innobackupex --defaults-file="/etc/xtrabackup_client/backup.cnf"
  --socket="..." --extra-lsndir="/etc/xtrabackup_client/"
  --stream=xbstream /tmp |
  ssh "$backup_username@$backup_server"  "cat - | xbstream -x -C /var/backups/xtrabackup/"

innobackupex --defaults-file="$mysql_defaults_file"
  --socket="..." --extra-lsndir="/etc/xtrabackup_client" --stream=xbstream
  --incremental --incremental-lsn="$to_lsn" /tmp |
  ssh "$backup_username@$backup_server" "cat - | xbstream -x -C /var/backups/xtrabackup_incremental/"

[client]
user=backup
password=secret

sudo -u mysql /usr/sbin/mysqld --basedir=/usr
  --datadir=/var/db/mysql --plugin-dir=/usr/lib/mysql/plugin
  --user=mysql --pid-file=/var/run/mysqld/mysqld.pid
  --socket=/var/run/mysqld/mysqld.sock --port=3306

2017-01-03 18:55:41 140551642929088 [Note] /usr/sbin/mysqld (mysqld 10.1.20-MariaDB-1~trusty) starting as process 24455 ...
2017-01-03 18:55:41 140551642929088 [Note] Using unique option prefix 'myisam_recover' is error-prone and can break in the future. Please use the full name 'myisam-recover-options' instead.
2017-01-03 18:55:41 140551642929088 [Note] InnoDB: Using mutexes to ref count buffer pool pages
2017-01-03 18:55:41 140551642929088 [Note] InnoDB: The InnoDB memory heap is disabled
2017-01-03 18:55:41 140551642929088 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2017-01-03 18:55:41 140551642929088 [Note] InnoDB: GCC builtin __atomic_thread_fence() is used for memory barrier
2017-01-03 18:55:41 140551642929088 [Note] InnoDB: Compressed tables use zlib 1.2.8
2017-01-03 18:55:41 140551642929088 [Note] InnoDB: Using Linux native AIO
2017-01-03 18:55:41 140551642929088 [Note] InnoDB: Using SSE crc32 instructions
2017-01-03 18:55:41 140551642929088 [Note] InnoDB: Initializing buffer pool, size = 256.0M
2017-01-03 18:55:41 140551642929088 [Note] InnoDB: Completed initialization of buffer pool
2017-01-03 18:55:41 140551642929088 [Note] InnoDB: Highest supported file format is Barracuda.
InnoDB: No valid checkpoint found.
InnoDB: If you are attempting downgrade from MySQL 5.7.9 or later,
InnoDB: please refer to http://dev.mysql.com/doc/refman/5.6/en/upgrading-downgrading.html
InnoDB: If this error appears when you are creating an InnoDB database,
InnoDB: the problem may be that during an earlier attempt you managed
InnoDB: to create the InnoDB data files, but log file creation failed.
InnoDB: If that is the case, please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.6/en/error-creating-innodb.html
2017-01-03 18:55:41 140551642929088 [ERROR] Plugin 'InnoDB' init function returned error.
2017-01-03 18:55:41 140551642929088 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
2017-01-03 18:55:41 140551642929088 [Note] Plugin 'FEEDBACK' is disabled.
2017-01-03 18:55:41 140551642929088 [ERROR] Unknown/unsupported storage engine: InnoDB
2017-01-03 18:55:41 140551642929088 [ERROR] Aborting