Locking Down Linux: Using Ubuntu as Your Primary OS, Part 4 (Auditing, Antivirus & Monitoring)

Jul 3, 2018 11:29 PM

Dec 3, 2020 09:13 PM

You've protected your Ubuntu system from physical attacks, annoyed network hackers, and sandboxed potentially malicious applications. Great! Now, the next logical steps to locking down your OS include thoroughly auditing Ubuntu for weak points, using antivirus software that respects your privacy, and monitoring system logs like a boss.

This is the final part of our mini-series on strengthening your primary Ubuntu system. You'll learn about hardening weak points in the OS using a well-respected, open-source auditing tool. Besides that, we'll check out ClamAV, an antivirus software that won't send your sensitive files to for-profit company servers. You'll also see how to allow or deny web access for all the apps on your computer. And when I say "monitoring system logs like a boss," I'm talking about the /var/log/ directory.

If you missed the beginning of this article series, you should check out the first part to learn more about my motivations for starting this four-part guide.

Part 3: Using Ubuntu as Your Primary OS (App Hardening & Sandboxing)

Step 1: Audit Your System with Lynis

Lynis, created by CISOfy, is a security auditing tool for Linux and UNIX-based operating systems that assists penetration testers with system hardening and information security compliance standards such as ISO27001, HIPAA, and PCI DSS. While Lynis is designed for companies and organizations, it can be used to audit normal Ubuntu installations with a high degree of definition and expertise.

Downloading Lynis

Lynis is available on GitHub and can be downloaded using the sudo wget 'github.com/CISOfy/lynis/archive/master.zip' command, as seen here:

~$ sudo wget 'https://github.com/CISOfy/lynis/archive/master.zip'

---- https://github.com/CISOfy/lynis/archive/master.zip
Resolving github.com (github.com)... 192.30.253.112
Connecting to github.com (github.com)|192.30.253.112|:443... connected.
HTTP request sent, awaiting response... 302 Found
Location: https://codeload.github.com/CISOfy/lynis/zip/master [following]
---- https://codeload.github.com/CISOfy/lynis/zip/master
Resolving codeload.github.com (codeload.github.com)... 192.30.253.120
Connecting to codeload.github.com (codeload.github.com)|192.30.253.120|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 345734 (338K) [application/zip]
Saving to: ‘master.zip’

master.zip                          100%[===================================================================>] 337.63K   237KB/s    in 1.4s

(237 KB/s) - ‘master.zip’ saved [345734/345734]

I'm using sudo for the following Lynis commands because the tool and its directories require privileged access to certain areas of the Ubuntu operating system to properly audit everything. Normally, it's unsafe to store and use binaries and applications in this way, but we'll be deleting Lynis immediately after using it.

Decompressing the Download

With the Lynis ZIP downloaded, use sudo unzip master.zip to decompress the archive.

~$ sudo unzip master.zip

Archive:  master.zip
6e0ac57b68bfd39dd7d464e93ec85203ee683313
   creating: lynis-master/
 extracting: lynis-master/.gitignore
  inflating: lynis-master/.travis.yml
  inflating: lynis-master/CHANGELOG.md
  inflating: lynis-master/CODE_OF_CONDUCT.md
  inflating: lynis-master/CONTRIBUTING.md
  inflating: lynis-master/CONTRIBUTORS.md
  inflating: lynis-master/FAQ
  inflating: lynis-master/INSTALL
  inflating: lynis-master/LICENSE
  inflating: lynis-master/README
  inflating: lynis-master/README.md
   creating: lynis-master/db/
  inflating: lynis-master/db/fileperms.db
  inflating: lynis-master/db/hints.db
 extracting: lynis-master/db/integrity.db
   creating: lynis-master/db/languages/
  inflating: lynis-master/db/languages/az
    linking: lynis-master/db/languages/br  -> pt
  inflating: lynis-master/db/languages/cn
  inflating: lynis-master/db/languages/de
  inflating: lynis-master/db/languages/en
    linking: lynis-master/db/languages/en-GB  -> en
    linking: lynis-master/db/languages/en-US  -> en
  inflating: lynis-master/db/languages/es
  inflating: lynis-master/db/languages/fi
  inflating: lynis-master/db/languages/fr
  inflating: lynis-master/db/languages/gr
  inflating: lynis-master/db/languages/he
  inflating: lynis-master/db/languages/hu
  inflating: lynis-master/db/languages/it
  inflating: lynis-master/db/languages/ja
  inflating: lynis-master/db/languages/nb-NO
  inflating: lynis-master/db/languages/nl
    linking: lynis-master/db/languages/nl-BE  -> nl
    linking: lynis-master/db/languages/nl-NL  -> nl
  inflating: lynis-master/db/languages/pl
  inflating: lynis-master/db/languages/pt
  inflating: lynis-master/db/languages/ru
  inflating: lynis-master/db/languages/se
  inflating: lynis-master/db/languages/tr
  inflating: lynis-master/db/malware-susp.db
  inflating: lynis-master/db/malware.db
 extracting: lynis-master/db/sbl.db
  inflating: lynis-master/db/tests.db
  inflating: lynis-master/default.prf
  inflating: lynis-master/developer.prf
   creating: lynis-master/extras/
  inflating: lynis-master/extras/README
   creating: lynis-master/extras/bash_completion.d/
  inflating: lynis-master/extras/bash_completion.d/lynis
  inflating: lynis-master/extras/build-lynis.sh
  inflating: lynis-master/extras/check-lynis.sh
  inflating: lynis-master/extras/files.dat
  inflating: lynis-master/extras/lynis.spec
   creating: lynis-master/extras/openbsd/
  inflating: lynis-master/extras/openbsd/+CONTENTS
   creating: lynis-master/extras/systemd/
  inflating: lynis-master/extras/systemd/lynis.service
  inflating: lynis-master/extras/systemd/lynis.timer
   creating: lynis-master/extras/travis-ci/
 extracting: lynis-master/extras/travis-ci/before_script.sh
   creating: lynis-master/include/
  inflating: lynis-master/include/binaries
  inflating: lynis-master/include/consts
  inflating: lynis-master/include/data_upload
  inflating: lynis-master/include/functions
  inflating: lynis-master/include/helper_audit_dockerfile
  inflating: lynis-master/include/helper_configure
  inflating: lynis-master/include/helper_show
  inflating: lynis-master/include/helper_system_remote_scan
  inflating: lynis-master/include/helper_update
  inflating: lynis-master/include/osdetection
  inflating: lynis-master/include/parameters
  inflating: lynis-master/include/profiles
  inflating: lynis-master/include/report
  inflating: lynis-master/include/tests_accounting
  inflating: lynis-master/include/tests_authentication
  inflating: lynis-master/include/tests_banners
  inflating: lynis-master/include/tests_boot_services
  inflating: lynis-master/include/tests_containers
  inflating: lynis-master/include/tests_crypto
  inflating: lynis-master/include/tests_custom.template
  inflating: lynis-master/include/tests_databases
  inflating: lynis-master/include/tests_dns
  inflating: lynis-master/include/tests_file_integrity
  inflating: lynis-master/include/tests_file_permissions
  inflating: lynis-master/include/tests_filesystems
  inflating: lynis-master/include/tests_firewalls
  inflating: lynis-master/include/tests_hardening
  inflating: lynis-master/include/tests_homedirs
  inflating: lynis-master/include/tests_insecure_services
  inflating: lynis-master/include/tests_kernel
  inflating: lynis-master/include/tests_kernel_hardening
  inflating: lynis-master/include/tests_ldap
  inflating: lynis-master/include/tests_logging
  inflating: lynis-master/include/tests_mac_frameworks
  inflating: lynis-master/include/tests_mail_messaging
  inflating: lynis-master/include/tests_malware
  inflating: lynis-master/include/tests_memory_processes
  inflating: lynis-master/include/tests_nameservices
  inflating: lynis-master/include/tests_networking
  inflating: lynis-master/include/tests_php
  inflating: lynis-master/include/tests_ports_packages
  inflating: lynis-master/include/tests_printers_spools
  inflating: lynis-master/include/tests_scheduling
  inflating: lynis-master/include/tests_shells
  inflating: lynis-master/include/tests_snmp
  inflating: lynis-master/include/tests_squid
  inflating: lynis-master/include/tests_ssh
  inflating: lynis-master/include/tests_storage
  inflating: lynis-master/include/tests_storage_nfs
  inflating: lynis-master/include/tests_system_integrity
  inflating: lynis-master/include/tests_time
  inflating: lynis-master/include/tests_tooling
  inflating: lynis-master/include/tests_usb
  inflating: lynis-master/include/tests_virtualization
  inflating: lynis-master/include/tests_webservers
  inflating: lynis-master/include/tool_tips
  inflating: lynis-master/lynis
  inflating: lynis-master/lynis.8
   creating: lynis-master/plugins/
  inflating: lynis-master/plugins/README
  inflating: lynis-master/plugins/custom_plugin.template
  inflating: lynis-master/plugins/plugin_pam_phase1
  inflating: lynis-master/plugins/plugin_systemd_phase1
finishing deferred symbolic links:
  lynis-master/db/languages/br -> pt
  lynis-master/db/languages/en-GB -> en
  lynis-master/db/languages/en-US -> en
  lynis-master/db/languages/nl-BE -> nl
  lynis-master/db/languages/nl-NL -> nl

Then, change (cd) into the newly created lynis-master/ directory:

~$ cd lynis-master

The Lynis binary should already have permissions to execute on your machine, but in case it doesn't, use the sudo chmod +x lynis command.

~/lynis-master$ sudo chmod +x lynis

Running Lynis

To test Lynis and view the available options, use the help (-h) command, i.e., sudo ./lynis -h.

~/lynis-master$ sudo ./lynis -h

[ Lynis 2.6.5 ]

################################################################################
  Lynis comes with ABSOLUTELY NO WARRANTY. This is free software, and you are
  welcome to redistribute it under the terms of the GNU General Public License.
  See the LICENSE file for details about using this software.

  2007-2018, CISOfy - https://cisofy.com/lynis/
  Enterprise support available (compliance, plugins, interface and tools)
################################################################################

[+] Initializing program
------------------------------------

  Usage: lynis command [options]

  Command:

    audit
        audit system                  : Perform local security scan
        audit system remote <host>    : Remote security scan
        audit dockerfile <file>       : Analyze Dockerfile

    show
        show                          : Show all commands
        show version                  : Show Lynis version
        show help                     : Show help

    update
        update info                   : Show update details

  Options:

    --no-log                          : Don't create a log file
    --pentest                         : Non-privileged scan (useful for pentest)
    --profile <profile>               : Scan the system with the given profile file
    --quick (-Q)                      : Quick mode, don't wait for user input

    Layout options
    --no-colors                       : Don't use colors in output
    --quiet (-q)                      : No output
    --reverse-colors                  : Optimize color display for light backgrounds

    Misc options
    --debug                           : Debug logging to screen
    --view-manpage (--man)            : View man page
    --verbose                         : Show more details on screen
    --version (-V)                    : Display version number and quit

    Enterprise options
    --plugindir <path>                : Define path of available plugins
    --upload                          : Upload data to central node

    More options available. Run './lynis show options', or use the man page.

To begin auditing the operating system, use the audit system arguments, such as sudo ./lynis audit system.

~/lynis-master$ sudo ./lynis audit system

[ Lynis 2.6.5 ]

[+] Initializing program
------------------------------------
  - Detecting OS...                                           [ DONE ]
  - Checking profiles...                                      [ DONE ]

  ---------------------------------------------------
  Program version:           2.6.5
  Operating system:          Linux
  Operating system name:     Ubuntu Linux
  Operating system version:  18.04
  Kernel version:            4.15.0
  Hardware platform:         x86_64
  Hostname:                  nullbyte
  ---------------------------------------------------
  Profiles:                  /home/tokyoneon/Desktop/lynis-master/default.prf
  Log file:                  /var/log/lynis.log
  Report file:               /var/log/lynis-report.dat
  Report version:            1.0
  Plugin directory:          ./plugins
  ---------------------------------------------------
  Auditor:                   [Not Specified]
  Language:                  en
  Test category:             all
  Test group:                all
  ---------------------------------------------------
  - Program update status...                                  [ UNKNOWN ]

================================================================================

  -[ Lynis 2.6.5 Results ]-

  Great, no warnings

  Suggestions (25):
  ----------------------------
  * Set a password on GRUB bootloader to prevent altering boot configuration (e.g. boot in single user mode without password) [BOOT-5122]
      https://cisofy.com/controls/BOOT-5122/

  * Install a PAM module for password strength testing like pam_cracklib or pam_passwdqc [AUTH-9262]
      https://cisofy.com/controls/AUTH-9262/

  * Configure minimum password age in /etc/login.defs [AUTH-9286]
      https://cisofy.com/controls/AUTH-9286/

  * Configure maximum password age in /etc/login.defs [AUTH-9286]
      https://cisofy.com/controls/AUTH-9286/

  * Default umask in /etc/login.defs could be more strict like 027 [AUTH-9328]
      https://cisofy.com/controls/AUTH-9328/

  * To decrease the impact of a full /home file system, place /home on a separated partition [FILE-6310]
      https://cisofy.com/controls/FILE-6310/

  * To decrease the impact of a full /tmp file system, place /tmp on a separated partition [FILE-6310]
      https://cisofy.com/controls/FILE-6310/

  * To decrease the impact of a full /var file system, place /var on a separated partition [FILE-6310]
      https://cisofy.com/controls/FILE-6310/

  * Disable drivers like USB storage when not used, to prevent unauthorized storage or data theft [STRG-1840]
      https://cisofy.com/controls/STRG-1840/

  * Check DNS configuration for the dns domain name [NAME-4028]
      https://cisofy.com/controls/NAME-4028/

  * Install debsums utility for the verification of packages with known good database. [PKGS-7370]
      https://cisofy.com/controls/PKGS-7370/

  * Install package apt-show-versions for patch management purposes [PKGS-7394]
      https://cisofy.com/controls/PKGS-7394/

  * Consider running ARP monitoring software (arpwatch,arpon) [NETW-3032]
      https://cisofy.com/controls/NETW-3032/

  * Check iptables rules to see which rules are currently not used [FIRE-4513]
      https://cisofy.com/controls/FIRE-4513/

  * Check what deleted files are still in use and why. [LOGG-2190]
      https://cisofy.com/controls/LOGG-2190/

  * Add a legal banner to /etc/issue, to warn unauthorized users [BANN-7126]
      https://cisofy.com/controls/BANN-7126/

  * Add legal banner to /etc/issue.net, to warn unauthorized users [BANN-7130]
      https://cisofy.com/controls/BANN-7130/

  * Enable process accounting [ACCT-9622]
      https://cisofy.com/controls/ACCT-9622/

  * Enable sysstat to collect accounting (no results) [ACCT-9626]
      https://cisofy.com/controls/ACCT-9626/

  * Enable auditd to collect audit information [ACCT-9628]
      https://cisofy.com/controls/ACCT-9628/

  * Install a file integrity tool to monitor changes to critical and sensitive files [FINT-4350]
      https://cisofy.com/controls/FINT-4350/

  * Determine if automation tools are present for system management [TOOL-5002]
      https://cisofy.com/controls/TOOL-5002/

  * One or more sysctl values differ from the scan profile and could be tweaked [KRNL-6000]
    - Solution : Change sysctl value or disable test (skip-test=KRNL-6000:<sysctl-key>)
      https://cisofy.com/controls/KRNL-6000/

  * Harden compilers like restricting access to root user only [HRDN-7222]
      https://cisofy.com/controls/HRDN-7222/

  * Harden the system by installing at least one malware scanner, to perform periodic file system scans [HRDN-7230]
    - Solution : Install a tool like rkhunter, chkrootkit, OSSEC
      https://cisofy.com/controls/HRDN-7230/

================================================================================

  Lynis security scan details:

  Hardening index : 67 [#############       ]
  Tests performed : 223
  Plugins enabled : 2

  Components:
  - Firewall               [V]
  - Malware scanner        [X]

  Lynis Modules:
  - Compliance Status      [?]
  - Security Audit         [V]
  - Vulnerability Scan     [V]

  Files:
  - Test and debug information      : /var/log/lynis.log
  - Report data                     : /var/log/lynis-report.dat

================================================================================

After performing over 200 tests, the Lynis output can get quite long. I've omitted most of the log but kept the "Suggestions" portion. I think this is one of Lynis' greatest strengths. It offers some helpful starting points for users interested in remediation. For example, Lynis recommends we "Harden the system by installating at least one malware scanner." This can be easily resolved by following the next step in this guide and installing antivirus software.

Removing Lynis Once Done

When you're completely done auditing your Ubuntu installation, you can remove Lynis using the below rm commands.

~$ sudo rm -rf /path/to/lynis-master/
~$ sudo rm -rf /path/to/master.zip

Step 2: Protect Against Malware with ClamAV

ClamAV is an open-source antivirus engine used in various situations, including email scanning, web scanning, and endpoint security. It provides several features Ubuntu users may appreciate:

Command-line scanner. This will allow users to quickly scan files downloaded from the internet from any terminal window.
Advanced database updater. ClamAV's virus database will update multiple times per day with support for scripted updates and digital signatures.
Support for many archive formats. The ClamAV scanner is capable of safely analyzing Zip, RAR, Dmg, Tar, Gzip, Bzip2, OLE2, Cabinet, CHM, BinHex, SIS, and other file formats.
Support for popular document formats. MS Office, MacOffice, HTML, Flash, RTF, and PDFs.

Unlike Avast, a popular antivirus company that regularly exports personal user documents to Avast servers, ClamAV scans filesystems for malware signatures locally. That's really all it does. It does not, by any means, provide bulletproof protection against highly sophisticated attacks, just common malware signatures found in the wild.

It's been said that Linux operating systems don't need antivirus software. I mostly agree with this statement. However, ClamAV is an excellent open-source project and may provide comfort to users who prefer to know their OS is safely analyzed for malware several times a day.

Installing ClamAV

ClamAV is available in the Ubuntu repositories and can be installed using the sudo apt install clamav command.

~$ sudo apt install clamav

Reading package lists... Done
Building dependency tree
Reading state information... Done
The following package was automatically installed and is no longer required:
  menu
Use 'sudo apt autoremove' to remove it.
The following additional packages will be installed:
  clamav-base clamav-freshclam libclamav7 libllvm3.9 libmspack0 libtfm1
Suggested packages:
  clamav-docs libclamunrar7
The following NEW packages will be installed:
  clamav clamav-base clamav-freshclam libclamav7 libllvm3.9 libmspack0 libtfm1
0 upgraded, 7 newly installed, 0 to remove and 0 not upgraded.
Need to get 12.5 MB of archives.
After this operation, 50.3 MB of additional disk space will be used.
Do you want to continue? [Y/n] y

Scanning Directories with ClamAV

The ClamAV databases will update as soon as it's installed and several times a day thereafter. The clamscan --help command can be used to view the scanners available options.

~$ clamscan --help

                       Clam AntiVirus Scanner 0.99.4
           By The ClamAV Team: http://www.clamav.net/about.html#credits
           (C) 2007-2018 Cisco Systems, Inc.

    --help                -h             Print this help screen
    --version             -V             Print version number
    --verbose             -v             Be verbose
    --archive-verbose     -a             Show filenames inside scanned archives
    --debug                              Enable libclamav's debug messages
    --quiet                              Only output error messages
    --stdout                             Write to stdout instead of stderr
    --no-summary                         Disable summary at end of scanning
    --infected            -i             Only print infected files
    --suppress-ok-results -o             Skip printing OK files
    --bell                               Sound bell on virus detection

    --tempdir=DIRECTORY                  Create temporary files in DIRECTORY
    --leave-temps[=yes/no(*)]            Do not remove temporary files
    --database=FILE/DIR   -d FILE/DIR    Load virus database from FILE or load
                                         all supported db files from DIR
    --official-db-only[=yes/no(*)]       Only load official signatures
    --log=FILE            -l FILE        Save scan report to FILE
    --recursive[=yes/no(*)]  -r          Scan subdirectories recursively
    --allmatch[=yes/no(*)]   -z          Continue scanning within file after finding a match
    --cross-fs[=yes(*)/no]               Scan files and directories on other filesystems
    --follow-dir-symlinks[=0/1(*)/2]     Follow directory symlinks (0 = never, 1 = direct, 2 = always)
    --follow-file-symlinks[=0/1(*)/2]    Follow file symlinks (0 = never, 1 = direct, 2 = always)
    --file-list=FILE      -f FILE        Scan files from FILE
    --remove[=yes/no(*)]                 Remove infected files. Be careful!
    --move=DIRECTORY                     Move infected files into DIRECTORY
    --copy=DIRECTORY                     Copy infected files into DIRECTORY
    --exclude=REGEX                      Don't scan file names matching REGEX
    --exclude-dir=REGEX                  Don't scan directories matching REGEX
    --include=REGEX                      Only scan file names matching REGEX
    --include-dir=REGEX                  Only scan directories matching REGEX

    --bytecode[=yes(*)/no]               Load bytecode from the database
    --bytecode-unsigned[=yes/no(*)]      Load unsigned bytecode
    --bytecode-timeout=N                 Set bytecode timeout (in milliseconds)
    --statistics[=none(*)/bytecode/pcre] Collect and print execution statistics
    --detect-pua[=yes/no(*)]             Detect Possibly Unwanted Applications
    --exclude-pua=CAT                    Skip PUA sigs of category CAT
    --include-pua=CAT                    Load PUA sigs of category CAT
    --detect-structured[=yes/no(*)]      Detect structured data (SSN, Credit Card)
    --structured-ssn-format=X            SSN format (0=normal,1=stripped,2=both)
    --structured-ssn-count=N             Min SSN count to generate a detect
    --structured-cc-count=N              Min CC count to generate a detect
    --scan-mail[=yes(*)/no]              Scan mail files
    --phishing-sigs[=yes(*)/no]          Signature-based phishing detection
    --phishing-scan-urls[=yes(*)/no]     URL-based phishing detection
    --heuristic-scan-precedence[=yes/no(*)] Stop scanning as soon as a heuristic match is found
    --phishing-ssl[=yes/no(*)]           Always block SSL mismatches in URLs (phishing module)
    --phishing-cloak[=yes/no(*)]         Always block cloaked URLs (phishing module)
    --partition-intersection[=yes/no(*)] Detect partition intersections in raw disk images using heuristics.
    --algorithmic-detection[=yes(*)/no]  Algorithmic detection
    --scan-pe[=yes(*)/no]                Scan PE files
    --scan-elf[=yes(*)/no]               Scan ELF files
    --scan-ole2[=yes(*)/no]              Scan OLE2 containers
    --scan-pdf[=yes(*)/no]               Scan PDF files
    --scan-swf[=yes(*)/no]               Scan SWF files
    --scan-html[=yes(*)/no]              Scan HTML files
    --scan-xmldocs[=yes(*)/no]           Scan xml-based document files
    --scan-hwp3[=yes(*)/no]              Scan HWP3 files
    --scan-archive[=yes(*)/no]           Scan archive files (supported by libclamav)
    --detect-broken[=yes/no(*)]          Try to detect broken executable files
    --block-encrypted[=yes/no(*)]        Block encrypted archives
    --block-macros[=yes/no(*)]           Block OLE2 files with VBA macros
    --nocerts                            Disable authenticode certificate chain verification in PE files
    --dumpcerts                          Dump authenticode certificate chain in PE files

    --max-filesize=#n                    Files larger than this will be skipped and assumed clean
    --max-scansize=#n                    The maximum amount of data to scan for each container file (**)
    --max-files=#n                       The maximum number of files to scan for each container file (**)
    --max-recursion=#n                   Maximum archive recursion level for container file (**)
    --max-dir-recursion=#n               Maximum directory recursion level
    --max-embeddedpe=#n                  Maximum size file to check for embedded PE
    --max-htmlnormalize=#n               Maximum size of HTML file to normalize
    --max-htmlnotags=#n                  Maximum size of normalized HTML file to scan
    --max-scriptnormalize=#n             Maximum size of script file to normalize
    --max-ziptypercg=#n                  Maximum size zip to type reanalyze
    --max-partitions=#n                  Maximum number of partitions in disk image to be scanned
    --max-iconspe=#n                     Maximum number of icons in PE file to be scanned
    --max-rechwp3=#n                     Maximum recursive calls to HWP3 parsing function
    --pcre-match-limit=#n                Maximum calls to the PCRE match function.
    --pcre-recmatch-limit=#n             Maximum recursive calls to the PCRE match function.
    --pcre-max-filesize=#n               Maximum size file to perform PCRE subsig matching.
    --enable-stats                       Enable statistical reporting of malware
    --disable-pe-stats                   Disable submission of individual PE sections in stats submissions
    --stats-timeout=#n                   Number of seconds to wait for waiting a response back from the stats server
    --stats-host-id=UUID                 Set the Host ID used when submitting statistical info.
    --disable-cache                      Disable caching and cache checks for hash sums of scanned files.

To scan every file and directory, use the below command.

~$ sudo clamscan -r / --log=/tmp/clamav_report.log

This is the scanner command in its simplest form. Clamscan will recursively (-r) scan everything (/) and save the scan report (--log) to the /tmp directory. Running such a scan can take a considerable amount of time, hours if you're scanning terabytes of data. It's recommended to run such scans overnight and view the results in the morning.

Malware Detections

As a quick demo for this article, I downloaded a malware repository from GitHub and ran clamscan against the directory containing the malware.

~$ sudo clamscan -ir malware-master/

malware-master/Zeus/output/builder/bot.exe.txt: Win.Spyware.Zbot-1275 FOUND
malware-master/Zeus/output/builder/zsb.exe: Win.Trojan.Zbot-62846 FOUND
malware-master/Zeus/output/server/zsbcs.exe: Win.Trojan.Botnet-6 FOUND
malware-master/Zeus/output/client32.bin: Win.Spyware.Zbot-1275 FOUND
malware-master/Alina/Panel/gate1.php: Php.Malware.ProPOS-2 FOUND
malware-master/mirai/loader/bins/dlr.mpsl: Unix.Malware.Agent-1753181 FOUND
malware-master/mirai/loader/bins/dlr.spc: Unix.Malware.Agent-1753190 FOUND
malware-master/mirai/loader/bins/dlr.arm7: Unix.Malware.Agent-1753196 FOUND
malware-master/mirai/loader/bins/dlr.x86: Unix.Malware.Agent-1753191 FOUND
malware-master/mirai/loader/bins/dlr.sh4: Unix.Malware.Agent-1753186 FOUND
malware-master/mirai/loader/bins/dlr.ppc: Unix.Malware.Agent-1753179 FOUND
malware-master/mirai/loader/bins/dlr.arm: Unix.Malware.Agent-1768364 FOUND
malware-master/mirai/loader/bins/dlr.m68k: Unix.Malware.Agent-1753197 FOUND
malware-master/mirai/loader/bins/dlr.mips: Unix.Malware.Agent-1753182 FOUND
malware-master/mirai/dlr/release/dlr.mpsl: Unix.Malware.Agent-1753187 FOUND
malware-master/mirai/dlr/release/dlr.spc: Unix.Malware.Agent-1753199 FOUND
malware-master/mirai/dlr/release/dlr.arm7: Unix.Malware.Agent-1753512 FOUND
malware-master/mirai/dlr/release/dlr.sh4: Unix.Malware.Agent-1753174 FOUND
malware-master/mirai/dlr/release/dlr.ppc: Unix.Malware.Agent-1753492 FOUND
malware-master/mirai/dlr/release/dlr.arm: Unix.Malware.Agent-1753516 FOUND
malware-master/mirai/dlr/release/dlr.m68k: Unix.Malware.Agent-1753177 FOUND
malware-master/mirai/dlr/release/dlr.mips: Unix.Malware.Agent-1753194 FOUND
malware-master/Grum/builder+bin/out.exe: Win.Trojan.Vilsel-2129 FOUND

----------- SCAN SUMMARY -----------
Known viruses: 6556187
Engine version: 0.99.4
Scanned directories: 1594
Scanned files: 17195
Infected files: 23
Data scanned: 366.88 MB
Data read: 294.26 MB (ratio 1.25:1)
Time: 71.994 sec (1 m 11 s)

In my example command, I included the -i argument, which tells clamscan to print only files detected by the scanner. We can see 17,195 files were scanned, 23 infections were detected, and the process took 71 seconds to complete.

For more on ClamAV, check out the official documentation.

Step 3: Monitor Applications' Intenet Access with OpenSnitch

OpenSnitch is a Linux port of the popular macOS application firewall, Little Snitch. OpenSnitch will give users a few seconds to allow or deny connections as they happen. Below is an example of an OpenSnitch prompt.

The OpenSnitch network statistics interface provides an overview of all of the previously allowed and denied connections.

Unfortunately, that's about all the interface has to offer at the moment. Later releases of OpenSnitch will no doubt contain more features and control over how this information is managed. While OpenSnitch is still very much in its infancy, I decided to include it in this article. Windows 10 users who are more comfortable with graphical applications (GUI) may find OpenSnitch useful for monitoring traffic originating from installed applications.

Command-line enthusiasts with an interest in raw, unfiltered packet analysis may prefer using Tshark to monitor traffic.

Installing Dependencies

Use the below command to install the dependencies required to run OpenSnitch.

~$ sudo apt install protobuf-compiler libpcap-dev libnetfilter-queue-dev python3-pip golang git go-dep

Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  dh-python golang-1.10 golang-1.10-doc golang-1.10-go golang-1.10-race-detector-runtime golang-1.10-src golang-doc golang-go
  golang-race-detector-runtime golang-src libexpat1-dev libnetfilter-queue1 libnfnetlink-dev libpcap0.8-dev libprotoc10 libpython3-dev
  libpython3.6-dev pkg-config python-pip-whl python3-dev python3-distutils python3-lib2to3 python3-setuptools python3-wheel python3.6-dev
Suggested packages:
  bzr git mercurial subversion python-setuptools-doc
The following NEW packages will be installed:
  dh-python golang golang-1.10 golang-1.10-doc golang-1.10-go golang-1.10-race-detector-runtime golang-1.10-src golang-doc golang-go
  golang-race-detector-runtime golang-src libexpat1-dev libnetfilter-queue-dev libnetfilter-queue1 libnfnetlink-dev libpcap-dev libpcap0.8-dev
  libprotoc10 libpython3-dev libpython3.6-dev pkg-config protobuf-compiler python-pip-whl python3-dev python3-distutils python3-lib2to3 python3-pip
  python3-setuptools python3-wheel python3.6-dev
0 upgraded, 30 newly installed, 0 to remove and 0 not upgraded.
Need to get 52.1 MB of archives.
After this operation, 280 MB of additional disk space will be used.
Do you want to continue? [Y/n] y

Use go to clone the Protocol Buffers repository. This command will not produce an output in the terminal.

~$ go get github.com/golang/protobuf/protoc-gen-go

Then, use Python3's pip to install the gRPC tools and other dependencies.

~$ python3 -m pip install --user grpcio-tools

Collecting grpcio-tools
  Downloading https://files.pythonhosted.org/packages/fb/8f/fc0c7cf8a5ed2aea405afb8712ea4181bbcf9510d731b7cd929427916f97/grpcio_tools-1.12.1-cp36-cp36m-manylinux1_x86_64.whl (22.2MB)
    100% |████████████████████████████████| 22.2MB 53kB/s
Collecting grpcio>=1.12.1 (from grpcio-tools)
  Downloading https://files.pythonhosted.org/packages/1f/ea/664c589ec41b9e9ac6e20cc1fe9016f3913332d0dc5498a5d7771e2835af/grpcio-1.12.1-cp36-cp36m-manylinux1_x86_64.whl (9.0MB)
    100% |████████████████████████████████| 9.0MB 133kB/s
Collecting protobuf>=3.5.0.post1 (from grpcio-tools)
  Downloading https://files.pythonhosted.org/packages/fc/f0/db040681187496d10ac50ad167a8fd5f953d115b16a7085e19193a6abfd2/protobuf-3.6.0-cp36-cp36m-manylinux1_x86_64.whl (7.1MB)
    100% |████████████████████████████████| 7.1MB 136kB/s
Collecting six>=1.5.2 (from grpcio>=1.12.1->grpcio-tools)
  Downloading https://files.pythonhosted.org/packages/67/4b/141a581104b1f6397bfa78ac9d43d8ad29a7ca43ea90a2d863fe3056e86a/six-1.11.0-py2.py3-none-any.whl
Collecting setuptools (from protobuf>=3.5.0.post1->grpcio-tools)
  Downloading https://files.pythonhosted.org/packages/7f/e1/820d941153923aac1d49d7fc37e17b6e73bfbd2904959fffbad77900cf92/setuptools-39.2.0-py2.py3-none-any.whl (567kB)
    100% |████████████████████████████████| 573kB 419kB/s
Installing collected packages: six, grpcio, setuptools, protobuf, grpcio-tools
Successfully installed grpcio-1.12.1 grpcio-tools-1.12.1 protobuf-3.6.0 setuptools-39.2.0 six-1.11.0

Use go get github.com/evilsocket/opensnitch to clone the OpenSnitch GitHub repository.

~$ go get github.com/evilsocket/opensnitch

package github.com/evilsocket/opensnitch: no Go files in /home/tokyoneon/go/src/github.com/evilsocket/opensnitch

Update the Golang PATH in the terminal using the below command. This will allow future terminal sessions to know where Go binaries and projects are stored.

~$ echo 'export GOPATH=$HOME/go' >> ~/.bashrc

Then, use the source command to update the current Golang PATH. This will allow the preceding commands to execute properly.

~$ source ~/.bashrc

Configuring & Installing OpenSnitch

Use make, a utility that will automatically determine which pieces of OpenSnitch need to be recompiled.

~$ make

make[1]: Entering directory '/home/tokyoneon/go/src/github.com/evilsocket/opensnitch/proto'
python3 -m grpc_tools.protoc -I. --python_out=../ui/opensnitch/ --grpc_python_out=../ui/opensnitch/ ui.proto
make[1]: Leaving directory '/home/tokyoneon/go/src/github.com/evilsocket/opensnitch/proto'
make[1]: Entering directory '/home/tokyoneon/go/src/github.com/evilsocket/opensnitch/daemon'
dep: WARNING: Unknown field in manifest: prune
make[1]: Leaving directory '/home/tokyoneon/go/src/github.com/evilsocket/opensnitch/daemon'
make[1]: Entering directory '/home/tokyoneon/go/src/github.com/evilsocket/opensnitch/ui'
The directory '/home/tokyoneon/.cache/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
The directory '/home/tokyoneon/.cache/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
Collecting grpcio==1.0.0 (from -r requirements.txt (line 1))
  Downloading https://files.pythonhosted.org/packages/ba/f7/2138b9148b2d68431ebb05d4871e2fc60deacb4ee282384171083b522823/grpcio-1.0.0.tar.gz (5.3MB)
    100% |████████████████████████████████| 5.3MB 181kB/s
Collecting grpcio-tools==1.10.1 (from -r requirements.txt (line 2))
  Downloading https://files.pythonhosted.org/packages/f0/f4/1e5a56b1c0ec2d802113c7f793fcb40ba4e9387b073c310e27ef8653b441/grpcio_tools-1.10.1-cp36-cp36m-manylinux1_x86_64.whl (22.2MB)
    100% |████████████████████████████████| 22.2MB 55kB/s
Collecting pyinotify==0.9.6 (from -r requirements.txt (line 3))
  Downloading https://files.pythonhosted.org/packages/e3/c0/fd5b18dde17c1249658521f69598f3252f11d9d7a980c5be8619970646e1/pyinotify-0.9.6.tar.gz (60kB)
    100% |████████████████████████████████| 61kB 81kB/s
Collecting unicode_slugify==0.1.3 (from -r requirements.txt (line 4))
  Downloading https://files.pythonhosted.org/packages/8c/ba/1a05f61c7fd72df85ae4dc1c7967a3e5a4b6c61f016e794bc7f09b2597c0/unicode-slugify-0.1.3.tar.gz
Collecting pyqt5==5.10.1 (from -r requirements.txt (line 5))
  Downloading https://files.pythonhosted.org/packages/e4/15/4e2e49f64884edbab6f833c6fd3add24d7938f2429aec1f2883e645d4d8f/PyQt5-5.10.1-5.10.1-cp35.cp36.cp37.cp38-abi3-manylinux1_x86_64.whl (107.8MB)
    100% |████████████████████████████████| 107.8MB 13kB/s
Collecting configparser==3.5.0 (from -r requirements.txt (line 6))
  Downloading https://files.pythonhosted.org/packages/7c/69/c2ce7e91c89dc073eb1aa74c0621c3eefbffe8216b3f9af9d3885265c01c/configparser-3.5.0.tar.gz
Requirement already satisfied: six>=1.5.2 in /home/tokyoneon/.local/lib/python3.6/site-packages (from grpcio==1.0.0->-r requirements.txt (line 1))
Collecting enum34>=1.0.4 (from grpcio==1.0.0->-r requirements.txt (line 1))
  Downloading https://files.pythonhosted.org/packages/af/42/cb9355df32c69b553e72a2e28daee25d1611d2c0d9c272aa1d34204205b2/enum34-1.1.6-py3-none-any.whl
Collecting futures>=2.2.0 (from grpcio==1.0.0->-r requirements.txt (line 1))
  Downloading https://files.pythonhosted.org/packages/cc/26/b61e3a4eb50653e8a7339d84eeaa46d1e93b92951978873c220ae64d0733/futures-3.1.1.tar.gz
Requirement already satisfied: protobuf>=3.0.0 in /home/tokyoneon/.local/lib/python3.6/site-packages (from grpcio==1.0.0->-r requirements.txt (line 1))
Collecting unidecode (from unicode_slugify==0.1.3->-r requirements.txt (line 4))
  Downloading https://files.pythonhosted.org/packages/59/ef/67085e30e8bbcdd76e2f0a4ad8151c13a2c5bce77c85f8cad6e1f16fb141/Unidecode-1.0.22-py2.py3-none-any.whl (235kB)
    100% |████████████████████████████████| 235kB 142kB/s
Collecting sip<4.20,>=4.19.4 (from pyqt5==5.10.1->-r requirements.txt (line 5))
  Downloading https://files.pythonhosted.org/packages/8a/ea/d317ce5696dda4df7c156cd60447cda22833b38106c98250eae1451f03ec/sip-4.19.8-cp36-cp36m-manylinux1_x86_64.whl (66kB)
    100% |████████████████████████████████| 71kB 80kB/s
Requirement already satisfied: setuptools in /home/tokyoneon/.local/lib/python3.6/site-packages (from protobuf>=3.0.0->grpcio==1.0.0->-r requirements.txt (line 1))
Installing collected packages: enum34, futures, grpcio, grpcio-tools, pyinotify, unidecode, unicode-slugify, sip, pyqt5, configparser
  Running setup.py install for futures ... done
  Found existing installation: grpcio 1.12.1
    Uninstalling grpcio-1.12.1:
      Successfully uninstalled grpcio-1.12.1
  Running setup.py install for grpcio ... done
  Found existing installation: grpcio-tools 1.12.1
    Uninstalling grpcio-tools-1.12.1:
      Successfully uninstalled grpcio-tools-1.12.1
  Running setup.py install for pyinotify ... done
  Running setup.py install for unicode-slugify ... done
  Running setup.py install for configparser ... done
Successfully installed configparser-3.5.0 enum34-1.1.6 futures-3.1.1 grpcio-1.0.0 grpcio-tools-1.10.1 pyinotify-0.9.6 pyqt5-5.10.1 sip-4.19.8 unicode-slugify-0.1.3 unidecode-1.0.22
make[1]: Leaving directory '/home/tokyoneon/go/src/github.com/evilsocket/opensnitch/ui'

Use the make install command with sudo to complete the installation.

~$ sudo make install

make[1]: Entering directory '/home/tokyoneon/go/src/github.com/evilsocket/opensnitch/daemon'
make[1]: Leaving directory '/home/tokyoneon/go/src/github.com/evilsocket/opensnitch/daemon'
make[1]: Entering directory '/home/tokyoneon/go/src/github.com/evilsocket/opensnitch/ui'
The directory '/home/tokyoneon/.cache/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
The directory '/home/tokyoneon/.cache/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
Processing /home/tokyoneon/go/src/github.com/evilsocket/opensnitch/ui
Installing collected packages: opensnitch-ui
  Running setup.py install for opensnitch-ui ... done
Successfully installed opensnitch-ui-1.0.0b0
make[1]: Leaving directory '/home/tokyoneon/go/src/github.com/evilsocket/opensnitch/ui'

Starting OpenSnitch at Boot

To start OpenSnitch with every boot, using the systemctl command with the enable argument.

~$ sudo systemctl enable opensnitchd

Created symlink /etc/systemd/system/multi-user.target.wants/opensnitchd.service → /etc/systemd/system/opensnitchd.service.

Reboot for the changes to take effect. OpenSnitch can be found in the icon tray. Click the "Statistics" button to bring up the user interface.

As applications attempt to access the internet, OpenSnitch will prompt you with the ability to allow or deny the activity.

Step 4: Regularly Monitor System Logs

Linux log files are stored in the /var/log/ directory. These files monitor system activity, background daemons, kernel messages, application and server logs, authentication logs, firewall logs, AppArmor logs, and much more.

To monitor logs in real time, use the find /var/log/ -type f $ -name "*.log" $ -exec tail -f "$file" {} + command.

~$ find /var/log/ -type f \( -name "*.log" \) -exec tail -f "$file" {} +

==> /var/log/ufw.log <==
kernel: [ 3488.126537] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=52.84.13.246 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=14998 DF PROTO=TCP SPT=51778 DPT=80 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3489.152073] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=52.84.13.246 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=14999 DF PROTO=TCP SPT=51778 DPT=80 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3491.168057] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=52.84.13.246 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=15000 DF PROTO=TCP SPT=51778 DPT=80 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3495.392064] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=52.84.13.246 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=15001 DF PROTO=TCP SPT=51778 DPT=80 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3503.584187] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=52.84.13.246 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=15002 DF PROTO=TCP SPT=51778 DPT=80 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3519.712123] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=52.84.13.246 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=15003 DF PROTO=TCP SPT=51778 DPT=80 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3900.250931] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=104.193.19.59 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=47090 DF PROTO=TCP SPT=35944 DPT=9999 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3901.280089] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=104.193.19.59 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=47091 DF PROTO=TCP SPT=35944 DPT=9999 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 4201.573248] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=91.189.91.157 LEN=76 TOS=0x10 PREC=0x00 TTL=64 ID=17312 DF PROTO=UDP SPT=43425 DPT=123 LEN=56

==> /var/log/kern.log <==
kernel: [ 3488.126537] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=52.84.13.246 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=14998 DF PROTO=TCP SPT=51778 DPT=80 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3489.152073] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=52.84.13.246 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=14999 DF PROTO=TCP SPT=51778 DPT=80 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3491.168057] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=52.84.13.246 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=15000 DF PROTO=TCP SPT=51778 DPT=80 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3495.392064] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=52.84.13.246 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=15001 DF PROTO=TCP SPT=51778 DPT=80 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3503.584187] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=52.84.13.246 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=15002 DF PROTO=TCP SPT=51778 DPT=80 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3519.712123] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=52.84.13.246 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=15003 DF PROTO=TCP SPT=51778 DPT=80 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3900.250931] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=104.193.19.59 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=47090 DF PROTO=TCP SPT=35944 DPT=9999 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 3901.280089] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=104.193.19.59 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=47091 DF PROTO=TCP SPT=35944 DPT=9999 WINDOW=29200 RES=0x00 SYN URGP=0
kernel: [ 4201.573248] [UFW BLOCK] IN= OUT=enp0s8 SRC=192.168.1.44 DST=91.189.91.157 LEN=76 TOS=0x10 PREC=0x00 TTL=64 ID=17312 DF PROTO=UDP SPT=43425 DPT=123 LEN=56

==> /var/log/alternatives.log <==
update-alternatives 2018-06-26 21:01:54: run with --install /usr/bin/identify-im6 identify-im6 /usr/bin/identify-im6.q16 10000 --slave /usr/share/man/man1/identify-im6.1.gz identify-im6.1.gz /usr/share/man/man1/identify-im6.q16.1.gz
update-alternatives 2018-06-26 21:01:54: run with --install /usr/bin/stream stream /usr/bin/stream-im6.q16 10000 --slave /usr/share/man/man1/stream.1.gz stream.1.gz /usr/share/man/man1/stream-im6.q16.1.gz
update-alternatives 2018-06-26 21:01:54: run with --install /usr/bin/stream-im6 stream-im6 /usr/bin/stream-im6.q16 10000 --slave /usr/share/man/man1/stream-im6.1.gz stream-im6.1.gz /usr/share/man/man1/stream-im6.q16.1.gz
update-alternatives 2018-06-26 21:01:54: run with --install /usr/bin/display display /usr/bin/display-im6.q16 10000 --slave /usr/share/man/man1/display.1.gz display.1.gz /usr/share/man/man1/display-im6.q16.1.gz
update-alternatives 2018-06-26 21:01:54: run with --install /usr/bin/display-im6 display-im6 /usr/bin/display-im6.q16 10000 --slave /usr/share/man/man1/display-im6.1.gz display-im6.1.gz /usr/share/man/man1/display-im6.q16.1.gz
update-alternatives 2018-06-26 21:01:54: run with --install /usr/bin/montage montage /usr/bin/montage-im6.q16 10000 --slave /usr/share/man/man1/montage.1.gz montage.1.gz /usr/share/man/man1/montage-im6.q16.1.gz
update-alternatives 2018-06-26 21:01:54: run with --install /usr/bin/montage-im6 montage-im6 /usr/bin/montage-im6.q16 10000 --slave /usr/share/man/man1/montage-im6.1.gz montage-im6.1.gz /usr/share/man/man1/montage-im6.q16.1.gz
update-alternatives 2018-06-26 21:01:54: run with --install /usr/bin/mogrify mogrify /usr/bin/mogrify-im6.q16 10000 --slave /usr/share/man/man1/mogrify.1.gz mogrify.1.gz /usr/share/man/man1/mogrify-im6.q16.1.gz
update-alternatives 2018-06-26 21:01:54: run with --install /usr/bin/mogrify-im6 mogrify-im6 /usr/bin/mogrify-im6.q16 10000 --slave /usr/share/man/man1/mogrify-im6.1.gz mogrify-im6.1.gz /usr/share/man/man1/mogrify-im6.q16.1.gz
update-alternatives 2018-06-26 21:01:55: run with --install /usr/bin/x-terminal-emulator x-terminal-emulator /usr/bin/gnome-terminal.wrapper 40 --slave /usr/share/man/man1/x-terminal-emulator.1.gz x-terminal-emulator.1.gz /usr/share/man/man1/gnome-terminal.1.gz

==> /var/log/installer/casper.log <==
This disc is called:
'Ubuntu 18.04 LTS _Bionic Beaver_ - Release amd64 (20180426)'
Copying package lists...gpgv: Signature made Thu Apr 26 18:43:31 2018 UTC
gpgv:                using RSA key D94AA3F0EFE21092
gpgv: Good signature from "Ubuntu CD Image Automatic Signing Key (2012) <[email protected]>"
Reading Package Indexes... Done
Writing new source list
Source list entries for this disc are:
deb cdrom:[Ubuntu 18.04 LTS _Bionic Beaver_ - Release amd64 (20180426)]/ bionic main restricted
Repeat this process for the rest of the CDs in your set.

==> /var/log/fontconfig.log <==
/usr/share/fonts/truetype/sinhala: skipping, existing cache is valid: 1 fonts, 0 dirs
/usr/share/fonts/truetype/tibetan-machine: skipping, existing cache is valid: 1 fonts, 0 dirs
/usr/share/fonts/truetype/tlwg: skipping, existing cache is valid: 58 fonts, 0 dirs
/usr/share/fonts/truetype/ttf-khmeros-core: skipping, existing cache is valid: 2 fonts, 0 dirs
/usr/share/fonts/truetype/ubuntu: skipping, existing cache is valid: 13 fonts, 0 dirs
/usr/share/fonts/type1: skipping, existing cache is valid: 0 fonts, 1 dirs
/usr/share/fonts/type1/gsfonts: skipping, existing cache is valid: 35 fonts, 0 dirs
/usr/local/share/fonts: skipping, existing cache is valid: 0 fonts, 0 dirs
/var/cache/fontconfig: cleaning cache directory
fc-cache: succeeded

==> /var/log/dpkg.log <==
2018-06-27 00:17:36 status installed apparmor-profiles:all 2.12-4ubuntu5
2018-06-27 00:17:36 trigproc man-db:amd64 2.8.3-2 <none>
2018-06-27 00:17:36 status half-configured man-db:amd64 2.8.3-2
2018-06-27 00:17:38 status installed man-db:amd64 2.8.3-2
2018-06-27 00:17:38 configure apparmor-utils:amd64 2.12-4ubuntu5 <none>
2018-06-27 00:17:38 status unpacked apparmor-utils:amd64 2.12-4ubuntu5
2018-06-27 00:17:38 status unpacked apparmor-utils:amd64 2.12-4ubuntu5
2018-06-27 00:17:38 status unpacked apparmor-utils:amd64 2.12-4ubuntu5
2018-06-27 00:17:38 status half-configured apparmor-utils:amd64 2.12-4ubuntu5
2018-06-27 00:17:38 status installed apparmor-utils:amd64 2.12-4ubuntu5

==> /var/log/unattended-upgrades/unattended-upgrades-shutdown.log <==

==> /var/log/boot.log <==
/dev/mapper/ubuntu--vg-root: clean, 164324/10379264 files, 1928530/41497600 blocks
  WARNING: Failed to connect to lvmetad. Falling back to device scanning.
  Volume group "ubuntu-vg" not found
  Cannot process volume group ubuntu-vg
  WARNING: Failed to connect to lvmetad. Falling back to device scanning.
  Reading all physical volumes.  This may take a while...
  Found volume group "ubuntu-vg" using metadata type lvm2
  WARNING: Failed to connect to lvmetad. Falling back to device scanning.
  2 logical volume(s) in volume group "ubuntu-vg" now active
/dev/mapper/ubuntu--vg-root: clean, 164321/10379264 files, 1928587/41497600 blocks

==> /var/log/apt/term.log <==
Unpacking apparmor-utils (2.12-4ubuntu5) ...
Selecting previously unselected package apparmor-profiles.
Preparing to unpack .../apparmor-profiles_2.12-4ubuntu5_all.deb ...
Unpacking apparmor-profiles (2.12-4ubuntu5) ...
Setting up python3-libapparmor (2.12-4ubuntu5) ...
Setting up python3-apparmor (2.12-4ubuntu5) ...
Setting up apparmor-profiles (2.12-4ubuntu5) ...
Processing triggers for man-db (2.8.3-2) ...
Setting up apparmor-utils (2.12-4ubuntu5) ...
Log ended: 2018-06-27  00:17:38

==> /var/log/apt/history.log <==
Commandline: apt-get remove apparmor-profiles
Requested-By: tokyoneon (1000)
Remove: apparmor-profiles:amd64 (2.12-4ubuntu5)

Commandline: apt-get install apparmor-profiles apparmor-utils
Requested-By: tokyoneon (1000)
Install: python3-libapparmor:amd64 (2.12-4ubuntu5, automatic), apparmor-profiles:amd64 (2.12-4ubuntu5), python3-apparmor:amd64 (2.12-4ubuntu5, automatic), apparmor-utils:amd64 (2.12-4ubuntu5)

==> /var/log/gpu-manager.log <==
Skipping "/dev/dri/card0", driven by "vboxvideo"
Skipping "/dev/dri/card0", driven by "vboxvideo"
Does it require offloading? no
last cards number = 1
Has amd? no
Has intel? no
Has nvidia? no
How many cards? 1
Has the system changed? No
Single card detected

==> /var/log/auth.log <==
CRON[7210]: pam_unix(cron:session): session closed for user root
sudo: pam_unix(sudo:auth): conversation failed
sudo: pam_unix(sudo:auth): auth could not identify password for [tokyoneon]
sudo: tokyoneon : TTY=pts/3 ; PWD=/home/tokyoneon ; USER=root ; COMMAND=/bin/su
sudo: pam_unix(sudo:session): session opened for user root by (uid=0)
su[7307]: Successful su for root by root
su[7307]: + /dev/pts/3 root:root
su[7307]: pam_unix(su:session): session opened for user root by (uid=0)
systemd-logind[859]: Existing logind session ID 2 used by new audit session, ignoring
systemd-logind[859]: New session c3 of user root.

==> /var/log/bootstrap.log <==
update-initramfs: deferring update (trigger activated)
Setting up ubuntu-minimal (1.417) ...
Processing triggers for libc-bin (2.27-3ubuntu1) ...
Processing triggers for systemd (237-3ubuntu10) ...
Processing triggers for ca-certificates (20180409) ...
Updating certificates in /etc/ssl/certs...
0 added, 0 removed; done.
Running hooks in /etc/ca-certificates/update.d...
done.
Processing triggers for initramfs-tools (0.130ubuntu3) ...

==> /var/log/auth.log <==
su[7307]: pam_unix(su:session): session closed for user root
sudo: pam_unix(sudo:session): session closed for user root
systemd-logind[859]: Removed session c3.
sudo: tokyoneon : TTY=pts/3 ; PWD=/home/tokyoneon ; USER=root ; COMMAND=/bin/su
sudo: pam_unix(sudo:session): session opened for user root by (uid=0)
su[7329]: Successful su for root by root
su[7329]: + /dev/pts/3 root:root
su[7329]: pam_unix(su:session): session opened for user root by (uid=0)
systemd-logind[859]: Existing logind session ID 2 used by new audit session, ignoring
systemd-logind[859]: New session c4 of user root.

This command will find any file (-type f) with the .log extension ($ -name "*.log" $) in the /var/log directory and use tail to print updates in the files as they occur (-f). Each log file will be encased in ascii arrows (==> filename.log <==). Anyone looking for find abnormalities on their system will find this useful.

We've Barely Scratched the Surface!

That concludes our series on strengthening your primary Ubuntu system...for now.

As I stated at the start of this series, this guide isn't a complete or comprehensive approach to securing a Linux system. There are many Kernel level modifications users can do to further improve Ubuntu's susceptibility to various attacks. We can also do more to secure the bootloader, enforce better login password policies, secure shared memory, browse the internet anonymously, and so much more.

Linux operating systems have incredible potential as a platform for security-focused users. I encourage readers to download the Beginning Ubuntu for Windows and Mac Users and Practical Linux Security Cookbook to gain a better understanding of the Ubuntu OS and its inner workings.

Cover image by Justin Meyers/Null Byte; Screenshots by tokyoneon/Null Byte