When you try to run the mysqldump command to make a backup of database then encounter the following error-exception:

mysqldump databasename  > databasename.sql

mysqldump: Got error: 1016: Can’t open file: ‘./databasename/wp_142_term_taxonomy.frm’ (errno: 24) when using LOCK TABLES

Solution: Open the file /etc/my.cnf and  add the following line and restart the mysql service on the server

root@server [~]#vi /etc/my.cnf

open-files-limit=20000

root@server [~]#/etc/init.d/mysql restart

Done