RE: [leafnode-list] Permissions

[tmcd@xxxxxxxx]

On Sun, 6 Jun 1999, Jeff Grossman <jeff@xxxxxxxxxxx> wrote:
> Thanks for the help.  Would you mind explaining a little of what you
> said?

Well, um, actually ... yes, I *would* mind, because much of it is in
the man page for chmod(1) and more is in the texinfo system.  (I use
GNU Emacs, so I can conveniently get at the latter info; I don't know
how to read it without Emacs.)  You can create files and directories
and try out the commands, as well.

Short form explanation:
    chmod [ugoa]*[+-=][rwxXstugo]* FILES...

u: change user permissions -- that is, for the owner of the file
g: change group permissions
o: change other permissions
a: all of u, g, and o
If you leave off all the letters, "a" is assumed.

+: give permission ("or" it in)
-: remove permission ("and" it out)
=: give exactly these permissions

r: read permission
w: write permission
x: execute permission
X: execute only if the file is a direc tory or already has execute
   permission for some user
s: setuid / setgid, depending on whether the lefthand s
t: sticky bit -- don't ask; pretty useless on modern systems for files
u: whatever the current user permissions are
g: whatever the current group permissions are
o: whatever the current other permissions are

The permission bits mean weird things for directories.

r: you can look at the directory contents.
w: you can change the dir contents: that is, you can create and delete
   files
x: you can search the directory: that is, you can cd into it and open
   files in it.  Thus, r without x on a directory is fairly useless, x
   without r is strange though occasionally useful
s: setuid: no effect that I see
   setgid: when you create a file in the directory, the group owner is
   the group name for the directory
t: files in the directory can only be deleted by their owner, even if
   other people have write permission to the directory.

>    chmod g+w failed.postings

Add group write permission, leaving everything else the same.

>     chmod u=rw,go=r mydata

For the user (that is, owner), give read and write permission; for the
group and others, give only read.  Since all of u, g, and o were
equalled, it turns off all other bits.  This is exactly identical to

    chmod 644 mydata

>     chmod a+x myscript

Give execute permission to everyone; the same as
    chmod +x myscript
since an omitted first letter means "a".

More examples:
    chmod go= private
Turn off all permissions (read, write, execute) to group and other.
    chmod = silly
Silly example: it turns off all permissions to everyone, including the
owner.  Equivalent to "chmod 0 silly".

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Tim McDaniel (home); Reply-To: tmcd@xxxxxxxx; 
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