK (Selective Acknowledgment) algorithm used in Linux.  We turned 
it off on the two endpoints using the following addition to 
/etc/sysctl.conf:

> # Turn off SACK
> net.ipv4.tcp_sack = 0

and execute "sysctl -p" to apply it.  You can also use "sysctl -w 
net.ipv4.tcp_sack=0" to turn it off temporarily.  Our file transfers 
worked just fine after the change.

I realize there are differences our situation and yours and this might 
not work in your case.  Given the length of this thread, though, it 
might be worth a try!
-- 
Jay Leafey - Memphis, TN
jay.leafey at mindless.com
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/x-pkcs7-signature
Size: 3274 bytes
Desc: S/MIME Cryptographic Signature
Url : http://lists.centos.org/pipermail/centos/attachments/20091222/75b11810/attachment.bin 


More information about the CentOS mailing list