dovecot - Feb 2009 - Effects of going read-only on dovecot & pop/imap clients

Hi all,

We need to set our filestore to read-only for quite a while, and I want
to mitigate the effects for our clients. First issue; dovecot. If we
just change the nfs mounts to read-only, dovecot complains:

2009-02-19T14:03:19+00:00 mail2 dovecot: pop3-login: Login:
user=<test2 at markandruth.co.uk>, method=PLAIN, rip=10.15.10.95,
lip=10.15.10.102:11002
2009-02-19T14:03:19+00:00 mail2 dovecot: POP3(test2 at markandruth.co.uk):
open() failed with file
/var/spool/mail/supplier_2/ma/rk/an/markandruth.co.uk/te/st/2_/test2/Mai
ldir/dovecot.index.log: Read-only file system
2009-02-19T14:03:19+00:00 mail2 dovecot: POP3(test2 at markandruth.co.uk):
open(/var/spool/mail/supplier_2/ma/rk/an/markandruth.co.uk/te/st/2_/test
2/Maildir/dovecot-uidlist.lock) failed: Read-only file system
2009-02-19T14:03:19+00:00 mail2 dovecot: POP3(test2 at markandruth.co.uk):
file_dotlock_create(/var/spool/mail/supplier_2/ma/rk/an/markandruth.co.u
k/te/st/2_/test2/Maildir/dovecot-uidlist) failed: Read-only file system
2009-02-19T14:03:19+00:00 mail2 dovecot: POP3(test2 at markandruth.co.uk):
Couldn't init INBOX: Internal error occurred. Refer to server log for
more information. [2009-02-19 14:03:19]
2009-02-19T14:03:19+00:00 mail2 dovecot: POP3(test2 at markandruth.co.uk):
Mailbox init failed bytes=0/95, top=0/0, retr=0/0, del=0/0, size=0

Even when I use :INDEX=MEMORY, it's still complaining about creating
.lock's or uidlist files and just issuing internal errors. Is there any
way to make dovecot just do as much as it can under the circumstances ie
allow read access to mails?

Also, has anyone got experience of how clients handle mailboxes being
read-only? My guess is that pop clients would probably break and
download the same messages over and over?

Thanks,

Mark

--
Mark Zealey -- Shared Hosting Team Leader
Product Development * Webfusion
123-reg.co.uk, webfusion.co.uk, donhost.co.uk, supanames.co.uk

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On Thu, 2009-02-19 at 14:17 +0000, Mark Zealey wrote:
> 2009-02-19T14:03:19+00:00 mail2 dovecot: POP3(test2 at markandruth.co.uk):
> open() failed with file
> /var/spool/mail/supplier_2/ma/rk/an/markandruth.co.uk/te/st/2_/test2/Mai
> ldir/dovecot.index.log: Read-only file system
..
> Even when I use :INDEX=MEMORY, it's still complaining about creating
> .lock's or uidlist files and just issuing internal errors. Is there any
> way to make dovecot just do as much as it can under the circumstances ie
> allow read access to mails?
Are you talking about only POP3 clients? I suppose in theory it should
be possible, but it's such a special case that I'm not going to bother
making Dovecot support that. Dovecot really wants to create
dovecot-uidlist files. But I suppose you could just have it create them
to some temp directories:

mail_location = maildir:~/Maildir:CONTROL=/tmp/%u:INDEX=MEMORY

And be sure to use:

pop3_uidl_format = %f
> Also, has anyone got experience of how clients handle mailboxes being
> read-only? My guess is that pop clients would probably break and
> download the same messages over and over?
If client has configured to leave mail on server it should work, but if
not it probably breaks.
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> Are you talking about only POP3 clients? I suppose in theory it should
> be possible, but it's such a special case that I'm not going to
bother
> making Dovecot support that. Dovecot really wants to create
> dovecot-uidlist files. But I suppose you could just have it 
> create them
> to some temp directories:
> 
> mail_location = maildir:~/Maildir:CONTROL=/tmp/%u:INDEX=MEMORY
Both IMAP and pop3 - I got the same errors with imap, but thanks to the
CONTROL= parameter that's fixed now.

I get a weird error the first time I log in:

2009-02-19T16:48:14+00:00 mail2 dovecot: POP3(test2 at markandruth.co.uk):
Disconnected: Mailbox is in inconsistent state. bytes=0/56, top=0/0,
retr=0/0, del=0/0, size=0
2009-02-19T16:48:14+00:00 mail2 dovecot: POP3(test2 at markandruth.co.uk):
Couldn't init INBOX: Mailbox was deleted under us

But second login is fine - must be something to do with the CONTROL
param.
> And be sure to use:
> 
> pop3_uidl_format = %f
Out of interest, why do we have to use that uidl format, or are you just
saying we have to use some uidl format? We migrated from courier and so
use "UID%u-%v".
> > Also, has anyone got experience of how clients handle 
> mailboxes being
> > read-only? My guess is that pop clients would probably break and
> > download the same messages over and over?
> 
> If client has configured to leave mail on server it should 
> work, but if
> not it probably breaks.
Hmm, weirdly enough (or perhaps not) dovecot looks successful if I
delete the message (chmod -r):

dele 1
+OK Marked to be deleted.
quit
+OK Logging out, messages deleted.

Do you think IMAP clients would handle the read-only situation better? I
can see that it correctly reports the mailbox as read-only if we chmod
-r files, however if the filesystem itself is mounted read-only, dovecot
reports the mailbox as being read-write (dovecot 1.1.6)

Thanks,

Mark