Disable IPv6 on CentOS 6

To disable IPv6 on CentOS 6, run the following commands:

echo 'net.ipv6.conf.all.disable_ipv6 = 1' >> /etc/sysctl.conf
echo 'net.ipv6.conf.default.disable_ipv6 = 1' >> /etc/sysctl.conf
echo 'NETWORKING_IPV6=no' >> /etc/sysconfig/network

Clearing Auditlog/Auditlog

From time to time, these tables gets pretty big, it is recommended to clear them once a week:

tabprune eventlog -a
tabprune auditlog -a

Also, it is recommended to create a cron job that will do it automatically:

crontab -e
00 00 * * Sun /opt/xcat/sbin/tabprune auditlog -a
00 00 * * Sun /opt/xcat/sbin/tabprune eventlog -a

Backup and Restore xCAT DB

To backup the current xCAT database, run the following command:

dumpxCATdb -p /path/to/save/xcatdb

To restore the database, use the following command:

restorexCATdb -p /path/where/xcatdb/was/saved

Install ClusterSSH on CentOS 6

ClusterSSH is a tool to control multiple machines using ssh at the same time, basically it opens a few xterm windows and what ever you type is being typed at all the windows. 

1. Download and install EPEL repository:

yum install -y http://mirror.nonstop.co.il/epel/6/i386/epel-release-6-8.noarch.rpm

2. Install ClusterSSH using Yum:

yum install clusterssh -y

3. Create a file named clusters in /etc/:

vi /etc/clusters
clusters = clusternameclustername = hostname1 hostname2 hostname3

4. At the terminal, execute the following command:

cssh clustername

CUPS: Usage

Some basic commands that enable us to print and maintain our CUPS server and printers

• lpq -a - Shows the queued jobs for all printers.
• lpq -Pprintername - Shows the queued jobs for a specific printer.
• lprm X - Deletes a specific print job.
• lprm - - Deletes all print jobs.
• lpr - Send a file to printer.
• lpr -Pprintername - Send a file to a non default printer.
• lpc status all - Shows the state of the printers.
• lpmove # printer - Move a specific job to an other printer
• lpmove printer1 printer2 - Move all jobs from one printer to an other.
• cupsaccept - Enable the printing queue.
• cupsreject - Disable the printing queue.
• cupsenable - Enable the printer.
• cupsdisable - Disable the printer, will still send to queue.
• cupsdisable -r XXXX - Disable the printer with a reason.

Dennis.

CUPS: 426 Upgrade Required

After installing cups on my CentOS server, I noticed that when trying to add a printer I encountered an error that said "426 Upgrade Required".

As you'll probably notice, the new address that is supplied for you contains https://, incase you don't want to use SSL certification you can disable it by adding a line to /etc/cups/cupsd.conf :

DefaultEncryption Never

Dennis.

CUPS: Web GUI

In order to access cups web GUI from an other computer, there is a need to edit /etc/cups/cupsd.conf:


# Only listen for connections from the local machine.
Listen localhost:631 # You can configure wich interface to listen to
Listen /var/run/cups/cups.sock

# Restrict access to the server...
<Location />
  Order allow,deny
  Allow 192.168.1.0/24 # Add this line and specify your network/hostname or ip.
</Location>

# Restrict access to the admin pages...
<Location /admin>
  Order allow,deny
  Allow 192.168.1.0/24 # Add this line and specify your network/hostname or ip.
</Location>

Dennis.