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What is a Zombie process?

Posted: October 18th, 2011, 2:12 am
by n2o2diver
I seem to have a small problem.
I have followed the guide step by step up to the install Webmin.

When I restart the server all is well. I can run webmin no problem.
I can run the TightVNC viewer and get the GUI, the problem is if I log off from the GUI and close the VNC then try to go back to it it doesn't work. The VNC launches but I don't get the GUI back. Unless I restart the server and go at it from scratch.

Then I notice a line that says 1 Zombie Process its that my problem?

Thanks for any help you can provide
Seam

Re: What is a Zombie process?

Posted: October 18th, 2011, 1:11 pm
by pete66
Hi Seam and welcome.

This explains what a zombie process is better than I can: http://en.wikipedia.org/wiki/Zombie_process

To solve your problem don't log out of the GUI session, just close VNC. When you go back in again via VNC your desktop will be how you left it.
The desktop will shutdown gracefully when you shutdown/restart your server so don't worry about leaving it active.

Hope this helps and have fun :twisted:

Pete.

Re: What is a Zombie process?

Posted: October 18th, 2011, 9:43 pm
by fpp
I'm not sure the two are 100% related.

I seldom use VNC and always leave it the way you describe. I still do get 'zombie' notices once in a while when logging in through ssh.
Most times just one, occasionally up to four.

My guess is that FlexRaid produces some of those, too. They seem harmless enough anyway.

Re: What is a Zombie process?

Posted: October 18th, 2011, 11:39 pm
by n2o2diver
Thanks for the info

I tried it your way Pete66 and it works fine like that.

I haven't made it as far as installing FLexRaid yet. :D

I have installed the putty, VNC and Webmin only

I did the create users and shares page also. I am very new to this and just following the guide pages one at a time.

The next pages LTSP, FLexRAid, NFS and KVM sure sound daunting and I'm not even sure what they do or why I might need them?

I would like to plug my printer into the server so I can print from any computer on the network not sure if that is covered in this guide.

Again this site is a wealth of info and I appreciate all the help

Re: What is a Zombie process?

Posted: October 19th, 2011, 7:59 pm
by fpp
If you're not clear on what LTSP, LFS, NFS and KVM can do for you, it's safe to assume you can leave them aside for the time being, until you feel more comfortable with Linux and want to get your feet wet.

FlexRAID is another matter. It's less well known than all the rest, confidential even at this time, but certainly the most useful of all for most people building a home Ubuntu server. If you have several hard disks, it will set them up so that the files you store on them are protected : if one of those disks fails, you can replace it with a new one and the software will recreate the files that were on it, using information stored on the other drives.

FlexRAID is a sophisticated piece of software, and relies on notions that are not trivial (anything but). Following Ian's excellent step-by-step guide, however, should let you set up a basic protected system simply enough.

Re: What is a Zombie process?

Posted: October 20th, 2011, 12:19 am
by n2o2diver
Thanks FPP!

I have two drives on order, so when they come in I will make sure to read up and use it. From what I have read there are two ways to RAID your drives, with hardware or software, is that right? I am assuming FlexRAID is strictly software based and will be the cheaper option.

I am having fun learning and last night I used wubi to dual boot my desktop with the latest version of Ubuntu to get more involved with it. Would you recommend any books or should I just read stuff online? I have read that there can be lots of wrong info out there. I am trying to find some classes locally to take just for fun.

I am finding that with these Linux based OS that all kinds of packages are out there and readily available to do just about anything you can think of. However the names of them are so cryptic its hard to figure out what they do and why you need them. A lot of times I know what I want the system to do but I don't know what you might "technically call it" then when I search so many things come back that it is overwhelming to try and figure out which one to use. Then of course everyone has their opinion on which one is better and you can watch a forum thread imploded as everyone starts arguing about it. Which in itself can be quite entertaining, but not if you need answers to your question.

Thanks for the help.

Re: What is a Zombie process?

Posted: October 20th, 2011, 7:28 pm
by fpp
Glad to be of help. Just one thing though : if you want FlexRAID to be of any interest to you, you will need at least three drives.

Technically it is possible to use it (or RAID1) with two, but in that case you will essentially be mirroring (duplicating) your data, so you won't gain anything capacity-wise.
The magic of FlexRaid (or RAID4, or RAID5) is that it uses parity computation to create redundancy for your data. This only takes one extra disk, whatever the capacity and number of drives.

If you have three 2GB drives, store data on the first two and use the third for parity. If one of the two data drives fails, the data on the remaining one and the parity information on the third will be combined to recreate the data on the lost one's replacement. So you have 4GB of failure-proof storage, although you only sacrificed 2GB for redundancy.

It only gets better as your add drives : a fourth, and you get 6GB of secure storage with still the one 2G parity disc. A fifth, 8GB, etc.
Sounds like magic but it really works. Hardware and software RAID4/5 have been doing this for decades.

FlexRaid uses the same principles but with a couple of twists : the data stays in its native form on each data disc, so they can still be used independently (whereas RAID "stripes" the data across all disks, so they are unreadable outside of the RAID array). Also, real RAID usually requires that all your disks be of the same size. FlexRaid only needs your parity disk to be as big as your largest data disk, so you can reuse older, smaller disks without any problems.

The catch is that, for this to work, you can lose at most one disk at a time -- and act fast to replace it when that happens, because meanwhile you are without protection.
Another benefit of FlexRaid is that if you are unlucky enough to lose two drives in rapid succession, you will lose "only" the data on those, the remaining disks being still readable. With regular RAID the entire array is hosed, and the only cure is having a separate backup (on tape) to restore from.

Re: What is a Zombie process?

Posted: October 21st, 2011, 10:58 pm
by n2o2diver
Thanks for all the great info fpp