[Bug 1831101] Re: rsync with remote sudo fails over ssh/pki with protocol mismatch error

Fri May 31 09:38:41 UTC 2019

I have set this up in Xenial/Bionic/Eoan
The following syncs nicely a dir created as root to need the sudo to read it:

$ rsync -AEaogt --rsync-path="sudo rsync" -e "ssh -o
StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null" /tmp/foo
ubuntu at 10.253.194.115:/tmp

This works among all pairs and cross releases.

Now lets brainstorm what might happen in your case ...

I have:
1. setup rsync to be sudo enabled without PW in /etc/sudoers
  %sudo ALL= NOPASSWD:/usr/bin/rsync
2. then I exchanged ssh keys between all nodes

That got it working, no more needed.

Did you use the same sudoers hint to make it PW-less?

I have read through your log twice but can't find anything obvious.
You could try to set up another user special to this use case.
And let that user have no .bashrc nor anything else (maybe the login with rsync triggers a different path and there you have output). At least that would be an easy try.

Most things you find on the net about this is about clearing the non
interactive login, but I think you have done that. What might be worth
to take a look is dropping strict host keycheck option and really make
sure all keys are accepted - maybe something with that is going on in
the background?

** Changed in: rsync (Ubuntu)
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1831101

Title:
  rsync with remote sudo fails over ssh/pki with protocol mismatch error

Status in rsync package in Ubuntu:
  Incomplete

Bug description:
  rsync with remote sudo fails over ssh on Ubuntu Mate 18.04.2

  rsync version 3.1.2 protocol version 31 - same on local and remote

  OpenSSH_7.6p1 Ubuntu-4ubuntu0.3, OpenSSL 1.0.2n 7 Dec 2017 - same on
  local and remote

  I have checked for spurious output from .bashrc using

  $ ssh user at host /bin/true > out.dat

  which results in

  $ ls -l *.dat
  -rw-rw-r-- 1 user user 0 May 22 23:33 out.dat

  -- The [redacted] command is

  rsync -AEavvvogt --rsync-path="sudo rsync" --debug=CONNECT -e "ssh -i
  /home/xxx/.ssh/id_rsa -tt -v -o StrictHostKeyChecking=no -o
  UserKnownHostsFile=/dev/null" --exclude-from=/home/xxx/backup.exclude
  --delete --link-dest=../$lastdt /etc $dest/$dt

  -- The [redacted] output is

  opening connection using: ssh -i /home/user/.ssh/id_rsa -tt -v -o
  StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -l user xxx
  "sudo rsync" --server -vvvlogDtpAre.iLsfxC --delete --link-dest
  ../20190506_021137 . /home/backups/xxx/20190522_232738 (20 args)

  OpenSSH_7.6p1 Ubuntu-4ubuntu0.3, OpenSSL 1.0.2n 7 Dec 2017

  debug1: Reading configuration data /etc/ssh/ssh_config

  debug1: /etc/ssh/ssh_config line 19: Applying options for *

  debug1: Connecting to xxx [192.168.1.120] port 22.

  debug1: Connection established.

  debug1: permanently_set_uid: 0/0

  debug1: identity file /home/user/.ssh/id_rsa type 0

  debug1: key_load_public: No such file or directory

  debug1: identity file /home/user/.ssh/id_rsa-cert type -1

  debug1: Local version string SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.3

  debug1: Remote protocol version 2.0, remote software version
  OpenSSH_7.6p1 Ubuntu-4ubuntu0.3

  debug1: match: OpenSSH_7.6p1 Ubuntu-4ubuntu0.3 pat OpenSSH* compat
  0x04000000

  debug1: Authenticating to xxx:22 as 'user'

  debug1: SSH2_MSG_KEXINIT sent

  debug1: SSH2_MSG_KEXINIT received

  debug1: kex: algorithm: curve25519-sha256

  debug1: kex: host key algorithm: ecdsa-sha2-nistp256

  debug1: kex: server->client cipher: <email address hidden> MAC:
  <implicit> compression: none

  debug1: kex: client->server cipher: <email address hidden> MAC:
  <implicit> compression: none

  debug1: expecting SSH2_MSG_KEX_ECDH_REPLY

  debug1: Server host key: xxx

  Warning: Permanently added 'xxx,192.168.1.120' (ECDSA) to the list of
  known hosts.

  debug1: rekey after 134217728 blocks

  debug1: SSH2_MSG_NEWKEYS sent

  debug1: expecting SSH2_MSG_NEWKEYS

  debug1: SSH2_MSG_NEWKEYS received

  debug1: rekey after 134217728 blocks

  debug1: SSH2_MSG_EXT_INFO received

  debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,ssh-rsa,rsa-
  sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384
  ,ecdsa-sha2-nistp521>

  debug1: SSH2_MSG_SERVICE_ACCEPT received

  debug1: Authentications that can continue: publickey,password

  debug1: Next authentication method: publickey

  debug1: Offering public key: RSA SHA256:xxx /home/user/.ssh/id_rsa

  debug1: Server accepts key: xxx

  debug1: Authentication succeeded (publickey).

  Authenticated to xxx ([192.168.1.120]:22).

  debug1: channel 0: new [client-session]

  debug1: Requesting <email address hidden>

  debug1: Entering interactive session.

  debug1: pledge: network

  debug1: client_input_global_request: rtype <email address hidden>
  want_reply 0

  debug1: tty_make_modes: no fd or tio

  debug1: Sending environment.

  debug1: Sending env LANG = en_GB.UTF-8

  debug1: Sending command: sudo rsync --server -vvvlogDtpAre.iLsfxC
  --delete --link-dest ../20190506_021137 .
  /home/backups/xxx/20190522_232738

  protocol version mismatch -- is your shell clean?

  (see the rsync man page for an explanation)

  rsync error: protocol incompatibility (code 2) at compat.c(178)
  [sender=3.1.2]

  [sender] _exit_cleanup(code=2, file=compat.c, line=178): about to call
  exit(2)

  -------------------------------------------------------

  /etc/sudoers contains

  user ALL= NOPASSWD:/usr/bin/rsync
  ...which I have tried placing above (as is the default) and below lines beginning %admin and %sudo and the space in "ALL= NOPASSWD..." doesn't seem to make any difference

  I followed the instructions at

  https://www.digitalocean.com/community/tutorials/how-to-copy-files-
  with-rsync-over-ssh

  https://askubuntu.com/questions/719439/using-rsync-with-sudo-on-the-
  destination-machine

  ...which worked on 16.04, so I wonder if there may be a bug, although
  grateful for any other suggestions, as I am unsure how to
  debug/investigate further

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