On Saturday 06 October 2007 07:46, Carl Hartung wrote:
> Hi All,
>
> I'm still running 10.2 :-) and looking to fill in some 'missing bits'
> of information. I've inserted two questions in the following excerpt
> from a *nix file systems tutorial that I found on the 'net:
>
> The permission flags are read left to right
>
> 1   directory flag, 'd' if a directory, '-' if a normal file,
>     something else occasionally may appear here for special devices.
>
> --> What specific documents, man, info, URL, etc., are available
> which describe these "something else" optional flags in detail?

Many are specific to a particular file system implementation, and are 
thus documented in a manual page or other document specific to that 
file system type. The generic ones are documented (at least on my 10.0 
system) in the section-8 man page for the "mount" command.


> 2,3,4         read, write, execute permissions for User
>
> 5,6,7         read, write, execute permissions for Group
>
> 8,9,10        read, write, execute permissions for Other
>
> Flag
> -    in any position means "not set"
> r    file is readable
> w    file is writeable (with directories, means files can be added or
> deleted) x    program or script is executable (directory contents can
> be listed) s    where 'x' would normally go is called the set-UID or
> set-groupID flag
>
> --> What would a 't' in the tenth position mean? Example:
>
> drwxrwxrwt  4 carl users 160 2007-10-06 09:46 hdb-test/

The ancient and now re-purposed "sticky" bit. It used to tell the kernel 
to keep a binary executable's pages on the swap device even when no 
process remained running that exectuable. There they could be more 
rapidly reused when that process was again invoked. File system 
improvements, shared-code, including shared object file libraries, 
virtual memory and other improvements have made this interpretation 
obsolete.

Nowadays it has been given an alternate meaning when applied to 
directories (meaning it does not actually conflict with the old 
meaning, which was only meaningful for binary executable files). In 
this context, it means that even if the directory's permissions would 
ordinarily allow a file to be deleted, the kernel will allow that 
deletion only if the requestor is the owner (or root, of course).

This allows for directories such as /tmp where anyone can create a file 
without danger of someone else removing it. All other permissions are 
enforced, so the usual means of interlocking on creation and access 
control are still in force.


> The relevant fstab line is:
>
> /dev/hdb3   /mnt/hdb-test   reiserfs   noauto,user,acl,user_xattr 1 2
>
> Thanks & regards!
>
> Carl


Randall Schulz
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