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Re: Getting rights right

Diogene Laerce wrote:
> Hi Bob,


> First thank you for the detailed answer, you kind of preventively
> answered to all my doubts or interrogations. :)

Yay!  Then I was successful!  :-)  \o/

> I try to set up a new line of security (files and network) as I just
> changed country and instead of being in one mostly targeting others, I
> am now in one mostly targeted by others. :D


> >   chmod -R u+rwX,go-rwx /home/user/Documents
> I ran this command to restart the process :
>      find /home/user/Documents -type f -exec chmod u+rw,go-rwx -R {} \;
> and will make executable all following files according the needs.

More comments from me about the above.  It is pretty good.  It doesn't
do anything bad.  But it could be better.

  find $directory -type f

That will find all files below the specified directory.

  -exec chmod u+rw,go-rwx -R {} \;

That will chmod each file (each due to "{} \;") to the specified
symbolic mode.  All good.

The -R is a little odd there.  That says to recursively change files
down a directory hierarchy.  Of course the find is only going to pass
it files so there won't ever be a directory seen.  The -R in that case
isn't doing any harm but neither is it doing anything at all.  Also
'find' is already the super powerful nice recursive command.  It is
the biggest and best tool in the toolbox.  Since recursive commands
can get away from people sometimes I think it best to use one of them
at a time.  :-)

The "{} \;" part is the traditional way to do -exec and you will find
it in many Unix text books forever.  It has some disadvantages though.
It invokes the command once for each file.  That isn't as efficient as
it could be.  More than a decade ago find was enhanced to include the
"{} +" construct as a new and better form of this.  For one "+" isn't
special to the shell and does not need to be escaped.  That is good by
itself.  But "{} +" also invokes the command once and passes the
entire argument list, or as much of the argument list as possible on
the system (it is system dependent), to the command.  Therefore it is
much more efficient since it reduces the number of fork and exec calls
and makes handling the large file lists more efficient.

If we polish up your command just a tiny bit we have this:

  find /home/user/Documents -type f -exec chmod u+rw,go-rwx {} +

Again, your original command is fine and got the job done.  I just
wanted to polish it up a small amount for next time.

> > That is usually called UPG (User Private Group).
> >...
> After reading this, I actually found that :
> umask and level of security : The umask command be used for setting
> different security levels as follows:
> umask value	Security level	Effective permission (directory)
> 022		Permissive	755
> 026		Moderate	751
> 027		Moderate	750
> 077		Severe		700
> in there :
> http://www.cyberciti.biz/tips/understanding-linux-unix-umask-value-usage.html

I gave that a quick skim and that article seems factually accurate.
However trying to assign human fuzzy names "Permissive, Moderate,
Severe" to them is completely arbitrary and I disagree with the
direction at that point.  I would rather have features and
capabilities line up with the particular goals to be accomplished.

Because frankly I would say for "Severe" security that I would turn
the power off!  That would be severe! :-)  Otherwise it is just
different settings for different features.

> And I was planning to set a "severe" security plan. Based on the
> thinking that I have 3 computers (that only I use) to run behind a box
> and that I thought wiser to set them to the maximum security first, find
> out what they will exchange in second and then update the permissions
> accordingly, as I have very little impact on the box security.

Given all of the above I think that is a reasonable plan.  I can't
argue with the direction of your thinking.  But I also understand how
these permissions work and how they interact.  So I personally
wouldn't be recommending "Severe".  I recommend a UPG "umask 02" which
isn't even an option from the above list.  If you are a sole user on
your own system then it doesn't really matter.

> I then opted for the umask 077. I'm not sure if it's really justified
> but it couldn't do no harm.. I guess. :)

But for example if you share files by making tar files and sending
them out then that "Severe" setting creates problems for others when
they unpack the files and the settings are propagated to them.  I
wouldn't make a software release bundle that way for example.  Also
for example if you interacted with others through a version control
server then permissions can leak through there too.  Again it all
depends upon what you are doing and how you are interacting with
others.  I am not saying you are doing any of those things but I think
eventually you will want to share some files with someone and then you
need to be aware of the file permissions.  The old saying is right
that the devil is in the details!

> Strangely, it seems that using symbolic mode instead of octal solved my
> issue : all files are treated and I have no random results anymore.

Hmm...  I don't know.  Both should work fine.  But the symbolic modes
are specifically targeting.  I like them better due to this.  They
have also been standardized too.  Standard is good.  So I usually
recommend them.  The octal modes are all setting.  Which sounds good
but often turns out to be bad since it is inflexibly rigid and tends
to break when everything isn't exactly so.

> Very thanks for your lights again, any indicators are always
> <blink>welcomed</blink>. :)



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