Howto Disable Firewall (iptables) in Linux (Redhat/Fedora/CentOS)

You can run the following to stop iptables from running, by default on Redhat Entrprise Linux 4 and 5, Fedora, and CentOS the firewall is enabled:

chkconfig iptables off
service iptables save
service iptables stop

Filed under: Uncategorized by — aaron @ 12:49 am

XenServer VM/VPS Will Not Reboot/How to force a shutdown

We have had an issue on a number of occasions where a VPS will not shutdown while using XenCenter, and just appears to freeze.  Even using the xe vm-shtudown command via the console does not work.

If you are having this issue you can run the following command:

xe vm-shutdown vm=[uuid] --force

Filed under: Uncategorized by — aaron @ 12:47 am

How to find out which processes are using RAM in Linux?

An easy quick way to find out which processes are using RAM in linux is the following:

top -c

Then

Shift + M

This will list the top processes using the most RAM.

Filed under: Uncategorized by — aaron @ 12:46 am

How to install Sendmail on a new server?

yum install sendmail

If you are getting the following error in /var/log/maillog while sending an email
————————–
Dec 4 09:01:28 servername sendmail[12467]: iA4H1SCV012467: to=whoever@domain.com, ctladdr=whatever
(whatever/groupid), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30059, relay=[127.0.0.1]
[127.0.0.1], dsn=4.0.0, stat=Deferred: Connection refused by [127.0.0.1]
——————————-

1) Make sure that 127.0.0.1 is listed in /etc/mail/access and /etc/hosts.

2) In the file /etc/mail/sendmail.mc comment out the line below by prepending it with ‘dnl”,like

dnl DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA’)

3 Rebuild sendmail.cf

m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

4)Restart sendmail

service sendmail restart

While rebuilding, some times we may encounter the following error:
=======================
/etc/mail/sendmail.mc:10: m4: cannot open `/usr/share/sendmail-cf/m4/cf.m4′: No such file or directory
======================
Then

>> yum install sendmail-cf

After that repeat, step 3 and 4. Now try to send mail using “mail -v” and it should work fine.

Thanks Gopi for this article!

Filed under: Uncategorized by — aaron @ 12:44 am

VMware ESXi/CentOS: Your cpu does not support long mode. Use a 32bit distribution.

If you receive the following error while you are installing CentOS on VMware ESXi:

Your cpu does not support long mode. Use a 32bit distribution.

Then you probably need to enable Intel VT (virtualization) or AMD-v in the BIOS.

If you are still having problems, make sure you have Paravirtualization disabled (VMI) as this is only supported by 32-bit guests.

Filed under: Uncategorized by — aaron @ 12:42 am