sandip's blog

Below is how I have migrated mail server with minimum downtime and routing mail to the new server via mailertable, if IP is still pointing to the old server and has not resolved for some ISPs.

• 48 hours prior to migration, set the TTL value for the mail server DNS A record to a short time like 15 minutes.
  
• Prepare for the migration, rsycing the mail spool folder and the user home mail folders.
  
  rsync --progress -a -e "ssh -i /root/.ssh/key -p 22" old.mailserver:/var/spool/mail/ /var/spool/mail/
rsync --progress -a -e "ssh -i /root/.ssh/key -p 22" old.mailserver:/var/www/web1/mail/ /var/www/web1/mail/
rsync --progress -a -e "ssh -i /root/.ssh/key -p 22" --exclude='*/bak' --exclude='*/web' old.mailserver:/var/www/web1/user/ /var/www/web1/user/
• At the time of migration, firewall incoming port 25 on the old mail server and update the DNS A record to point to the new server.
  
• Run rsync the final time.
  
• Setup Sendmail with mailertable to relay mail coming in to the old server over to the new mail server. This is a similar setup for secondary mail servers.
  
• Add "FEATURE(`mailertable', `hash -o /etc/mail/mailertable.db')dnl" to "/etc/mail/sendmail.mc" if it does not already exist.
  
• Create "/etc/mail/mailertable" file with contents of the routing table:
  
  domain.tld esmtp:[xxx.xxx.xxx.xxx]
  
  The square brackets skips checking MX records, so IP can be used instead.
• Remove domain name from "/etc/mail/local-host-names" so mails do not get delivered locally.
  
• Edit "/etc/mail/access" to relay mail for the domain.
  
  TO:domain.tld RELAY
• Rebuild the access and mailertable databases.
  
  cd /etc/mail
makemap hash access.db < access
makemap hash mailertable.db < mailertable
• Restart sendmail and open up the firewall.
  
• Test by telneting to port 25 on the old servers' IP and sending email. This should get relayed over to the new server.
  
• Use a new subdomain and redirect existing webmail url to the new server.

If you've just made any changes to the nameservers, you can verify if this has propagated at the root level.

Check root servers for the corresponding tld first. So for .com domains:

The output is as below:

Now query the root servers for the corresponding domain:

The additional section from the result with the IP address show the glue records.

Try setting up ssh client with compression and use arcfour/blowfish encryption instead. Also avoid ipv6 lookup and reuse connections using
socket:

Add below to ~/.ssh/config

In order to extend an lvm partition, I had to unmount the mounted volume.

When I tried to umount the volume, it complained about device being busy.

When I tried to find the process using the device with, `fuser -m /dev/vg0/lv0` it returned nothing. So did a lazy umount with:

However, after extending the partition with lvextend and running e2fsck on the volume, it then complained that the device was still busy and failed to check the volume.

I then realized that most probably caused by nfs mounts. Once I stopped the nfs service, I was successfully able to check the volume.

Current versions of vzdump has dependency for cstream and perl-LockFile-Simple, both available via rpmforge. Below is how I got it to install and run on CentOS-5.5 x86_64 architecture.

It's necessary to export the location of the PVE libraries that vzdump requires. This can be added to ".bash_profile":

Below is command to run process with the least CPU and IO priority.

You could also include the same in the beginning of the script:

References:

• Using ionice
  
• Avoid Sudden I/O Outburst

On CentOS, php-fpm can be easily installed via CentALT yum repository. This requires epel repository too and will pull down any dependencies if needed.

• Install EPEL release:
  
  rpm -Uvh http://download.fedora.redhat.com/pub/epel/5/x86_64/epel-release-5-3.noarch.rpm
• Install CentALT release:
  
  rpm -Uvh http://centos.alt.ru/repository/centos/5/x86_64/centalt-release-5-3.noarch.rpm
• Install via yum:
  
  yum --enablerepo=CentALT --enablerepo=epel install php-fpm
• Look through and edit /etc/php-fpm.conf . The config options are well commented... also available at php-fpm.org
  
• The default settings should work quite well.
  
• Bring up the service via:
  
  /etc/init.d/php-fpm start

Below is a sample expect script to handle ssh password prompt should you not get the ssh keys to be working between hosts:

blkid can be used to display the swap label:

Below is a list of smartctl commands I frequently use to quickly verify disk health and status, specially when you have smartd logging errors to messages log file.

• Print all SMART (Self-Monitoring, Analysis and Reporting Technology) information for drive /dev/sda (Primary Master).
  smartctl -a /dev/sda

• Enable SMART on device.
  smartctl --smart=on /dev/sda

• Get info about the device:
  smartctl -i /dev/sda

• Show the capabilities of drive. Also provides status when tests are being carried out.
  smartctl -c /dev/sda

• Basic health status:
  smartctl -H /dev/sda

• Display attributes. The attributes to look out for failing disk is Reallocated_Sector_Ct, Reallocated_Event_Count, Current_Pending_Sector and Offline_Uncorrectable. Their RAW_VALUE should normally be "0".
  smartctl -A /dev/sda

• Immediate offline test which updates attributes value. Good to run after a badblocks fsck check before checking on the attributes values.
  smartctl -t offline /dev/sda

• Run a thorough long test if you see suspect attributes with -A option as mentioned above.
  smartctl -t long /dev/sda

• Examine self-test log. Shows if tests failed or passed.
  smartctl -l selftest /dev/sda

• Display most recent error log.
  smartctl -l error /dev/sda

There are more examples in man smartctl.