A ps to the perms msg

[Gene Heskett]

On Thursday 12 July 2012 18:13:57 Colin Law did opine:

> On 12 July 2012 21:46, PleegWat <pleegwat at telfort.nl> wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> > 
> > On 07/12/2012 10:10 PM, Colin Law wrote:
> >> On 12 July 2012 18:14, Gene Heskett <gheskett at wdtv.com> wrote:
> >>> On Thursday 12 July 2012 13:07:22 Colin Law did opine:
> >>>> On 12 July 2012 15:40, Gene Heskett <gheskett at wdtv.com> wrote:
> >>>>> Greets all;
> >>>>> 
> >>>>> I just changed /var/spool/cron/crontabs/gene so its owned by
> >>>>> me again, but I am still being denied crontab -e permissions.
> >>>>> Probably because /var/spool/cron/crontabs is also owned by
> >>>>> root:root.  But since that directory contains ALL the
> >>>>> crontabs, I can't just willy nilly change that to, so I am
> >>>>> reduced to scratching my thinning hair and muttering WTF?
> >>>> 
> >>>> On mine, /var/spool/cron/crontabs/<user> is owned by <user> but
> >>>> group crontab.  Try crontab for the group if you have not
> >>>> already done that. the crontabs folder is owned by
> >>>> root:crontab.
> >>> 
> >>> Thank you, now I can edit it.  But looking in that directory, is
> >>> not root supposed to have a system stuff file there, something to
> >>> run logrotate for example?  Mine seems like it is the only one
> >>> there. ??
> >> 
> >> There is nothing in mine except the ordinary users.  I don't know
> >> how it does logrotate and so on.
> > 
> > This is done by anacron instead. Anacron has the ability to 'catch up'
> > on tasks that were scheduled while your PC was offline, which is
> > especially useful on  desktop machines.
> > 
> >>> Also, I am not a member of the crontab group in /etc/group.  That
> >>> also seems strange since I am the only meat & bones composed
> >>> user, with sudo rights on the machine.  Stranger and stranger
> >>> this rootless ubuntu is becoming.
> >> 
> >> I am not a member of crontab either, so again I don't know how it
> >> works.  No doubt someone more knowledgeable will elucidate
> >> ........
> > 
> > It works here, and I'm also not in the crontab group. The magic is
> > that /usr/bin/crontab is owned by root:crontab and has the setgid bit
> > set. That means that, when you are using that binary, that binary can
> > use the permissions of the crontab group even though you are not
> > ordinarily a member of it.
> > 
> > /var/spool/cron/crontab also has some interesting permissions: It has
> > group write but not group read. That means that, even as the crontab
> > group, you cannot list the files in that directory, but you can create
> > files. It also has the sticky bit set, which means that you can only
> > delete files in that directory if you own them (rather than being able
> > to delete any file in that directory).
> 
> Excellent, all is now explained (except how the OP's permissions got
> messed up in the first place).  Many thanks for the explanation.
> 
> Colin

And that, Colin, IS the $64 million question.  It is not the first time in 
the about a month I've been on this distro that root has suddenly become 
the owner of a whole tree of stuff.  In my home dir yet!

I changed to ubuntu-10.04.4 LTS basically so all my machines were running 
the same distro, 2 others are married to kernel 2.6.32-122-rtai as they are 
running machine tools (lathe, mill) in real time.  This machine is my do 
almost everything else machine.

Thanks.

Cheers, Gene
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