mysql server start failed

I am running ubuntu server. When I tried to login to mysql(which was running),I got the following error

ERROR 2002 (HY000): Can't connect to local MySQL server through socket         '/var/run/mysqld/mysqld.sock' (2)

But mysqld.sock file doesn't exist inside /var/run/mysqld folder. On executing ps aux | grep mysql command,I realized that mysql server was not running.

I then tried to restart mysql server using

service mysql start
service mysql restart
/etc/init.d/mysql start

But,the start process failed in all 3 cases. /var/log/mysql/mysql.log and /var/log/mysql/mysql.err files are empty.

But /var/log/error.log shows following information:

140425 12:49:05 [Warning] Using unique option prefix myisam-recover instead of myisam-recover-options is deprecated and will be removed in a future release. Please use the full name instead.
140425 12:49:05 [Note] Plugin 'FEDERATED' is disabled.
140425 12:49:05 InnoDB: The InnoDB memory heap is disabled
140425 12:49:05 InnoDB: Mutexes and rw_locks use GCC atomic builtins
140425 12:49:05 InnoDB: Compressed tables use zlib 1.2.8
140425 12:49:05 InnoDB: Using Linux native AIO
140425 12:49:05 InnoDB: Initializing buffer pool, size = 3.0G
140425 12:49:05 InnoDB: Completed initialization of buffer pool
InnoDB: Error: log file ./ib_logfile0 is of different size 0 5242880 bytes
InnoDB: than specified in the .cnf file 0 26214400 bytes!
140425 12:49:05 [ERROR] Plugin 'InnoDB' init function returned error.
140425 12:49:05 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
140425 12:49:05 [ERROR] /usr/sbin/mysqld: unknown variable 'record_buffer=64M'
140425 12:49:05 [ERROR] Aborting

140425 12:49:05 [Note] /usr/sbin/mysqld: Shutdown complete

Solution 1:

Open a terminal(Ctrl+Alt+t) and do the following:

sudo service mysql stop
sudo rm /var/lib/mysql/ib_logfile0
sudo rm /var/lib/mysql/ib_logfile1

and comment out the line record_buffer=64M in /etc/mysql/my.cnf ^[1]

and then restart msyql using:

sudo service mysql restart

(Source)

Solution 2:

This solved my problem:

mkdir /var/run/mysqld

touch /var/run/mysqld/mysqld.sock

chown -R mysql /var/run/mysqld

/etc/init.d/mysql restart

Solution 3:

I solved the problem in the following way:

chown -R mysql:mysql /var/lib/mysql
mysql_install_db --user=mysql -ldata=/var/lib/mysql/

In another context, I faced it because the mysql daemon failed to start. So start daemon with command - mysqld start and then try to start the service.

Solution 4:

I had the same error message and the same emptyness in the log files. In my config-file (my.cnf) I had specified that I wanted to use myisam tables, by adding this line in the [mysqld]-section:

default-table-type = myisam

After upgrading mysql it seems this causes mysql not to start. I have changed this to:

default-storage-engine = myisam

and now everything works fine.

Solution 5:

Increasing the available RAM by adding new Swap space might also help. Steps are here

Make sure that you create /swapfile of the size smaller than the available space shown by

df -h

For example for me output of df- h was:

Filesystem      Size  Used Avail Use% Mounted on
/dev/xvda1      7.8G  1.2G  6.3G  16% /
none            4.0K     0  4.0K   0% /sys/fs/cgroup
udev            492M   12K  492M   1% /dev
tmpfs           100M  336K   99M   1% /run

So I created using 2 G

sudo fallocate -l 2G /swapfile

And then just start the service

sudo /etc/init.d/mysql restart

Hope this helps. All the best.