/dev, /etc, /var- and mkrwsize()

[shaulka at 012.net.il]

> >   With 2.10 and hardly anything added to the default nfsroot, du shows:
> >     16K for /dev, 1.8M for /etc and 78M for /var.
> > The large consumers of those 78M are:
> >     17M     nfsroot/var/lib/apt
> >     5.8M    nfsroot/var/lib/dpkg
> >     15M     nfsroot/var/cache
> >     41M     nfsroot/var/tmp
> >
> > Perhaps mkrwsize() from subroutines-linux should create a
> >     5m for /etc
> >     another 10m for /var, where for /var the large consumers from above
> > will be excluded
> >    and another 100k for /dev
> >

> Could you please elaborate on the use of these directories? Usually I wouldn't
> expect to much to be written to the NFSROOT ...

  One can learn about the use of  those directories from the Filesystem Hierarchy 
Standard (FHS). Copied from http://www.pathname.com/fhs/pub/fhs-2.3.html:

    - The /dev directory is the location of special or device files.
       (As  an  aside, I believe that udev does a similar thing by design.)
    - The /etc hierarchy contains configuration files. A "configuration file" is a local
       file used to control the operation of a program; it must be static and cannot
       be an executable binary.
    - /var contains variable data files. This includes spool directories and files,
      administrative and logging data, and transient and temporary files.

Those statements are elaborated at that URL.

>  PS.: Or is it just the LVM things you mentionend lately?

  Indeed I am looking at it because of lvm. If I had the whole of /etc rw I wouldn't have to
give special care to the lvmtab file. And mind you that mkrwsize handles only directories,
not  files. I also believe that others see here a problem too. When announcing mkrw(),
Thomas Lange wrote in the changelog that he wish the unuions were already here. And,  
since we are talking about automation, we have to try and plan for all sorts of requirments, 
as well as scalability. For example, I don't know what will be required to install a machine  
that has raid.