dovecot - Aug 2007 - Userdb and home directories

Greetings -

I've just discovered an oddity I didn't know I had...

We have two NetApp filers: one serves people's home directories; the  
other their message store and control files filestores.

At the moment the first of the two filers is not accessible to my  
Dovecot system and I assumed all would be well because, as far as I  
knew, I wasn't using it at all.

However in practice Dovecot DOES appear to be using it: it is trying  
to chdir() to my home directory when I login, finds it can't at the  
moment (because of a problem giving "Permission denied"), and closes  
the connection.

I've read the pages on home directories and the userdb on the Wiki  
and it advises that having a home directory is beneficial.  I'm happy  
to create a subdirectory for this within a user's control files  
directory, but do NOT want it on our normal filestore: we can't have  
mail inaccessible because a user's home directory is inaccessible  
because the other filer is out of action.

We use shadow for the passdb and passwd for the userdb (see dovecot - 
n output below).  I'm trying to work out how to override the home  
directory returned from NIS.  Ultimately I'd like to use this template:

     /mailstore/control/%1Ln/%Ln/home

but for the time being while I'm trying to work out how to do it have  
my own area hard-coded in (as it's only me logging in to the test  
system):

     /mailstore/control/p/pmb1/home

I'm specifying this with the "args" directive in the userdb
section
as follows:

    args = home=/mailstore/control/p/pmb1/home

but it isn't being picked up.  What am I doing wrong, please?
(We want to continue using uids and gids etc from NIS so I don't  
think using the static userdb is the right thing to do?)

Cheers,
Mike B-)

Output of dovecot -n
--------------------
# 1.0.3: /usr/local/dovecot-1.0.3/etc/dovecot.conf
log_path: /logfiles/mail/live/dovecot
info_log_path: /logfiles/mail/live/dovecot-info
disable_plaintext_auth: no
login_dir: /var/run/dovecot/login
login_executable: /usr/local/dovecot-1.0.3/libexec/dovecot/imap-login
login_log_format_elements: user=<%Lu> method=%m rip=%r lip=%l %c
login_process_per_connection: no
login_greeting_capability: yes
login_process_size: 64
login_processes_count: 10
max_mail_processes: 10000
mail_location: maildir:/mailstore/messages/%1Ln/%Ln/Maildir:INDEX=/ 
mailstore/index/%1Ln/%Ln:CONTROL=/mailstore/control/%1Ln/%Ln
maildir_copy_with_hardlinks: yes
mail_plugins: quota imap_quota
mail_log_prefix: [%p]%Us(%Lu):
imap_client_workarounds: delay-newmail outlook-idle
namespace:
   type: private
   separator: /
   inbox: yes
auth default:
   mechanisms: plain login
   cache_size: 1024
   cache_ttl: 600
   username_chars:  
abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890
   username_format: %Ln
   passdb:
     driver: shadow
   userdb:
     driver: passwd
     args: home=/mailstore/control/p/pmb1/home
plugin:
   quota: fs


-- 
The Computing Service, University of York, Heslington, York Yo10 5DD, UK
Tel:+44-1904-433811  FAX:+44-1904-433740

* Unsolicited commercial e-mail is NOT welcome at this e-mail address. *

Greetings -

I'm just feeling I need to clarify my previous message a bit to  
explain the problem better...

On 3 Aug 2007, at 11:33, Mike Brudenell wrote:
> We have two NetApp filers: one serves people's home directories;  
> the other their message store and control files filestores.
>
> At the moment the first of the two filers is not accessible to my  
> Dovecot system and I assumed all would be well because, as far as I  
> knew, I wasn't using it at all.
We have two NetApp filers.  One serves people's real home  
directories, and the other is serving the mailstore.  The mailstore  
comprises two separate areas: one with quotas to store the messages  
in Maildir format; the second without quotas to store the control  
files for each user.  The general format of these are:

     Message store:  /mailstore/messages/<letter>/<username>
     Control files:  /mailstore/control/<letter>/<username>

where <letter> is the first character of the <username>

We want the mail service to operate as a "black box", with all  
necessary files stored on its filer.

In particular we do not want anything storing within someone's home  
directory, and want the mail service to continue if the filer service  
home directories is unavailable.

I am using "passdb shadow" and "userdb passwd" to
authenticate and
get users' details.  These are being read from NIS, with each user  
having their own uid and gid.

Because it is the general NIS map its home directory field specifies  
the user's real home directory on the other filer.

Because I don't use "%h" anywhere in Dovecot's configuration I
had
assumed it did not use the home directory at all, and hence is  
independent of the other filer.  However this morning's issue has  
shown this is not the case...

As things stand Dovecot is using chdir() to move to the user's home  
directory, apparently in the early setup after logging in.  As the  
home directories are currently unavailable to my test Dovecot  
service, giving a "Permission denied" error, Dovecot is aborting the  
session and so I'm not able to read mail.

We can't have this for our production service so I'm trying to find  
out how to make things truly independent of the other (home  
directories) filer.  I've read in the Wiki that it's best to set up a  
home directory for users and will be happy to have this as a  
subdirectory below the control files' directory. For example

     /mailstore/control/p/pmb1/home/...

However I can't find a way of telling Dovecot NOT to use the home  
directory returned from the "userdb passwd" lookup, and instead use  
the above.

I know setting the home directory is possible from "userdb static",  
but we don't want everyone to use a single uid/gid: we want them each  
to use their own uids and gids so the filestore-based quotas work.

Can someone guide me in this please?
Either how to override the home directory setting, or an alternative  
way of configuring things to give the "black box" environment we are  
after?

With many thanks,
Mike B-)

-- 
The Computing Service, University of York, Heslington, York Yo10 5DD, UK
Tel:+44-1904-433811  FAX:+44-1904-433740

* Unsolicited commercial e-mail is NOT welcome at this e-mail address. *

Greetings -

A lot of reading and testing has led me part-way to an answer.  If  
anyone can help me get all the way there I'll be really grateful: I  
only have 48 hours now before the system has to go live!

The problem...

We are using "userdb passwd" to get a user's details from our main
NIS map.  This returns uid, gid and normal home directory for each user.

However for mail I don't make any use of the home directory, wanting  
a "sealed black box" environment that isn't dependent on our other
file server with home directories on it: just the file server with  
the mail directories.

I understand now that I can change a user's home directory between  
the imap-login and imap processes by altering the configuration file  
to point at a script
     mail_executable = /usr/local/dovecot/libexec/postlogin-script
and have the script alter the HOME environment variable:
     HOME=`printf '/mailstore/control/%1.1s/%s/home' "$USER"
"$USER"`

[Quick side-question: should I be using $USER or $RESTRICTED_USER  
here?  I can't work out what the difference between them is.  Both  
are set within Dovecot's standard environment.]

HOWEVER...

The problem I'm trying to avoid is having Dovecot refuse to log  
someone in if their home directory gives a "Permission denied" error  
(eg, when their home directory filer is in a funny state).  This test  
appears to be done very early on, in the imap-login process (I  
think): definitely before the post-login script runs.

Is there some way of overriding the home directory used in the very  
early (imap-login?) process?  At present I can only think of either:

     a) Edit /etc/passwd with a dummy home directory for all users to  
appease
        the very early check, then use the postlogin script to set  
the real
        home directory up for the main imap process, or

     b) Edit the source code to do likewise.

I keep hoping I've missed something and there is a cleaner way to  
override the value for home returned by the passwd userdb before its  
initial use in src/master/mail-process.c create_mail_process()

Any help gratefully received!

Cheers,
Mike B-)


On 3 Aug 2007, at 11:33, Mike Brudenell wrote:
> We use shadow for the passdb and passwd for the userdb (see dovecot  
> -n output below).  I'm trying to work out how to override the home  
> directory returned from NIS.  Ultimately I'd like to use this  
> template:
>
>     /mailstore/control/%1Ln/%Ln/home
>
> but for the time being while I'm trying to work out how to do it  
> have my own area hard-coded in (as it's only me logging in to the  
> test system):
>
>     /mailstore/control/p/pmb1/home
>
> I'm specifying this with the "args" directive in the userdb
section
> as follows:
>
>    args = home=/mailstore/control/p/pmb1/home
>
> but it isn't being picked up.  What am I doing wrong, please?
> (We want to continue using uids and gids etc from NIS so I don't  
> think using the static userdb is the right thing to do?)
-- 
The Computing Service, University of York, Heslington, York Yo10 5DD, UK
Tel:+44-1904-433811  FAX:+44-1904-433740

* Unsolicited commercial e-mail is NOT welcome at this e-mail address. *