Is bin ever written to?

[Sarunas Burdulis]

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Knapp wrote:
> On Tue, Dec 23, 2008 at 10:09 PM, Loïc Grenié <loic.grenie at gmail.com> wrote:
>> 2008/12/23 Knapp <magick.crow at gmail.com>:
>>> On Tue, Dec 23, 2008 at 8:22 PM, Smoot Carl-Mitchell <smoot at tic.com> wrote:
>>>> On Tue, 2008-12-23 at 20:05 +0100, Knapp wrote:
>>>>> I was wondering if anything in a set up system ever needs to write to
>>>>> /bin or /sbin or /usr/bin or /usr/sbin?
>>>>> I was thinking of putting them in a ram disk with SquashFS to speed up
>>>>> the system but it can only read and not write.
>>>>> As far as I know the only time writing is needed is with a system update.
>>>> You are correct.  The only time the "bin" directories are written is
>>>> during system updates.
>>>>
>>>> I am not sure how much improvement you will see by putting the common
>>>> system commands in a ram disk.  The demand paging system keeps
>>>> frequently accessed pages in memory anyway. The only way to know is to
>>>> try it and see what kind of improvement you see.
>>>> --
>>>> Smoot Carl-Mitchell
>>> Any other ideas of what might best be on a ram disk?
>>> All the hidden home files was suggested because programs like FF might
>>> be speeded up and then at shutdown the ramdisk could be written to the
>>> home dir. This posses a risk, if there is a power outage but other
>>> than that should be safe.
>>    The kernel writers usually says that it's much better to NOT use a ramdisk
>>  and let the kernel do the cache (it's also much safer in case of power
>>  outage). You lose the first time you read a file, but the rest of the time it
>>  remains in memory (in you read it often). Except if you have a very
>>  specific use, you'd better not put anything on your ramdisk and not do
>>  any ramdisk.
>>
>>     The first time you read a file, the kernel copies it into memory.
>> It remains
>>  there unless there is not enough memory for the rest of the system. In that
>>  case the least used files are canceled from memory. This means that the
>>  kernel will create a "virtual ramdisk" in the cache where all the
>> files that you
>>  use often will remain. Each of those "usual" files will be read only
>> once during
>>  each normal session. If you use all your memory for some memory intensive
>>  program, the cache will be canceled, but your memory will be available for
>>  your program (which will not, or less, swap) instead of being locked for a
>>  ramdisk.
>>
>>           Loïc
> 
> OK, then how do you explain the increadible speed of distros like Damn
> Small Linux with a ram boot? Even big programs like FF run in a blink
> on my 386 laptop. 
Well, maybe 'cause it's "damn small"?

> On my amd 64 bit machine stating FF takes time even
> if I do it 2 times in a row. I want that sort of speed on my much
> faster desktop!
You can use strace and compare number of files opened in both cases. All
the files in your FF profile, add-ons/plugins, libraries etc. It's not
just /usr/bin/firefox. Do you want all that in RAM disk?...

You may also experiment with the swappiness setting in sysfs, i.e.
balance in RAM usage (see, for ex., here:
http://www.linux.com/feature/146599).

In practice however a faster hard disk or RAID setup will most likely
make the biggest difference.

Sarunas



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