/etc/hostname -> Assigns a name to local machine and you can set the name of the machine by editing this file. It can be a FQDN eg. vps.example.com. You will also need ...]]> I have often found myself in difficult situations without knowing what exactly is the difference between host and hostname

/etc/hostname -> Assigns a name to local machine and you can set the name of the machine by editing this file. It can be a FQDN eg. vps.example.com. You will also need to edit /etc/sysconfig/network to specify the hostname in Centos, if /etc/hostname is missing etc.

/etc/hosts -> Maps hostnames to IP addresses locally. It has nothing to do with DNS or FQDN. You have to specify hostname and IP address for resolving on line by line.

67.1.2.3.5 vps.example.com  vps vps

Imagine this, you are on a server disconnected from the internet and when you type vps.example.com on your browser, it resolves to the IP you specified on the /etc/hosts file.

I recently had an issue with mysql database and the datbase has grown too large about 200k records and i was needing to delete all junk and needless data of approx 50k rows in my table. As soon as i hit delete sql query using WHERE clause, it almost took ...]]>

I recently had an issue with mysql database and the datbase has grown too large about 200k records and i was needing to delete all junk and needless data of approx 50k rows in my table. As soon as i hit delete sql query using WHERE clause, it almost took about 1 hr and the task was still running and i noticed that the query was able to do delete of only 10k rows which to me is amazingly slow.

Running this DELETE query had locked all tables causing the site to go down and users see “Too many sql connections” and the server load was almost at 35/1.0

Always Run DELETE for large rows using LIMIT

I had to resort to killing the mysql process and restart the mysql server to bring back the site online. So never use delete directly on large datasets without using LIMIT because it puts enormous load on your server. You can set limit to either 100 rows or 1000 rows not more than that.

DELETE from <tbldata> where date <= ’2009′ LIMIT 500

I did quite a research on using delete and it turns out that delete is amazingly slow on databases and the only way is to run delete on small chunks of data. You can write a php script running as cron which execute delete when the server is idle.

Keep in mind that running DELETE will LOCK your tables. So perform this operation only when the server is idle.

So whats the solution?

The only way you can clean up your table is using the following methods.

1. Apply DELETE on small chunks of rows usually by limiting to max 10000 rows. Do this only your server is IDLE.

2. Make sure you create INDEX in your table on the auto_increment primary key and this way delete can speed up things enormously.  I created a index on certain fields in the table and ran DELETE with LIMIT 10000 and it took about 1.2 second to perform the operation which is just fine i guess.

2. Another method is copy the data you want to save to a new table, and then use TRUNCATE on the old table and then copy back. This way your users will see less down time and this method is the fastest although its bit indirect.

Compatibility is one of the most important issues when it comes to WordPress. If you want to install a a copy on your local machine, then you have to follow some simple steps.

First, download the archive on wordpress.org. For the purpose of this tutorial we are going to use wordpress-2.9.tar.gz ...]]>

Compatibility is one of the most important issues when it comes to WordPress. If you want to install a a copy on your local machine, then you have to follow some simple steps.

First, download the archive on wordpress.org. For the purpose of this tutorial we are going to use wordpress-2.9.tar.gz archive, which is usually automatically saved in / home / username / Downloads.
Open a new Terminal and create a wordpress folder in / home / username with the command

mkdir wordpress

Being in the username folder, and make sure you have full rights on wordpress folder. You can do this by using the command

chmod 777 wordpress

Before writing the actual commands we must have that specific folder in the path of the terminal. Navigation is very similar to Windows, including the cd with no parameters to access the home folder  or cd / path / folder to access a certain path.

Using this simple command, we navigate to the folder where wordpress-2.9.tar.gz is situated and we write the command:

wordpress-2.9.tar.gz cp / home / nume_user / wordpress

This will copy the archive to the wordpress folder. Then we move into the wordpress folder (cd / home / user_name / wordpress) where we write the unzip command:

tar-zxvf wordpress-2.9.tar.gz

This will create another folder in wordpress with the same name, which will be necessary to install the actual copy on your local machine. You can also rename this folder using:

mv wordpress the_name_you_want

Previous commands can also be accessed very easily from the GUI, but for those who want to develop in Linux it is better to learn the basic commands in Terminal. The Apache server accesses the files in / var / www, so we cannot install WordPress locally, until we change the settings for Apache.

sudo gedit / etc/apache2/apache2.conf

We use sudo because this is a file that only the administrator of your machine can access. You will also be asked for the root password after pressing enter. Next, in apache2.conf we write the following lines:

Save and access in the Terminal: sudo gedit / etc / hosts adding a line with 127.0.0.1 Where and www.wordpress.ro.im.localhost. Restart apache:

sudo / etc/init.d/apache2 restart

Thus configured, we can access the website at http://www.wordpress.ro.im.localhost. This allows the installation of multiple platforms of wordpress and their separate configurations. Furthermore, the actual location for each will be in / home / user_name / wordpress / website_name.

About Author:

Brad’s a Linux enthusiast and is currently working on migrating his latest project (made in WordPress), Findermind.com to a new Ubuntu dedicated server.

Lets say you have to import a large text file to mysql and fields are totally irregular but only separated by spaces. For example.  Since it is only text file and highly irregular data you have to use other methods to import data to database.

17876           ...]]>

Lets say you have to import a large text file to mysql and fields are totally irregular but only separated by spaces. For example.  Since it is only text file and highly irregular data you have to use other methods to import data to database.

17876           BILL            hc-device          4.76                FC900888        0.88776           USD

There are 3 ways to import text data into mysql

1. Use a fixed width data import method

Try to analyse and measure the data in text file and you will have a brief idea on length of fields.

LOAD DATA LOCAL
INFILE '<file name>' INTO TABLE <table>
(@var1)
SET
 `name`=SUBSTR(@var1,1,25),
 `address`=SUBSTR(@var1,26,25),
 `zip`=SUBSTR(@var1,51,10),
 `phone`=SUBSTR(@var1,61,10)
IGNORE 35 LINES

2.  MySQL Load Data INFILE method

Usually mysql does not interpret multiple spaces as one, you have to group all spaces first using sed command line, then you can import using load data infile.

sed 's/ \+/ /g' thefile > thefile.new

The above command groups all spaces into one and (the regular expression does it) and the resulting data is output written into new file. Once done we can feed  the new file to load data infile.

LOAD DATA INFILE '<filename>' INTO TABLE <table>
FIELDS TERMINATED BY ' '
LINES TERMINATED BY '\n';

3. Parsing a text file using PHP

You can parse the text file using preg_split and matching regular expressions using php. The code below will separate columns separated by spaces.

<?php

$fileHandle= @fopen("data.txt", "r");
if ($fileHandle) {
 while (!feof($fileHandle)) {
 $i++;
 $lines = fgets($fileHandle, 4096);

 $columns = preg_split("/\s+/", $lines);
 if(preg_match('/[0-9]+/', $columns[1])) {
 echo $columns[0] . '---> '. $columns[1] . ' = '. $columns[2] . $columns[3] . $columns[4] .'<br>';
 // Once columns isolated, you can insert into mysql

mysql_query("INSERT into <table> (col1,col2,col3) VALUES (columns[0], columns[1]. columns[2])") or die(mysql_error());
}

}
 fclose($fileHandle);
}

?>

The performance was ...]]> I cant believe how slow the performance of mysql was, assuming that  i had a large database table of over 100k record. I technically directly imported to mysql from csv and there was no primary key in the database. Infact i never used a auto incrementing primary key.

The performance was too slow and some pages took over 5 seconds to load. i had a suspicion that missing primary key is causing this slowness and quickly created auto increment id and a full text index. I got a significant boost in performance and there was never slowness after this.

From this experience, i learnt  how important is primary key for mysql performance.

i was thrown this error

Access Denied user@localhost using password ...]]> I was on shared hosting and thought i could import a CSV file using PHP to mySQL database and whe

 LOAD DATA INFILE '/home7/topbestg/OFFICES2_ALL.CSV'
 REPLACE INTO TABLE `tbl`
 FIELDS TERMINATED BY ',' ENCLOSED BY '\"'
 LINES TERMINATED BY '\n'
 IGNORE 1 LINES;

i was thrown this error

Access Denied user@localhost using password YES

Fix:

Just add LOCAL to your load data statement and be sure the csv file you are trying to import on your local server

LOAD DATA LOCAL INFILE '/home/ex/DATA.CSV'
 REPLACE INTO TABLE `tbl`
 FIELDS TERMINATED BY ',' ENCLOSED BY '\"'
 LINES TERMINATED BY '\n'
 IGNORE 1 LINES;

and bingo! it worked like a charm!

Here is this one command which worked ...]]> i have been looking everywhere for one easy command to setup CRON job in cpanel.  My requirement was i wanted to send a simple invoice for my client every month and i dont want want cron outputs to sent as junk to my email.

Here is this one command which worked very neatly work. I created a simple php file to send email and i dont want the php file to be accessed by public and bots by placing in public_html folder because placing it openly is susceptible to spam. so i placed the file above public_html folder so that it is not accessed by public.

Here is this command you have to add

php -q /home/pbu/cron/laterooms.php > /dev/null

and from the below shown image, this above commands runs on 15th of every month running the php file. Note that i have created a separate folder cron just to organize the cron jobs.

You can also use another command wget to run a cron job, but that will send you irritating emails everytime the php script is run.

wget -O /dev/null http://www.prurgent.com/news/rss.php

CRON worked like a charm running automated scripts.