Archive for 'Redhat'

Zombie Process

It's a pretty much common question asked in most of the interviews related to Linux, and most of the time people got it confused with Orphan Process. But these two are totally different from each other. A Zombie Process is nearly the same thing which we see in lot of horror movies. Like the dead people which don't have any life force left, Zombie processes are the dead processes sitting in the process table and doing nothing.

To explain this in much better way, "Zombie process or defunct process is a process that have completed the execution, have released all the resources (CPU, memory) but still had an entry in the process table."

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Though this warning looks pretty much scary but the reason for this is very much simple and the solution as well.

Q. When did you get this error ?

A. The possible reasons for getting this error are:

  • You have re-installed you system and trying to ssh to the newly installed system.
  • You have assigned the IP address of one system to another system and trying to ssh.
  • You system is dual boot with different ssh keys in both flavors of linux.
  • You are using an IP for load balancing and trying to ssh to the same IP.
  • You generated new ssh keys for your system. (Read this article for the re-generation of the host keys: Generate SSH host keys)
  • Someone trying to do some nasty things, or you can say man-in-the-middle attack.

There could be lots of solution for this problem, which are explained below:

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How To : Generate SSH Host keys

SSH is a service which most of system administrators use for remote administration of servers. When you install a fresh system, then at the start of the ssh service, it generates the host keys for your system which later on used for authentication. But if due to some reason you need to generate the host keys, then the process is …

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How To: Change time/date in linux from Command Prompt

In every system, there are two clocks which comes into action while setting the time, one is hardware clock and the other is linux (OS) clock. The hardware clock determines the system clock on system boot. While the system is running, changes to one of these doesn't affect the other. Normally you can follow any procedure, like first update one clock and then sync it with the other but it is always advised to first update the hardware clock and then let the linux clock sync it with it at the next reboot. Changing the system clock by using the date program on a running system could cause date discontinuities and consequently problems. Down here, I will be discussing both ways.

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How To: Change Timezone in Linux/Unix

In a linux/unix system, the time is the number of seconds elapsed since midnight UTC on the morning of January 1, 1970, not counting leap seconds.

There are different ways and procedures to change timezones in different flavors of linux/unix (which i will explain later in this HowTo) but universla procedure to do it in all flavors is explained below:

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