Hide php version and apache version

Most of hacker may find the bug based on apache version and hack the server.
So you had better hide the apache version.


By default, the apache will send apache version to client in every http header.

Another, the php will send the php version to client.

Now I give the way how to hide the apache version and php version

1. Hide apache version

ServerTokens controls whether Server response header field, which is sent back to clients, includes a descriptions of the generic OS-type of the server.

open httpd.conf and change

ServerSignature On => ServerSignature Off
ServerTokens os=>ProductOnly

2. Hide php version

expose_php = On =>expose_php = Off

MySQL index performance and example

The aims for index in MySQL is to find row quickly. For example, there is a table like


CREATE TABLE test (
    id         INT NOT NULL,
    last_name  CHAR(30) NOT NULL,
    first_name CHAR(30) NOT NULL,
    PRIMARY KEY (id),   
);

If we execute
select * from test where last_name = 'Obama';

the MySQL will check all records in table test. It will be the O(n) questions.

If we use index for this table, it is not necessary to check each row from 0 to n.  How to improve the performance to search one or more special rows in table?

For example, when we want to find a keyword in a book, we find it in the index list and then get the page no from it. We can find it quickly based on the book index.  MySQL may also use this method to get it by index.

Now we use command

alter table test add index(last_name);

We have added one index on table test for last_name. if we execute
select * from test where last_name = 'Obama';

MySQL will find it from its index files, not from record 1 to last one. Of course, we should use more disk space to store the index files.

There are three ways to create index


Index for one column

alter table test add index(last_name);


Parts index for one column

alter table test add index(last_name(4));

it will save space.

Index for multiple columns

alter table test add index(last_name, first_name);

In fact, the MySQL will one execute one index for last_name or first_name. MySQL will determine which one is used dynamically. E.g. If first_name is less, first_name will be used.

invalid command
 SELECT * FROM test WHERE first_name='Michael';
SELECT * FROM test WHERE last_name='Widenius' OR first_name='Michael';

valid command


SELECT * FROM test WHERE last_name='Widenius';
SELECT * FROM test WHERE last_name='Widenius' AND first_name='Michael';
SELECT * FROM test WHERE last_name='Widenius' AND (first_name='Michael' OR first_name='Monty');
SELECT * FROM test WHERE last_name='Widenius' AND first_name >='M' AND first_name < 'N';



Unique Index for one column

alter table test add unique (last_name);

It will check the unique attribute before insert a new record

Data structure
Index will use B-Tree to create a index file.

Get all index columns
show indexes from test;

When will you should use index
1. find a fixed string, e.g. where last_name='obama';
2. join two table, e.g. on table_a.last_name =b_table.last_name
3. find a range e.g. where id > 100
4. Min(), Max()
5. order by , group by

use select, show databases, show tables, external sql file of mysql by shell script utility

usually we use shell to backup, update the database. Now I give one example for you to use mysql based on shell script.

Four Shell Example for:
select
show databases;
show tables;
sql.sql file

Execute one select command

> ./bash.sh host user dbnam
-------------------------bash.sh-------------------------------------

#!/bin/sh

HOST=localhost
if [ $1 ]
then
   HOST=$1
fi

user=root
if [ $2 ]
then
   user=$2
fi

db=dbname
if [ $3 ]
then
   db=$3
fi

mysql="$(which mysql)"

read -s -p "Please input the db pass: " pass


if [ $pass ]
then

  DBS="$($mysql -h$HOST -u$user -p$pass -D$db -e 'select uid from dd0a05_users limit 0, 10')"

  for db in $DBS
  do
   echo $db
  done

else
   echo 'No db pass'
fi
------------------------------end bash.sh-------------------------------------------


Execute 'show databases' command

> ./bash.sh host user dbnam
-------------------------bash.sh-------------------------------------

#!/bin/sh

HOST=localhost
if [ $1 ]
then
   HOST=$1
fi

user=root
if [ $2 ]
then
   user=$2
fi

db=dbname
if [ $3 ]
then
   db=$3
fi

mysql="$(which mysql)"

read -s -p "Please input the db pass: " pass


if [ $pass ]
then

  DBS="$($mysql -h$HOST -u$user -p$pass  -e 'show databases')"

  for db in $DBS
  do
   echo $db
  done

else
   echo 'No db pass'
fi
------------------------------end bash.sh-------------------------------------------


Execute 'show tables' command

> ./bash.sh host user dbnam
-------------------------bash.sh-------------------------------------

#!/bin/sh

HOST=localhost
if [ $1 ]
then
   HOST=$1
fi

user=root
if [ $2 ]
then
   user=$2
fi

db=dbname
if [ $3 ]
then
   db=$3
fi

mysql="$(which mysql)"

read -s -p "Please input the db pass: " pass


if [ $pass ]
then

  DBS="$($mysql -h$HOST -u$user -p$pass -D$db -e 'show tables')"

  for db in $DBS
  do
   echo $db
  done

else
   echo 'No db pass'
fi
------------------------------end bash.sh-------------------------------------------


Execute external files 'sql.sql' command

> ./bash.sh host user dbnam
-------------------------bash.sh-------------------------------------

#!/bin/sh

HOST=localhost
if [ $1 ]
then
   HOST=$1
fi

user=root
if [ $2 ]
then
   user=$2
fi

db=dbname
if [ $3 ]
then
   db=$3
fi

mysql="$(which mysql)"

read -s -p "Please input the db pass: " pass


if [ $pass ]
then

  DBS="$($mysql -h$HOST -u$user -p$pass -D$db < sql.sql)"

  for db in $DBS
  do
   echo $db
  done

else
   echo 'No db pass'
fi
------------------------------end bash.sh-------------------------------------------