MariaDB [test]> CREATE TABLE ct (a INT NOT NULL PRIMARY KEY, b INT NOT NULL) ENGINE=CONNECT TABLE_TYPE=csv FILE_NAME='ct.csv';
Query OK, 0 rows affected, 1 warning (0.13 sec)

Warning (Code 1105): Open(rb) error 2 on /usr/local/mariadb-10.0.8-linux-x86_64/data/./test/ct.csv: No such file or directory
MariaDB [test]> ALTER TABLE ct ADD UNIQUE INDEX uni_a_b (a,b);
ERROR 2013 (HY000): Lost connection to MySQL server during query
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (111 "Connection refused")
ERROR: Can't connect to the server

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (111 "Connection refused")

140319  1:48:31 [ERROR] mysqld got signal 11 ;
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 http://kb.askmonty.org/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: 10.0.8-MariaDB-log
key_buffer_size=134217728
read_buffer_size=131072
max_used_connections=1
max_threads=501
thread_count=2
It is possible that mysqld could use up to 
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 1224384 K  bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x0x7f6b17be7008
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 = 0x7f6b32c4dd28 thread_stack 0x48000
/usr/local/mysql/bin/mysqld(my_print_stacktrace+0x2e)[0xb9020e]
/usr/local/mysql/bin/mysqld(handle_fatal_signal+0x44c)[0x70ceac]
/lib/x86_64-linux-gnu/libpthread.so.0(+0xf030)[0x7f6b3421e030]
/lib/x86_64-linux-gnu/libc.so.6(rewind+0x1)[0x7f6b33122121]
/usr/local/mysql/lib/plugin/ha_connect.so(_ZN6DOSFAM6RewindEv+0x18)[0x7f6b07ad11a8]
/usr/local/mysql/lib/plugin/ha_connect.so(_ZN6TDBDOS6OpenDBEP7_global+0x165)[0x7f6b07adf3a5]
/usr/local/mysql/lib/plugin/ha_connect.so(_ZN6TDBCSV6OpenDBEP7_global+0x24a)[0x7f6b07ae3cba]
/usr/local/mysql/lib/plugin/ha_connect.so(_ZN6TDBDOS9MakeIndexEP7_globalP8INDEXDEFb+0x1b5)[0x7f6b07ade8c5]
/usr/local/mysql/lib/plugin/ha_connect.so(_ZN10ha_connect13external_lockEP3THDi+0x4b4)[0x7f6b07ab9b54]
/usr/local/mysql/bin/mysqld(_ZN7handler16ha_external_lockEP3THDi+0x72)[0x70e152]
/usr/local/mysql/bin/mysqld(_Z19mysql_unlock_tablesP3THDP13st_mysql_lockb+0x5c)[0x7e230c]
/usr/local/mysql/bin/mysqld(_Z17mysql_lock_removeP3THDP13st_mysql_lockP5TABLE+0x91)[0x7e24d1]
/usr/local/mysql/bin/mysqld(_Z25close_all_tables_for_nameP3THDP11TABLE_SHARE17ha_extra_functionP5TABLE+0xd4)[0x54f434]
/usr/local/mysql/bin/mysqld[0x613bf0]
/usr/local/mysql/bin/mysqld(_Z17mysql_alter_tableP3THDPcS1_P14HA_CREATE_INFOP10TABLE_LISTP10Alter_infojP8st_orderb+0x35dc)[0x618f0c]
/usr/local/mysql/bin/mysqld(_ZN19Sql_cmd_alter_table7executeEP3THD+0x508)[0x663ca8]
/usr/local/mysql/bin/mysqld(_Z21mysql_execute_commandP3THD+0x7e2)[0x590392]
/usr/local/mysql/bin/mysqld(_Z11mysql_parseP3THDPcjP12Parser_state+0x25a)[0x59790a]
/usr/local/mysql/bin/mysqld(_Z16dispatch_command19enum_server_commandP3THDPcj+0x1827)[0x5996a7]
/usr/local/mysql/bin/mysqld(_Z10do_commandP3THD+0xe5)[0x599da5]
/usr/local/mysql/bin/mysqld(_Z26threadpool_process_requestP3THD+0xf8)[0x6a95e8]
/usr/local/mysql/bin/mysqld[0x6e11f8]
/usr/local/mysql/bin/mysqld[0xa30e7b]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x6b50)[0x7f6b34215b50]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7f6b331920ed]

Trying to get some variables.
Some pointers may be invalid and cause the dump to abort.
Query (0x7f6b314cb020): is an invalid pointer
Connection ID (thread ID): 4
Status: NOT_KILLED

Optimizer switch: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on,extended_keys=off,exists_to_in=off

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.