mysql will not start

[linux_matt]

I use mysql for mythtv but it has suddenly stopped running up with systemd. would be grateful for any help in resolving this. Version of mysql is

mysql Ver 14.14 Distrib 5.6.20, for Linux (i686) using EditLine wrapper

At the end of this message is some information from the log file /var/log/mysql.err

immediately below is the output from systemctl status mysqld.service

Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled)
Active: failed (Result: start-limit) since Sun 2014-09-21 22:28:36 BST; 4 days ago
Process: 6701 ExecStartPost=/usr/libexec/mysqld-wait-ready $MAINPID (code=exited, status=1/FAILURE)
Process: 6700 ExecStart=/usr/bin/mysqld_safe --basedir=/usr (code=exited, status=0/SUCCESS)
Main PID: 6700 (code=exited, status=0/SUCCESS)

Sep 21 22:28:35 myth systemd[1]: Failed to start MySQL database server.
Sep 21 22:28:35 myth systemd[1]: Unit mysqld.service entered failed state.
Sep 21 22:28:36 myth systemd[1]: mysqld.service holdoff time over, schedu...t.
Sep 21 22:28:36 myth systemd[1]: Stopping MySQL database server...
Sep 21 22:28:36 myth systemd[1]: Starting MySQL database server...
Sep 21 22:28:36 myth systemd[1]: mysqld.service start request repeated to...t.
Sep 21 22:28:36 myth systemd[1]: Failed to start MySQL database server.
Sep 21 22:28:36 myth systemd[1]: Unit mysqld.service entered failed state.
Hint: Some lines were ellipsized, use -l to show in full.

Log file:

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 = 0 thread_stack 0x30000
/usr/sbin/mysqld(my_print_stacktrace+0x28)[0x849bfc8]
/usr/sbin/mysqld(handle_fatal_signal+0x3b3)[0x824f8f3]
linux-gate.so.1(__kernel_sigreturn+0x0)[0xb76f2400]
/usr/sbin/mysqld[0x85dd66a]
/usr/sbin/mysqld[0x85dfac4]
/usr/sbin/mysqld[0x8561a4a]
/usr/sbin/mysqld[0x84b77c7]
/usr/sbin/mysqld(_Z24ha_initialize_handlertonP13st_plugin_int+0x41)[0x819ebe1]
/usr/sbin/mysqld[0x82d00e8]
/usr/sbin/mysqld(_Z11plugin_initPiPPci+0x7f8)[0x82d4298]
/usr/sbin/mysqld(_Z11mysqld_mainiPPc+0x8a6)[0x8198be6]
/usr/sbin/mysqld(main+0x1b)[0x817901b]
/lib/libc.so.6(__libc_start_main+0xf3)[0xb717d933]
/usr/sbin/mysqld[0x818df2c]
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.
140921 22:28:34 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
140921 22:28:35 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
2014-09-21 22:28:35 0 [Warning] Using unique option prefix key_buffer instead of key_buffer_size is deprecated and will be removed in a future release. Please use the full name instead.
2014-09-21 22:28:35 0 [Warning] The syntax '--language/-l' is deprecated and will be removed in a future release. Please use '--lc-messages-dir' instead.
2014-09-21 22:28:35 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2014-09-21 22:28:35 7155 [Warning] Using pre 5.5 semantics to load error messages from /usr/share/mysql/english/.
2014-09-21 22:28:35 7155 [Warning] If this is not intended, refer to the documentation for valid usage of --lc-messages-dir and --language parameters.
2014-09-21 22:28:35 7155 [Warning] Buffered warning: Changed limits: max_open_files: 1024 (requested 5000)

2014-09-21 22:28:35 b722d700 InnoDB: Warning: Using innodb_additional_mem_pool_size is DEPRECATED. This option may be removed in future releases, together with the option innodb_use_sys_malloc and with the InnoDB's internal memory allocator.
2014-09-21 22:28:35 7155 [Note] InnoDB: Using atomics to ref count buffer pool pages
2014-09-21 22:28:35 7155 [Note] InnoDB: The InnoDB memory heap is disabled
2014-09-21 22:28:35 7155 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2014-09-21 22:28:35 7155 [Note] InnoDB: Memory barrier is not used
2014-09-21 22:28:35 7155 [Note] InnoDB: Compressed tables use zlib 1.2.8
2014-09-21 22:28:35 7155 [Note] InnoDB: Using Linux native AIO
2014-09-21 22:28:35 7155 [Note] InnoDB: Not using CPU crc32 instructions
2014-09-21 22:28:35 7155 [Note] InnoDB: Initializing buffer pool, size = 16.0M
2014-09-21 22:28:35 7155 [Note] InnoDB: Completed initialization of buffer pool
2014-09-21 22:28:35 7155 [Note] InnoDB: Highest supported file format is Barracuda.
2014-09-21 22:28:35 7155 [Note] InnoDB: The log sequence numbers 35824214 and 35824214 in ibdata files do not match the log sequence number 37722030 in the ib_logfiles!
2014-09-21 22:28:35 7155 [Note] InnoDB: Database was not shutdown normally!
2014-09-21 22:28:35 7155 [Note] InnoDB: Starting crash recovery.
2014-09-21 22:28:35 7155 [Note] InnoDB: Reading tablespace information from the .ibd files...
2014-09-21 22:28:35 7155 [Note] InnoDB: Restoring possible half-written data pages
2014-09-21 22:28:35 7155 [Note] InnoDB: from the doublewrite buffer...
InnoDB: Last MySQL binlog file position 0 503949, file name ./mysqld-bin.000006
21:28:35 UTC - 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.
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.

key_buffer_size=16777216
read_buffer_size=262144
max_used_connections=0
max_threads=151
thread_count=0
connection_count=0
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 133772 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 = 0 thread_stack 0x30000
/usr/sbin/mysqld(my_print_stacktrace+0x28)[0x849bfc8]
/usr/sbin/mysqld(handle_fatal_signal+0x3b3)[0x824f8f3]
linux-gate.so.1(__kernel_sigreturn+0x0)[0xb77bd400]
/usr/sbin/mysqld[0x85dd66a]
/usr/sbin/mysqld[0x85dfac4]
/usr/sbin/mysqld[0x8561a4a]
/usr/sbin/mysqld[0x84b77c7]
/usr/sbin/mysqld(_Z24ha_initialize_handlertonP13st_plugin_int+0x41)[0x819ebe1]
/usr/sbin/mysqld[0x82d00e8]
/usr/sbin/mysqld(_Z11plugin_initPiPPci+0x7f8)[0x82d4298]
/usr/sbin/mysqld(_Z11mysqld_mainiPPc+0x8a6)[0x8198be6]
/usr/sbin/mysqld(main+0x1b)[0x817901b]
/lib/libc.so.6(__libc_start_main+0xf3)[0xb7248933]
/usr/sbin/mysqld[0x818df2c]
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.
140921 22:28:35 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended