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Thread: FTP/SFTP stalls when transmitting files

  1. #1
    Join Date
    May 2008
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    3

    FTP/SFTP stalls when transmitting files

    Hello,

    I'm have a very strange problem, that I can't figure out how to fix.

    The problem is when I try to transmit a file via ftp or sftp, to an web server outside of my network, using Ubuntu 8.10. I previous didn't have problems with Ubuntu 7.04.

    The problem is that when I try to transmit a large file, that is stall at somewhere between 1-4 MBs, and never recovers. The actual place it stalls varies each time I try to transmit the file, but it is always between 1-4MBs.

    I can how ever transmit files over sftp to another computer in my own network. I tested files as larger as 800MB to see if I could reproduce the failure. I then transmitted that same large file from my other computer (MAC OSX) to the site that failed with my ubuntu install, and I have been sucessful.

    So the problem seems to be with my ubuntu machine. I can't figure out why I can't transmit large files from it. I've check and I don't even have a firewall setup on my ubunut, as I thought that this might be part of the problem.

    If anyone has any suggestions on how to troubleshoot this, I would really appreciate the help. I'm tempted to try going back to ubuntu 7.04.

  2. #2
    Join Date
    Apr 2007
    Location
    Germany
    Beans
    952
    Distro
    Ubuntu 10.04 Lucid Lynx

    Re: FTP/SFTP stalls when transmitting files

    i have a (somewhat) similar problem (i think) - can you please try to drop your mtu to 1490 bytes instead of the normal 1500 on the sending machine and see if the transfers still stalls ?

    make sure you drop the mtu on the source machine - NOT the router. You can drop the mtu on an ubuntu machine with this command:
    Code:
    sudo ifconfig %device mtu 1490
    where %device is eth0, wlan0 ath0 or something like that (depending on your device)

    let's see if you get the same results as me...
    Calvin: I'm being educated against my will! My rights are being trampled!
    Hobbes: Is it a right to remain ignorant?
    Calvin: I don't know, but I refuse to find out!

  3. #3
    Join Date
    May 2008
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    3

    Re: FTP/SFTP stalls when transmitting files

    I tried reducing the mtu to 1490, but I still see the problem with the uploads stalling at about the same point, 1MB - 4MB.

    I'm willing to try other ideas, as well.

  4. #4
    Join Date
    Apr 2007
    Location
    Germany
    Beans
    952
    Distro
    Ubuntu 10.04 Lucid Lynx

    Re: FTP/SFTP stalls when transmitting files

    i've been searching myself a little - but i have no idea how to even start debugging that problem (apart from doing paket dumps and looking where the connections stalls, e.g. which part of the connection will suddenly not pass pakets anymore)...

    i'd use wireshark or tcpdump for that - but that is really only an idea and i don't know if anything can even be seen there... really ;(
    Calvin: I'm being educated against my will! My rights are being trampled!
    Hobbes: Is it a right to remain ignorant?
    Calvin: I don't know, but I refuse to find out!

  5. #5
    Join Date
    Aug 2007
    Beans
    1

    Re: FTP/SFTP stalls when transmitting files

    Quote Originally Posted by SpaceTeddy View Post
    i have a (somewhat) similar problem (i think) - can you please try to drop your mtu to 1490 bytes instead of the normal 1500 on the sending machine and see if the transfers still stalls ?

    make sure you drop the mtu on the source machine - NOT the router. You can drop the mtu on an ubuntu machine with this command:
    Code:
    sudo ifconfig %device mtu 1490
    where %device is eth0, wlan0 ath0 or something like that (depending on your device)

    let's see if you get the same results as me...
    This did the trick for me. I have been trying to sync a few GB of files between my workstation, my laptop and my server at home. Between the workstation and the laptop (sitting across the room), no problem, between the workstation and my home server, repeated stalls even after upgrading rsync to v3.0.2(?). Setting the mtu as you suggested fixed the problem
    (well, I transferred a random directory containing 60MB with no hitch).
    Thanks!

    - k

  6. #6
    Join Date
    Apr 2007
    Beans
    9

    Re: FTP/SFTP stalls when transmitting files

    I am running into Exactly same issue.

    Uploading via FTP will stall.

    Changing MTU to 1490 makes it a LITTLE better, (it does not down right cancels the upload, but it stalls about once every 30 MB transfer for about 10 seconds)

    This did NOT happen with Ubuntu 6.10.

    Please help.

  7. #7
    Join Date
    Apr 2007
    Beans
    9

    Re: FTP/SFTP stalls when transmitting files

    Ok, here is something new.

    IF using PORT setting (and not PASV) and when I limit the upload transfer speed to 400KB/s then, stalling frequency lessens severely.
    (I can transfer around 100MB before stalling out, still not good, but MAYBE tolerable)

    I transfer 1GB+ regularly to my xbox from my computer and when I had 6.10, I had ZERO issues uploading.

    Now, I installed the Hardy, I am having issues (upgrade was needed because I could not upgrade packages anymore for my 6.10)

    I have seen another forum that this may be due to router interface. Maybe it is time for me to reboot all my routers, it has been few weeks.

  8. #8
    Join Date
    Apr 2007
    Beans
    9

    Re: FTP/SFTP stalls when transmitting files

    It has been couple of weeks and still no resolution.

    I noticed that this problem worsens when there is rather moderate/heavy load on network.

    Even when throttling at 350KB/sec it stalls frequently (around every 10-30MB)

    Please help as I am not planning to go back to 6.10 if I can help it (maybe 7.04 may help?)

    Does anyone know what changed in network/ftp side for 8.10?

    Thanks.

  9. #9
    Join Date
    Feb 2006
    Beans
    1

    Re: FTP/SFTP stalls when transmitting files

    I have used psftp, an option in putty without any problems, while the regular sftp stalled.

  10. #10
    Join Date
    Apr 2007
    Beans
    9

    Re: FTP/SFTP stalls when transmitting files

    Well, the way I finally resolved this issue is:

    By installing OpenSUSE 11.

    After installing OpenSUSE 11, no issues with FTP at all.

    I can upload at 1.5MB/sec without any issues using gftp (which was what I was using when I was on Ubuntu).
    No stalling, no re-connect.

    Overall, I believe NX connection feel smoother as well.

    I think there is definite issue with networking component issue on 8.04.
    (Although, I never achieved steady 1.5MB/sec upload even using 6.10, which is odd - Best I got was around 800KB-1MB/sec many times falling below 500KB/sec, but never stalled out though)

    There was no change to the networking components.

    Maybe this posting will help people, (either to debug the issue, or IF FTP upload is important to them, solution seems to be installing another distro)

    PS: I installed and ran FTP server on Ubuntu 8.04 as well, which is little bit better than upload, but not much better, downloading from my server, it would require about 5 reconnects to download 800MB file.

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