Loop device

[email.listen at googlemail.com]

Am Mon, 5. June 2006 14:10 schrieb Thilo Six:
> email.listen at googlemail.com wrote the following on 05.06.2006 10:39:
>
> <snip>
>
> > Hhhm could be done a bit more elegant (imho)?
> > Preloading kernel modules is a waste of recources, so unused kernel
> > modules use memory.
> > Ok, it's not much memory they use but may be it's a more elegant way to
> > have an /etc/filesystems file
> > I would prefer an /etc/filesystems file
> >
> > Not to forget it's easier to copy /etc/filesystems to other machines than
> > to adapt each /etc/modules file. This because /etc/modules differ from
> > machine to machine due to different hardware but /etc/filesystems
> > doesn't.
>
> <snip>
>
> > regards,
> > thomas
>
> OK now i have looked a bit more deeply at it at seems /etc/filesystems
> is commonly used in the *nix world and therefore i agree it is more
> portable.
>
> One question remains:
> > (don't forget the * at the end)
>
> Why is the * at the end important?
>
> Because:
> http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.
>ibm.aix.doc/files/aixfiles/filesystems.htm ---------------------
> Note:
> The asterisk (*) is the comment character used in the /etc/filesystems
> file. ---------------------

Arrgglll, pitfall, pitfall, ....

Thilo, pardon me you just made two fundamental mistakes.
But on the other hand this is a good example for pitfalls of different Unix 
systems. :)

first:
Given that a documetation to a command you refer on other Unix'es may be 
correct for GNU/Linux also. I would consider it as a mistake pointing novice 
GNU/Linux users to such places. This because novice users tend to browse the 
doc's aside those you refered but this doc's may be wrong for GNU/Linux 
systems. See below the example for killall.

second and worst:
Never refer to other than GNU/Linux documentations for Linux commands. 
Even if there is such a command for other Unix flavours. The differences in 
behaviour may vary from none to dramatically.

Let me give two examples:
1. Your example of filesystems on IBM-AIX differs the GNU/Linux one.
For GNU/Linux Systems the asterisk (*) at the end of the filesystems file says 
that mount will read /proc/filesystems afterwards. If no * is given only the 
ones listed in /etc/filesystems are used. (BTW. this is a good way to 
restrict a system)
Have a look at [1]

2. Comands on different Unix systems may differ dramatically.
The difference of filesystems in AIX and GNU/Linux is small, there are others 
which may become very harmfull.

So for example on GNU/Linux systems there is a command called 'killall'
E.G. the use of killall on GNU/Linux systems is:
 killall nameofproc
where nameofproc may be such as mplayer or another running command you want to 
stop.

BUT:
Using killall on an older SUN Solaris machine has a dramaticall different 
behaviour.
On Solaris a killall command kills _all_ runing processes!
(BTW. that's why I tend to prefer the use of pkill instead of killall on 
GNU/Linux, so does SUN since Solaris 8. ;-)

See also http://en.wikipedia.org/wiki/Linuxism

>
> Here is an example i found on the net:
> http://cvs.pld.org.pl/setup/etc/filesystems?rev=1.2
---8<---
ext2
vfat
minix
nodev proc
nodev devpts
iso9660
---8<---
- IMO 'nodev proc' is obsolete because it is initialised at boot
- 'nodev devpts' devpts is obsolete on systems using udev, e.g. dapper
- The asterisk (*) in the last line is missing. So only filesystems listed 
  are used 

regards,
thomas


[1] http://www.die.net/doc/linux/man/man8/mount.8.html
    or man mount 
(BTW. one of the most extensive man pages on GNU/Linux systems.)

If no -t option is given, or if the auto type is specified, mount will try to 
guess the desired type. If mount was compiled with the blkid library, the 
guessing is done by this library. Otherwise, mount guesses itself by probing 
the superblock; if that does not turn up anything that looks familiar, mount 
will try to read the file /etc/filesystems, or, if that does not 
exist, /proc/filesystems. All of the filesystem types listed there will be 
tried, except for those that are labeled "nodev" (e.g., devpts, proc, nfs, 
and nfs4). If /etc/filesystems ends in a line with a single * only, mount 
will read /proc/filesystems afterwards.