Linux web hosting and server support tips

Tag: centOS

How to remove or compress huge MySQL general and query log table

How to remove or compress huge MySQL general and query log table

If you have enabled MySQL general or slow logging, it can create quite big log, depending upon your MySQL usage/queries.
So we may have to periodically clear them to save space.

Please note that MySQL can save logs to either table or files. This document assumes you are using table as log output.

Files: slow_log.CSV and general_log.CSV (The location and the name of the file can be different)

By default, logging is to CSF file.

MYSQL supports run time clearing of these logs. So no need to restart the MySQL service.
Never delete the CSV file directly. It can crash MySQL.

Slow query log

SET GLOBAL slow_query_log='OFF';
CREATE TABLE slow_log2 LIKE slow_log;
RENAME TABLE slow_log TO slow_log_backup, slow_log2 TO slow_log;
gzip /var/db/mysql/mysql/slow_log_backup.CSV 
DROP TABLE  slow_log_backup;
SET GLOBAL slow_query_log = 'ON';

General log

USE mysql;
SET GLOBAL general_log = 'OFF';
DROP TABLE IF EXISTS general_log2;
CREATE TABLE general_log2 LIKE general_log;
RENAME TABLE general_log TO general_log_backup, general_log2 TO general_log;
gzip /var/db/mysql/mysql/general_log_backup.CSV 
DROP TABLE  general_log_backup;

What we did is create new log table, move current log file to a backup copy and compress the backup and remove it.

Run Postfix on multiple ports

Adding additional SMTP listenerports

By default postfix run on port 25 and 587(TLS). However some ISPs block port 25. In that case you can configure the postfix mail server to listen on addional ports too, for example port 26 or some random 5125.

This configuration is done in the configuration file. Edit it in your editor of choice.

This file is in the following format:

# ==========================================================================
# service type private unpriv chroot wakeup maxproc command + args
# (yes) (yes) (yes) (never) (100)
# ==========================================================================

The first column is the port number that you want to listen on. The default SMTP port 25 line will read as follows:

smtp inet n - - - - smtpd

To add an additional listener port of 5125, insert the the following after the above:

5125 inet n - n - - smtpd

Save the file and restart postfix service

service postfix restart

Now you can use port 25, 587 and 5125 to connect to your mail server.

CSR generation for UCC certificates

Unified Communications (UC) Certificates (also called SAN Certificates) use Subject Alternative Names o secure multiple sites (e.g. fully qualified domain names) with one certificate. Four SANs are included in the base price of the UC Certificate, but you can purchase additional names at any time during the lifetime of the certificate.

With a UC Certificate, you can secure:

The CSR generation process is little different for creating an UCC certificates. We will have to create a Openssl based configuration file and then create private key and CSR from it.

Step 1: Create a custom OpenSSL Conf file.

The following is an example conf file that can be used for creation of a SAN/UCC cert. Save it as multissl.conf

[ req ]
default_bits = 2048
default_keyfile = privkey.pem
distinguished_name = req_distinguished_name
req_extensions = req_ext # The extentions to add to the self signed cert

[ req_distinguished_name ]
countryName = Country Name (2 letter code)
countryName_default = US
stateOrProvinceName = State or Province Name (full name)
stateOrProvinceName_default = Iowa
localityName = Locality Name (eg, city)
localityName_default = Iowa City
organizationName = Organization Name (eg, company)
organizationName_default = The University of Iowa
organizationalUnitName = Organizational Unit Name (eg, section)
organizationalUnitName_default = Domain Control Validated
commonName = Common Name (eg, YOUR SSL domain name)
commonName_max = 64

[ req_ext ]
subjectAltName = @alt_names

DNS.1 =
DNS.2 =
DNS.3 =


The alt_names section (DNS.1, DNS.2, ….) are the list of all other domain names you wish to secure with this cert. Additional can be added such as DNS.4, etc.
The following examples assume that you name the above config file file multissl.conf (if it is named differently you must adjust the filename in the below examples accordingly.
Step 2: Generate the Private key and CSR with OpenSSL

Execute the following OpenSSL command

$ openssl req -nodes -newkey rsa:2048 -keyout serverfqdn.key -out multidomain.csr -config multissl.conf

* Replace “serverfqdn” with the fully qualified domain name of the server (ie: Note: it may also be helpful to add a year to the filename.

You will then see output and be prompted for configuration as seen in the following example. Enter your details accordingly.

$ openssl req -nodes -newkey rsa:2048 -keyout serverfqdn.key -out multidomain.csr -config multissl.conf
Generating a 2048 bit RSA private key
writing new private key to ‘serverfqdn.key’
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter ‘.’, the field will be left blank.
Country Name (2 letter code) [US]:US
State or Province Name (full name) [Iowa]:Iowa
Locality Name (eg, city) [Iowa City]:Iowa City
Organization Name (eg, company) [The University of Iowa]:My Company name
Organizational Unit Name (eg, section) [Domain Control Validated]:IT SUPPORT
Common Name (eg, YOUR SSL domain name) []

Note: Replace with the “primary” domain name you want secured with this certificate (likely, but not necessarily the hostname of the machine).

At this point you should have the new key file, and CSR. Save the key file in a secure place, it will be needed to apply the new certificate. The CSR can now be submitted to request the SSL Cert.

How to Disable SSLv3 for Apache,Nginx, Litespeed, cPanel

The POODLE bug is a new bug discovered by Google in the SSLv3 protocol. The fix is easy, disable support for SSLv3.

See the google security blog for more info on the bug:



To fix the bug, disable SSLv3 and use a secure cipherlist. SSL v2 is also insecure, so we need to disable it too.

So edit the Apache config file and add following

SSLProtocol All -SSLv2 -SSLv3

All is a shortcut for +SSLv2 +SSLv3 +TLSv1 or – when using OpenSSL 1.0.1 and later – +SSLv2 +SSLv3 +TLSv1 +TLSv1.1 +TLSv1.2, respectively. The above line enables everything except SSLv2 and SSLv3

And then restart the Apache service

service httpd restart



If you have a cPanel server, you should not edit Apache configurations directly, instead you can do this from WHM.




1. Visit your server’s WHM Panel ( https://<yourserversip>:2087 )
2. Navigate to the Apache Configuration Panel of WHM.
3. Scroll down to the ‘Include Editor’ Section of the Apache Configuration.
4. Click ‘Pre Main Include’, which will jump to the corresponding section. Via the drop-down selector, choose ‘All Versions’.
5. An empty dialogue box will appear allowing you to input the needed configuration updates. In this box, copy and paste the following:

SSLProtocol All -SSLv2 -SSLv3
SSLHonorCipherOrder On


For Nginx

If you’re running an NGINX web server that currently uses SSLv3, you need to edit the NGINX configuration (nginx.conf). You will need to add the following line to your server directive:

ssl_protocols TLSv1 TLSv1.1 TLSv1.2;

Then restart the nginx service

service nginx restart

For LiteSpeed:

Update to LiteSpeed version 4.2.18.

For more information about Litespeed & POODLE:

Note about Mail Servers:

The POODLE attack requires the client to retry connecting several times in order to downgrade to SSLv3, and typically only browsers will do this. Mail Clients are not as susceptible to POODLE. However, users who want better security should switch to Dovecot until we upgrade Courier to a newer version.

For cpsrvd:

1. Go to WHM => Service Configuration => cPanel Web Services Configuration
2. Make sure that the “TLS/SSL Protocols” field contains “SSLv23:!SSLv2:!SSLv3”.
3. Select the “Save” button at the bottom.

For cpdavd:

1. Go to WHM => Service Configuration => cPanel Web Disk Configuration
2. Make sure that the “TLS/SSL Protocols” field contains “SSLv23:!SSLv2:!SSLv3”.
3. Select the “Save” button at the bottom.

For Dovecot:

1. Go to WHM => Service Configuration => Mailserver Configuration.
2. SSL Protocols should contain “!SSLv2 !SSLv3”. If it does not, replace the text in this field.
3. Go to the bottom of the page, and select the Save button to restart the service.

For Courier:

Courier has released a new version to mitigate this as of 10/22, until we have an opportunity to review, test, and publish the new version of Courier please switch to Dovecot for enhanced security.

For Exim:

1. Go to Home » Service Configuration » Exim Configuration Manager
2. Under Advanced Editor, look for ‘openssl_options’.
3. Make sure the field contains “+no_sslv2 +no_sslv3”.
4.Go to the bottom of the page, and select the Save button to restart the service.


For Lighttpd:

Lighttpd releases before 1.4.28 allow you to disable SSLv2 only.

If you are running at least 1.4.29, put the following lines in your configuration file:

ssl.use-sslv2 = "disable"
ssl.use-sslv3 = "disable"

How to verify the Poodle is disabled

You can use a website like for a web based check.


Manual check

To make sure services on your server are not accepting SSLv3 connections, you can run the openssl client on your server against the SSL ports. This command is run as follows:

openssl s_client -connect -ssl3

If it fails (which is what you want), you should see something like this at the top of the output:

3078821612:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1257:SSL alert number 40
3078821612:error:1409E0E5:SSL routines:SSL3_WRITE_BYTES:ssl handshake failure:s3_pkt.c:596:

Shellshock How to check if you are vulnerable

A new vulnerability has been found that potentially affects most versions of the Linux and Unix operating systems, in addition to Mac OS X. Known as the “Bash Bug” or “ShellShock,” the GNU Bash Remote Code Execution Vulnerability could allow an attacker to gain control over a targeted computer if exploited successfully. And because Bash is everywhere on Linux and UNix-like machines and interacts with all parts of the operating system, everyone anticipates that it will have lot of repercussions.

How does Shellshock work?

Shellshock exploits a flaw in how Bash parses environment variables; Bash allows functions to be stored in environment variables, but the issue is Bash will execute any code placed after the function in the environment variable value.

For example, an environment variable setting of VAR=() { ignored; }; /bin/id will execute /bin/id when the environment is imported into the bash process.

I am vulnerable?

You can check if you’re vulnerable by running the following lines in your default shell.

env X=”() { :;} ; echo vulnerable” `which bash` -c “echo Check completed”

If you see the word “vulnerable” echo’d back , then you’re at risk.

How Shellshock is Impacting the Web

The most likely route of attack is through Web servers utilizing CGI (Common Gateway Interface), the widely-used system for generating dynamic Web content. An attacker can potentially use CGI to send a malformed environment variable to a vulnerable Web server. The attacker is able to inject environment variables inside all bash process spawned by a web server under the CGI specification. This will occur directly if the CGI script is programmed in bash or indirectly by system calls inside other types of CGI scripts since the environment will propagate to the sub-shell. The vulnerability will automatically be triggered at the shell process instantiation. Furthermore if specific headers are used as attack points, the payload may not appear in the webserver logs, letting a compromise occur with virtually no trace of the intrusion.


CGI stores the HTTP headers in environment variables. Let’s say the is running a CGI application written in Bash script.

We can modify the HTTP headers such that it will exploit the shellshock vulnerability in the target server and executes our code.

curl -k -H “User-Agent: () { :;}; echo Hacked > /tmp/Hacked.txt”

Here, the curl is sending request to the target website with the User-Agent containing the exploit code. This code will create a file “Hacked.txt” in the “/tmp” directory of the server.

What can I do to protect myself?

Major operating software vendors including RedHaT, CentOS, etc are already released a initial patch for this bug.



Red Hat—*



If a patch is unavailable for a specific distribution of Linux or Unix, it is recommended that users switch to an alternative shell until one becomes available.

Need expert assistanace?

I can help you to patch your server against this bug and make sure you and your customers are secure. Mail me at therealfreelancer[at]gmail[dot]com.

Apache: Multiple SSL websites on a single IP address

Apache: Multiple SSL websites on a single IP address

Update: This is a new update from a cPanel Tech
“There is nothing to enable. As long as you are using cPanel & WHM version 11.38 on CentOS, RHEL, or CloudLinux version 6 or newer, SNI works out of the box”.

One of the frustrating limitations in supporting secure websites has been the inability to share IP addresses among SSL websites.
When website administrators and IT personnel are restricted to use a single SSL Certificate per socket (combination of IP Address and socket) it can cost a lot of money. Well we can actually share IP addresses for multiple secure websites. Solving this limitation required an extension to the Transport Layer Security (TLS) protocol that includes the addition of what hostname a client is connecting to when a handshake is initiated with a web server. The name of the extension is Server Name Indication (SNI). SNI is supported in Apache v2.2.12 , and OpenSSL v0.9.8j or later.

With SNI, you can have many virtual hosts sharing the same IP address and port, and each one can have its own unique certificate

Prerequisites to use SNI

Use OpenSSL 0.9.8f or later
Build OpenSSL with the TLS Extensions option enabled (option enable-tlsext; OpenSSL 0.9.8k and later has this enabled by default).
Apache must have been built with that OpenSSL (./configure –with-ssl=/path/to/your/openssl). In that case, mod_ssl will automatically detect the availability of the TLS extensions and support SNI.
Apache must use that OpenSSL at run-time, which might require setting LD_LIBRARY_PATH or equivalent to point to that OpenSSL, maybe in bin/envvars. (You’ll get unresolved symbol errors at Apache startup if Apache was built with SNI but isn’t finding the right openssl libraries at run-time.)

Setting up SNI with Apache

The configuration is pretty simple and straight forward, though I recommend making a backup of your existing httpd.conf file before proceeding.

# Ensure that Apache listens on port 443
Listen 443

# Listen for virtual host requests on all IP addresses
NameVirtualHost *:443

# Go ahead and accept connections for these vhosts
# from non-SNI clients
SSLStrictSNIVHostCheck off

# Because this virtual host is defined first, it will
# be used as the default if the hostname is not received
# in the SSL handshake, e.g. if the browser doesn't support
# SNI.
DocumentRoot /www/example2

# Other directives here
SSLEngine On
SSLCertificateFile /path/to/
SSLCertificateKeyFile /path/to/
SSLCertificateChainFile /path/to/CA.crt

DocumentRoot /www/example2

# Other directives here
SSLEngine On
SSLCertificateFile /path/to/
SSLCertificateKeyFile /path/to/
SSLCertificateChainFile /path/to/CA.crt


That it!!!. Just restart APache service. Now go and check your Websites using https. That should be working.

Plesk support SNI from 10.2.x version onwards.

SNI will work on following Operating systems out of box

OpenSuSE Linux 11.3 or later.
Ubuntu Linux 10.4 or later.
Debian Linux 6.0 or later.
RedHat Linux 6.0 or later.
CentOS Linux 60.0 or later

Supported Desktop Browsers
Internet Explorer 7 and later
Firefox 2 and later
Opera 8 with TLS 1.1 enabled
Google Chrome:
Supported on Windows XP on Chrome 6 and later
Supported on Vista and later by default
OS X 10.5.7 in Chrome Version 5.0.342.0 and later
Chromium 11.0.696.28 and later
Safari 2.1 and later (requires OS X 10.5.6 and later or Windows Vista and later).
Note: No versions of Internet Explorer on Windows XP support SNI


Simple BIND DNS server


This is simple BIND dns server setup. You can use this for a reference. Yes, it will work because i have tested in real dedicated servers.


If the DNS daemon is not installed on your server, installing it is very simple. Using the built in package manager “YUM” (YellowDog Updater Modified) you can install the DNS daemon with “yum install bind”. The resulting screen will appear something like the below image, type “y” to continue the installation.

Yum Bind


Configuration Files

There are very few files for the BIND daemon configuration that the user will need to modify. First is the main configuration file which is referred to as named.conf and is found in the /etc directory. The other file you will need to address is the zone file for your specific domain. These files are normally located in /var/named and have filenames like

Let’s start with the named.conf file. Using your favorite editor (if you do not have one I recommend nano as a simple text editor) open the file for editing. An example of this command using nano would be “nano /etc/named.conf”. This file can contain hundreds of options and settings, but we’re only going to concern ourselves with a select few for this configuration.

For security we will disable recursion. This is important due to spoofed DNS queries to DNS servers which allow recursion used to attack/overload a remote DNS host. So find the line that contains “recursion” and change the “yes” to “no”. This line will be in the options section, but if you cannot locate the line, use the “CTRL+W” key command to locate where the line is.

In this same section we also want to change the “listen-on” line. By default the server only listens on its local loopback port. The IP address “” for IPv4 and “::1” for IPv6 is already entered into this line, remove these loopback addresses and enter your IP address or “” for IPv4 and “::” for IPv6. These changes will allow your publically accessible IP addresses to respond to DNS queries. The last line in this section that must be changed is the “allow-query” line. The default setting is to not allow other hosts to query your DNS server. Change the word “localhost” in this line to “” to allow anyone to query your server for the DNS information regarding the domains you host on the server.

You’re not finished with this file yet. You need to add an entry to tell the DNS server to load the zone file for the domain you want to host. Use the down arrow to move to the last line of the file and hit enter once or twice.

You are going to enter these lines, replacing “yourdomain.tld” with your domain name. For example replace “yourdomain.tld” with “”. Do not put a www or mail or any other text in front of the domain name, those are hostnames or subdomains are not configured in this file.

zone “yourdomain.tld” {
type master;
file “/var/named/yourdomain.tld.db”;
notify yes;
allow-transfer { Slave-DNS-Server; };

The line that begins with “notify” and the line that follows only apply if you are using a slave DNS server and should be omitted if you are hosting your DNS on a single server. However, I must mention that a single server DNS configuration is not recommended.

Save this file with “CTRL+O” and exit the file with CTRL+X”.


Create DNS Zone File for Your Domain

Now you need to create the file that the configuration in /etc/named.conf pointed to. This file also has a very specific structure and syntax. The file you want to create will be in the /var/named directory. To create the file and edit it all at once type “/var/named/yourdomain.tld.db” replacing the “yourdomain.tld” as you did when entering the data in the named.conf file.

After you open the new file it will be empty. The contents of the file will be grouped by purpose, the first section is information for the DNS server to manage the DNS zone’s status, configuration and updates.

$TTL 86400 ; Time To Live before remote DNS server removes stale records from cache
@ IN SOA ns1.yourdomain.tld. useremail.yourdomain.tld. ( ; Responsible name server and responsible email address without the “@” symbol.

1123161063 ; serial number
10800 ; refresh (3 hours)
3600 ; retry (1 hour)
604800 ; expire (1 week)
3600 ; minimum (1 hour)

The above text is the first section of the file. The text in red can be left out or copied into teh file, that text is descriptive as to what the items is. Some further explanation is:

TTL – This is the time a remote DNS server will hold a record in its cache before refreshing the cache for a new record when requested again. Shorten this number to make frequent changes or a week before a major change to propagate changes quickly. Increase this number to reduce overall load on the server and allow remote DNS servers to provide data from cache and not query the server as frequently.

SOA – “Start of Authority” record. This is a specific record type used to provide responsible server and persons data.

Serial Number – This number tacks zone file versions among multiple primary/secondary DNS servers.

The remaining numbers tell the DNS servers when to refresh or expire records, and can safely be left at the default setting.

The next records that must be added to the zone file are the NS records to provide the name server data to querying clients. The NS records will look like this:

IN NS ns1.yourdomain.tld.
IN NS ns2.yourdomain.tld.

Please make note of the “.” (dot) behind records that contain hostnames. This is an important item throughout the files. These nameserver (NS) records generally match the nameserver records you create with your registrar and must contain valid hostnames that are valid “A” records within the domain they refer to. Additionally these nameservers referred to in these lines must host your domain.

The next record you should insert into the file is the MX record which identifies the Mail Exchanger (MX) host for your domain. This record should appear like this:

IN MX 10 mail.yourdomain.tld.

The hostname you use for this record must be a valid “A” record or “CNAME” record in the domain and should respond to email transfers for your domain.

Now we begin the main record portion of the file. The records you will now enter refer to hosts within the domain. Here is an example of some of the records you may enter:

mail IN A
www  IN CNAME yourdomain.tld.
ns1  IN A
ns2  IN A

After you look over these lines I want to point out a few items.

  • The “A” records for the “NS” records above are created here.
  • The “A” record for the “MX” record above is created here.
  • The “A” record for requests which contain no hostname is the first in the list.
  • The other “A” records are miscellaneous records for hostname that are common.

Once the records are entered, save this file with “CTRL+O” and exit the file with CTRL+X”.


Applying The New Configuration

Now that all of the data is entered for your domain simply applying these changes should activate the DNS zone on your server. To apply the changes restarting the DNS daemon is required. Use this command to restart the daemon:

“service named restart”

The textual output on the server should indicate success or failure. If success is indicated there is only one last item to check and that is the firewall rules to ensure the client queries will be allowed. Use this command to query the firewall rules for UDP port 53 access:

“iptables -vnL | grep 53″

The server should respond with a line similar to this:

”   0     0 ACCEPT     udp  —  *      *             state NEW udp dpt:53″

If this response is not received please review your IPtables rules to make changes to allow the queries.





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