redhat

How to bind a range of IP’s in Redhat based linux

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How to bind a range of IP’s in Linux
This method is used by Redhat Linux based servers (Centos/RedhatEnterprise/FedoraCore).

Create a file called /etc/sysconfig/network-scripts/ifcfg-eth0-range0
And in the file place these 3 lines but change the IP’s to match YOUR assigned range.

## Start

IPADDR_START=67.18.xxx.xxx
IPADDR_END=67.18.xxx.xxx
CLONENUM_START=0

# Example | IPADDR_START=67.18.333.440
# Example | IPADDR_END=67.18.333.444
# Example | CLONENUM_START=0

## END

The CLONENUM_START should be the number at which the alias interfaces should start. If you add your 5 IP’s to this server and then want to bind a second set of IP’s you create a second file named ‘ifcfg-eth0-range1’ and change the CLONENUM_START to match the last interface alias. IE ‘eth0:5’ = CLONENUM_START=5

After you have created the above file execute the command ‘service network restart’ and your IP’s will be all setup.

*CPANEL NOTE*
Please do not use this method of binding additional IPs if you are using Cpanel. Bind the IPs through the Cpanel interface.

Linux Memory Management

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Scenario: Customer is concerned that only 100MB of their 2GB of memory is as unused or free when running the free command. However, no processes appear to be consuming large amounts of memory, and the server is not running slow.

Cause: This is not a problem, but rather a result of the way linux manages its memory. On boot linux will typically display a large amount of free memory, as no processes have started to address it yet. Once processes run, Linux will cache that memory so it is quickly addressed for the next session. What this means is that on *most* linux distros, you’ll notice that a very small amount of memory is free, even though the machine is having no problems processing data (unlike, for instance a Windows server that would be quite slow with 150K of “free” memory). The best way to judge if the server is running low on memory, is if the swap space is being addressed. If the swap is occasionally hit, using a very small amount of memory, there is no cause for concern as that space will still be addressed. However, if a large amount of swap space is being used (50% or more) then the client may want to consider a memory upgrade.

Basically, the free memory isn’t the amount of memory that is not doing something, it’s the sum total of LowMem and HiMem that he kernel has left to address.

Users Can’t Change Password – cPanel

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When trying to change their password in cPanel, users get the following error:

There was an error manipulating the password file.
This generally means you entered your old password incorrectly.

This has been seen on CentOS and Redhat servers running cPanel 11. The known fix is to run:

chmod +s /usr/bin/passwd