The commands to check CentOS version

The following table contains most common and recommended ways on how to check CentOS version on your CentOS Linux server or desktop.

$ rpm -q centos-releaseCentOS version valid for CentOS 6 and higher. Causes to reveal major, minor and asynchronous CentOS version.
$ lsb_release -dRequires redhat-lsb package to be installed before execution.
$ rpm -E %{rhel}RPM macro to reveal a major CentOS version
$ rpm –eval %{centos_ver}RPM macro to display a major version of CentOS
$ cat /etc/centos-releaseLinux cat command to output content of the /etc/centos-release to query CentOS version. Works with CentOS 6 and higher.

In case the above-provided commands did not help you to obtain the CentOS version number you may try the following alternative commands.

Although available only for CentOS version 7 and above the hostnamectl command might provide you with a significant clue about your OS version number:

$ hostnamectl 
   Static hostname: localhost.localdomain
         Icon name: computer-vm
           Chassis: vm
        Machine ID: fe069af6a1764e07be909d7cf64add99
           Boot ID: b81bb73dc549484c8927e830e149eb55
    Virtualization: kvm
  Operating System: CentOS Linux 7 (Core)
       CPE OS Name: cpe:/o:centos:centos:7
            Kernel: Linux 3.10.0-862.6.3.el7.x86_64
      Architecture: x86-64

For more answers try to query all release files within the /etc directory:

$ cat /etc/*elease
CentOS Linux release 7.5.1804 (Core) 
NAME="CentOS Linux"
VERSION="7 (Core)"
ID_LIKE="rhel fedora"
PRETTY_NAME="CentOS Linux 7 (Core)"


CentOS Linux release 7.5.1804 (Core) 
CentOS Linux release 7.5.1804 (Core)

Bash Script to check CentOS version

The following bash script can be used to obtain the CentOS version number given that the /etc/centos-release file exists and is populated.

The below script serves as an example, feel free to modify wherever appropriate. For more information about Bash Scripting visit our bash scripting tutorial:


full=`cat /etc/centos-release | tr -dc '0-9.'`
major=$(cat /etc/centos-release | tr -dc '0-9.'|cut -d \. -f1)
minor=$(cat /etc/centos-release | tr -dc '0-9.'|cut -d \. -f2)
asynchronous=$(cat /etc/centos-release | tr -dc '0-9.'|cut -d \. -f3)

echo CentOS Version: $full
echo Major Relase: $major
echo Minor Relase: $minor
echo Asynchronous Relase: $asynchronous


$ ./ 
CentOS Version: 7.5.1804
Major Relase: 7
Minor Relase: 5
Asynchronous Relase: 1804

Python program to check CentOS version

The following python script will output the distribution name along with the OS version number:


import platform
print platform.linux_distribution()

Alternatively, one can execute python code directly from the shell:

$ python -c 'import platform; print platform.linux_distribution()'


$ python 
('CentOS Linux', '7.5.1804', 'Core')

How to generate linux server certificates

  1. Generate a Private Key
openssl genrsa -des3 -out server.key 1024
  1. Generate a CSR (Certificate Signing Request)
openssl req -new -key server.key -out server.csr
  1. Remove Passphrase from Key
cp server.key
openssl rsa -in -out server.key
  1. Generating a Self-Signed Certificate
openssl x509 -req -days 1365 -in server.csr -signkey server.key -out server.crt
  1. Installing the Private Key and Certificate
cp server.crt /etc/pki/tls/certs/ssl.crt
cp server.key /etc/pki/tls/private/ssl.key


ISPConfig: replace apache with nginx

This Article from here

In this tutorial i show you how to replace apache with nginx using ISPConfig I performed the migration for serveral sites running Joomla 2.x, Joomla 3.x, WordPress and some static / self-written pages.

The server runs ISPConfig installed using the Perfect Server Howto from

There are some differents between apache and nginx so you may have to adjust some settings for your web-sites.
nginx does not support .htaccess
nginx does not use different apache-modules like mod_rewrite

You can use different online-converters like to move the configs from apache to nginx. But keep in mind, that it´s not guranteed, that the convert works with out any errors. I used for different (very simple) htaccess without any problems

If you change the webserver in ISPConfig from apache to nginx, you can´t see your additional apache directives in the interface (but they are still in the database). You can browse through all you websites and write down the directives or you can grab them from the databse using phpmyadmin or mysql with this sql-command:
SELECT domain, apache_directives FROM web_domain WHERE apache_directives != '';

To find all .htaccess files, you ran run find /var/www/clients/ -name .htaccess -not -path "*/stats/*".

1. install nginx
apt-get install nginx

2. install php-fpm
apt-get install php5-fpm
and make sure, that /etc/php5/fpm/php.ini contains:


Restart php-fpm with /etc/init.d/php5-fpm reload.

Now nginx is installed but apache is still your active webserver.

3. enable Maintaince mode
Enable the Maintenance Mode in ISPConfig under System / Mainconfig on the tab Misc to prevent changes during the migration.

4. switch to nginx in ISPConfig
Login as root into phpmyadmin, open the database dbispconfig, select the table server and edit the server.

Scroll down to config and find the line [global] finden. In the next line replace




Scroll futher down to the line [web] And change the next line from




6. Create ispconfig.vhost in /etc/nginx/sites-available:
vi /etc/nginx/sites-avaliable/ispconfig.vhost
and paste one of the following contents:

with SSL:

server {
listen 8080;
ssl on;
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
ssl_certificate /usr/local/ispconfig/interface/ssl/ispserver.crt
ssl_certificate_key /usr/local/ispconfig/interface/ssl/ispserver.key;
server_name _;

root /usr/local/ispconfig/interface/web/;

client_max_body_size 20M;

location / {
index index.php index.html;

# serve static files directly
location ~* ^.+.(jpg|jpeg|gif|css|png|js|ico|html|xml|txt)$ {
access_log off;

location ~ \.php$ {
try_files $uri =404;
include /etc/nginx/fastcgi_params;
fastcgi_pass unix:/var/lib/php5-fpm/ispconfig.sock;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
#fastcgi_param PATH_INFO $fastcgi_script_name;
fastcgi_buffer_size 128k;
fastcgi_buffers 256 4k;
fastcgi_busy_buffers_size 256k;
fastcgi_temp_file_write_size 256k;

location ~ /\. {
deny all;

without SSL:

server {
listen 8080;
ssl off;
server_name _;

root /usr/local/ispconfig/interface/web/;

client_max_body_size 20M;

location / {
index index.php index.html;

# serve static files directly
location ~* ^.+.(jpg|jpeg|gif|css|png|js|ico|html|xml|txt)$ {
access_log off;

location ~ \.php$ {
try_files $uri =404;
include /etc/nginx/fastcgi_params;
fastcgi_pass unix:/var/lib/php5-fpm/ispconfig.sock;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
#fastcgi_param PATH_INFO $fastcgi_script_name;
fastcgi_buffer_size 128k;
fastcgi_buffers 256 4k;
fastcgi_busy_buffers_size 256k;
fastcgi_temp_file_write_size 256k;

location ~ /\. {
deny all;

And create the symlink with
ln -s /etc/nginx/sites-available/ispconfig.vhost /etc/nginx/sites-enabled/000-ispconfig.vhost

7. adjust websites
Disable the Maintaince Mode and convert existing htaccess-file and apache-directives and insert the new values in the webinterface for each website.

If you did not change all websites, run the resyn-tool for the websites.

8. disable apache and start nginx
/etc/init.d/apache2 stop
update-rc.d -f apache2 remove
/etc/init.d/nginx start


If you need to switch-back to apache, just revert the steps 4. and 8.

18 commands to monitor network bandwidth on Linux server

This post mentions some linux command line tools that can be used to monitor the network usage. These tools monitor the traffic flowing through network interfaces and measure the speed at which data is currently being transferred. Incoming and outgoing traffic is shown separately.

Some of the commands, show the bandwidth used by individual processes. This makes it easy to detect a process that is overusing network bandwidth.

The tools have different mechanisms of generating the traffic report. Some of the tools like nload read the “/proc/net/dev” file to get traffic stats, whereas some tools use the pcap library to capture all packets and then calculate the total size to estimate the traffic load.

Here is a list of the commands, sorted by their features.

1. Overall bandwidth - nload, bmon, slurm, bwm-ng, cbm, speedometer, netload

2. Overall bandwidth (batch style output) - vnstat, ifstat, dstat, collectl

2. Bandwidth per socket connection - iftop, iptraf, tcptrack, pktstat, netwatch, trafshow

3. Bandwidth per process - nethogs

1. Nload

Nload is a commandline tool that allows users to monitor the incoming and outgoing traffic separately. It also draws out a graph to indicate the same, the scale of which can be adjusted. Easy and simple to use, and does not support many options.

So if you just need to take a quick look at the total bandwidth usage without details of individual processes, then nload will be handy.

$ nload

nload command linux

Installing Nload – Fedora and Ubuntu have got it in the default repos. CentOS users need to get nload from Epel repositories.

# fedora or centos
$ yum install nload -y

# ubuntu/debian
$ sudo apt-get install nload

2. iftop

Iftop measures the data flowing through individual socket connections, and it works in a manner that is different from Nload. Iftop uses the pcap library to capture the packets moving in and out of the network adapter, and then sums up the size and count to find the total bandwidth under use.

Although iftop reports the bandwidth used by individual connections, it cannot report the process name/id involved in the particular socket connection. But being based on the pcap library, iftop is able to filter the traffic and report bandwidth usage over selected host connections as specified by the filter.

$ sudo iftop -n

The n option prevents iftop from resolving ip addresses to hostname, which causes additional network traffic of its own.

iftop command linux

Install iftop – Ubuntu/Debian/Fedora users get it from default repos. CentOS users get it from Epel.

# fedora or centos
yum install iftop -y

# ubuntu or debian
$ sudo apt-get install iftop

3. iptraf

Iptraf is an interactive and colorful IP Lan monitor. It shows individual connections and the amount of data flowing between the hosts. Here is a screenshot

$ sudo iptraf

iptraf linux command

Install iptraf

# Centos (base repo)
$ yum install iptraf

# fedora or centos (with epel)
$ yum install iptraf-ng -y

# ubuntu or debian
$ sudo apt-get install iptraf iptraf-ng

4. nethogs

Nethogs is a small ‘net top’ tool that shows the bandwidth used by individual processes and sorts the list putting the most intensive processes on top. In the event of a sudden bandwidth spike, quickly open nethogs and find the process responsible. Nethogs reports the PID, user and the path of the program.

$ sudo nethogs

nethogs command linux

Install Nethogs – Ubuntu, Debian, Fedora users get from default repos. CentOS users need Epel

# ubuntu or debian (default repos)
$ sudo apt-get install nethogs

# fedora or centos (from epel)
$ sudo yum install nethogs -y

5. bmon

Bmon (Bandwidth Monitor) is a tool similar to nload that shows the traffic load over all the network interfaces on the system. The output also consists of a graph and a section with packet level details.

bmon linux network monitor

Install Bmon – Ubuntu, Debian and Fedora users can install from default repos. CentOS users need to setup repoforge, since its not available in Epel.

# ubuntu or debian
$ sudo apt-get install bmon

# fedora or centos (from repoforge)
$ sudo yum install bmon

Bmon supports many options and is capable of producing reports in html format. Check the man page for more information

6. slurm

Slurm is ‘yet’ another network load monitor that shows device statistics along with an ascii graph. It supports 3 different styles of graphs each of which can be activated using the c, s and l keys. Simple in features, slurm does not display any further details about the network load.

$ slurm -s -i eth0

slurm command linux

Install slurm

# debian or ubuntu
$ sudo apt-get install slurm

# fedora or centos
$ sudo yum install slurm -y

7. tcptrack

Tcptrack is similar to iftop, and uses the pcap library to capture packets and calculate various statistics like the bandwidth used in each connection. It also supports the standard pcap filters that can be used to monitor specific connections.

tcptrack command linux

Install tcptrack – Ubuntu, Debian and Fedora have it in default repos. CentOS users need to get it from RepoForge as it is not available in Epel either.

# ubuntu, debian
$ sudo apt-get install tcptrack

# fedora, centos (from repoforge repository)
$ sudo yum install tcptrack

8. Vnstat

Vnstat is bit different from most of the other tools. It actually runs a background service/daemon and keeps recording the size of data transfer all the time. Next it can be used to generate a report of the history of network usage.

$ service vnstat status
 * vnStat daemon is running

Running vnstat without any options would simply show the total amount of data transfer that took place since the date the daemon is running.

$ vnstat
Database updated: Mon Mar 17 15:26:59 2014

   eth0 since 06/12/13

          rx:  135.14 GiB      tx:  35.76 GiB      total:  170.90 GiB

                     rx      |     tx      |    total    |   avg. rate
       Feb '14      8.19 GiB |    2.08 GiB |   10.27 GiB |   35.60 kbit/s
       Mar '14      4.98 GiB |    1.52 GiB |    6.50 GiB |   37.93 kbit/s
     estimated      9.28 GiB |    2.83 GiB |   12.11 GiB |

                     rx      |     tx      |    total    |   avg. rate
     yesterday    236.11 MiB |   98.61 MiB |  334.72 MiB |   31.74 kbit/s
         today    128.55 MiB |   41.00 MiB |  169.56 MiB |   24.97 kbit/s
     estimated       199 MiB |      63 MiB |     262 MiB |

To monitor the bandwidth usage in realtime, use the ‘-l’ option (live mode). It would then show the total bandwidth used by incoming and outgoing data, but in a very precise manner without any internal details about host connections or processes.

$ vnstat -l -i eth0
Monitoring eth0...    (press CTRL-C to stop)

   rx:       12 kbit/s    10 p/s          tx:       12 kbit/s    11 p/s

Vnstat is more like a tool to get historic reports of how much bandwidth is used everyday or over the past month. It is not strictly a tool for monitoring the network in real time.

Vnstat supports many options, details about which can be found in the man page.

Install vnstat

# ubuntu or debian
$ sudo apt-get install vnstat

# fedora or centos (from epel)
$ sudo yum install vnstat

9. bwm-ng

Bwm-ng (Bandwidth Monitor Next Generation) is another very simple real time network load monitor that reports a summary of the speed at which data is being transferred in and out of all available network interfaces on the system.

$ bwm-ng
bwm-ng v0.6 (probing every 0.500s), press 'h' for help
  input: /proc/net/dev type: rate
  /         iface                   Rx                   Tx                T
==           eth0:           0.53 KB/s            1.31 KB/s            1.84
KB             lo:           0.00 KB/s            0.00 KB/s            0.00
--          total:           0.53 KB/s            1.31 KB/s            1.84

If the console size is sufficiently large, bwm-ng can also draw bar graphs for the traffic using the curses2 output mode.

$ bwm-ng -o curses2

Install Bwm-NG – On CentOS bwm-ng can be installed from Epel.

# ubuntu or debian
$ sudo apt-get install bwm-ng

# fedora or centos (from epel)
$ sudo apt-get install bwm-ng

10. cbm – Color Bandwidth Meter

A tiny little simple bandwidth monitor that displays the traffic volume through network interfaces. No further options, just the traffic stats are display and updated in realtime.

cbm linux network monitor

$ sudo apt-get install cbm

11. speedometer

Another small and simple tool that just draws out good looking graphs of incoming and outgoing traffic through a given interface.

$ speedometer -r eth0 -t eth0

speedometer linux network monitor

Install speedometer

# ubuntu or debian users
$ sudo apt-get install speedometer

12. Pktstat

Pktstat displays all the active connections in real time, and the speed at which data is being transferred through them. It also displays the type of the connection, i.e. tcp or udp and also details about http requests if involved.

$ sudo pktstat -i eth0 -nt

pktstat linux network monitor

$ sudo apt-get install pktstat

13. Netwatch

Netwatch is part of the netdiag collection of tools, and it too displays the connections between local host and other remote hosts, and the speed at which data is transferring on each connection.

$ sudo netwatch -e eth0 -nt

netwatch linux network monitor

$ sudo apt-get install netdiag

14. Trafshow

Like netwatch and pktstat, trafshow reports the current active connections, their protocol and the data transfer speed on each connection. It can filter out connections using pcap type filters.

Monitor only tcp connections

$ sudo trafshow -i eth0 tcp

trafshow linux network monitor

$ sudo apt-get install netdiag

15. Netload

The netload command just displays a small report on the current traffic load, and the total number of bytes transferred since the program start. No more features are there. Its part of the netdiag.

$ netload eth0

netload linux network monitor

$ sudo apt-get install netdiag

16. ifstat

The ifstat reports the network bandwidth in a batch style mode. The output is in a format that is easy to log and parse using other programs or utilities.

$ ifstat -t -i eth0 0.5
  Time           eth0       
HH:MM:SS   KB/s in  KB/s out
09:59:21      2.62      2.80
09:59:22      2.10      1.78
09:59:22      2.67      1.84
09:59:23      2.06      1.98
09:59:23      1.73      1.79

Install ifstat – Ubuntu, Debian and Fedora users have it in the default repos. CentOS users need to get it from Repoforge, since its not there in Epel.

# ubuntu, debian
$ sudo apt-get install ifstat

# fedora, centos (Repoforge)
$ sudo yum install ifstat

17. dstat

Dstat is a versatile tool (written in python) that can monitor different system statistics and report them in a batch style mode or log the data to a csv or similar file. This example shows how to use dstat to report network bandwidth

$ dstat -nt
-net/total- ----system----
 recv  send|     time     
   0     0 |23-03 10:27:13
1738B 1810B|23-03 10:27:14
2937B 2610B|23-03 10:27:15
2319B 2232B|23-03 10:27:16
2738B 2508B|23-03 10:27:17

Install dstat

$ sudo apt-get install dstat

18. collectl

Collectl reports system statistics in a style that is similar to dstat, and like dstat it is gathers statistics about various different system resources like cpu, memory, network etc. Over here is a simple example of how to use it to report network usage/bandwidth.

$ collectl -sn -oT -i0.5
waiting for 0.5 second sample...
#         <----------Network---------->
#Time       KBIn  PktIn  KBOut  PktOut 
10:32:01      40     58     43      66 
10:32:01      27     58      3      32 
10:32:02       3     28      9      44 
10:32:02       5     42     96      96 
10:32:03       5     48      3      28

Install Collectl

# Ubuntu/Debian users
$ sudo apt-get install collectl

$ sudo yum install collectl


Those were a few handy commands to quickly check the network bandwidth on your linux server. However these need the user to login to the remote server over ssh. Alternatively web based monitoring tools can also be used for the same task.

Ntop and Darkstat are some of the basic web based network monitoring tools available for Linux. Beyond these lie the enterprise level monitoring tools like Nagios that provide a host of features to not just monitor a server but entire infrastructure.

Install and configure Milter Manager

Install to CentOS 7

Install to CentOS 7 — How to install milter manager to CentOS 7

About this document

This document describes how to install milter manager to CentOS 7. See Install for general install information.

In this document, CentOS 7.6 is used. Sudo is used to run a command with root privilege. If you don’t use sudo, use su instead.

Install packages

Postfix is used as MTA because it’s installed by default.

Spamass-milter, clamav-milter and milter-greylist are used as milters. Milter packages registered in EPEL are used.

Register EPEL like the following:

% sudo yum install -y epel-release

Now, you install milters:

% sudo yum install -y spamass-milter-postfix clamav-scanner-systemd clamav-update clamav-milter clamav-milter-systemd milter-greylist

And you install RRDtool for generating graphs:

% sudo yum install -y rrdtool

Build and Install

milter manager can be installed by yum.

Register milter manager yum repository like the following:

% curl -s | sudo bash

See also: <URL:>

Now, you install milter manager:

% sudo yum install -y milter-manager


Here is a basic configuration policy.

milter-greylist should be applied only if S25R condition is matched to reduce needless delivery delay. But the configuration is automatically done by milter manager. You need to do nothing for it.

It’s difficult that milter manager runs on SELinux. Disable SELinux policy module for Postfix and Milter.

% sudo semodule -d postfix
% sudo semodule -d milter

Configure spamass-milter

At first, you configure spamd.

spamd adds “[SPAM]” to spam mail’s subject by default. If you don’t like the behavior, edit /etc/mail/spamassassin/


rewrite_header Subject [SPAM]


# rewrite_header Subject [SPAM]

Add the following configuration to /etc/mail/spamassassin/ This configuration is for adding headers only if spam detected.

remove_header ham Status
remove_header ham Level

Start spamd on startup:

% sudo systemctl enable spamassassin

Start spamd:

% sudo systemctl start spamassassin

Here are spamass-milter’s configuration items:

  • Disable needless body change feature.
  • Reject if score is larger than or equal to 15.

Change /etc/sysconfig/spamass-milter:


#EXTRA_FLAGS="-m -r 15"


EXTRA_FLAGS="-m -r 15"

Start spamass-milter on startup:

% sudo systemctl enable spamass-milter

Start spamass-milter:

% sudo systemctl start spamass-milter

Configure clamav-milter

Update ClamAV virus database and start clamd.

Edit /etc/freshclam.conf like the following. It comments out “Example”, changes “NotifyClamd” value and uncomments other items.


#LogFacility LOG_MAIL
#NotifyClamd /path/to/clamd.conf


LogFacility LOG_MAIL
NotifyClamd /etc/clamd.d/scan.conf

Run freshclam by hand at the first time:

% sudo freshclam

Configure clamd.

Edit /etc/clamd.d/scan.conf like the following. It comments out “Example” and uncomments other items:


#LogFacility LOG_MAIL
#LocalSocket /run/clamd.scan/clamd.sock


LogFacility LOG_MAIL
LocalSocket /run/clamd.scan/clamd.sock

Start clamd on startup:

% sudo systemctl enable [email protected]

Start clamd:

% sudo systemctl start [email protected]

Configure clamav-milter.

Edit /etc/mail/clamav-milter.conf like the following. It comments out “Example”, change “ClamdSocket” value and uncomments other items:


#MilterSocket /run/clamav-milter/clamav-milter.socket
#MilterSocketMode 660
#ClamdSocket tcp:scanner.mydomain:7357
#LogFacility LOG_MAIL


MilterSocket /run/clamav-milter/clamav-milter.socket
MilterSocketMode 660
ClamdSocket unix:/run/clamd.scan/clamd.sock
LogFacility LOG_MAIL

Add “clamilt” user to “clamscan” group to access clamd’s socket:

% sudo usermod -G clamscan -a clamilt

Start clamav-milter on startup:

% sudo systemctl enable clamav-milter

Start clamav-milter:

% sudo systemctl start clamav-milter

Configure milter-greylist

Change /etc/mail/greylist.conf for the following configurations:

  • use the leading 24bits for IP address match to avoid Greylist adverse effect for sender uses some MTA case.
  • decrease retransmit check time to 10 minutes from 30 minutes (default value) to avoid Greylist adverse effect.
  • increase auto whitelist period to a week from 1 day (default value) to avoid Greylist adverse effect.
  • don’t use Greylist when trusted domain passes SPF. (Trusted domains are configured in milter manager)
  • use Greylist by default.

The configuration relaxes Greylist check to avoid Greylist adverse effect. It increases received spam mails but you should give priority to avoid false positive rather than false negative. You should not consider that you blocks all spam mails by Greylist. You can blocks spam mails that isn’t blocked by Greylist by other anti-spam technique such as SpamAssassin. milter manager helps constructing mail system that combines some anti-spam techniques.


socket "/run/milter-greylist/milter-greylist.sock"
# ...
racl whitelist default


socket "/run/milter-greylist/milter-greylist.sock" 660
# ...
subnetmatch /24
greylist 10m
autowhite 1w
sm_macro "trusted_domain" "{trusted_domain}" "yes"
racl whitelist sm_macro "trusted_domain" spf pass
racl greylist sm_macro "trusted_domain" not spf pass
racl greylist default

Start milter-greylist on startup:

% sudo systemctl enable milter-greylist

Start milter-greylist:

% sudo systemctl start milter-greylist

Configure milter manager

Add “milter-manager” user to “clamilt” group to access clamav-milter’s socket:

% sudo usermod -G clamilt -a milter-manager

Add “milter-manager” user to “mail” group and “grmilter” group to access milter-greylist’s socket:

% sudo usermod -G mail -a milter-manager
% sudo usermod -G grmilter -a milter-manager

Add “milter-manager” user to “postfix”” group to access spamass-milter’s socket:

% sudo usermod -G postfix -a milter-manager

milter manager detects milters that installed in system. You can confirm spamass-milter, clamav-milter and milter-greylist are detected:

% sudo /usr/sbin/milter-manager -u milter-manager -g milter-manager --show-config

The following output shows milters are detected:

define_milter("milter-greylist") do |milter|
  milter.connection_spec = "unix:/run/milter-greylist/milter-greylist.sock"
  milter.enabled = true
define_milter("clamav-milter") do |milter|
  milter.connection_spec = "unix:/var/run/clamav-milter/clamav-milter.socket"
  milter.enabled = true
define_milter("spamass-milter") do |milter|
  milter.connection_spec = "unix:/run/spamass-milter/postfix/sock"
  milter.enabled = true

You should confirm that milter’s name, socket path and “enabled = true”. If the values are unexpected, you need to change /etc/milter-manager/milter-manager.local.conf. See Configuration for details of milter-manager.local.conf.

But if we can, we want to use milter manager without editing miter-manager.local.conf. If you report your environment to the milter manager project, the milter manager project may improve detect method.

milter manager’s configuration is finished.

Start to milter manager on startup:

% sudo systemctl enable milter-manager

Start to milter manager:

% sudo systemctl start milter-manager

milter-test-server is usuful to confirm milter manager was ran:

% sudo -u milter-manager milter-test-server -s unix:/var/run/milter-manager/milter-manager.sock

Here is a sample success output:

status: accept
elapsed-time: 0.128 seconds

If milter manager fails to run, the following message will be shown:

Failed to connect to unix:/var/run/milter-manager/milter-manager.sock

In this case, you can use log to solve the problem. milter manager is verbosily if –verbose option is specified. milter manager outputs logs to standard output if milter manager isn’t daemon process.

You can add the following configuration to /etc/sysconfig/milter-manager to output verbose log to standard output:

OPTION_ARGS="--verbose --no-daemon"

Restart milter manager:

% sudo systemctl restart milter-manager

Some logs are output if there is a problem. Running milter manager can be exitted by Ctrl+c.

OPTION_ARGS configuration in /etc/sysconfig/milter-manager should be commented out after the problem is solved to run milter manager as daemon process. And you should restart milter manager.

Configure Postfix

Enables Postfix:

% sudo systemctl enable postfix
% sudo systemctl start postfix

Configure Postfix for milters. Append following lines to /etc/postfix/

milter_protocol = 6
milter_default_action = accept
milter_mail_macros = {auth_author} {auth_type} {auth_authen}

For details for each lines.

milter_protocol = 6Use milter protocol version 6.
milter_default_action = acceptMTA receives mails when MTA cannot access milter. Although there are problems between MTA and milter, MTA can deliver mails to clients. But until you recover milter, perhaps MTA receives spam mails and virus mails.

If you can recover the system quickly, you can specify ‘tempfail’ instead of ‘accept’. Default value is ‘tempfail’.

milter_mail_macros = {auth_author} {auth_type} {auth_authen}MTA gives information related SMTP Auth to milters. milter-greylist etc. uses it.

Register milter manager to Postfix. It’s important that spamass-milter, clamav-milter and milter-greylist aren’t needed to be registered because they are used via milter manager.

Append following lines to /etc/postfix/

smtpd_milters = unix:/var/run/milter-manager/milter-manager.sock

Reload Postfix’s configuration.

% sudo systemctl reload postfix

milter manager logs to syslog. If milter manager works well, some logs can be shown in /var/log/maillog. You need to send a test mail for confirming.


There are many configurations to work milter and Postfix together. They can be reduced by introducing milter manager.

Without milter manager, you need to specify sockets of spamass-milter, clamav-milter and milter-greylist to /etc/postfix/ With milter manager, you don’t need to specify sockets of them, just specify a socket of milter manager. They are detected automatically. You don’t need to take care some small mistakes like typo.

milter manager also detects which ‘/sbin/chkconfig -add’ is done or not. If you disable a milter, you use the following steps:

% sudo systemctl stop milter-greylist
% sudo systemctl disable milter-greylist

You need to reload milter manager after you disable a milter.

% sudo systemctl reload milter-manager

milter manager detects a milter is disabled and doesn’t use it. You don’t need to change /etc/postfix/

You can reduce maintainance cost by introducing milter manager if you use some milters on CentOS.

milter manager also provides tools to help operation. Installing them is optional but you can reduce operation cost too. If you also install them, you will go to Install to CentOS (optional) .