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Les Mikesell 09-06-2012 05:40 PM

centos email server suddenly much slower. What to do?
 
On Thu, Sep 6, 2012 at 12:14 PM, Marco Fioretti
<marco.fioretti@gmail.com> wrote:
> Greetings,
> I run my own email server for some domains I administer, on a centos
> vps server with a very small number of users.
>
> The only services are smtp, imap/pop, webmail
>
> Everything was running without problems until this morning. I left
> home for 1/2 hours, and when I came back everything had become about
> 100x slower (seriously!). The services were/are still all up and
> running, but practically unusable (even running mutt in my ssh session
> is almost frozen).
>
> I have not changed/updated anything in the last 1/2 weeks. I have
> already done a few checks with the VPS provider, and it looks like:
>
> network & hardware are OK
>
> there seem to be no strange processes running. I didn't manage to save
> the output of "top", but it didn't show anything that (AFAICT, of
> course) should not be there on an email server
>
> however, there is something that is using "much more memory than
> normal" (see the comment below from the hosting sysadmin after he
> checked user_beancounters). Initially we thought it was apache, but
> even switching it off didn't change anything. What now?
>
> Any help to understand what the heck happened, and find out what
> exactly _started_ to cause this problem is very welcome!

One thing to check is that the DNS servers in /etc/resolv.conf are
answering quickly (dig some_name.domain @server_ip). Mail services
use DNS extensively and if the first server fails there is a timeout
before trying the 2nd choice. Things will still work but slower and
you may end up with enough processes running to run out of RAM and
start swapping. Also check your outbound mail queue in case some
spam attempt has succeeded in generating bounces.

--
Les Mikesell
lesmikesell@gmail.com
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Marco Fioretti 09-06-2012 05:58 PM

centos email server suddenly much slower. What to do?
 
> One thing to check is that the DNS servers in /etc/resolv.conf are
> answering quickly (dig some_name.domain @server_ip).

The server runs no DNS server itself.

I ran dig www.google.it @213.179.193.200 (ie the complete real IP of
my primary dns server as listed in /etc/resolv.conf) and this is the
result:
[root@vps728 ~]# dig www.google.it @213.179.193.200

; <<>> DiG 9.2.4 <<>> www.google.it @213.179.193.200
; (1 server found)
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 37012
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 4, ADDITIONAL: 0

;; QUESTION SECTION:
;www.google.it. IN A

;; ANSWER SECTION:
www.google.it. 300 IN A 173.194.35.151
www.google.it. 300 IN A 173.194.35.152
www.google.it. 300 IN A 173.194.35.159

;; AUTHORITY SECTION:
google.it. 10800 IN NS ns2.google.com.
google.it. 10800 IN NS ns3.google.com.
google.it. 10800 IN NS ns4.google.com.
google.it. 10800 IN NS ns1.google.com.

;; Query time: 2011 msec
;; SERVER: 213.179.193.200#53(213.179.193.200)
;; WHEN: Thu Sep 6 13:41:43 2012
;; MSG SIZE rcvd: 161

as far as the queue goes, it was empty. I run postsuper -d ALL and
postuper -d ALL deferred, just in case, but no change

Thanks,
Marco
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Steve Clark 09-06-2012 06:08 PM

centos email server suddenly much slower. What to do?
 
On 09/06/2012 01:58 PM, Marco Fioretti wrote:
> 2011 msec

Pretty slow my dig to the same server ran in 113 msec

dig www.google.it @213.179.193.200

; <<>> DiG 9.7.4-P1-RedHat-9.7.4-2.P1.fc14 <<>> www.google.it @213.179.193.200
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17288
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 4, ADDITIONAL: 0

;; QUESTION SECTION:
;www.google.it. IN A

;; ANSWER SECTION:
www.google.it. 230 IN A 173.194.35.152
www.google.it. 230 IN A 173.194.35.159
www.google.it. 230 IN A 173.194.35.151

;; AUTHORITY SECTION:
google.it. 10079 IN NS ns3.google.com.
google.it. 10079 IN NS ns4.google.com.
google.it. 10079 IN NS ns1.google.com.
google.it. 10079 IN NS ns2.google.com.

;; Query time: 113 msec
;; SERVER: 213.179.193.200#53(213.179.193.200)
;; WHEN: Thu Sep 6 14:07:38 2012
;; MSG SIZE rcvd: 161

--
Stephen Clark
*NetWolves*
Director of Technology
Phone: 813-579-3200
Fax: 813-882-0209
Email: steve.clark@netwolves.com
http://www.netwolves.com
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Laurent 09-06-2012 09:42 PM

centos email server suddenly much slower. What to do?
 
Le 2012-09-06 19:14, Marco Fioretti a écrit*:
> Greetings,
> I run my own email server for some domains I administer, on a centos
> vps server with a very small number of users.
>
> The only services are smtp, imap/pop, webmail
>


> however, there is something that is using "much more memory than
> normal" (see the comment below from the hosting sysadmin after he
> checked user_beancounters). Initially we thought it was apache, but
> even switching it off didn't change anything. What now?

My 2 cents. You probably checked a lot of things.

- a filesystem (almost) full ?
- did you check the logs ? any errors ?
- a user sending/receiving a large e-mail ? what is the maximum size of
an e-mail in your MTA settings ?
- more mail-services-related processes ?
- did you try to stop mail services to see if the server usability is
back ?
- do you run antispam and/or antivirus on incoming/outgoing e-mails ?

- to help with DNS, you can probably enable nscd or setup dnsmasq, so
it would reduce DNS queries sent to DNS servers.

--
Laurent.
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