Contents
1. Antivirus software Clamav installed
Install Clam AntiVirus, a free anti-virus software for Linux, as an anti-virus measure.
By installing this anti-virus software, you can not only scan the entire server for viruses, but also scan incoming and outgoing mail for viruses if you build and configure a mail server.
1.1 Install
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# apt install clamav clamav-daemon |
1.2 Virus Definition Update
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# systemctl stop clamav-freshclam # freshclam |
ERROR: /var/log/clamav/freshclam.log is locked by another process
ERROR: Problem with internal logger (UpdateLogFile = /var/log/clamav/freshclam.log).
ERROR: initialize: libfreshclam init failed.
ERROR: Initialization error!
If the above error occurs, delete the log file once and change the log rotate settings as follows.
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# rm /var/log/clamav/freshclam.log # touch /var/log/clamav/freshclam.log # chown clamav:clamav /var/log/clamav/freshclam.log |
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# freshclam ue Oct 11 08:34:44 2022 -> ClamAV update process started at Tue Oct 11 08:34:44 2022 Tue Oct 11 08:34:44 2022 -> daily.cvd database is up-to-date (version: 26685, sigs: 2007556, f-level: 90, builder: raynman) Tue Oct 11 08:34:44 2022 -> main.cvd database is up-to-date (version: 62, sigs: 6647427, f-level: 90, builder: sigmgr) Tue Oct 11 08:34:44 2022 -> bytecode.cvd database is up-to-date (version: 333, sigs: 92, f-level: 63, builder: awillia2) |
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# systemctl start clamav-freshclam |
Edit configuration file
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# vi /etc/logrotate.d/clamav-freshclam create 640 clamav adm ↓ create 640 clamav clamav |
Automatic virus definition update confirmation
Ensure that the service is registered for automatic virus definition updates.
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# service clamav-freshclam status |
It appears as follows
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● clamav-freshclam.service - ClamAV virus database updater Loaded: loaded (/lib/systemd/system/clamav-freshclam.service; enabled; vendor preset: enab> Active: active (running) since Tue 2022-10-11 08:36:04 JST; 1min 45s ago Docs: man:freshclam(1) man:freshclam.conf(5) https://docs.clamav.net/ Main PID: 1564 (freshclam) Tasks: 1 (limit: 2300) Memory: 1.8M CPU: 8ms CGroup: /system.slice/clamav-freshclam.service mq1564 /usr/bin/freshclam -d --foreground=true Oct 11 08:36:04 Lepard systemd[1]: Started ClamAV virus database updater. Oct 11 08:36:04 Lepard freshclam[1564]: Tue Oct 11 08:36:04 2022 -> ClamAV update process start> Oct 11 08:36:04 Lepard freshclam[1564]: Tue Oct 11 08:36:04 2022 -> daily.cvd database is up-to> Oct 11 08:36:04 Lepard freshclam[1564]: Tue Oct 11 08:36:04 2022 -> main.cvd database is up-to-> Oct 11 08:36:04 Lepard freshclam[1564]: Tue Oct 11 08:36:04 2022 -> bytecode.cvd database is up |
Logs are recorded in the file /var/log/clamav/freshclam.log.
1.3 Virus Check Confirmation
①Running manual virus checks
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# clamscan --infected --remove --recursive /home ----------- SCAN SUMMARY ----------- Known viruses: 8639598 Engine version: 0.103.7 Scanned directories: 3 Scanned files: 7 Infected files: 0 Data scanned: 0.00 MB Data read: 0.00 MB (ratio 0.00:1) Time: 19.171 sec (0 m 19 s) Start Date: 2022:10:11 08:39:24 End Date: 2022:10:11 08:39:43 |
Infected files: 0, so no virus
②Virus detection by downloading test viruses
Download a harmless virus and test it for detection.
Log in as a general user and check
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# su - <user name> $ wget http://www.eicar.org/download/eicar.com $ clamscan --infected --remove --recursive /home /home/huong/eicar.com: Win.Test.EICAR_HDB-1 FOUND /home/huong/eicar.com: Removed. ----------- SCAN SUMMARY ----------- Known viruses: 8639598 Engine version: 0.103.7 Scanned directories: 3 Scanned files: 8 Infected files: 1 Data scanned: 0.00 MB Data read: 0.00 MB (ratio 0.00:1) Time: 12.765 sec (0 m 12 s) Start Date: 2022:10:11 08:41:32 End Date: 2022:10:11 08:41:45 |
As you can see, the virus is notified with the message "FOUND" and "Infected files: 1". The "--remove" option was also added, so the test virus was removed.
1.4 Create a script file to do a full scan
①Create a script file storage directory (/opt/script) in advance.
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$ su - Password: # mkdir /opt/script |
②Create script file
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# vi /opt/script/clam-full.sh |
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#!/bin/sh echo ========================================= date hostname clamscan / \ --infected \ --recursive \ --log=/var/log/clamav/clamscan.log \ --move=/var/log/clamav/virus \ --exclude-dir=^/boot \ --exclude-dir=^/sys \ --exclude-dir=^/proc \ --exclude-dir=^/dev \ --exclude-dir=^/var/log/clamav/virus if [ $? = 0 ]; then echo “Virus not detected.” else echo “Virus detection!!” fi |
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# chmod +x /opt/script/clam-full.sh |
If not, a runtime error will occur because the above script specifies it as an excluded directory.
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# mkdir /var/log/clamav/virus |
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# /opt/script/clam-full.sh |
Logs are recorded in the /var/log/clamav/clamscan.log file.
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# crontab -e 0 2 * * mon /opt/script/clam-full.sh >> /var/log/clamav/clamascan.log |
2. Mail server installation
Postfix was developed as a Mail Transport Agent (MTA) to replace sendmail, and is a mail server that is highly compatible with sendmail, secure, easy to maintain, and fast.
In addition, since Postfix only functions as an SMTP server for sending mail, the POP server Dovecot for receiving mail will be installed separately in the latter half.
2.1 Postfix : Installation Configuration
①Install Postfix
Install Postfix and build an SMTP server; SMTP uses 25/TCP.
To prevent unauthorized mail relay, use the SASL function of Dovecot, described below, and configure Postfix so that authentication is also required for sending.
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# apt -y install postfix sasl2-bin |
You will be asked to select general configuration settings, select "No configuration " to set them manually later
②Edit configuration file (main.cf)
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# cp /usr/share/postfix/main.cf.dist /etc/postfix/main.cf # vi /etc/postfix/main.cf |
Editorial content
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# Line 78: Uncomment mail_owner = postfix # Line 94: Uncomment and specify host name myhostname = mail.<domain name> # Line 102: Uncomment and specify domain name mydomain = <domain name> # Line 123: Uncomment myorigin = $mydomain # Line 137: Uncomment inet_interfaces = all # Line 185: Uncomment185 mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain # Line 228: Uncomment local_recipient_maps = unix:passwd.byname $alias_maps # Line 270: Uncomment mynetworks_style = subnet # Line 287: Own network addition mynetworks = 127.0.0.0/8, 192.168.11.0/24 # Line 407: Uncomment alias_maps = hash:/etc/aliases # Line 418: Uncomment alias_database = hash:/etc/aliases # Line 440: Uncomment440 home_mailbox = Maildir/ # Line 576: Make it a comment and add below it #smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu) smtpd_banner = $myhostname ESMTP # Line 650：add sendmail_path = /usr/sbin/postfix # Line 655：add newaliases_path = /usr/bin/newaliases # Line 660：add mailq_path = /usr/bin/mailq # Line 666：add setgid_group = postdrop # Line 670：Comment #html_directory = # Line 674：Comment #manpage_directory = # Line 679：Comment #sample_directory = # Line 683：Comment #readme_directory = # Add to last line # SMTP VRFY command is disabled disable_vrfy_command = yes # Requests a HELO command from the client smtpd_helo_required = yes # Limit sent/received mail size to 10M message_size_limit = 10485760 # Limit mailbox size to 1G mailbox_size_limit = 1073741824 # SMTP-Auth Settings smtpd_sasl_type = dovecot smtpd_sasl_path = private/auth smtpd_sasl_auth_enable = yes smtpd_sasl_security_options = noanonymous smtpd_sasl_local_domain = $myhostname smtpd_recipient_restrictions = permit_mynetworks, permit_auth_destination, permit_sasl_authenticated, reject |
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# vi /etc/postfix/master.cf |
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smtp inet n - y - - smtpd #smtp inet n - y - 1 postscreen #smtpd pass - - y - - smtpd #dnsblog unix - - y - 0 dnsblog #tlsproxy unix - - y - 0 tlsproxy submission inet n - y - - smtpd # -o syslog_name=postfix/submission # -o smtpd_tls_security_level=encrypt -o smtpd_sasl_auth_enable=yes # -o smtpd_tls_auth_only=yes |
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# newaliases # systemctl restart postfix |
2.2 Dovecot : Installation Configuration
①Install Dovecot
Install Dovecot and build a POP/IMAP server, using 110/TCP for POP and 143/TCP for IMAP.
②Configure Dovecot to provide SASL functionality for Postfix
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# apt -y install dovecot-core dovecot-pop3d dovecot-imapd # vi /etc/dovecot/dovecot.conf Line 30：Uncomment listen = *, :: |
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# vi /etc/dovecot/conf.d/10-auth.conf Line 10：Uncomment and change (also allow plain text authentication) disable_plaintext_auth = no Line 100：add auth_mechanisms = plain login |
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# vi /etc/dovecot/conf.d/10-mail.conf Line 30：Change to Maildir format mail_location = maildir:~/Maildir |
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# vi /etc/dovecot/conf.d/10-master.conf Line 107-109：Uncommented and added # Postfix smtp-authi unix_listener /var/spool/postfix/private/auth { mode = 0666 user = postfix group = postfix } |
③Reflect settings, reboot
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# systemctl restart dovecot |
2.3 Email User Account Registration
Register a user account for e-mail.
This setting is for when a user account on the OS is also used for e-mail.
If you want to use mail with a user account on the OS, no additional configuration is required, just register the OS user
①Mail client installed
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# apt -y install mailutils |
②Mailboxes are set to refer to Maildir
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# echo 'export MAIL=$HOME/Maildir/' >> /etc/profile.d/mail.sh |
2.4 Opening Ports
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# ufw allow pop3 # ufw allow imap # ufw allow smtp # ufw reload |
2.5 operation check ①
①Send test mail to yourself [mail (user name)@(host name)].
user name : huong
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# su - huong $ mail huong@localhost Cc: Subject: Test Mail This is the first mail. |
Check incoming mail
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$ mail "/home/huong/Maildir/": 1 message 1 new >N 1 huong Tue Oct 11 00:35 13/431 Test Mail ? 1 Return-Path: <huong@Lepard> X-Original-To: huong@localhost Delivered-To: huong@localhost Received: by mail.korodes.com (Postfix, from userid 1000) id B80F040630; Tue, 11 Oct 2022 09:35:36 +0900 (JST) To: <huong@localhost> Subject: Test Mail X-Mailer: mail (GNU Mailutils 3.10) Message-Id: <20221011003536.B80F040630@mail.korodes.com> Date: Tue, 11 Oct 2022 09:35:36 +0900 (JST) From: huong <huong@Lepard> This is the first mail. ? |
2.6 operation check ②
Set up and confirm your account in Mozilla Thunderbird
①Start Thunderbird, and click "Tools", "Account Settings".
②「Account Actions」「Add Mail Account」
③Your full name" is an optional name
Email addtess" is "huong@korodes.com" added earlier
Password" is the password for user huong
Click on "Configure manually"
④Set "INCOMMING SERVER" and "OUTGOING SERVER" as shown below and click "Re-test".
⑤The "Server Found" message appears.(The following settings were found by probinfg the given server)
After clicking "Done," the following "Warning" appears, but there is no problem, so click "Confirm.
⑥Click "Finish" when "Account syccessfuly created" is displayed.
3 Applied ClamAV to mail server Postfix
Set up Postfix and Clamav to work together to scan incoming and outgoing mail in real time.
①Install Amavisd and Clamav Daemon and start Clamav Daemon
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# apt -y install clamav-daemon amavisd-new |
If the server is not using a fully qualified domain name (FQDN) as the hostname, Amavis may fail to start. Also, since the OS hostname may change, set a valid hostname directly in the Amavis configuration file
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# vi /etc/amavis/conf.d/05-node_id use strict; # $myhostname is used by amavisd-new for node identification, and it is # important to get it right (e.g. for ESMTP EHLO, loop detection, and so on) . chomp($myhostname = `hostname --fqdn`); # To manually set $myhostname, edit the following line with the correct Full y # Qualified Domain Name (FQDN) and remove the # at the beginning of the line . # $myhostname = "mail.<domain name>"; 1; # ensure a defined return |
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# vi /etc/amavis/conf.d/15-content_filter_mode Uncomment and enable virus scan @bypass_virus_checks_maps = ( \%bypass_virus_checks, \@bypass_virus_checks_acl, \$bypass_virus_checks_re); |
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# echo '<yourDomain>' > /etc/mailname |
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# vi /etc/postfix/main.cf Add to last line content_filter=smtp-amavis:[127.0.0.1]:10024 |
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# vi /etc/postfix/master.cf |
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# Add all the following lines to the last line smtp-amavis unix - - n - 2 smtp -o smtp_data_done_timeout=1200 -o smtp_send_xforward_command=yes -o disable_dns_lookups=yes 127.0.0.1:10025 inet n - n - - smtpd -o content_filter= -o local_recipient_maps= -o relay_recipient_maps= -o smtpd_restriction_classes= -o smtpd_client_restrictions= -o smtpd_helo_restrictions= -o smtpd_sender_restrictions= -o smtpd_recipient_restrictions=permit_mynetworks,reject -o mynetworks=127.0.0.0/8 -o strict_rfc821_envelopes=yes -o smtpd_error_sleep_time=0 -o smtpd_soft_error_limit=1001 -o smtpd_hard_error_limit=1000 |
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# usermod -G clamav amavis # usermod -G amavis clamav # systemctl restart clamav-daemon amavis postfix |
