Blogs

The "H" option in both ps and top lists the threads:

Examples:

For port redirection to work inside OpenVZ containers, ipt_REDIRECT kernel module needs to be loaded in the host. Edit "/etc/sysconfig/vz" and add it to the IPTABLES list.

This should then allow to redirect ports. So if you need to proxy existing apache via nginx or lighttpd and you do not want to switch apaches' default port 80, then the below rules will do the appropriate redirection to port 81 where nginx/lighttpd server is listening, serving static content and proxying to apache for dynamic content:

Where 192.168.10.2 is the internal IP resolver of domain/host.

If you are switching out static content that have gotten cached in nginx, the head of the cached files usually stores the file path that can be greped for and the file removed. One you hit the url again, it will recreate the new cached file at the same location.

Below are one liners to clean out all comment and blank lines with grep and sed, usually in config files.

or

If you notice that /etc/shadow file password is using DES encryption, MD5 encryption can be enabled via:

If authconfig is not present edit, "/etc/pam.d/system-auth" and add "md5 shadow" to line starting with "password sufficient pam_unix.so" so it looks like below:

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":