Re: emacsserver unstable?

[Peter Dyballa <Peter_Dyballa@Web.DE>]

Am 25.07.2007 um 00:01 schrieb Sven Bretfeld:

> What, then, is a hardlink?

In MS-DOS it's a cross-referenced file => damaged file system.

In a UNIX file system (ufs, or BSD Fast File System) a file can be  
one or a whole series of blocks on a disk in one file system. These  
can be addressed from one single "inode" (member of a directory  
structure) or more than one inode. On the same volume/partition/slice  
one file can be referenced from more than one directory, i.e. it  
seems to exist more than once. There is no original. The ls command  
shows a link count (3 in this example), and also an inode number  
(9099707):

	9099707 -rw-r--r--   3 pete  admin  123 25 Jul 00:17 drei
	9099707 -rw-r--r--   3 pete  admin  123 25 Jul 00:17 eins
	9099707 -rw-r--r--   3 pete  admin  123 25 Jul 00:17 zwei

No hard link consumes any disk space. It is restricted to the same  
file system. When you need a link to a file in another file system,  
it has to be a symbolic link. This one is kind of a regular file  
which passes every access to the file it points to. A sym-link costs  
as many bytes disk space as the pointer is long (plus the inode entry):

	9099811 lrwxr-xr-x   1 pete  admin   72 25 Jul 00:17 sym-link -> / 
usr/local/texlive/2007/texmf-dist/fonts/type1/public/archaic/linb10.pfb
	pete 165 /\ echo -n /usr/local/texlive/2007/texmf-dist/fonts/type1/ 
public/archaic/linb10.pfb | wc -c
	      72

Sym-links can also point to files on another computer. The target to  
which a sym-link points does not necessarily need to exist. When you  
remove a sym-link, only the sym-link file is removed (the target can  
continue to exist or not-exist as before). When you remove (or  
unlink) a file with a (hard) link count of 1, some disk space is  
freed and the last link to the block(s) that built the disk space of  
a file, is wiped out, data is lost, the file gone.

Question: what happens when you create a hard link to a symbolic link  
that has its target a) in the same file system, b) in another file  
system?

--
Greetings

   Pete

"If builders built buildings the way programmers write programs, then  
the first woodpecker that came along would destroy civilization."
                                  -- Weinberg's Second Law