Sunday, February 19, 2012

Installing A Web, Email & MySQL Database Cluster On Debian 6.0 With ISPConfig 3



This tutorial describes the installation of a clustered web, email, database and DNS server to be used for redundancy, high availability and load balancing on Debian 6 with the ISPConfig 3 control panel. MySQL Master/Master replication will be used to replicate the MySQL client databases between the servers and Unison will be used to Sync the /var/www (websites) and /var/vmail (email account data) folders.

1 Setting Up The Two Base Systems

In this setup there will be one master server (which runs the ISPConfig control panel interface) and one slave server which mirrors the web (apache), email (postfix and dovecot) and database (MySQL) services of the master server.
To install the clustered setup, we need two servers with a Debian 6.0 minimal install. The base setup is described in the following tutorial in the steps 1 - 8:
http://www.howtoforge.com/perfect-server-debian-squeeze-with-bind-and-dovecot-ispconfig-3
Install only steps 1 - 8 of the perfect server tutorial and not the other steps as they differ for a clustered setup!
In my example I use the following hostnames and IP addresses for the two servers:
Master Server
Hostname: server1.example.tld
IP-address: 192.168.0.105
Slave server
Hostname: server2.example.tld
IP-address: 192.168.0.106
Whereever these hostnames or IP addresses occur in the next installation steps you will have to change them to match the IP's and hostnames of your servers.

2 Installing The Two Servers

The following steps have to be executed on the master and on the slave server. If a specific step is only for the master or slave, then I've added a note in the description in red.
vi /etc/hosts
127.0.0.1       localhost
192.168.0.105   server1.example.tld
192.168.0.106   server2.example.tld

# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts
Set the hostname of the server:
echo server1.example.tld > /etc/hostname
/etc/init.d/hostname.sh start
Use server1.example.tld on the first server and server2.example.tld on the second server.
Edit the sources.list file...
vi /etc/apt/sources.list
... and ensure that your /etc/apt/sources.list contains the squeeze-updates repository (this makes sure you always get the newest updates for the ClamAV virus scanner - this project publishes releases very often, and sometimes old versions stop working). 
[...]
deb http://ftp.de.debian.org/debian/ squeeze-updates main
[...]
Run
apt-get update
apt-get upgrade
to install the latest updates (if there are any).
It is a good idea to synchronize the system clock with an NTP (network time protocol) server over the Internet. Simply run
apt-get -y install ntp ntpdate
and your system time will always be in sync.
On server 1:
Now we create a private/public key pair on server1.example.tld:
ssh-keygen -t dsa
root@server1:~# ssh-keygen -t dsa
Generating public/private dsa key pair.
Enter file in which to save the key (/root/.ssh/id_dsa): <-- ENTER
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase): <-- ENTER
Enter same passphrase again: <-- ENTER
Your identification has been saved in /root/.ssh/id_dsa.
Your public key has been saved in /root/.ssh/id_dsa.pub.
The key fingerprint is:
1b:95:bc:4a:f4:9f:d8:ea:24:31:0f:c9:72:d5:a7:80 root@server1.example.com
The key's randomart image is:
+--[ DSA 1024]----+
| |
| o o |
| E * . . |
| o = o o |
| . S o . |
| + O + . |
| + + + |
| o . |
| .o |
+-----------------+
root@server1:~#
It is important that you do not enter a passphrase otherwise the mirroring will not work without human interaction so simply hit ENTER!
Next, we copy our public key to server2.example.tld:
ssh-copy-id -i $HOME/.ssh/id_dsa.pub root@192.168.0.106
root@server1:~# ssh-copy-id -i $HOME/.ssh/id_dsa.pub root@192.168.0.101
The authenticity of host '192.168.0.101 (192.168.0.101)' can't be established.
RSA key fingerprint is 25:d8:7a:ee:c2:4b:1d:92:a7:3d:16:26:95:56:62:4e.
Are you sure you want to continue connecting (yes/no)? <-- yes (you will see this only if this is the first time you connect to server2)
Warning: Permanently added '192.168.0.101' (RSA) to the list of known hosts.
root@192.168.0.101's password: <-- server2 root password
Now try logging into the machine, with "ssh 'root@192.168.0.101'", and check in:
.ssh/authorized_keys
to make sure we haven't added extra keys that you weren't expecting.
Now check on server2 if server1's public key has correctly been transferred:
server2:
cat $HOME/.ssh/authorized_keys
ssh-dss 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 root@server1.example.tld
Install postfix, dovecot and mysql with one single command:
apt-get -y install postfix postfix-mysql postfix-doc mysql-client mysql-server openssl getmail4 rkhunter binutils dovecot-imapd dovecot-pop3d sudo
Enter the new password for the MySQL root user when requested by the installer. You should choose the same password for both servers. Then answer the next questions as decsribed below:
General type of configuration? <-- Internet site
Mail name? <-- server1.mydomain.tld
SSL certificate required <-- Ok
Use server1.example.tld on the first server and server2.example.tld on the second server.
We want MySQL to listen on all interfaces, not just localhost, therefore we edit /etc/mysql/my.cnf and comment out the line bind-address = 127.0.0.1:
vi /etc/mysql/my.cnf
[...]  

# Instead of skip-networking the default is now to listen only on  
# localhost which is more compatible and is not less secure.  
#bind-address           = 127.0.0.1  

[...]
Then restart MySQL:
/etc/init.d/mysql restart
Now we prepare the MySQL servers for mysql master/master replication.
On server 1:
Log into MySQL on the shell with...
mysql -u root -p
... and enter the MySQL root passord that you had choosen during mysql install. Then execute this commnd on the MySQL shell:
GRANT REPLICATION SLAVE ON *.* TO 'slaveuser'@'%' IDENTIFIED BY 'slave_user_password';
FLUSH PRIVILEGES;
quit;
Replace 'slave_user_password' with a secure password that you want to use for the slave to connect to the master server. Replace this placeholder in the next steps with the password that you had choosen wherever the placeholder occurs.
Now let's configure our 2 MySQL nodes:
On server 1:
vi /etc/mysql/my.cnf
Search for the section that starts with [mysqld], and put the following options into it (commenting out all existing conflicting options):
[...]
[mysqld]
server-id = 1
replicate-same-server-id = 0
auto-increment-increment = 2
auto-increment-offset = 1
 
master-host = 192.168.0.106
master-user = slaveuser
master-password = slave_user_password
master-connect-retry = 60   
 
expire_logs_days        = 10
max_binlog_size         = 500M
log_bin                        = /var/log/mysql/mysql-bin.log  
[...]
Then stop MySQL:
/etc/init.d/mysql stop
Now do nearly the same on server2...
On server 2:
vi /etc/mysql/my.cnf
Search for the section that starts with [mysqld], and put the following options into it (commenting out all existing conflicting options):
[...]
[mysqld]
server-id = 2
replicate-same-server-id = 0
auto-increment-increment = 2
auto-increment-offset = 2
   
master-host = 192.168.0.105
master-user = slaveuser
master-password = slave_user_password
master-connect-retry = 60
 
expire_logs_days        = 10
max_binlog_size         = 500M
log_bin                        = /var/log/mysql/mysql-bin.log  
[...]
Then stop MySQL:
/etc/init.d/mysql stop
Now we have to sync the two mysql servers. We do this by copying over the mysql data directory from the master to the slave and also the debian configuration file that contains the debian-sys-maint user. This can be done as we stopped mysql before on both servers.
On server 1:
scp -pr /var/lib/mysql/* root@server2.example.tld:/var/lib/mysql/
scp -pr /etc/mysql/debian.cnf root@server2.example.tld:/etc/mysql/debian.cnf
Now we start MySQL on the master server again:
/etc/init.d/mysql start
Log into the MySQL shell as root user...
mysql -u root -p
... and execute this command in the MySQL shell...
SHOW MASTER STATUS;
... to get the MySQL master status:
mysql> SHOW MASTER STATUS;
+------------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000002 | 106 | | |
+------------------+----------+--------------+------------------+
1 row in set (0.00 sec)
The information that we need for the next step is the binlog file mysql-bin.000002 and the binlog position 106. We need the same details for server2 later below.
Now execute this command in the MySQL shell on the master to connect it to the slave:
STOP SLAVE;
CHANGE MASTER TO MASTER_HOST='192.168.0.106', MASTER_USER='slaveuser', MASTER_PASSWORD='slave_user_password', MASTER_LOG_FILE='mysql-bin.000002', MASTER_LOG_POS=106;
START SLAVE;
Then check the slave status:
SHOW SLAVE STATUS \G
It is important that both Slave_IO_Running and Slave_SQL_Running have the value Yes in the output.
On server 2:
Log into the MySQL shell as root user...
mysql -u root -p
... and execute this command in the MySQL shell:
STOP SLAVE;
CHANGE MASTER TO MASTER_HOST='192.168.0.105', MASTER_USER='slaveuser', MASTER_PASSWORD='slave_user_password', MASTER_LOG_FILE='mysql-bin.000002', MASTER_LOG_POS=106;
START SLAVE;
Then check the slave status:
SHOW SLAVE STATUS \G
It is important that both Slave_IO_Running and Slave_SQL_Running have the value Yes in the output
The configuration of the mysql master/master replication is finished now and we proceed to install the other software packages.

To install amavisd-new, SpamAssassin, and ClamAV, we run:
apt-get install amavisd-new spamassassin clamav clamav-daemon zoo unzip bzip2 arj nomarch lzop cabextract apt-listchanges libnet-ldap-perl libauthen-sasl-perl clamav-docs daemon libio-string-perl libio-socket-ssl-perl libnet-ident-perl zip libnet-dns-perl
The ISPConfig 3 setup uses amavisd which loads the SpamAssassin filter library internally, so we can stop SpamAssassin to free up some RAM:
/etc/init.d/spamassassin stop
update-rc.d -f spamassassin remove
Then install Apache2, PHP5, phpMyAdmin, FCGI, suExec, Pear, and mcrypt can be installed as follows:
apt-get install apache2 apache2.2-common apache2-doc apache2-mpm-prefork apache2-utils libexpat1 ssl-cert libapache2-mod-php5 php5 php5-common php5-gd php5-mysql php5-imap phpmyadmin php5-cli php5-cgi libapache2-mod-fcgid apache2-suexec php-pear php-auth php5-mcrypt mcrypt php5-imagick imagemagick libapache2-mod-suphp libruby libapache2-mod-ruby php5-xcache
You will see the following question:
Web server to reconfigure automatically: <-- apache2
Configure database for phpmyadmin with dbconfig-common? <-- No
Then run the following command to enable the Apache modules suexec, rewrite, ssl, actions, and include:
a2enmod suexec rewrite ssl actions include ruby dav_fs dav auth_digest
PureFTPd and quota can be installed with the following command:
apt-get -y install pure-ftpd-common pure-ftpd-mysql quota quotatool
Edit the file /etc/default/pure-ftpd-common...
vi /etc/default/pure-ftpd-common
... and make sure the start mode is set to standalone and set VIRTUALCHROOT=true:
[...]
STANDALONE_OR_INETD=standalone
[...]
VIRTUALCHROOT=true
[...]
Edit the file /etc/inetd.conf to prevent inetd from trying to start ftp:
vi /etc/inetd.conf
If there is a line beginning withftp stream tcp, comment it out (if there's no such file, then that is fine, and you don't have to modify /etc/inetd.conf):
[...]
#:STANDARD: These are standard services.
#ftp    stream  tcp     nowait  root    /usr/sbin/tcpd /usr/sbin/pure-ftpd-wrapper
[...]
If you had to modify /etc/inetd.conf, restart inetd now:
/etc/init.d/openbsd-inetd restart
Now we configure PureFTPd to allow FTP and TLS sessions. FTP is a very insecure protocol because all passwords and all data are transferred in clear text. By using TLS, the whole communication can be encrypted, thus making FTP much more secure.
If you want to allow FTP and TLS sessions, run:
echo 1 > /etc/pure-ftpd/conf/TLS
In order to use TLS, we must create an SSL certificate. I create it in /etc/ssl/private/, therefore I create that directory first:
mkdir -p /etc/ssl/private/
Afterwards, we can generate the SSL certificate as follows:
openssl req -x509 -nodes -days 7300 -newkey rsa:2048 -keyout /etc/ssl/private/pure-ftpd.pem -out /etc/ssl/private/pure-ftpd.pem
Country Name (2 letter code) [AU]: <-- Enter your Country Name (e.g., "DE").
State or Province Name (full name) [Some-State]: <-- Enter your State or Province Name.
Locality Name (eg, city) []: <-- Enter your City.
Organization Name (eg, company) [Internet Widgits Pty Ltd]: <-- Enter your Organization Name (e.g., the name of your company).
Organizational Unit Name (eg, section) []: <-- Enter your Organizational Unit Name (e.g. "IT Department").
Common Name (eg, YOUR name) []: <-- Enter the Fully Qualified Domain Name of the system (e.g. "server1.example.com").
Email Address []: <-- Enter your Email Address.
Change the permissions of the SSL certificate:
chmod 600 /etc/ssl/private/pure-ftpd.pem
Then restart PureFTPd:
/etc/init.d/pure-ftpd-mysql restart
Edit /etc/fstab. Mine looks like this (I added ,usrjquota=aquota.user,grpjquota=aquota.group,jqfmt=vfsv0 to the partition with the mount point /):
vi /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
#                
proc            /proc           proc    defaults        0       0
# / was on /dev/sda1 during installation
UUID=92bceda2-5ae4-4e3a-8748-b14da48fb297 /               ext3    errors=remount-ro,usrjquota=aquota.user,grpjquota=aquota.group,jqfmt=vfsv0 0       1
# swap was on /dev/sda5 during installation
UUID=e24b3e9e-095c-4b49-af27-6363a4b7d094 none            swap    sw              0       0
/dev/scd0       /media/cdrom0   udf,iso9660 user,noauto     0       0
/dev/fd0        /media/floppy0  auto    rw,user,noauto  0       0
To enable quota, run these commands:
mount -o remount /
quotacheck -avugm
quotaon -avug
Install BIND DNS Server:
apt-get -y install bind9 dnsutils
Install vlogger, webalizer, and awstats:
apt-get -y install vlogger webalizer awstats geoip-database
Open /etc/cron.d/awstats afterwards...
vi /etc/cron.d/awstats
... and comment out both cron jobs in that file:
#*/10 * * * * www-data [ -x /usr/share/awstats/tools/update.sh ] && /usr/share/awstats/tools/update.sh

# Generate static reports:
 #10 03 * * * www-data [ -x /usr/share/awstats/tools/buildstatic.sh
Install Jailkit: Jailkit is needed only if you want to chroot SSH users. It can be installed as follows (important: Jailkit must be installed before ISPConfig - it cannot be installed afterwards!):
apt-get -y install build-essential autoconf automake1.9 libtool flex bison
cd /tmp
wget http://olivier.sessink.nl/jailkit/jailkit-2.14.tar.gz
tar xvfz jailkit-2.14.tar.gz
cd jailkit-2.14
./configure
make
make install
cd ..
rm -rf jailkit-2.14*
Install fail2ban: This is optional but recommended, because the ISPConfig monitor tries to show the log:
apt-get install fail2ban
To make fail2ban monitor PureFTPd and Dovecot, create the file /etc/fail2ban/jail.local:
vi /etc/fail2ban/jail.local
[pureftpd]
enabled  = true
port     = ftp
filter   = pureftpd
logpath  = /var/log/syslog
maxretry = 3

[dovecot-pop3imap]
enabled = true
filter = dovecot-pop3imap
action = iptables-multiport[name=dovecot-pop3imap, port="pop3,pop3s,imap,imaps", protocol=tcp]
logpath = /var/log/mail.log
maxretry = 5
Then create the following two filter files:
vi /etc/fail2ban/filter.d/pureftpd.conf
[Definition]
failregex = .*pure-ftpd: \(.*@\) \[WARNING\] Authentication failed for user.*
ignoreregex =
vi /etc/fail2ban/filter.d/dovecot-pop3imap.conf
[Definition]
failregex = (?: pop3-login|imap-login): .*(?:Authentication failure|Aborted login \(auth failed|Aborted login \(tried to use disabled|Disconnected \(auth failed|Aborted login \(\d+ authentication attempts).*rip=(?P\S*),.*
ignoreregex =
Restart fail2ban afterwards:
/etc/init.d/fail2ban restart
To install the SquirrelMail webmail client, run:
apt-get install squirrelmail
Then create the following symlink...
ln -s /usr/share/squirrelmail/ /var/www/webmail
... and configure SquirrelMail:
squirrelmail-configure
We must tell SquirrelMail that we are using Dovecot-IMAP/-POP3:
SquirrelMail Configuration : Read: config.php (1.4.0)
---------------------------------------------------------
Main Menu --
1.  Organization Preferences
2.  Server Settings
3.  Folder Defaults
4.  General Options
5.  Themes
6.  Address Books
7.  Message of the Day (MOTD)
8.  Plugins
9.  Database
10. Languages

D.  Set pre-defined settings for specific IMAP servers

C   Turn color on
S   Save data
Q   Quit

Command >> <-- D


SquirrelMail Configuration : Read: config.php
---------------------------------------------------------
While we have been building SquirrelMail, we have discovered some
preferences that work better with some servers that don't work so
well with others.  If you select your IMAP server, this option will
set some pre-defined settings for that server.

Please note that you will still need to go through and make sure
everything is correct.  This does not change everything.  There are
only a few settings that this will change.

Please select your IMAP server:
    bincimap    = Binc IMAP server
    courier     = Courier IMAP server
    cyrus       = Cyrus IMAP server
    dovecot     = Dovecot Secure IMAP server
    exchange    = Microsoft Exchange IMAP server
    hmailserver = hMailServer
    macosx      = Mac OS X Mailserver
    mercury32   = Mercury/32
    uw          = University of Washington's IMAP server
    gmail       = IMAP access to Google mail (Gmail) accounts

    quit        = Do not change anything
Command >> <-- dovecot


SquirrelMail Configuration : Read: config.php
---------------------------------------------------------
While we have been building SquirrelMail, we have discovered some
preferences that work better with some servers that don't work so
well with others.  If you select your IMAP server, this option will
set some pre-defined settings for that server.

Please note that you will still need to go through and make sure
everything is correct.  This does not change everything.  There are
only a few settings that this will change.

Please select your IMAP server:
    bincimap    = Binc IMAP server
    courier     = Courier IMAP server
    cyrus       = Cyrus IMAP server
    dovecot     = Dovecot Secure IMAP server
    exchange    = Microsoft Exchange IMAP server
    hmailserver = hMailServer
    macosx      = Mac OS X Mailserver
    mercury32   = Mercury/32
    uw          = University of Washington's IMAP server
    gmail       = IMAP access to Google mail (Gmail) accounts

    quit        = Do not change anything
Command >> dovecot

              imap_server_type = dovecot
         default_folder_prefix = 
                  trash_folder = Trash
                   sent_folder = Sent
                  draft_folder = Drafts
            show_prefix_option = false
          default_sub_of_inbox = false
show_contain_subfolders_option = false
            optional_delimiter = detect
                 delete_folder = false

Press enter to continue... <-- press ENTER


SquirrelMail Configuration : Read: config.php (1.4.0)
---------------------------------------------------------
Main Menu --
1.  Organization Preferences
2.  Server Settings
3.  Folder Defaults
4.  General Options
5.  Themes
6.  Address Books
7.  Message of the Day (MOTD)
8.  Plugins
9.  Database
10. Languages

D.  Set pre-defined settings for specific IMAP servers

C   Turn color on
S   Save data
Q   Quit

Command >> <-- S


SquirrelMail Configuration : Read: config.php (1.4.0)
---------------------------------------------------------
Main Menu --
1.  Organization Preferences
2.  Server Settings
3.  Folder Defaults
4.  General Options
5.  Themes
6.  Address Books
7.  Message of the Day (MOTD)
8.  Plugins
9.  Database
10. Languages

D.  Set pre-defined settings for specific IMAP servers

C   Turn color on
S   Save data
Q   Quit

Command >> <-- Q
Next we enable a global Alias /webmail for Squirrelmail:
cd /etc/apache2/conf.d/
ln -s ../../squirrelmail/apache.conf squirrelmail.conf
/etc/init.d/apache2 reload
Now open /etc/apache2/conf.d/squirrelmail.conf...
vi /etc/apache2/conf.d/squirrelmail.conf
... and add the following lines to the container that makes sure that mod_php is used for accessing SquirrelMail, regardless of what PHP mode you select for your website in ISPConfig:
[...]
Alias /webmail /usr/share/squirrelmail

   Options FollowSymLinks

   AddType application/x-httpd-php .php
   php_flag magic_quotes_gpc Off
   php_flag track_vars On
   php_admin_flag allow_url_fopen Off
   php_value include_path .
   php_admin_value upload_tmp_dir /var/lib/squirrelmail/tmp
   php_admin_value open_basedir /usr/share/squirrelmail:/etc/squirrelmail:/var/lib/squirrelmail:/etc/hostname:/etc/mailname
   php_flag register_globals off


   DirectoryIndex index.php

 
# access to configtest is limited by default to prevent information leak

   order deny,allow
   deny from all
   allow from 127.0.0.1


[...]
Create the directory /var/lib/squirrelmail/tmp...
mkdir /var/lib/squirrelmail/tmp
... and make it owned by the user www-data:
chown www-data /var/lib/squirrelmail/tmp
Reload Apache again:
/etc/init.d/apache2 reload
That's it already - /etc/apache2/conf.d/squirrelmail.conf defines an alias called /squirrelmail that points to SquirrelMail's installation directory /usr/share/squirrelmail.
You can now access SquirrelMail from your web site as follows:
http://www.example.com/squirrelmail
You can also access it from the ISPConfig control panel vhost as follows (this doesn't need any configuration in ISPConfig):
http://server1.example.com:8080/squirrelmail
Next we install Unison. Unison is used to sync the /var/www and /var/vmail directories between master and slave
apt-get install unison
Now we install a unison configuration file on the first server.
On server 1:
Create a new file /root/.unison/default.prf on server1...
mkdir /root/.unison
vi /root/.unison/default.prf
... and add the following content:
# Roots of the synchronization
root = /var
root = ssh://192.168.0.106//var/
 
# Paths to synchronize
path = www
path = vmail
 
# Some regexps specifying names and paths to ignore
#ignore = Path stats    ## ignores /var/www/stats
#ignore = Path stats/*  ## ignores /var/www/stats/*
#ignore = Path */stats  ## ignores /var/www/somedir/stats, but not /var/www/a/b/c/stats
#ignore = Name *stats   ## ignores all files/directories that end with "stats"
#ignore = Name stats*   ## ignores all files/directories that begin with "stats"
#ignore = Name *.tmp    ## ignores all files with the extension .tmp
   
#          When set to true, this flag causes the user interface to skip
#          asking for confirmations on non-conflicting changes. (More
#          precisely, when the user interface is done setting the
#          propagation direction for one entry and is about to move to the
#          next, it will skip over all non-conflicting entries and go
#          directly to the next conflict.)
auto=true
   
#          When this is set to true, the user interface will ask no
#          questions at all. Non-conflicting changes will be propagated;
#          conflicts will be skipped.
batch=true
   
#          !When this is set to true, Unison will request an extra
#          confirmation if it appears that the entire replica has been
#          deleted, before propagating the change. If the batch flag is
#          also set, synchronization will be aborted. When the path
#          preference is used, the same confirmation will be requested for
#          top-level paths. (At the moment, this flag only affects the
#          text user interface.) See also the mountpoint preference.
confirmbigdel=true
   
#          When this preference is set to true, Unison will use the
#          modification time and length of a file as a `pseudo inode
#          number' when scanning replicas for updates, instead of reading
#          the full contents of every file. Under Windows, this may cause
#          Unison to miss propagating an update if the modification time
#          and length of the file are both unchanged by the update.
#          However, Unison will never overwrite such an update with a
#          change from the other replica, since it always does a safe
#          check for updates just before propagating a change. Thus, it is
#          reasonable to use this switch under Windows most of the time
#          and occasionally run Unison once with fastcheck set to false,
#          if you are worried that Unison may have overlooked an update.
#          The default value of the preference is auto, which causes
#          Unison to use fast checking on Unix replicas (where it is safe)
#          and slow checking on Windows replicas. For backward
#          compatibility, yes, no, and default can be used in place of
#          true, false, and auto. See the section "Fast Checking" for more
#          information.
fastcheck=true

#          When this flag is set to true, the group attributes of the
#          files are synchronized. Whether the group names or the group
#          identifiers are synchronizeddepends on the preference numerids.
group=true
   
#          When this flag is set to true, the owner attributes of the
#          files are synchronized. Whether the owner names or the owner
#          identifiers are synchronizeddepends on the preference
#          extttnumerids.
owner=true
   
#          Including the preference -prefer root causes Unison always to
#          resolve conflicts in favor of root, rather than asking for
#          guidance from the user. (The syntax of root is the same as for
#          the root preference, plus the special values newer and older.)
#          This preference is overridden by the preferpartial preference.
#          This preference should be used only if you are sure you know
#          what you are doing!
prefer=newer
   
#          When this preference is set to true, the textual user interface
#          will print nothing at all, except in the case of errors.
#          Setting silent to true automatically sets the batch preference
#          to true.
silent=true
   
#          When this flag is set to true, file modification times (but not
#          directory modtimes) are propagated.
times=true
We want to automate synchronization, that is why we create a cron job for it on server1.example.tld:
crontab -e
*/5 * * * * /usr/bin/unison &> /dev/null
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