Info: Using unique option prefix 'backup' is error-prone and can break in the future. Please use the full name 'backup_encrypted' instead.
190110 03:51:49 Connecting to MySQL server host: localhost, user: root, password: set, port: 19300, socket: /var/run/mysqld/mysqld.sock
Using server version 10.4.2-MariaDB-debug-log
Can not open directory /var/lib/mysql: No such file or directory
Warning: option 'datadir' points to nonexistent directory '/var/lib/mysql'
Warning: option 'datadir' has different values:
  '/var/lib/mysql' in defaults file
  '/home/travis/logs/vardir/data/' in SHOW VARIABLES
/home/travis/server/bin/mariabackup based on MariaDB server 10.4.2-MariaDB Linux (x86_64) 
mariabackup: uses posix_fadvise().
mariabackup: cd to /home/travis/logs/vardir/data/
Loading encryption plugin
	 Encryption plugin parameter :  '--file_key_management_encryption_algorithm=aes_cbc'
	 Encryption plugin parameter :  '--file_key_management_filekey='
	 Encryption plugin parameter :  '--file_key_management_filename=/home/travis/mariadb-toolbox/data/keys.txt'
mariabackup: open files limit requested 0, set to 30000
mariabackup: using the following InnoDB configuration:
mariabackup:   innodb_data_home_dir = 
mariabackup:   innodb_data_file_path = ibdata1:12M:autoextend
mariabackup:   innodb_log_group_home_dir = ./
2019-01-10 03:51:49 0x7fa4fbbdb740 InnoDB: Using Linux native AIO
2019-01-10  3:51:49 0 [Note] InnoDB: Number of pools: 1
mariabackup: Generating a list of tablespaces
2019-01-10  3:51:49 0 [Warning] InnoDB: Allocated tablespace ID 3 for mysql/transaction_registry, old maximum was 0
2019-01-10  3:51:49 0 [ERROR] InnoDB: Operating system error number 2 in a file operation.
2019-01-10  3:51:49 0 [ERROR] InnoDB: The error means the system cannot find the path specified.
2019-01-10  3:51:49 0 [ERROR] InnoDB: If you are installing InnoDB, remember that you must create directories yourself, InnoDB does not create them.
2019-01-10  3:51:49 0 [ERROR] InnoDB: File ./test/#sql-6041_11.ibd: 'open' returned OS error 71.
2019-01-10 03:51:49 0x7fa4fbbdb740  InnoDB: Assertion failure in file /home/travis/src/storage/innobase/fil/fil0fil.cc line 657
InnoDB: Failing assertion: success
InnoDB: We intentionally generate a memory trap.
InnoDB: Submit a detailed bug report to https://jira.mariadb.org/
InnoDB: If you get repeated assertion failures or crashes, even
InnoDB: immediately after the mysqld startup, there may be
InnoDB: corruption in the InnoDB tablespace. Please refer to
InnoDB: https://mariadb.com/kb/en/library/innodb-recovery-modes/
InnoDB: about forcing recovery.
190110  3:51:49 [ERROR] mysqld got signal 6 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.

To report this bug, see https://mariadb.com/kb/en/reporting-bugs

We will try our best to scrape up some info that will hopefully help
diagnose the problem, but since we have already crashed, 
something is definitely wrong and this may fail.

Server version: 10.4.2-MariaDB-debug
key_buffer_size=0
read_buffer_size=131072
max_used_connections=0
max_threads=1
thread_count=0
It is possible that mysqld could use up to 
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 5736 K  bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x0
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong...
stack_bottom = 0x0 thread_stack 0x49000
/home/travis/server/bin/mariabackup(my_print_stacktrace+0x40)[0x55e5bbe1dff5]
/home/travis/server/bin/mariabackup(handle_fatal_signal+0x3e1)[0x55e5bb6f127a]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x11390)[0x7fa4fb7c3390]
/lib/x86_64-linux-gnu/libc.so.6(gsignal+0x38)[0x7fa4f9845428]
/lib/x86_64-linux-gnu/libc.so.6(abort+0x16a)[0x7fa4f984702a]
/home/travis/server/bin/mariabackup(+0xfc703a)[0x55e5bbb9003a]
/home/travis/server/bin/mariabackup(+0xd38cdf)[0x55e5bb901cdf]
ut/ut0mem.cc:42(ut_strlcpy(char*, char const*, unsigned long))[0x55e5bb905105]
fil/fil0fil.cc:658(fil_node_open_file(fil_node_t*))[0x55e5bb1e3d2e]
fil/fil0fil.cc:1647(fil_space_t::open())[0x55e5bb1e4126]
mariabackup/xtrabackup.cc:3136(xb_load_single_table_tablespace(char const*, char const*, bool))[0x55e5bb1e46c1]
mariabackup/xtrabackup.cc:3251(enumerate_ibd_files(void (*)(char const*, char const*, bool)))[0x55e5bb1e6509]
mariabackup/xtrabackup.cc:3421(xb_load_tablespaces())[0x55e5bb1eda33]
mariabackup/xtrabackup.cc:4250(xtrabackup_backup_func())[0x55e5bb1ed283]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7fa4f9830830]
/home/travis/server/bin/mariabackup(_start+0x29)[0x55e5bb1dcef9]
The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains
information that should help you find out what is causing the crash.
Aborted (core dumped)