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I've used from some time rsync/ssh to backup my shared host contents to my personal Synology NAS (212j for that matter), and it worked quite well. For information, I use a password-less ssh connection.

3 days ago, I updated my NAS software and since (or at least I believe it's since that), the backup won't work anymore. I get the following error on the host: 

rsync: writefd_unbuffered failed to write 4 bytes to socket [sender]: Broken pipe (32)
ERROR: module is read only

..which I do not understand. beside that nothing changed that I know of in both source and destination that can be related to rsync or ssh, I did check a few things and all seems to be alright:

  • I can still connect through ssh from the host to my NAS with the good user, so ssh stuff like keys haven't changed.
  • I also have the correct file permissions on the NAS (I checked, and also tried to create files, directories, .. with the user used by rsync through ssh).

I read here and there that the error means that I have to ensure that my rsyncd.conf have the right read only = no in it, but as far as I know, I never used rsyncd as well as I never configured anything for it and until now it worked like a charm..

I use the following command to do the backup:

rsync -ab --recursive \
--files-from="$FILES_FROM" \
--backup-dir=backup_$SUFFIX \
--delete \
--filter='protect backup_*' \
$WDIRECTORY/ \
remote_backup:$REMOTE_BACKUP/

So I'm stuck and really can't figure out what happened.

Edit:

As suggested in comments, I also tried passing commands to ssh (but not from inside a ssh session), that worked as expected, and also tried a single rsync command, which didnt worked, failing just like the complete backup command. 

(sharedHost):hostuser:~ > touch test.txt
(sharedHost):hostuser:~ > rsync test.txt remote_backup:backups/test.txt
ERROR: module is read only
rsync error: syntax or usage error (code 1) at main.c(1034) [Receiver=3.0.8]
rsync: connection unexpectedly closed (9 bytes received so far) [sender]
rsync error: error in rsync protocol data stream (code 12) at io.c(601) [sender=3.0.7]

and

(sharedHost):hostuser:~ > ssh remote_backup 'touch /abs_path_to_backups/backups/test2.txt && echo "ProoF" > /abs_path_to_backups/backups/test2.txt'
(sharedHost):hostuser:~ > ssh remote_backup 'cat /abs_path_to_backups/backups/test2.txt'
ProoF
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  • Try doing the remote update tests, but with commands given to ssh on the command line instead of through a ssh login session. Also be sure the target space is not full.
    – Skaperen
    Sep 8, 2012 at 17:23
  • Thanks for your suggestions. I edited the question with their result. Also, the target space is not full at all (I was already sure, but I checked again)
    – user978548
    Sep 10, 2012 at 12:41

6 Answers 6

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21

I had the same problem after updating my Synology NAS to DSM 4.1. I also do rsync over SSH. In my situation using rsync user root@ip also worked but left the files on the server with owner root which I did not want.

I found in the NAS admin userinterface, that for some reason in ControlPanel->Users->MyRSyncUser->Edit->"Priviliges setup" there was no read/write access to the homes. My RSYNC destination is under the homes.

Setting this to privilidge worked for me. I hope this helps.

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7
  • Thank you so much ! That worked ! Next time I update DSM, I'll double-check the permissions..
    – user978548
    Oct 11, 2012 at 22:39
  • 12
    This seems to work if I use full path names (i.e., rsync something nas:/volume2/homes/foo/bar/ instead of rsync something nas:bar/).
    – Jukka Suomela
    Dec 14, 2013 at 22:37
  • full path was the last step for me in annoying bout of debugging. thanks!
    – joevallender
    Jun 5, 2014 at 15:30
  • 1
    The problem with this solution (I've not found a better one) is that it gives the user privileges on all user homes, not just their own.
    – CryingCyclops
    Jun 18, 2015 at 7:30
  • 2
    I had this problem, but it wasn't caused by permissions, but simply by misspelling the remote path. the Synology rsync will not tell you that -- just that the path you specify is "read only"
    – dovetalk
    Nov 9, 2021 at 0:47
14

I got rid of ERROR: module is read only by changing the remote path from /var/services/homes/rsync to /volume2/homes/rsync

DSM 5.1

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1
  • 1
    Yes this worked for me too: You definitely need the volume in the DiskStation path: USERNAME@DiskStation:/volume1/somebackupDir works, USERNAME@DiskStation:/somebackupDir gives error receiving incremental file list ERROR: module is write only rsync error: syntax or usage error (code 1) at main.c(782) [sender=3.0.9]
    – Paulus
    Feb 25, 2021 at 10:01
5

I encountered the same problem after upgrading a synology ds1010+ to dsm 4.1-2661.

I don't have the time to understand what happened to the rsync provided by synology but it does not seem standard. So here is my workaround...

I didn't want to hack the privileges (multi-user setup), so I've recompiled rsync in static on my laptop, then I've transfered the binary on the sinology nas.

wget https://rsync.samba.org/ftp/rsync/rsync-3.0.9.tar.gz
tar xzvf rsync-3.0.9.tar.gz
cd rsync-3.0.9
export CFLAGS=--static
./configure
make

scp rsync <login>@<nas_hostname>:

You can tell rsync to use your new binary instead of the default one, with this parameter:

--rsync-path=<myhome>/rsync

Now I can continue using duplicity with rsync, by adding the following parameter to duplicity:

--rsync-options="--rsync-path=<myhome>/rsync"
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2
  • This is what I did with my DS212j, except I used ipkg to install the new rsync. Synology's directions for installing ipkg are here.
    – Jason
    Jun 9, 2013 at 19:42
  • I couldn't find anything on ipkg for DSM 5.2, so for my DS215j I did as follows to compile (I already had the cross-compiler arm-unknown-eabi-gcc lying around) ./configure --host=armv7 CFLAGS=-static EXEEXT=-static --prefix=/opt CC=arm-unknown-linux-gnueabi-gcc && make && arm-unknown-linux-gnueabi-strip rsync && make DESTDIR=$PWD/../prefix install. Put the binary in /opt/bin/ on the NAS. Also have to give my backup user a shell in /etc/passwd by changing /sbin/nologin to /bin/sh (There should be some more secure options).
    – thomasa88
    Feb 10, 2016 at 8:36
1

I had the same kind of issue, but I wasn't using a dedicated user for rsync.

I had to fix privileges in Control Panel -> Shared folders.

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0

I had similar issue while connecting to Synology 211j over Putty's ssh. I had to enable

"Control Panel -> Network backup -> Enable network backup service".

It is working now.

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-1

I got it working by logging in as root instead of admin or regular user.

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