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I recently created a swap file on my centos 6 based VPS using this guide. Now I wanted to extend this swap and I was reading through this guide. However, I think I've created a swap file than a partition. How do I go about extending this swapfile? The current size is 512M and I need to extend it by another 1G. Any help would be appreciated since I'm a linux newbie.

Dani_l · Accepted Answer · 2015-12-09 15:39:34Z

Can you show the results of

cat /proc/swaps

so we can be sure of your situation?

BTW - did you make sure the swap space (file or partition) is in your /etc/fstab?

If you created an lvm swap partition, extending it is easy and you can use the same guide - basically:

swap off; lvextend -L +1G VolGroup/LVswap; mkswap /dev/VolGroup-LVswap; swapon -a
If you indeed created a file - you can either repeat the procedure, create another 1G file and let swap handle it (swap space does not have to be contiguous)
Or you could simply remove the file (swapoff /path/to/swapfile; rm !$) and recreate it in a new size
Or you can use dd to extend your swap file (again - make sure to swapoff first)

dd oflag=append conv=notrunc if=/dev/zero of=/swapfile bs=1MB count=1024

UPDATE

It's advisable to use the free command first, to ascertain swap is not used. As long as swap usage is 0, and no process is going to require more memory then physically available, there should be no issues.
Every swap device must be present in /etc/fstab for swapon -a to detect them all.
If using procedure (3) above, to keep swap "downtime" to a minimum, you can do the following:

3.1 Create new swapfile
3.2 Modify /etc/fstab to point to new swap file.
3.3 swapoff <path/to/OLD/swapfile>
3.4 swapon -a
3.5 rm <path/to/OLD/swapfile>

Optionally combine 3.3 and 3.4 as: swapoff /path/to/OLD/swapfile && swapon -a will ensure least amount of time without swap.

Thanks Dani_l. I actually followed step 3 to create a new swapfile, deactivated the smaller one and then deleted it. Activated the new one. Replaced the smaller one in /etc/fstab with the new one. Now I have one contigous swap file of 2G. I did think of step 2 but I did not know they need not be contigous. Thanks again! — hpb, Jul 12 '14 at 19:36
are the potential issues on doing swapoff on a swap file in use? also, after swapon, are there any extra steps needed to get the system to recognize the larger file? — Gaia, Apr 16 '15 at 17:00

Volker E. · Accepted Answer · 2015-05-15 17:33:31Z

I had the same issue as all of our servers run older versions of MySQL. This can be solved by running a PHP script. Save this code to a file and run it entering the database name, user and password and it'll change the collation from utf8mb4/utf8mb4_unicode_ci to utf8/utf8_general_ci

<!DOCTYPE html>
<html>
<head>
  <title>DB-Convert</title>
  <style>
    body { font-family:"Courier New", Courier, monospace;" }
  </style>
</head>
<body>

<h1>Convert your Database to utf8_general_ci!</h1>

<form action="db-convert.php" method="post">
  dbname: <input type="text" name="dbname"><br>
  dbuser: <input type="text" name="dbuser"><br>
  dbpass: <input type="text" name="dbpassword"><br>
  <input type="submit">
</form>

</body>
</html>
<?php
if ($_POST) {
  $dbname = $_POST['dbname'];
  $dbuser = $_POST['dbuser'];
  $dbpassword = $_POST['dbpassword'];

  $con = mysql_connect('localhost',$dbuser,$dbpassword);
  if(!$con) { echo "Cannot connect to the database ";die();}
  mysql_select_db($dbname);
  $result=mysql_query('show tables');
  while($tables = mysql_fetch_array($result)) {
          foreach ($tables as $key => $value) {
           mysql_query("ALTER TABLE $value CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci");
     }}
  echo "<script>alert('The collation of your database has been successfully changed!');</script>";
}

?>

Helped me a lot. spent nearly days to get this fixed on my old server. you are life saver indeed. ;) — Keep Coding, Jun 25 at 19:20
For me it worked. Remember to name the file db-convert.php — Fred K, Sep 4 at 15:46

Evster · Answer 3 · 2015-04-30 18:08:46Z

up vote 58 down vote

The technique in this post worked for me
1) Click the "Export" tab for the database
2) Click the "Custom" radio button
3) Go the section titled "Format-specific options" and change the dropdown for "Database system or older MySQL server to maximize output compatibility with:" from NONE to MYSQL40.
4) Scroll to the bottom and click "GO".
I'm not certain if doing this causes any data loss, however in the one time I've tried it I did not notice any. Neither did anyone who responded in the forums linked to above.

answered Apr 30 at 18:08

Evster
7641512

Worked for me too, thanks! – nach May 2 at 17:10

Thanks for it's work fine – Mansukh Khandhar Jun 26 at 11:22

didn't work for me, i got the error #1231 - Variable 'character_set_client' can't be set to the value of 'NULL' – nerdess Jun 26 at 21:48

G-e-n-i-u-s!!!! – Fred K Jul 3 at 8:02

This is absolute amazing. It worked perfectly. +1 – Student T Oct 1 at 10:55

show 1 more comment

Rangel R. Morais · Answer 4 · 2015-07-19 23:01:13Z

up vote 9 down vote

The best thing to do is export your database to .sql, open it on notepad++ and go to "search and replace". Then you put "mb4" on search and nothing on replace. It will replace the utf8mb4_unicode_ci to utf8_unicode_ci. Now you go to your phpmyadmin( destination ) and set the db collation to utf8_unicode_ci. ( Operations > Collation ).
WORKS PERFECTLLY

answered Jul 19 at 23:01

Rangel R. Morais
9913

Wow, this actually worked perfectly for me! – Luuk Van Dongen Jul 30 at 10:06

thanks - got me out of a hole – maxelcat Sep 8 at 15:49

add a comment

flomei · Answer 5 · 2015-05-05 22:07:40Z

Seems like your host does not provide a MySQL-version which is capable to run tables with utf8mb4 collation.
The WordPress tables were changed to utf8mb4 with Version 4.2 (released on April, 23rd 2015) to support Emojis, but you need MySQL 5.5.3 to use it. 5.5.3. is from March 2010, so it should normally be widely available. Cna you check if your hoster provides that version?
If not, and an upgrade is not possible, you might have to look out for another hoster to run the latest WordPress versions (and you should always do that for security reasons).

You can check your version of MySQL via command line with "mysql -V" — Edd Smith, Apr 29 at 9:51

Markouver · Answer 6 · 2015-05-14 23:05:49Z

Wordpress 4.2 introduced support for "utf8mb4" character encoding for security reasons, but only MySQL 5.5.3 and greater support it. The way the installer (and updater) handles this is that it checks your MySQL version and your database will be upgraded to utfmb4 only if it's supported.
This sounds great in theory but the problem (as you've discovered) is when you are migrating databases from a MySQL server that supports utf8mb4 to one that doesn't. While the other way around should work, it's basically a one-way operation.
As pointed out by Evster you might have success using PHPMYAdmin's "Export" feature. Use "Export Method: Custom" and for the "Database system or older MySQL server to maximize output compatibility with:" dropdown select "MYSQL 40".
For a command line export using mysqldump. Have a look at the flag:

$ mysqldump --compatible=mysql4

Note: If there are any 4-byte characters in the database they will be corrupted.
Lastly, for anyone using the popular WP Migrate DB PRO plugin, a user in this Wordpress.org thread reports that the migration is always handled properly but I wasn't able to find anything official.

The WP Migrate DB plugin translates the database from one collation to the other when it moves 4.2 sites between hosts with pre- or post-5.5.3 MySQL

At this time, there doesn't appear to be a way to opt out of the database update. So if you are using a workflow where you are migrating a site from a server or localhost with MySQL > 5.5.3 to one that uses an older MySQL version you might be out of luck.

If you then try and import the mysql4 compatible dump into a post v5.5.3 database (I'm using 5.5.28) then it fails because the script includes TYPE=MyISAM that was removed in v5.1. Do a search and replace with ENGINE=MyISAM. I couldn't see a way around this using the mysqldump output options. — icc97, Aug 4 at 21:27

Isk1n · Answer 7 · 2015-06-07 14:04:04Z

There is a line in wp-config.php:

define('DB_CHARSET', 'utf8mb4');

If you follow Markouver's / Evster's instructions, don't forget to change this line on production server to

define('DB_CHARSET', 'utf8');

in order to fix broken 4-byte characters

Micha Wiedenmann · Answer 8 · 2015-08-19 11:41:34Z

After the long time research i have found the solution for above:

Firstly you change the wp-config.php> Database DB_CHARSET default to "utf8"
Click the "Export" tab for the database
Click the "Custom" radio button
Go the section titled "Format-specific options" and change the dropdown for "Database system or older MySQL server to maximize output compatibility with:" from NONE to MYSQL40.
Scroll to the bottom and click go

Then you are on.

This worked for me, thanks! – Darren Riches Nov 2 at 15:24 — Darren Riches, Nov 2 at 15:24

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