# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# [Upgrading from CentOS 7.0 to 7.4]
# [출처:http://blog.dailystuff.nl/2017/10/upgrading-from-centos-7-3-to-7-4/]
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
$ cat /etc/redhat-release
CentOS Linux release 7.3.1611 (Core)'
[root@ipm-2018-v2 ~]# cat /etc/redhat-release
CentOS Linux release 7.0.1406 (Core)
$ sudo yum clean all
$ sudo yum upgrade
$ sudo systemctl reboot
[root@ipm-2018-v2 ~]# sudo yum clean all
Loaded plugins: fastestmirror
Cleaning repos: base centosplus extras updates
Cleaning up everything
Cleaning up list of fastest mirrors
[root@ipm-2018-v2 ~]# sudo yum upgrade
[root@ipm-2018-v2 ~]# sudo systemctl reboot
$ cat /etc/redhat-release
CentOS Linux release 7.4.1708 (Core)
[root@ipmiracle-centos-7-web ~]# cat /etc/redhat-release
CentOS Linux release 7.2.1511 (Core)
# 최신 버전으로 업그레이드가 되지 않았다면, 아래 명령을 반복한다.
$ sudo yum clean all
$ sudo yum upgrade
$ sudo systemctl reboot
[root@ipm-2018-v2 ~]# cat /etc/redhat-release
CentOS Linux release 7.5.1804 (Core)
# 그래도 최신 버전으로 업그레이드가 되지 않았다면,,
[ 출처: http://godlvkhj.tistory.com/178 [하은양 믿음군 효실맘 호홍홍집s] ]
$ vi /etc/yum.repos.d/CentOS-Base.repo
위 파일이 있어야 한다.
ktcloud 의 경우,
=> CentOS-Base.repo.org
라는 이름으로 변경이 되어 있어서 자동 업데이트가 안되었던 것..
1. 의존성 라이브러리 설치
□ 아래는 라이브러리가 설치되어있는지 확인해보는 부분이며 APM에 꼭 필요한 패키지가 있습니다.
[root@localhost ~]# rpm -qa libjpeg* libpng* freetype* gd-* gcc gcc-c++ gdbm-devel libtermcap-devel
libpng-1.5.13-7.el7_2.x86_64
gcc-c++-4.8.5-11.el7.x86_64
freetype-2.4.11-12.el7.x86_64
libjpeg-turbo-1.2.90-5.el7.x86_64
libpng12-1.2.50-10.el7.x86_64
gcc-4.8.5-11.el7.x86_64
□ Yum 으로 아래의 필요한 라이브러리를 한번에 전부 설치합니다. (한번에 관련된 의존성도 같이 설치가 됩니다.)
[root@localhost ~]# yum install libjpeg* libpng* freetype* gd-* gcc gcc-c++ gdbm-devel libtermcap-devel
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# [Apache 설치]
# [출처:http://aeac.tistory.com/21]
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
2. [APM] Apache, MariaDB, PHP 설치 [설치순서 : Apache, Maria, PHP 진행]
□ 아파치(Apache 2.4) 설치
[root@localhost ~]# yum install httpd
[root@localhost ~]# systemctl start httpd
□ 부팅후 자동 실행 설정
[root@localhost ~]# systemctl enable httpd
Created symlink from /etc/systemd/system/multi-user.target.wants/httpd.service to /usr/lib/systemd/system/httpd.service.
□ 부팅후 자동 실행 설정(해제)
[root@localhost ~]# systemctl disable httpd
Removed symlink /etc/systemd/system/multi-user.target.wants/httpd.service.
□ Service 명령어 이용 가능
[root@localhost ~]# service httpd start(stop)
□ 마리아(Maria DB 10.3) 설치
Here is your custom MariaDB YUM repository entry for CentOS. Copy and paste it into a file under /etc/yum.repos.d/ (we suggest naming the file MariaDB.repo or something similar).
# http://downloads.mariadb.org/mariadb/repositories/
[mariadb]
name = MariaDB
baseurl = http://yum.mariadb.org/10.3/centos7-amd64
gpgkey=https://yum.mariadb.org/RPM-GPG-KEY-MariaDB
gpgcheck=1
After the file is in place, install MariaDB with:
[root@localhost ~]# sudo yum install MariaDB-server MariaDB-client
If you haven't already accepted the MariaDB GPG key, you will be prompted to do so. See "Installing MariaDB with yum" for detailed information.
Please see Installing OQGraph for details on additional install steps needed for that storage engine.
[ 출처: http://cionman.tistory.com/22 [Suwoni블로그] ]
MariaDB 설정
MariaDB 서비스를 부팅시 자동으로 실행되게 설정을 변경합니다.
systemctl enable mariadb
MariaDB를 시작합니다.
systemctl start mariadb
MariaDB의 root암호 및 기본 보안 설정을 하기위해 아래의 명령어를 실행합니다.
mysql_secure_installation
보안상 기본포트를 변경을 하려고 합니다.
Selinux의 보안 정책상 특정 port 이외에는 변경을 막고 있는데요, 확인작업은 아래 명령어을 실행합니다.
semanage port -l | grep mysqld_port_t
이제 MariaDB 에서 port를 변경하기 위하여 /etc/my.cnf.d/server.cnf파일을 에디터로 오픈하고,
[mysqld] 항목 아래에 변경할 port를 입력하고 저장합니다.
vi /etc/my.cnf.d/server.cnf
MariaDB를 restart 합니다.
systemctl restart mariadb
설정한 포트로 방화벽 포트를 오픈 합니다.
firewall-cmd --permanent --add-port=3456/tcp
firewall데몬을 리로드 해주어야 적용이 됩니다.
firewall-cmd --reload
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# [Apache / php7.2 설치]
# [출처: https://www.youtube.com/watch?v=vdzgoyU14fM]
# □ 출처: http://ellordnet.tistory.com/166 [IT in MT]
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0. 버전확인. (아직 설치되어 있지 않음)
[root@localhost mysql]# php -v
-bash: php: command not found
[root@ipm-2018-test ~]# sudo yum update
1. epel-release 설치 (EPEL; Extra Packages for Enterprise Linux)
[root@ipm-2018-test ~]# sudo yum install epel-release
2. 7.2설치를 위한 repository 추가(CentOS7에서는 5.4버전이 설치되므로)
[root@ipm-2018-test ~]# sudo yum install http://rpms.remirepo.net/enterprise/remi-release-7.rpm
3. yum-utils설치
[root@ipm-2018-test ~]# sudo yum install yum-utils
4. php7.2 설치
[root@ipm-2018-test ~]# sudo yum-config-manager --enable remi-php72
[root@ipm-2018-test ~]# sudo yum info php
[root@ipm-2018-test ~]# sudo yum -y install php
[root@ipm-2018-test ~]# sudo yum install php-mysqlnd
[root@ipm-2018-test ~]# sudo systemctl restart httpd
[root@ipm-2018-test ~]# php -v
PHP 7.2.7 (cli) (built: Jun 20 2018 08:21:26) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.2.0, Copyright (c) 1998-2018 Zend Technologies
========================================================== N/S matched: php72 ==========================================================
php72-php-pecl-handlebars-devel.x86_64 : php72-php-pecl-handlebars developer files (header)
php72-php-pecl-propro-devel.x86_64 : php72-php-pecl-propro developer files (header)
php72-php-pecl-psr-devel.x86_64 : php72-php-pecl-psr developer files (header)
php72-php-pecl-raphf-devel.x86_64 : php72-php-pecl-raphf developer files (header)
php72-php-pecl-swoole-devel.x86_64 : php72-php-pecl-swoole developer files (header)
php72-php-pecl-swoole2-devel.x86_64 : php72-php-pecl-swoole2 developer files (header)
php72-php-pecl-xmldiff-devel.x86_64 : php72-php-pecl-xmldiff developer files (header)
php72-php-pecl-yaconf-devel.x86_64 : php72-php-pecl-yaconf developer files (header)
php72-runtime.x86_64 : Package that handles php72 Software Collection.
php72-scldevel.x86_64 : Package shipping development files for php72
php72.x86_64 : Package that installs PHP 7.2
php72-build.x86_64 : Package shipping basic build configuration
php72-php.x86_64 : PHP scripting language for creating dynamic web sites
php72-php-ast.x86_64 : Abstract Syntax Tree
php72-php-bcmath.x86_64 : A module for PHP applications for using the bcmath library
php72-php-brotli.x86_64 : Brotli Extension for PHP
php72-php-channel-horde.noarch : Adds pear.horde.org channel to PEAR
php72-php-cli.x86_64 : Command-line interface for PHP
php72-php-common.x86_64 : Common files for PHP
php72-php-componere.x86_64 : Composing PHP classes at runtime
php72-php-dba.x86_64 : A database abstraction layer module for PHP applications
php72-php-dbg.x86_64 : The interactive PHP debugger
php72-php-devel.x86_64 : Files needed for building PHP extensions
php72-php-embedded.x86_64 : PHP library for embedding in applications
php72-php-enchant.x86_64 : Enchant spelling extension for PHP applications
php72-php-fpm.x86_64 : PHP FastCGI Process Manager
php72-php-gd.x86_64 : A module for PHP applications for using the gd graphics library
php72-php-geos.x86_64 : PHP module for GEOS
php72-php-gmp.x86_64 : A module for PHP applications for using the GNU MP library
php72-php-horde-horde-lz4.x86_64 : Horde LZ4 Compression Extension
php72-php-imap.x86_64 : A module for PHP applications that use IMAP
php72-php-interbase.x86_64 : A module for PHP applications that use Interbase/Firebird databases
php72-php-intl.x86_64 : Internationalization extension for PHP applications
php72-php-ioncube-loader.x86_64 : Loader for ionCube Encoded Files with ionCube 24 support
php72-php-json.x86_64 : JavaScript Object Notation extension for PHP
php72-php-ldap.x86_64 : A module for PHP applications that use LDAP
php72-php-libvirt.x86_64 : PHP language binding for Libvirt
php72-php-libvirt-doc.noarch : Document of php-libvirt
php72-php-litespeed.x86_64 : LiteSpeed Web Server PHP support
php72-php-lz4.x86_64 : LZ4 Extension for PHP
php72-php-mbstring.x86_64 : A module for PHP applications which need multi-byte string handling
php72-php-mysqlnd.x86_64 : A module for PHP applications that use MySQL databases
php72-php-oci8.x86_64 : A module for PHP applications that use OCI8 databases
php72-php-odbc.x86_64 : A module for PHP applications that use ODBC databases
php72-php-opcache.x86_64 : The Zend OPcache
php72-php-pdo.x86_64 : A database access abstraction module for PHP applications
php72-php-pdo-dblib.x86_64 : PDO driver Microsoft SQL Server and Sybase databases
php72-php-pear.noarch : PHP Extension and Application Repository framework
php72-php-pecl-amqp.x86_64 : Communicate with any AMQP compliant server
php72-php-pecl-apcu.x86_64 : APC User Cache
php72-php-pecl-apcu-bc.x86_64 : APCu Backwards Compatibility Module
php72-php-pecl-apcu-devel.x86_64 : APCu developer files (header)
php72-php-pecl-apfd.x86_64 : Always Populate Form Data
php72-php-pecl-apm.x86_64 : Alternative PHP Monitor
php72-php-pecl-bitset.x86_64 : BITSET library
php72-php-pecl-cassandra.x86_64 : DataStax PHP Driver for Apache Cassandra
php72-php-pecl-cmark.x86_64 : CommonMark extension
php72-php-pecl-couchbase2.x86_64 : Couchbase Server PHP extension
php72-php-pecl-crypto.x86_64 : Wrapper for OpenSSL Crypto Library
php72-php-pecl-dbase.x86_64 : dBase database file access functions
php72-php-pecl-dio.x86_64 : Direct I/O functions
php72-php-pecl-druid.x86_64 : A Druid driver for PHP
php72-php-pecl-ds.x86_64 : Data Structures for PHP
php72-php-pecl-eio.x86_64 : Provides interface to the libeio library
php72-php-pecl-env.x86_64 : Load environment variables
php72-php-pecl-ev.x86_64 : Provides interface to libev library
php72-php-pecl-event.x86_64 : Provides interface to libevent library
php72-php-pecl-fann.x86_64 : Wrapper for FANN Library
php72-php-pecl-gearman.x86_64 : PHP wrapper to libgearman
php72-php-pecl-gender.x86_64 : Gender Extension
php72-php-pecl-geoip.x86_64 : Extension to map IP addresses to geographic places
php72-php-pecl-geospatial.x86_64 : PHP Extension to handle common geospatial functions
php72-php-pecl-gmagick.x86_64 : Provides a wrapper to the GraphicsMagick library
php72-php-pecl-gnupg.x86_64 : Wrapper around the gpgme library
php72-php-pecl-grpc.x86_64 : General RPC framework
php72-php-pecl-handlebars.x86_64 : Handlebars templating language
php72-php-pecl-hdr-histogram.x86_64 : PHP extension wrapper for the C hdrhistogram API
php72-php-pecl-hprose.x86_64 : Hprose for PHP
php72-php-pecl-hrtime.x86_64 : High resolution timing
php72-php-pecl-http.x86_64 : Extended HTTP support
php72-php-pecl-http-devel.x86_64 : Extended HTTP support developer files (header)
php72-php-pecl-igbinary.x86_64 : Replacement for the standard PHP serializer
php72-php-pecl-igbinary-devel.x86_64 : Igbinary developer files (header)
php72-php-pecl-imagick.x86_64 : Extension to create and modify images using ImageMagick
php72-php-pecl-imagick-devel.x86_64 : imagick extension developer files (header)
php72-php-pecl-inotify.x86_64 : Inotify
php72-php-pecl-ip2location.x86_64 : Get geo location information of an IP address
php72-php-pecl-json-post.x86_64 : JSON POST handler
php72-php-pecl-jsond.x86_64 : JavaScript Object Notation
php72-php-pecl-jsond-devel.x86_64 : JSOND developer files (header)
php72-php-pecl-krb5.x86_64 : Kerberos authentification extension
php72-php-pecl-krb5-devel.x86_64 : Kerberos extension developer files (header)
php72-php-pecl-leveldb.x86_64 : LevelDB PHP bindings
php72-php-pecl-libsodium.x86_64 : Wrapper for the Sodium cryptographic library
php72-php-pecl-lua.x86_64 : Embedded lua interpreter
php72-php-pecl-lzf.x86_64 : Extension to handle LZF de/compression
php72-php-pecl-mailparse.x86_64 : PHP PECL package for parsing and working with email messages
php72-php-pecl-mcrypt.x86_64 : Bindings for the libmcrypt library
php72-php-pecl-memcache.x86_64 : Extension to work with the Memcached caching daemon
php72-php-pecl-memcached.x86_64 : Extension to work with the Memcached caching daemon
php72-php-pecl-memprof.x86_64 : Memory usage profiler
php72-php-pecl-mogilefs.x86_64 : PHP client library to communicate with the MogileFS storage
php72-php-pecl-molten.x86_64 : Extension for application tracing
php72-php-pecl-mongodb.x86_64 : MongoDB driver for PHP
php72-php-pecl-mosquitto.x86_64 : Extension for libmosquitto
php72-php-pecl-msgpack.x86_64 : API for communicating with MessagePack serialization
php72-php-pecl-msgpack-devel.x86_64 : MessagePack developer files (header)
php72-php-pecl-mustache.x86_64 : Mustache templating language
php72-php-pecl-mysql.x86_64 : MySQL database access functions
php72-php-pecl-mysql-xdevapi.x86_64 : MySQL database access functions
php72-php-pecl-nsq.x86_64 : PHP extension for NSQ client
php72-php-pecl-oauth.x86_64 : PHP OAuth consumer extension
php72-php-pecl-opencensus.x86_64 : A stats collection and distributed tracing framework
php72-php-pecl-parle.x86_64 : Parsing and lexing
php72-php-pecl-pcs.x86_64 : PHP Code Service
php72-php-pecl-pcs-devel.x86_64 : PHP Code Service (header)
php72-php-pecl-pdflib.x86_64 : Package for generating PDF files
php72-php-pecl-pq.x86_64 : PostgreSQL client library (libpq) binding
php72-php-pecl-propro.x86_64 : Property proxy
php72-php-pecl-protobuf.x86_64 : Mechanism for serializing structured data
php72-php-pecl-psr.x86_64 : PSR interfaces
php72-php-pecl-radius.x86_64 : Radius client library
php72-php-pecl-raphf.x86_64 : Resource and persistent handles factory
php72-php-pecl-rar.x86_64 : PHP extension for reading RAR archives
php72-php-pecl-rdkafka.x86_64 : Kafka client based on librdkafka
php72-php-pecl-redis.x86_64 : Extension for communicating with the Redis key-value store
php72-php-pecl-redis4.x86_64 : Extension for communicating with the Redis key-value store
php72-php-pecl-ref.x86_64 : Soft and Weak references support in PHP
php72-php-pecl-request.x86_64 : Server-side request and response objects
php72-php-pecl-rpminfo.x86_64 : RPM information
php72-php-pecl-rrd.x86_64 : PHP Bindings for rrdtool
php72-php-pecl-scrypt.x86_64 : Scrypt hashing function
php72-php-pecl-seaslog.x86_64 : An effective, fast, stable log extension for PHP
php72-php-pecl-selinux.x86_64 : SELinux binding for PHP scripting language
php72-php-pecl-solr2.x86_64 : API orient챕e objet pour Apache Solr
php72-php-pecl-sphinx.x86_64 : PECL extension for Sphinx SQL full-text search engine
php72-php-pecl-ssdeep.x86_64 : Wrapper for libfuzzy library
php72-php-pecl-ssh2.x86_64 : Bindings for the libssh2 library
php72-php-pecl-stackdriver-debugger.x86_64 : Investigate your code behavior in production
php72-php-pecl-stats.x86_64 : Routines for statistical computation
php72-php-pecl-stomp.x86_64 : Stomp client extension
php72-php-pecl-swoole.x86_64 : PHP's asynchronous concurrent distributed networking framework
php72-php-pecl-swoole-serialize.x86_64 : Fast and Small serialize
php72-php-pecl-swoole2.x86_64 : PHP's asynchronous concurrent distributed networking framework
php72-php-pecl-swoole4.x86_64 : PHP's asynchronous concurrent distributed networking framework
php72-php-pecl-sync.x86_64 : Named and unnamed synchronization objects
php72-php-pecl-taint.x86_64 : XSS code sniffer
php72-php-pecl-tcpwrap.x86_64 : Tcpwrappers binding
php72-php-pecl-termbox.x86_64 : A termbox wrapper for PHP
php72-php-pecl-timecop.x86_64 : Time travel and freezing extension
php72-php-pecl-trace.x86_64 : Trace is a low-overhead tracing tool for PHP
php72-php-pecl-trader.x86_64 : Technical Analysis for traders
php72-php-pecl-translit.x86_64 : Transliterates non-latin character sets to latin
php72-php-pecl-uopz.x86_64 : User Operations for Zend
php72-php-pecl-uploadprogress.x86_64 : An extension to track progress of a file upload
php72-php-pecl-uuid.x86_64 : Universally Unique Identifier extension for PHP
php72-php-pecl-uv.x86_64 : Libuv wrapper
php72-php-pecl-varnish.x86_64 : Varnish Cache bindings
php72-php-pecl-vips.x86_64 : PHP extension for interfacing with libvips
php72-php-pecl-vld.x86_64 : Dump the internal representation of PHP scripts
php72-php-pecl-weakref.x86_64 : Implementation of weak references
php72-php-pecl-xattr.x86_64 : Extended attributes
php72-php-pecl-xdebug.x86_64 : PECL package for debugging PHP scripts
php72-php-pecl-xdiff.x86_64 : File differences/patches
php72-php-pecl-xlswriter.x86_64 : An efficient and fast xlsx file export extension
php72-php-pecl-xmldiff.x86_64 : XML diff and merge
php72-php-pecl-xxtea.x86_64 : XXTEA encryption algorithm extension for PHP
php72-php-pecl-yac.x86_64 : Lockless user data cache
php72-php-pecl-yaconf.x86_64 : Yet Another Configurations Container
php72-php-pecl-yaf.x86_64 : Yet Another Framework
php72-php-pecl-yaml.x86_64 : PHP Bindings for yaml
php72-php-pecl-yar.x86_64 : Light, concurrent RPC framework
php72-php-pecl-yaz.x86_64 : Z39.50/SRU client
php72-php-pecl-zip.x86_64 : Une extension de gestion des ZIP
php72-php-pecl-zmq.x86_64 : ZeroMQ messaging
php72-php-pggi.x86_64 : GTK bindings
php72-php-pgsql.x86_64 : A PostgreSQL database module for PHP
php72-php-phalcon3.x86_64 : Phalcon Framework
php72-php-phpiredis.x86_64 : Client extension for Redis
php72-php-pinba.x86_64 : Client extension for Pinba statistics server
php72-php-process.x86_64 : Modules for PHP script using system process interfaces
php72-php-pspell.x86_64 : A module for PHP applications for using pspell interfaces
php72-php-recode.x86_64 : A module for PHP applications for using the recode library
php72-php-smbclient.x86_64 : PHP wrapper for libsmbclient
php72-php-snappy.x86_64 : Snappy Extension for PHP
php72-php-snmp.x86_64 : A module for PHP applications that query SNMP-managed devices
php72-php-snuffleupagus.x86_64 : Security module for php7
php72-php-soap.x86_64 : A module for PHP applications that use the SOAP protocol
php72-php-sodium.x86_64 : Wrapper for the Sodium cryptographic library
php72-php-sqlsrv.x86_64 : Microsoft Drivers for PHP for SQL Server
php72-php-tarantool.x86_64 : PHP driver for Tarantool/Box
php72-php-tidy.x86_64 : Standard PHP module provides tidy library support
php72-php-wkhtmltox.x86_64 : HTML Converter
php72-php-xml.x86_64 : A module for PHP applications which use XML
php72-php-xmlrpc.x86_64 : A module for PHP applications which use the XML-RPC protocol
php72-php-zephir-parser.x86_64 : Zephir parser extension
php72-php-zstd.x86_64 : Zstd Extension for PHP
php72-uwsgi-plugin-php.x86_64 : uWSGI - Plugin for PHP support
php72-zephir.noarch : Zephir language for creation of extensions for PHP.
php72-zephir-parser.x86_64 : Zephir parser extension
방화벽 설정 on CentOS 7
TroubleShooting/Linux 2015.12.23 18:01CentOS 7 은 기존 iptables 를 사용하지않고 firewalld 라는 명령어로 방화벽 설정을 할 수 있다. 새로 추가된 기능을 사용해보면 좋겠지만, 배우는 비용이 있으니 기존 방식대로 설정하는 방법을 사용해보자.
1. firewalld 서비스 비활성화
# systemctl stop firewalld
# systemctl mask firewalld
2. iptables-services 패키지 설치
# yum install iptables-services
3. iptables 서비스 활성화
# systemctl enable iptables
4. 방화벽 서비스 시작
# systemctl start iptables
5. 방화벽 설정 내용 확인
# iptables -L -n
6. 방화벽 설정 변경
- outbound 는 허용.
- inbound 는 특정 주소(1.2.3.4) 또는 특정 주소 대역(192.168.1.0/24)에서 22(sshd) 번 포트로 가는 것만 허용. 특정 주소 대역에서 3306 포트로 가는 것도 허용.
# iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
# iptables -A INPUT -s 1.2.3.4/32 -p tcp -m tcp --dport 22 -j ACCEPT
# iptables -A INPUT -s 192.168.1.0/24 -p tcp -m tcp --dport 22 -j ACCEPT
# iptables -A INPUT -s 192.168.1.0/24 -p tcp -m tcp --dport 3306 -j ACCEPT
# iptables -P OUTPUT ACCEPT
# iptables -P INPUT DROP
7. 방화벽 설정 내용 저장
# iptables-save | tee /etc/sysconfig/iptables
or
# iptables-save > /etc/sysconfig/iptables
참고 사이트
http://stackoverflow.com/questions/24756240/how-can-i-use-iptables-on-centos-7
https://www.digitalocean.com/community/tutorials/how-to-set-up-a-basic-iptables-firewall-on-centos-6