identifying what's running ( was Re: [Novalug] "10 Linux commands you've never used" article)

[Kevin Dwyer]

On Fri, Feb 23, 2007 at 11:15:43AM -0800, Beartooth wrote:
> On Thu, 22 Feb 2007, Garrett Nievin wrote:
> 
> >Try chmod 755 WhatsitDo2.  You need to see the "x" bit on in 
> >the "ls -l" listing...
> 
> 	OK : I've run into chmod with number code before. Like 
> chmod itself, I have a vague abstract idea of what it does -- and 
> can never quite seem to keep it straight in my head. <sigh>
> 
> 	Is it a fact that "chmod 755" and "chmod +x" and "chmod 
> u+x" are a classic linuxian example of three ways to do the same 
> thing? If so, is there one of them I'm more likely to get 
> straight first than the others? I've gotta sneakin hunch I'm 
> creepin' up on the level where I'm bound to start needing a lot 
> of the commands I've shied off learning for years, for fear of 
> destroying something...

The octal notation is a concatenation of the sums of individual values.

The bits: execute=1, write=2, read=4

So, 755 (there is an assumed leading 0 to hold the place of the
setuid/sticky bits), means user:(4+2+1),group:(4+1),other:(4+1).
Replace 4, 2, and 1 with the permissions above and you know the ways
this file may be accessed.

-kpd