[CentOS] Server hangs on CentOS 5.5

Simon Matter simon.matter at invoca.ch
Fri Mar 11 13:51:53 UTC 2011

> Am 03/11/2011 03:03 AM, schrieb Nico Kadel-Garcia:
>> On Thu, Mar 10, 2011 at 6:49 PM, B.J.
>> McClure<keepertoad at bellsouth.net>  wrote:
>>> B.J. McClure keepertoad at bellsouth.net
>>> Sent from MacBook-Air
>>> On Mar 10, 2011, at 5:28 PM, Nico Kadel-Garcia wrote:
>>>> On Thu, Mar 10, 2011 at 11:13 AM, Michael Eager<eager at eagerm.com>
>>>> wrote:
>>>>> Previous cleaning have been with canned compressed air. Thanks
>>>>> for the caution about vacuums and static.  I may use the vacuum
>>>>> on the case fans from the outside.  The case should provide an
>>>>> adequate static shield.
>>>> I've had good results with a damp, soft cloth or Q-tip with
>>>> distilled water for awkward bits. and filters, and that cloth for
>>>> the case itself. It also looks noticeably newer, which helps with
>>>> walking investors through a small machine room.
>>> I must respectfully disagree with any application of water,
>>> distilled or otherwise to things electronic.  I was taught in the
>>> Navy, and my engineering career has confirmed, that cleaning of
>>> electronic components should be done with low pressure, dried,
>>> compressed air.  50 psi max.  If some solvent must be used, try
>>> alcohol.  Evaporates quickly, leaves no residue and has an affinity
>>> for water.
>> Typical drug-store alcohol is "rubbing alcohol", and is 30% water.
>> I designed medical electronics for a dozen years. Acohol has its
>> uses, but water is much cheaper, safer, and you don't have fumes to
>> deal with. Shall we discuss the effectives of surface etch resist
>> and cladding in protecting circuit boards from damage, and the
>> effects of alcohol on low cost electronic sockets?
> I agree with Nico, I have been working for a large PC-Manufacturer in
> Europe for many years and alcohol was never a good idea for cleaning
> pcbs, not in production nor in the field.
> Either we used trichloroethane or trichlorotrifluoroethane for washing
> and cleaning of mainboards (which became a bit unpopular due to its
> effects on the ozone layer...) or we used water-based cleaning fluids
> (aka 'water'). But that was only in the production process of the pcbs.
> Almost never in the field, except when real repairs on the mainboard had
> to be done on site (soldering).
> Yes, it can be true with 'navy-strength' electronics that you actually
> can use alcohol for the purpose of cleaning electronic boards, but in
> low-cost electronics, it's a total no-go, because it disolves the
> coating of the pcbs and most often harms - as Nico wrote - the sockets
> and chip packages. We're talking about low-cost electronics here...
> Though, when cleaning machines in the field, I very rarely ever used
> something else then compressed air. Actually, I would suggest to
> everyone not to clean the inside of a box with any kind of fluid, since
> it actually won't do anything positive besides changing the looks.

After decades in the high precision and electronics industry, I can tell
you for sure that compressed air is not seen as a good choice. It blows
the dust where it doesn't belong. That may not be a big problem with a
cheap PC, but it's not professional at all.

If you want to do it the professional way, go to an ESD protected room,
take an ESD vac and an ESD brush, wear your ESD shoes and wrist strap, and
clean *carefully*. Compressed air may additionally be used in certain
places, but not more.


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