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

[Christian Ehrhardt ]

Thanks Gareth to come back and document the fix for your case!
This will certainly help other users finding this bug if they run into the same.

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

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

Status in rsync package in Ubuntu:
  Invalid

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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