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https://blog.hostonnet.com/mysql-out-of ... ening-file

When i take backup of a MySQL Database with large number of tables, i get following error

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# mysqldump freeforums > freeforums.sql
mysqldump: Got error: 23: Out of resources when opening file './freeforums/casualcity_topics_watch.MYD' (Errcode: 24) when using LOCK TABLES
#
When restoring this Database, i got similar error

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# mysql freeforums < freeforums.sql
ERROR 23 (HY000) at line 25: Out of resources when opening file './freeforums/' (Errcode: 24 - Too many open files)
#
Solution

This was caused due to open_files_limit limit.

To fix, i edit /etc/my.cnf

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vi /etc/my.cnf
Added open_files_limit under [mysqld_safe] section.

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open_files_limit = 50000
Here is the content of /etc/my.cnf file with open_files_limit added

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# cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid
open_files_limit = 50000

#
Now you need to restart MySQL

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service mysql stop
service mysql start
Related Kernel Parameters

To see maximum allowed file handlers on your system, run

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cat /proc/sys/fs/file-max
To see current usage, run

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cat /proc/sys/fs/file-nr
This will show

Total allocated file handles.
Number of currently used file handles.
Maximum file handles that can be allocated.
To change value of file-max, edit /etc/sysctl.conf

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vi /etc/sysctl.conf
Add

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fs.file-max=65536
Now run

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sysctl -a
This will apply the changes to Kernel with out rebooting.