Change timezone in CentOS/Red Hat Linux (RHEL)/Fedora

Edit /etc/sysconfig/clock.
Change ZONE line to your preferred time zone. You can see a list of time zones listed under /usr/share/zoneinfo/.

For example, to use the Los Angeles time zone listed under /usr/share/zoneinfo/America/Los_Angeles:
ZONE=”America/Los_Angeles”.

Run the following command:
tzdata-update

Run the data command to make sure that the changes you made took affect.
# date
Wed Jan 29 16:46:43 PST 2014

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Flushing Cache in Memcache

If you’re using a web application with Memcache, you may find that when resorting data (whether application files or database), you may run into strange erorrs when bringing your application back online. For example, errors regarding missing application classes or missing database tables. The resolution is to clear out your Memcache cache.

Telnet to your Memcache server. For example, if your Memcache instance is located on the local server, you can Telnet to it as such –
telnet 127.0.0.1 11211

Then, issue the flush_all command –
flush_all

You should get the following returned status –
OK

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Postfix as a local relay

This can be used for situations where you have an internet facing machine (web server) and back-end machines (application server, database server, etc.).

In our examples, we’ll assume the following:
Internet facing web server IP is 192.168.1.2
Back-end database IP is 192.168.1.3
Back-end database IP is 192.168.1.4

On your Internet facing machine, edit /etc/postfix/main.cf and add your back-end server IP’s to your mynetworks section or add a new one. For example:
mynetworks = 127.0.0.0/8, 192.168.1.3, 192.168.1.4

On each back-end machine, add the following to /etc/postfix/main.cf:
relayhost = 192.168.1.2

Try sending an email using mailx. You should see the following in your mail log on each back-end server (Notice the relay line):
ADA08211D5: to=, relay=192.168.1.2[192.168.1.2]:25, delay=0.18, delays=0.05/0.02/0.09/0.01, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as CF54E21217)

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Upgrade to CentOS 5.9


yum clean all
yum -y upgrade glibc* yum* rpm* python*
yum -y upgrade

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RHEL 6.4 Beta

Red Hat has announced the availability of RHEL 6.4 Beta.

Interesting New Changes

  • pNFS (Parallel NFS)
  • Swap on NFS
  • Hyper-V Drivers
  • VMware and Microsoft Hyper-V para-virtualization drivers
  • KVM virtualization virtio-scsi support

RHEL 6.4 Beta Release Notes
RHEL 6.4 Beta Technical Notes

At this rate, RHEL 6.4 should be released around Q1 of 2013.

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vSphere 5.1 changes

San Diego Linux’s favorite blogger, Vladen Seget, has posted an informative article with a nice breakdown about the license changes in VMware Vsphere 5.1 with a highlight on the free version of ESXi.

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New vSphere Licensing and Pricing


New white paper from VMware

The biggest highlight:
VMware vSphere 5 licensing removes all restrictions on physical cores and physical RAM.

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VMware local disk vMotion in vSphere 5.1

During the 2012 VMworld, VMware announced a new feature is vSphere v5.1 which would allow vMotion from local disk to a destination (local disk, iSCSI, NFS, etc).  This type of vMotion (called Enhanced vMotion) combines a traditional vMotion of the VM instance and Storage vMotion so that the entire VM, along with virtual disks, are moved to a new destination.  This eliminates the shared storage requirement for vMotion.

This, combined with the removal of vRAM license limitations, makes vSphere 5.1 a very attractive offering for SMB’s.

You can see this new vMotion in action at VMworld 2012 here –

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CentOS 6.3 Released

CentOS has released version 6.3 of their rebuild of the Red Hat enterprise Linux distribution.  This release announcement should be a surprise to most users, as the CentOS team was able to rebuild RHEL 6.3 for CentOS release in under 3 weeks!  Good work guys and our sincere congratulations from the San Diego Linux team.

H-Online has a great article about the new features in RHEL 6.3.  Most, if not all, features are available in CentOS 6.3.

 

You can read the full release announcement here.

You can read the full release notes here.

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New Redhat/CentOS 6 Kernel – IMPORTANT FOR KVM USERS

 

A new kernel was released from RedHat that fixes a lot of KVM bugs and security vulnerabilities.  CentOS has already pushed this kernel to their repositories.

You can find the details about this new kernel here.

Upgrade your KVM guests and hosts soon!

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