To upload the cron job from a file to another user, combine it with -u option.

# crontab -u root /home/oracle/mycronjobs.txt

Divides the buffer pool into a user-specified number of separate regions, each with its own LRU list and related data structures, to reduce contention during concurrent memory read and write operations. The size specified by innodb_buffer_pool_size is divided among all the buffer pool instances. For best efficiency, specify a combination of innodb_buffer_pool_instances and innodb_buffer_pool_size so that each buffer pool instance is at least 1 gigabyte.

log a command to console and to 2 files separately stdout and stderr

# command > >(tee stdout.log) 2> >(tee stderr.log >&2)
_____

Real full backup copy of /etc folder
# rsync -a /etc /destination

If your repository is available on a server for e.g. 10.10.10.6, you need to point it to that server in your config file.

# cat /etc/yum.repos.d/rhel.repo
[base]
name=RHEL 5 $releasever - $basearch - Base
baseurl=http://10.10.10.6/yum/rhel/5/base/
enabled=1
gpgcheck=0

If the internet is not working from a server, you need to change one file.

cat /etc/resolove.conf

nameserver 8.8.8.8
nameserver 10.10.10.1
nameserver 10.10.10.6

/etc/init.d/network restart

The mail command will not work if the internet is down.

If you need fresh mysql installation you need to run script to create default mysql database and system tables. The script is called "mysql_install_db" and is either in the bin or in scripts directory of your mysql installation. Change the my.cnf to reflect new datadir and run mysql_install_db for it to create mysql database and system tables in the new datatir and then start mysqld_safe.

The mysql general logs use the following date format to display current date.

date '+%y%m%d %H:%M:%S'

The same can be used in the shell script to echo date at the beginning of the line.

If you want someone to access all the files and locations that mysql has access to, then add the username to the mysql group.

vi /etc/group

mysql:x:27:santosh

init_connect can be used to disable foreign key checks.
mysql> SET GLOBAL init_connect='SET foreign_key_checks = 0';

As well something similar for the GLOBAL options my.cnf file.
init_connect='SET foreign_key_checks = 0';

The super user will bypass the init-connect directives. So the user without the super privilege can take benefit of this setting.

Here is the list error codes mysql will return when it fails to connect to the mysql instance.

101 error: Can not connect to MySQL server (101)
102 error: '(proxy) all backends are down'
103 error: 'Access denied for user 'user'@'10.10.10.10' (using password: NO)'
104 error: 'Access denied for user 'user'@'10.10.10.10' (using password: YES)'
105 error: 'Host '10.10.10.10' is not allowed to connect to this MySQL server'
111 error: 'Lost connection to MySQL server at 'reading initial communication packet', system error: 111'
113 error: 'Lost connection to MySQL server at 'reading initial communication packet', system error: 113'
114 error: Unknown MySQL server host (3)