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December 7, 2017
07 Dec 2017

Why you should move to CWP (CentOS WebPanel) instead of using cPanel

After reading above line the first thing that will come to cpanel lovers mind will be “Is this guy an idiot?”. cPanel is one of the most advanced, stable and reliable control panel with vast number of features that makes server management extremely easy. Also almost every hosting company providing linux shared hosting uses cPanel on their shared servers. So why would anyone ever want to stop using cPanel? I too agree that cPanel is the number one control panel available in market today. So why did I recommended using CWP? The reason is pricing. A dedicated server cPanel license today costs $45 per month. Which for most people is very high price. Especially when they have just 2 or 3 websites and they never even login to control panel once the site is uploaded and live. So there is no point in paying such high price per month when you only use less than 5% of the features available in cPanel and those features are already available in other free control panels. You can use that money on upgrading hardware instead e.g extra RAM, high power cpu etc.

Why did you specifically recommend CWP when there are lots of other open source and free control panel available?
Yes, there are lots of other popular opensource and free control panel available like Webmin + Virtualmin, VestaCP, ISPConfig etc. The reason for me recommending CWP is due to it’s cPanel migration feature. You can take regular cpanel backup and restore it directly on CWP Server. It will restore the emails, addon domains etc automaticaly. But in other control panels you have to do the migration manually. Also people who has used cPanel before can easily become accustomed to CWP. Second reason is that CWP team is releasing updates regularly. Which makes it a little more secure as compared to other free control panels.

Conclusion: CWP is recommended for people hosting private websites who doesn’t want to pay for control panel license. If you are going use the server for shared hosting  or hosting large number of accounts then  I will highly recommended  you to use some advanced control panel like cPanel, Plesk, DirectAdmin etc. because managing shared hosting will be very difficult without the use of some advanced control panel.

1 Comment/0 Tweets/in Linux Server Support
November 6, 2017
06 Nov 2017

How query cache can cause performance problems?

How query cache can cause performance problems?

Whenever query cache is enabled, any query executed has to access it for one reason or another. For example, the text of a reading query has to be looked up against the cache contents in search for the previously buffered result that could be returned, a freshly generated result from a SELECT statement has to be stored into the cache, but also writing to any table triggers invalidation of all cache entries associated with the particular table, regardless of the original modification size. All this activity relies on a single, global mutex lock. The lock is used to guarantee consistency for the cache contents and for the results returned from it. It implements concurrency control in such way that, while one thread (i.e. one query) is changing anything in the cache, no other query can access it until the lock is released.

Such architecture is not a problem unless a combination of factors occurs that results in the query cache mutex being locked extremely frequently or for extended periods of time. When it happens, in the best case it just builds some serialization around the execution of queries, which means higher response times. In the worst cases, it may bring a database instance almost to a stop when very few queries can make it past the lock. The factors mentioned earlier are:

  • high concurrency – many queries sent concurrently over a large number of connections
  • workload type – often a good mix of reads and writes
  • query cache size – invalidating results, which all happens under the lock, takes longer with more data cached

There are no rules that would allow anyone to predict what combination of these can actually trigger the problem and therefore enabling the query cache always exposes MySQL instance to the possibility of it occurring. Since out of the three factors only size can be controlled, to minimize the risk, it is advised to be conservative when setting database options and never allow query cache size larger than one or two hundred megabytes. In many opinions, it is even best to disable it entirely as there are not too many workloads, where the cache can actually be efficient.

0 Comments/0 Tweets/in Linux Server Support
October 26, 2017
26 Oct 2017

How to upgrade MariaDB in Plesk CentOS 7

CentOS 7 already comes with MariaDB but the version is older. You may need to upgrade it to latest version so that your magento and other scripts can work properly.

First of all create backup of all the databases using below command.

mkdir /mysqlbackup
MYSQL_PWD=`cat /etc/psa/.psa.shadow` mysqldump -u admin –all-databases > /mysqlbackup/all-databases.sql

Now stop the MariaDB

systemctl stop mariadb

Remove the additional mariadb packages if installed

rpm -e mariadb-bench

Create a copy of databae directory in separate folder

cp -ar /var/lib/mysql/ /var/lib/mysql_bakup

Add the mariadb repo

#cat /etc/yum.repos.d/MariaDB10.1.repo
[mariadb]
name = MariaDB
baseurl = http://yum.mariadb.org/10.1/centos7-amd64
gpgkey = https://yum.mariadb.org/RPM-GPG-KEY-MariaDB
gpgcheck = 1

Perfrom the upgrade

yum install mariadb

Start the mariadb

systemctl start mariadb

Run mysql upgrade

MYSQL_PWD=`cat /etc/psa/.psa.shadow` mysql_upgrade -uadmin

Execute this command to update the package version inside Plesk

plesk sbin packagemng -sdf

Remove the init package if installed

rm /etc/init.d/mysql
systemctl daemon-reload

And you are done. Mariadb is now updated to 10.1. You can add mariadb newer version repo if want the latest version.

 

 

0 Comments/0 Tweets/in Linux Server Support
August 25, 2017
25 Aug 2017

nconf stopped working after update to nagios 4

I recently updated our nagios monitoring system from Nagios 3 to Nagios 4 and nconf started giving below error when I generate the new configuration files.

Error: Service has no hosts and/or service_description (config file 'nconf/temp/Default_collector/advanced_services.cfg', starting on line 195)

It was no surprise because the last release of nconf was on Dec 2011 which is around 6 years back. So no wonder it was not working with nagios 4.

Solution:

I searched a lot with no solutions and was thinking of switching to NagiosQL when I came across this post http://forum.nconf.org/viewtopic.php?f=17&t=872#p3050 I gave it a try and it worked like charm.

[root@nagios nconf]# unzip nconf-1.3.0-0_not_used_advanced_services_wont_be_written.patch.zip
 Archive:  nconf-1.3.0-0_not_used_advanced_services_wont_be_written.patch.zip
 inflating: nconf-1.3.0-0_not_used_advanced_services_wont_be_written.patch

[root@nagios nconf]#  patch -p0 --verbose < nconf-1.3.0-0_not_used_advanced_services_wont_be_written.patch
 Hmm...  Looks like a unified diff to me...
 The text leading up to this was:
 --------------------------
 |--- bin/lib/NConf/ExportNagios.pm.orig 2011-12-24 13:57:38.620626845 +0100
 |+++ bin/lib/NConf/ExportNagios.pm      2011-12-24 14:02:16.870751718 +0100
 --------------------------
 Patching file bin/lib/NConf/ExportNagios.pm using Plan A...
 Hunk #1 succeeded at 1014.
 Hunk #2 succeeded at 1078.
 Hunk #3 succeeded at 1111.
 done

You will also have to add below line in config/nconf.php

define('CHECK_STATIC_SYNTAX', 0);
1 Comment/0 Tweets/in Linux Server Support
August 9, 2014
09 Aug 2014

Upstream timed out (110: Connection timed out) while reading response header from upstream

Today I found below error in the nginx logs.
Upstream timed out (110: Connection timed out) while reading response header from upstream

This error generally occurs when nginx is configured as reverse proxy to other webserver like Apache and till now I was fixing it by increasing the proxy_read_timeout in nginx configuration.

Nginx Reverse Proxy

Increase the proxy_read_timeout in nginx configuration file.

proxy_read_timeout 600;

But this server was standalone nginx server with php-fpm.  So I had to increase the fastcgi_read_timeout.

Standalone Nginx + PHP-FPM

Increase the fastcgi_read_timeout

fastcgi_read_timeout 600;
2 Comments/0 Tweets/in Nginx
July 31, 2014
31 Jul 2014

How to check if the disk is SSD?

Most of the data centers and hosting providers are now offering SSD (Solid-state drive). If you run the fdisk command to check the drives it’s still going to show as sda/hda. Since kernel 2.6.29 Linux automatically detects SSD. Now to verify sda for SDD. Simple cat the /sys/block/sda/queue/rotational file. If the output is “0” then that  means it’s a SSD.

root@host [~]# cat /sys/block/sda/queue/rotational
0
root@host [~]#

If the result is
1 -> Regular SATA disk
0 -> SDD

0 Comments/1 Tweets/in cPanel, Linux Server Support, Plesk
July 18, 2014
18 Jul 2014

Varnish: VCL version declaration missing Update your VCL to Version 4 syntax

Today I installed latest version of varnish on a new server and configured it manually. I tried to start it but it was failing. So I did a configuration file test and it gave below error.

# varnishd -C -f /etc/varnish/default.vcl
Message from VCC-compiler:
VCL version declaration missing
Update your VCL to Version 4 syntax, and add
        vcl 4.0;
on the first line the VCL files.
('input' Line 1 Pos 1)
backend default {
#######----------

Running VCC-compiler failed, exit 1

VCL compilation failed

If you read the error carefully then it says that the vcl-compiler requires additional line “vcl 4.0;” added at the top of the configuration file. This happened because Varnish 3.0 configuration syntax is not fully compatible with varnish 4.0. You will have to make a few simple changes to make it work.

vcl 4.0;
backend default {
        .host="XX.XX.XX.XX";
        .port="8082";
}

So after adding the line. The varnish started running perfectly.

root@ [~]# /etc/init.d/varnish restart
Stopping Varnish Cache:                                    [  OK  ]
Starting Varnish Cache: 0
                                                           [  OK  ]
root@ [~]#
0 Comments/0 Tweets/in cPanel, Linux Server Support, Plesk
July 12, 2014
12 Jul 2014

How to install VIRTUALIZOR on OVH Servers

OVH provide dedicated servers with their own customized kernels. Also the loaded disk partitions too will look odd to you. Now if you directly run the virtualizor installation script then it will get installed but it will not work. Because the Xen/KVM kernel and modules will not be loaded.

So we will have to first have to replace it with normal kernel and also remount the partitions too.

Install the kernel

[root@server ~]# yum install kernel
.....................
Installed:
  kernel.x86_64 0:2.6.32-431.20.3.el6
Complete!

Now remount the partitions

[root@server ~]# rm -rf /etc/mtab
[root@server ~]# mount -o remount -a

Add kernel new kernel entries to grub file and reboot the server.

[root@server ~]# new-kernel-pkg --mkinitrd --depmod --install  2.6.32-431.20.3.el6.x86_64
[root@server ~]# reboot

NOTE: Check grub.conf and make sure that regular vmlinuz kernel is configured to load instead of bzImage kernel provide by OVH. Then reboot the server.

Now all is set and we can start the installation of Virtualizor. Below are the steps for installing XEN virtualization.

[root@server ~]# wget -N http://files.virtualizor.com/install.sh
[root@server ~]# chmod 0755 install.sh
[root@server ~]# ./install.sh email=user@domain.com kernel=xen lvg=vg0

“vg0” is the logical volume that I created.

It will take some time fo the installation to complete and you will see something like this

Congratulations, Virtualizor has been successfully installed

API KEY : f3bm1ds8iq3nmcrgt2gf8wqy3zk2xiqk
API Password : ctm3qbnxzuux9i8uwnwji39d0urgu8qf

You can login to the Virtualizor Admin Panel
using your ROOT details at the following URL :
https://xx.xx.xx.xx:4085/
OR
http://xx.xx.xx.xx:4084/

You will need to reboot this machine to load the correct kernel
Do you want to reboot now ? [y/N]

Press “y” and reboot the server. And all is done. You can now access the Virtualizor admin panel from https://xx.xx.xx.xx:4085/. You should login with your severs root login details.

NOTE: In case you are not able to access the admin panel then your firewall must be blocking it. You should unblock the ports

iptables -I INPUT -p tcp --dport 4084 -j ACCEPT
iptables -I INPUT -p tcp --dport 4085 -j ACCEPT
1 Comment/0 Tweets/in Linux Server Support, Virtualization
July 5, 2014
05 Jul 2014

SMTP Authenticated email using Python script

email-from-python-script

System administrators generally use the sendmail or mail utility from mailx to send emails. Which automatically send the email from username@hostname. But there are times when you want to send email from external email server and it requires SMTP authentication. Python is a very powerful scripting language and we can use this below simple script send SMTP authenticated emails.

#!/usr/bin/python

import smtplib

email_to = 'emailto@gmail.com'
username = 'username@sender-domain.com'
password = 'password of username@sender-domain.com'

smtpserver = smtplib.SMTP("sender-domain.com",25)
smtpserver.ehlo()
smtpserver.login(username,password)
header = 'To:' + email_to + '\n' + 'From: ' + username + '\n' + 'Subject: Python SMTP Auth\n'
msg = header + '\n\n This is a test message generated from python script \n\n'
smtpserver.sendmail(username, email_to, msg)
smtpserver.close()
print 'Email sent successfully'
0 Comments/1 Tweets/in Scripts
July 5, 2014
05 Jul 2014

dovecot: auth: Error: Cpanel::MailAuth: Failed to getpwnam

cpanel-email-authentication-failed

If you are not able to access email even with correct username and password and you see below error in the /var/log/maillog

Jul  5 18:15:20 hostname dovecot: auth: Error: Cpanel::MailAuth: Failed to getpwnam for user webmaster
Jul  5 18:15:38 hostname dovecot: auth: Error: Cpanel::MailAuth: Login not permitted to account with a uid lower then 500 (498)
Jul  5 18:15:56 hostname dovecot: auth: Error: Cpanel::MailAuth: Failed to getpwnam for user admin
Jul  5 18:54:38 hostname dovecot: auth: Error: Cpanel::MailAuth: Failed to getpwnam for user info
Jul  5 18:54:45 hostname dovecot: auth: Error: Cpanel::MailAuth: Failed to getpwnam for user info
Jul  5 18:55:06 hostname dovecot: auth: Error: Cpanel::MailAuth: Failed to getpwnam for user info

Reason:

This happens if hostname is same as domain. The mail server will try to authenticate against system user of the server instead of virtual domains on the server.

Solution:

Change the hostname of the server to something else other than domain name. e.g. if your domain is domain.com then you can set the hostname as host.domain.com

Also make sure that there is entry of the domain in both /etc/localdomains and /etc/userdomains.

 

0 Comments/0 Tweets/in cPanel