You need to use the dd command to create swap file. The mkswap command is used to set up a Linux swap area on a device or in a file.
a) Login as the root user.
b) Type following command to create 512MB swap file (1024 * 512MB = 524288 block size):
# dd if=/dev/zero of=/swapfile1 bs=1024 count=524288
c) Set up a Linux swap area:
# mkswap /swapfile1
d) Activate /swapfile1 swap space immediately:
# swapon /swapfile1
e) To activate /swapfile1 after Linux system reboot, add entry to /etc/fstab file. Open this file using a text editor such as vi:
# vi /etc/fstab
Append the following line:
/swapfile1 swap swap defaults 0 0
So next time Linux comes up after reboot, it enables the new swap file for you automatically.
g) How do I verify swap is activated or not?
Simply use the free command:
$ free -m
Wednesday, March 28, 2012
* How to replace Apache with Lighttpd on Cpanel
Lighttpd is another free webserver that is becoming more popular due to it's performance boosts over Apache and thus improving the overall server performance. This guide will show you how it's possible to replace Apache with Lighttpd while running CPanel.
Things to do prior to making the switch:
1. Make sure to recompile Apache with fastcgi support. This can be done via WHM --> Apache Configuration.
2. This setup is better for servers with a few large sites than a host with many smaller sites as a Shared host would have. If Apache is working fine, there is no need to do this.
3. If you need to have sites with SSL enabled, it will be a little trickier and will not be covered in this how-to. You can reference this link for more details:
http://redmine.lighttpd.net/wiki/1/DocsSL
4. When creating accounts after making the switch to Lighttpd, you will still use the Create Account feature, but since httpd will not be running, you will have to manually add the virtual host details to the lighttpd.conf file or hosts.conf as we will have in this example.
Step 1
Download and compile Lighttpd:
1. First get the source from www.lighttpd.net and follow the instructions there.
2. To configure: ./configure --with-openssl --with-zlib --with-bzip2 --with-memcache
NOTE: may need to install pcre-devel (yum install pcre-devel)
3. Follow the instructions here to get lighttpd configured after the install: http://redmine.lighttpd.net/projects...tallFromSource You may need to change the path in /etc/init.d/lighttpd file to /usr/local/sbin/lighttpd for it to start.
4. Configure the lighttpd.conf file in /etc/lighttpd/. Example of a working lighttpd.conf:
Code:
server.modules = ( "mod_fastcgi", "mod_rewrite", "mod_dirlisting", "mod_auth", "mod_setenv", "mod_status" )
server.document-root = "/usr/local/apache/htdocs"
server.errorlog = "/etc/lighttpd/error.log"
server.username = "nobody"
server.groupname = "nobody"
index-file.names = ( "index.html", "index.htm", "index.php" )
server.tag = "Web Services"
status.status-url = "/lighttpd-status"
static-file.exclude-extensions = ( ".php", ".pl", ".fcgi" )
server.port = 80
include "includes/mime.conf"
include "includes/optimizations.conf"
include "includes/php.conf"
include "includes/hosts.conf"
You can get the server.document-root from the existing httpd.conf file for Apache for the main VirtualHost.
5. In the /etc/lighttpd directory, create the includes directory:
Code:
mkdir includes
and create the mime.conf, optimizations.conf, php.conf and hosts.conf files in the includes directory. Chmod them to 644:
Code:
chmod -R 644 includes
run this command within the /etc/lighttpd directory.
6. Now we need to populate the created conf files that lighttpd will load upon startup.
mime.conf:
Code:
mimetype.assign = (
".pdf" => "application/pdf",
".sig" => "application/pgp-signature",
".spl" => "application/futuresplash",
".class" => "application/octet-stream",
".ps" => "application/postscript",
".torrent" => "application/x-bittorrent",
".dvi" => "application/x-dvi",
".gz" => "application/x-gzip",
".pac" => "application/x-ns-proxy-autoconfig",
".swf" => "application/x-shockwave-flash",
".tar.gz" => "application/x-tgz",
".tgz" => "application/x-tgz",
".tar" => "application/x-tar",
".zip" => "application/zip",
".mp3" => "audio/mpeg",
".m3u" => "audio/x-mpegurl",
".wma" => "audio/x-ms-wma",
".wax" => "audio/x-ms-wax",
".ogg" => "application/ogg",
".wav" => "audio/x-wav",
".gif" => "image/gif",
".jpg" => "image/jpeg",
".jpeg" => "image/jpeg",
".png" => "image/png",
".xbm" => "image/x-xbitmap",
".xpm" => "image/x-xpixmap",
".xwd" => "image/x-xwindowdump",
".css" => "text/css",
".html" => "text/html",
".htm" => "text/html",
".js" => "text/javascript",
".asc" => "text/plain",
".c" => "text/plain",
".cpp" => "text/plain",
".log" => "text/plain",
".conf" => "text/plain",
".text" => "text/plain",
".txt" => "text/plain",
".dtd" => "text/xml",
".xml" => "text/xml",
".mpeg" => "video/mpeg",
".mpg" => "video/mpeg",
".mov" => "video/quicktime",
".qt" => "video/quicktime",
".avi" => "video/x-msvideo",
".asf" => "video/x-ms-asf",
".asx" => "video/x-ms-asf",
".wmv" => "video/x-ms-wmv",
".bz2" => "application/x-bzip",
".tbz" => "application/x-bzip-compressed-tar",
".tar.bz2" => "application/x-bzip-compressed-tar",
"" => "application/octet-stream"
)
optimizations.conf:
Code:
server.event-handler = "linux-sysepoll"
server.max-fds = 32768
server.network-backend = "linux-sendfile"
server.max-connections = 8192
server.max-keep-alive-requests = 15
server.max-keep-alive-idle = 15
server.max-read-idle = 15
server.max-write-idle = 15
server.max-worker = 1
The 'server.max-worker' variable should be changed according to how many CPUs the server has, and if it's a 64bit system. If it's a 32bit system, and the load stays low, keep it at 1. To get rid of keep-alive, set both of the keep-alive lines to 0. Max connections can be alterted to your needs
php.conf:
Code:
fastcgi.server = ( ".php" =>
( "localhost" =>
(
"socket" => "/tmp/php-fastcgi.socket-" + var.PID,
"bin-path" => "/usr/bin/php-cgi",
"max-procs" => 20,
"idle-timeout" => 10,
"bin-environment" => (
"PHP_FCGI_CHILDREN" => "20",
"PHP_FCGI_MAX_REQUESTS" => "500" ),
)
)
)
To get the bin-path, just run
Code:
whereis php-cgi
and that will show you the path. You have to compile Apache with fastcgi support first via WHM as mentioned previously. PHP can run as DSO/CLI still via WHM.
hosts.conf:
Code:
$HTTP["host"] =~ "^(www\.|)domain\.com$" {
server.document-root = "/home/domain/public_html/"
}
$HTTP["host"] =~ "^(www\.|)domain2\.com$" {
server.document-root = "/home/domain2/public_html/"
}
Adjust this file to your needs. Look at your Apache's httpd.conf file and setup each vhost using the above templates for each domain/subdomain you have in httpd.conf. If you wish to add logs to each domain, you can add the following lines to each one of the vhosts above between the {} brackets:
Code:
server.errorlog = "/var/log/lighttpd/domain/error.log"
accesslog.filename = "/var/log/lighttpd/domain/access.log"
server.error-handler-404= "/e404.php"
Now you should be all done with the main lighttpd configuration, so go ahead and turn it on:
Code:
/etc/init.d/lighttpd start
7. Now we need to turn off Apache so it does not start on boot or start by Cpanel. To do this, login to WHM and go to Service Manager, then uncheck both of the boxes for httpd. You can also run the following command to turn it off via shell:
Code:
chkconfig httpd off
This will ensure Apache won't start.
At this point, you should be running completely on lighttpd. Everything else in Cpanel/WHM will work as usual (mysql, dns, email, etc..). If you need to recompile php, you can do so via Apache Configuration, just be sure to turn off Apache again after you recompile.
source: http://forums.ayksolutions.com/showthread.php?p=829
Things to do prior to making the switch:
1. Make sure to recompile Apache with fastcgi support. This can be done via WHM --> Apache Configuration.
2. This setup is better for servers with a few large sites than a host with many smaller sites as a Shared host would have. If Apache is working fine, there is no need to do this.
3. If you need to have sites with SSL enabled, it will be a little trickier and will not be covered in this how-to. You can reference this link for more details:
http://redmine.lighttpd.net/wiki/1/DocsSL
4. When creating accounts after making the switch to Lighttpd, you will still use the Create Account feature, but since httpd will not be running, you will have to manually add the virtual host details to the lighttpd.conf file or hosts.conf as we will have in this example.
Step 1
Download and compile Lighttpd:
1. First get the source from www.lighttpd.net and follow the instructions there.
2. To configure: ./configure --with-openssl --with-zlib --with-bzip2 --with-memcache
NOTE: may need to install pcre-devel (yum install pcre-devel)
3. Follow the instructions here to get lighttpd configured after the install: http://redmine.lighttpd.net/projects...tallFromSource You may need to change the path in /etc/init.d/lighttpd file to /usr/local/sbin/lighttpd for it to start.
4. Configure the lighttpd.conf file in /etc/lighttpd/. Example of a working lighttpd.conf:
Code:
server.modules = ( "mod_fastcgi", "mod_rewrite", "mod_dirlisting", "mod_auth", "mod_setenv", "mod_status" )
server.document-root = "/usr/local/apache/htdocs"
server.errorlog = "/etc/lighttpd/error.log"
server.username = "nobody"
server.groupname = "nobody"
index-file.names = ( "index.html", "index.htm", "index.php" )
server.tag = "Web Services"
status.status-url = "/lighttpd-status"
static-file.exclude-extensions = ( ".php", ".pl", ".fcgi" )
server.port = 80
include "includes/mime.conf"
include "includes/optimizations.conf"
include "includes/php.conf"
include "includes/hosts.conf"
You can get the server.document-root from the existing httpd.conf file for Apache for the main VirtualHost.
5. In the /etc/lighttpd directory, create the includes directory:
Code:
mkdir includes
and create the mime.conf, optimizations.conf, php.conf and hosts.conf files in the includes directory. Chmod them to 644:
Code:
chmod -R 644 includes
run this command within the /etc/lighttpd directory.
6. Now we need to populate the created conf files that lighttpd will load upon startup.
mime.conf:
Code:
mimetype.assign = (
".pdf" => "application/pdf",
".sig" => "application/pgp-signature",
".spl" => "application/futuresplash",
".class" => "application/octet-stream",
".ps" => "application/postscript",
".torrent" => "application/x-bittorrent",
".dvi" => "application/x-dvi",
".gz" => "application/x-gzip",
".pac" => "application/x-ns-proxy-autoconfig",
".swf" => "application/x-shockwave-flash",
".tar.gz" => "application/x-tgz",
".tgz" => "application/x-tgz",
".tar" => "application/x-tar",
".zip" => "application/zip",
".mp3" => "audio/mpeg",
".m3u" => "audio/x-mpegurl",
".wma" => "audio/x-ms-wma",
".wax" => "audio/x-ms-wax",
".ogg" => "application/ogg",
".wav" => "audio/x-wav",
".gif" => "image/gif",
".jpg" => "image/jpeg",
".jpeg" => "image/jpeg",
".png" => "image/png",
".xbm" => "image/x-xbitmap",
".xpm" => "image/x-xpixmap",
".xwd" => "image/x-xwindowdump",
".css" => "text/css",
".html" => "text/html",
".htm" => "text/html",
".js" => "text/javascript",
".asc" => "text/plain",
".c" => "text/plain",
".cpp" => "text/plain",
".log" => "text/plain",
".conf" => "text/plain",
".text" => "text/plain",
".txt" => "text/plain",
".dtd" => "text/xml",
".xml" => "text/xml",
".mpeg" => "video/mpeg",
".mpg" => "video/mpeg",
".mov" => "video/quicktime",
".qt" => "video/quicktime",
".avi" => "video/x-msvideo",
".asf" => "video/x-ms-asf",
".asx" => "video/x-ms-asf",
".wmv" => "video/x-ms-wmv",
".bz2" => "application/x-bzip",
".tbz" => "application/x-bzip-compressed-tar",
".tar.bz2" => "application/x-bzip-compressed-tar",
"" => "application/octet-stream"
)
optimizations.conf:
Code:
server.event-handler = "linux-sysepoll"
server.max-fds = 32768
server.network-backend = "linux-sendfile"
server.max-connections = 8192
server.max-keep-alive-requests = 15
server.max-keep-alive-idle = 15
server.max-read-idle = 15
server.max-write-idle = 15
server.max-worker = 1
The 'server.max-worker' variable should be changed according to how many CPUs the server has, and if it's a 64bit system. If it's a 32bit system, and the load stays low, keep it at 1. To get rid of keep-alive, set both of the keep-alive lines to 0. Max connections can be alterted to your needs
php.conf:
Code:
fastcgi.server = ( ".php" =>
( "localhost" =>
(
"socket" => "/tmp/php-fastcgi.socket-" + var.PID,
"bin-path" => "/usr/bin/php-cgi",
"max-procs" => 20,
"idle-timeout" => 10,
"bin-environment" => (
"PHP_FCGI_CHILDREN" => "20",
"PHP_FCGI_MAX_REQUESTS" => "500" ),
)
)
)
To get the bin-path, just run
Code:
whereis php-cgi
and that will show you the path. You have to compile Apache with fastcgi support first via WHM as mentioned previously. PHP can run as DSO/CLI still via WHM.
hosts.conf:
Code:
$HTTP["host"] =~ "^(www\.|)domain\.com$" {
server.document-root = "/home/domain/public_html/"
}
$HTTP["host"] =~ "^(www\.|)domain2\.com$" {
server.document-root = "/home/domain2/public_html/"
}
Adjust this file to your needs. Look at your Apache's httpd.conf file and setup each vhost using the above templates for each domain/subdomain you have in httpd.conf. If you wish to add logs to each domain, you can add the following lines to each one of the vhosts above between the {} brackets:
Code:
server.errorlog = "/var/log/lighttpd/domain/error.log"
accesslog.filename = "/var/log/lighttpd/domain/access.log"
server.error-handler-404= "/e404.php"
Now you should be all done with the main lighttpd configuration, so go ahead and turn it on:
Code:
/etc/init.d/lighttpd start
7. Now we need to turn off Apache so it does not start on boot or start by Cpanel. To do this, login to WHM and go to Service Manager, then uncheck both of the boxes for httpd. You can also run the following command to turn it off via shell:
Code:
chkconfig httpd off
This will ensure Apache won't start.
At this point, you should be running completely on lighttpd. Everything else in Cpanel/WHM will work as usual (mysql, dns, email, etc..). If you need to recompile php, you can do so via Apache Configuration, just be sure to turn off Apache again after you recompile.
source: http://forums.ayksolutions.com/showthread.php?p=829
How to backup your linux VPS.
Backup script for vps
#!/bin/sh
####################################
#
# Backup to NFS mount script.
#
####################################
# What to backup.
backup_files="/"
# Where to backup to.
dest="/home/backup"
# Create archive filename.
day=$(date +%A)
hostname=$(hostname -s)
archive_file="$hostname-$day.tgz"
# Print start status message.
echo "Backing up $backup_files to $dest/$archive_file"
date
echo
# Backup the files using tar.
tar czf $dest/$archive_file $backup_files
# Print end status message.
echo
echo "Backup finished"
date
# Long listing of files in $dest to check file sizes.
ls -lh $dest
#!/bin/sh
####################################
#
# Backup to NFS mount script.
#
####################################
# What to backup.
backup_files="/"
# Where to backup to.
dest="/home/backup"
# Create archive filename.
day=$(date +%A)
hostname=$(hostname -s)
archive_file="$hostname-$day.tgz"
# Print start status message.
echo "Backing up $backup_files to $dest/$archive_file"
date
echo
# Backup the files using tar.
tar czf $dest/$archive_file $backup_files
# Print end status message.
echo
echo "Backup finished"
date
# Long listing of files in $dest to check file sizes.
ls -lh $dest
Wednesday, March 14, 2012
enable php function
1. Remove all functions from disable_functions in php.ini
2. Add functions in php.ini suhosin.executor.func.blacklist = “” those you want to disable globally.
After that in the virtual host section of a domain you can add below code to enable a function only for one domain:
………..
php_admin_value suhosin.executor.func.blacklist = “shell_exec”
……
In this example shell_exec has been enabled for the VirtualHost.
PS:virtual host settings will work only if suhosin is installed in the server
2. Add functions in php.ini suhosin.executor.func.blacklist = “” those you want to disable globally.
After that in the virtual host section of a domain you can add below code to enable a function only for one domain:
………..
php_admin_value suhosin.executor.func.blacklist = “shell_exec”
……
In this example shell_exec has been enabled for the VirtualHost.
PS:virtual host settings will work only if suhosin is installed in the server
Thursday, March 8, 2012
Install nginx
Login to SSH and do this
cd /usr/local/src
wget http://nginxcp.com/latest/nginxadmin.tar
tar xf nginxadmin.tar
cd publicnginx
./pythonfix
./nginxinstaller install
It's Done...... Now go to WHM and search for nginx, You will see it there
are you getting "502 Bad Gateway" error ?
here is the solution
go to WHM and search for "tweak settings"
open it and search for "Apache non-SSL" and set it to "0.0.0.0:8081"
cd /usr/local/src
wget http://nginxcp.com/latest/nginxadmin.tar
tar xf nginxadmin.tar
cd publicnginx
./pythonfix
./nginxinstaller install
It's Done...... Now go to WHM and search for nginx, You will see it there
are you getting "502 Bad Gateway" error ?
here is the solution
go to WHM and search for "tweak settings"
open it and search for "Apache non-SSL" and set it to "0.0.0.0:8081"
mass upload bash script (good for Megaupload)
#!/bin/bash
ftp -inv << FTP
open ftp.eu.filesonic.com
user USERNAME PASSWORD
lcd /YOUR/FOLDER/WITH/FILES
mput *.zip
bye
FTP
ftp -inv << FTP
open ftp.eu.filesonic.com
user USERNAME PASSWORD
lcd /YOUR/FOLDER/WITH/FILES
mput *.zip
bye
FTP
Wednesday, March 7, 2012
GRUB Commands
GRUB has a powerful command line option. All you have to do to start the command line is to use the command grub.
You can see a list of the possible commands by using the help.
PHP Code:
grub> help
blocklist FILE boot
cat FILE chainloader [--force] FILE
clear color NORMAL [HIGHLIGHT]
configfile FILE device DRIVE DEVICE
displayapm displaymem
find FILENAME geometry DRIVE [CYLINDER HEAD SECTOR [
halt [--no-apm] help [--all] [PATTERN ...]
hide PARTITION initrd FILE [ARG ...]
kernel [--no-mem-option] [--type=TYPE] makeactive
map TO_DRIVE FROM_DRIVE md5crypt
module FILE [ARG ...] modulenounzip FILE [ARG ...]
pager [FLAG] partnew PART TYPE START LEN
parttype PART TYPE quit
reboot root [DEVICE [HDBIAS]]
rootnoverify [DEVICE [HDBIAS]] serial [--unit=UNIT] [--port=PORT] [--
setkey [TO_KEY FROM_KEY] setup [--prefix=DIR] [--stage2=STAGE2_
terminal [--dumb] [--no-echo] [--no-ed terminfo [--name=NAME --cursor-address
testvbe MODE unhide PARTITION
uppermem KBYTES vbeprobe [MODE]
The displaymem command will show you what GRUB thinks is the system address space map of the machine. The lower memory is the address space in the first megabyte of memory.
PHP Code:
grub> displaymem
EISA Memory BIOS Interface is present
Address Map BIOS Interface is present
Lower memory: 640K, Upper memory (to first chipset hole): 3072K
[Address Range Descriptor entries immediately follow (values are 64-bit)]
Usable RAM: Base Address: 0x0 X 4GB + 0x0,
Length: 0x0 X 4GB + 0xa0000 bytes
Reserved: Base Address: 0x0 X 4GB + 0xa0000,
Length: 0x0 X 4GB + 0x60000 bytes
Usable RAM: Base Address: 0x0 X 4GB + 0x100000,
Length: 0x0 X 4GB + 0x300000 bytes
PHP Code:
grub> find /sbin/init
(hd0,1)
enter find ( and then tab
PHP Code:
grub> find (hd0,
Use the tab
PHP Code:
grub> find (hd0,
Possible partitions are:
Partition num: 0, Filesystem type is ext2fs, partition type 0x83
Partition num: 1, Filesystem type is ext2fs, partition type 0x83
Partition num: 2, Filesystem type is ext2fs, partition type 0x83
Partition num: 4, Filesystem type unknown, partition type 0x8e
Partition num: 5, Filesystem type unknown, partition type 0x8e
Disk /dev/hda: 8589 MB, 8589934592 bytes
255 heads, 63 sectors/track, 1044 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/hda1 * 1 13 104391 83 Linux
/dev/hda2 14 523 4096575 83 Linux
/dev/hda3 524 650 1020127+ 83 Linux
/dev/hda4 651 1044 3164805 5 Extended
/dev/hda5 651 663 104391 8e Linux LVM
/dev/hda6 664 676 104391 8e Linux LVM
grub> find /grub/menu.lst
(hd0,0)
PHP Code:
grub> find /sbin/init
(hd0,1)
You can see a list of the possible commands by using the help.
PHP Code:
grub> help
blocklist FILE boot
cat FILE chainloader [--force] FILE
clear color NORMAL [HIGHLIGHT]
configfile FILE device DRIVE DEVICE
displayapm displaymem
find FILENAME geometry DRIVE [CYLINDER HEAD SECTOR [
halt [--no-apm] help [--all] [PATTERN ...]
hide PARTITION initrd FILE [ARG ...]
kernel [--no-mem-option] [--type=TYPE] makeactive
map TO_DRIVE FROM_DRIVE md5crypt
module FILE [ARG ...] modulenounzip FILE [ARG ...]
pager [FLAG] partnew PART TYPE START LEN
parttype PART TYPE quit
reboot root [DEVICE [HDBIAS]]
rootnoverify [DEVICE [HDBIAS]] serial [--unit=UNIT] [--port=PORT] [--
setkey [TO_KEY FROM_KEY] setup [--prefix=DIR] [--stage2=STAGE2_
terminal [--dumb] [--no-echo] [--no-ed terminfo [--name=NAME --cursor-address
testvbe MODE unhide PARTITION
uppermem KBYTES vbeprobe [MODE]
The displaymem command will show you what GRUB thinks is the system address space map of the machine. The lower memory is the address space in the first megabyte of memory.
PHP Code:
grub> displaymem
EISA Memory BIOS Interface is present
Address Map BIOS Interface is present
Lower memory: 640K, Upper memory (to first chipset hole): 3072K
[Address Range Descriptor entries immediately follow (values are 64-bit)]
Usable RAM: Base Address: 0x0 X 4GB + 0x0,
Length: 0x0 X 4GB + 0xa0000 bytes
Reserved: Base Address: 0x0 X 4GB + 0xa0000,
Length: 0x0 X 4GB + 0x60000 bytes
Usable RAM: Base Address: 0x0 X 4GB + 0x100000,
Length: 0x0 X 4GB + 0x300000 bytes
PHP Code:
grub> find /sbin/init
(hd0,1)
enter find ( and then tab
PHP Code:
grub> find (hd0,
Use the tab
PHP Code:
grub> find (hd0,
Possible partitions are:
Partition num: 0, Filesystem type is ext2fs, partition type 0x83
Partition num: 1, Filesystem type is ext2fs, partition type 0x83
Partition num: 2, Filesystem type is ext2fs, partition type 0x83
Partition num: 4, Filesystem type unknown, partition type 0x8e
Partition num: 5, Filesystem type unknown, partition type 0x8e
Disk /dev/hda: 8589 MB, 8589934592 bytes
255 heads, 63 sectors/track, 1044 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/hda1 * 1 13 104391 83 Linux
/dev/hda2 14 523 4096575 83 Linux
/dev/hda3 524 650 1020127+ 83 Linux
/dev/hda4 651 1044 3164805 5 Extended
/dev/hda5 651 663 104391 8e Linux LVM
/dev/hda6 664 676 104391 8e Linux LVM
grub> find /grub/menu.lst
(hd0,0)
PHP Code:
grub> find /sbin/init
(hd0,1)
Understanding MX records
Notice the line with the ``MX'' in it. This is called the MX record.
mydomain.com. 14400 IN MX 0 mydomain.com.
The MX record shows that all emails @ mydomain.com should be routed to the mail server at mydomain.com. The DNS record shows that mydomain.com is located at 216.34.94.184. This means that email meant for liz@mydomain.com will be routed to the email server at 216.34.94.184. This finishes the task of the MX record. The email server on that server(say sendmail) then takes over, collects the email and then proceeds to distribute it to the user ``liz''.
It is important that there be a dot(``.'') after the domain name in the MX record. If the dot is absent, it routes to ``mydomain.com.mydomain.com''. The number 0, indicates Preferance number. Mail is always routed to the server which has the lowest Preferance number. If there is only one mail server, it is safe to mark it 0.
Multiple mail servers
Multiple email servers are useful for the sake of redundancy. If the Highest Priority email server (one with the lowest Preference number) is down, then the email is routed to the Server with the second highest Preference number.
For example
mydomain.com. 14400 IN A 216.34.94.184
server2.mydomain.com. 14400 IN A 216.34.94.185
mydomain.com. 14400 IN MX 0 mydomain.com.
mydomain.com. 14400 IN MX 30 server2.mydomain.com.
You can have unlimited MX entries for Fallback.
If all the MX records are equal Preference numbers, the client simply attempts all equal Preference servers in random order, and then goes to MX record with the next highest Preference number.
Pointing MX records to an IP
Its not possible to have an MX record pointing directly to an IP. For example 'mydomain.com. 14400 IN MX 0 216.34.94.184`` is wrong. Define an ``A Record'' first and then have the MX record pointing to it.
server2.mydomain.com. 14400 IN A 216.34.94.185
mydomain.com. 14400 IN MX 30 server2.mydomain.com.
MX records for Subdomains
A Subdomain is something like this ``Subdomain.mydomain.com''. Assume you want to send an email to liz@subdomain.mydomain.com and to capture that on another server.
mydomain.com. 14400 IN A 216.34.94.184
server2.mydomain.com. 14400 IN A 216.34.94.185
mydomain.com. 14400 IN MX 30 mydomain.com.
subdomain.mydomain.com. 14400 IN MX 30 server2.mydomain.com.
In this configuration, liz@subdomain.mydomain.com would go to 216.34.94.185 and liz@mydomain.com would go to 216.34.94.184.
Testing the MX record
Once you setup your MX record, always test it to see if it is setup correctly. You can do with tools like nslookup.
[root@localhost sangeetha]# nslookup
> set q=mx
> yahoo.com
Server: 192.168.1.1 Address: 192.168.1.1#53
Non-authoritative answer:
yahoo.com mail exchanger = 1 mx1.mail.yahoo.com.
yahoo.com mail exchanger = 1 mx2.mail.yahoo.com.
yahoo.com mail exchanger = 1 mx3.mail.yahoo.com.
yahoo.com mail exchanger = 5 mx4.mail.yahoo.com.
Authoritative answers can be found from:
yahoo.com nameserver = ns2.yahoo.com.
yahoo.com nameserver = ns3.yahoo.com.
yahoo.com nameserver = ns4.yahoo.com.
yahoo.com nameserver = ns5.yahoo.com.
yahoo.com nameserver = ns1.yahoo.com.
mx1.mail.yahoo.com internet address = 4.79.181.14
mx1.mail.yahoo.com internet address = 4.79.181.15
mx1.mail.yahoo.com internet address = 67.28.113.10
mx1.mail.yahoo.com internet address = 67.28.113.11
ns1.yahoo.com internet address = 66.218.71.63
ns2.yahoo.com internet address = 66.163.169.170
ns3.yahoo.com internet address = 217.12.4.104
ns4.yahoo.com internet address = 63.250.206.138
ns5.yahoo.com internet address = 216.109.116.17
>
How spammers read your MX
Spammers will typically target your lowest priority Email servers, in the hopes of encountering a poorly configured box. The Spam program reads the MX records, locates the Email server with the lowest Priority(highest Preference number) and attempts to spam with that server.
So it is important to equally update all your email servers with Antivirus and Antispam.
mydomain.com. 14400 IN MX 0 mydomain.com.
The MX record shows that all emails @ mydomain.com should be routed to the mail server at mydomain.com. The DNS record shows that mydomain.com is located at 216.34.94.184. This means that email meant for liz@mydomain.com will be routed to the email server at 216.34.94.184. This finishes the task of the MX record. The email server on that server(say sendmail) then takes over, collects the email and then proceeds to distribute it to the user ``liz''.
It is important that there be a dot(``.'') after the domain name in the MX record. If the dot is absent, it routes to ``mydomain.com.mydomain.com''. The number 0, indicates Preferance number. Mail is always routed to the server which has the lowest Preferance number. If there is only one mail server, it is safe to mark it 0.
Multiple mail servers
Multiple email servers are useful for the sake of redundancy. If the Highest Priority email server (one with the lowest Preference number) is down, then the email is routed to the Server with the second highest Preference number.
For example
mydomain.com. 14400 IN A 216.34.94.184
server2.mydomain.com. 14400 IN A 216.34.94.185
mydomain.com. 14400 IN MX 0 mydomain.com.
mydomain.com. 14400 IN MX 30 server2.mydomain.com.
You can have unlimited MX entries for Fallback.
If all the MX records are equal Preference numbers, the client simply attempts all equal Preference servers in random order, and then goes to MX record with the next highest Preference number.
Pointing MX records to an IP
Its not possible to have an MX record pointing directly to an IP. For example 'mydomain.com. 14400 IN MX 0 216.34.94.184`` is wrong. Define an ``A Record'' first and then have the MX record pointing to it.
server2.mydomain.com. 14400 IN A 216.34.94.185
mydomain.com. 14400 IN MX 30 server2.mydomain.com.
MX records for Subdomains
A Subdomain is something like this ``Subdomain.mydomain.com''. Assume you want to send an email to liz@subdomain.mydomain.com and to capture that on another server.
mydomain.com. 14400 IN A 216.34.94.184
server2.mydomain.com. 14400 IN A 216.34.94.185
mydomain.com. 14400 IN MX 30 mydomain.com.
subdomain.mydomain.com. 14400 IN MX 30 server2.mydomain.com.
In this configuration, liz@subdomain.mydomain.com would go to 216.34.94.185 and liz@mydomain.com would go to 216.34.94.184.
Testing the MX record
Once you setup your MX record, always test it to see if it is setup correctly. You can do with tools like nslookup.
[root@localhost sangeetha]# nslookup
> set q=mx
> yahoo.com
Server: 192.168.1.1 Address: 192.168.1.1#53
Non-authoritative answer:
yahoo.com mail exchanger = 1 mx1.mail.yahoo.com.
yahoo.com mail exchanger = 1 mx2.mail.yahoo.com.
yahoo.com mail exchanger = 1 mx3.mail.yahoo.com.
yahoo.com mail exchanger = 5 mx4.mail.yahoo.com.
Authoritative answers can be found from:
yahoo.com nameserver = ns2.yahoo.com.
yahoo.com nameserver = ns3.yahoo.com.
yahoo.com nameserver = ns4.yahoo.com.
yahoo.com nameserver = ns5.yahoo.com.
yahoo.com nameserver = ns1.yahoo.com.
mx1.mail.yahoo.com internet address = 4.79.181.14
mx1.mail.yahoo.com internet address = 4.79.181.15
mx1.mail.yahoo.com internet address = 67.28.113.10
mx1.mail.yahoo.com internet address = 67.28.113.11
ns1.yahoo.com internet address = 66.218.71.63
ns2.yahoo.com internet address = 66.163.169.170
ns3.yahoo.com internet address = 217.12.4.104
ns4.yahoo.com internet address = 63.250.206.138
ns5.yahoo.com internet address = 216.109.116.17
>
How spammers read your MX
Spammers will typically target your lowest priority Email servers, in the hopes of encountering a poorly configured box. The Spam program reads the MX records, locates the Email server with the lowest Priority(highest Preference number) and attempts to spam with that server.
So it is important to equally update all your email servers with Antivirus and Antispam.
How to enable quotas on an ext4 file system. Centos 6 (Works with WHM
If you are receiving the following error when trying to enable quotas in WHM:
========
quotacheck: Cannot find filesystem to check or filesystem not mounted with quota option
=======
You should first try doing both of the following via SSH:
/scripts/fixquotas
/scripts/fixcommonproblems
Then try to enable quotas, if the error is still occurring you may need to edit your fstab file, this can be tricky. First you will need to run:
vi /etc/fstab
Then you will need to locate where your directories are mounted on. For example, if you have this line:
/dev/mapper/vg-root / ext4 discard,noatime 1 1
You will need to replace it with:
/dev/mapper/vg-root / ext4 discard,noatime,usrquota 1 1
You should now reboot your system and once booted go into WHM and click Enable Quotas or run:
/scripts/fixquotas
========
quotacheck: Cannot find filesystem to check or filesystem not mounted with quota option
=======
You should first try doing both of the following via SSH:
/scripts/fixquotas
/scripts/fixcommonproblems
Then try to enable quotas, if the error is still occurring you may need to edit your fstab file, this can be tricky. First you will need to run:
vi /etc/fstab
Then you will need to locate where your directories are mounted on. For example, if you have this line:
/dev/mapper/vg-root / ext4 discard,noatime 1 1
You will need to replace it with:
/dev/mapper/vg-root / ext4 discard,noatime,usrquota 1 1
You should now reboot your system and once booted go into WHM and click Enable Quotas or run:
/scripts/fixquotas
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