Failed to connect to the source server by SSH: Incompatible ssh server (no acceptable macs)

Created:

2016-11-16 13:11:45 UTC

Modified:

2017-08-16 04:36:40 UTC

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Failed to connect to the source server by SSH: Incompatible ssh server (no acceptable macs)

Applicable to:

  • Plesk 12.5 for Linux
  • Plesk Onyx for Linux

Symptoms

  1. Migration fails with error:

    [INFO] START: Check connections
    [ERROR] Failed to perform action: Check connections
    Error while checking connection settings: 'Failed to connect to the source server by SSH: Incompatible ssh server (no acceptable macs)'
    Migration was stopped.
  2. A source server is connected through Paramiko implementation of SSH2.

  3. SSH is configured without Paramiko preferred Message Authentication Code (MAC) algorithms on the source server:

    # grep "MACs" /etc/ssh/sshd_config
    MACs hmac-sha2-512,hmac-sha2-256,hmac-ripemd160

Cause

This is Plesk Migrator bug with ID PMT-2360 which is planned to be fixed in future Plesk Migrator updates.

Resolution:

Paramiko prefers the following MACs:

hmac-sha1
hmac-md5
hmac-sha1-96
hmac-md5-96
  1. Connect to the server using SSH.
  2. Add the following MACs to /etc/ssh/sshd_config, for example:

    # vi /etc/ssh/sshd_config
    MACs hmac-sha1,hmac-md5,hmac-sha1-96,hmac-md5-96

  3. Reload SSH server:

    # service sshd reload

  4. Restart migration.

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2 Comments

  • 0
    Avatar
    Denver Prophit Jr.

    Can you specify the KEX algorithm you need also?

  • 0
    Avatar
    Vitaly Zhidkov

    @Denver, try the following:

    KexAlgorithms diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1
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