CentOS 5 Minimalist

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Virtualization is very popular nowadays. There is no need to have hundreds of phisical computers, one powerful server can manage 10+ virtual machines on its own. I worked on a distributed application with share nothing architecture that requiered minimum of 8 nodes and a master server. The nodes interact with master server via API calls and constantly processed little chunks of data (time consuming task with little CPU usage) and reported back to the master server. The problem arrised when VMware Server started getting slugish,  therefore all the nodes became very slow. To fix the problem I came out with idea to minimize the nodes at much as possible, living only importan operating system and application specific services running. In this article you will find out how to setup RHEL (Cent OS 5) server with minimal resource usage and how to work around crazy RHEL caching that uses 50%+ of RAM.

SUMMARY

• Configuration Time: 10 Minutes
• Installation Time: 5-10 Minutes
• Maximum memory used during the installation process: 80 MB
• OS Runtime Max RAM Used: 116 MB
• OS HD Space Used: 1.2G

Running for 10 minutes:

Running for 1 hour:

Settings vfs_cache_pressure and running for 2 hours:

As you can see after settings vfs_cache_pressure Linux Kernel is cleaning page_cache and innode_cache. We can see 200%+ increase in free memory.

VM SPECS

• RAM: 128 MB
• HDD Size: 4 GB

TO DO

1. Download CentOS 5 [i386] Download

   You can download 64-bit architecture here. You will require more memory for 64-bit architecture (At least 256 MB).

2. Start installation in the Graphical Mode
3. When you get to the screen below, do the following:
   • Uncheck ALL, except for Server.
   • Select Customize Now to configure software packages.

     Desktop - Gnome/KDE because we do not need it, this option will be loading Desktop environment into the memory during each boot, wasting precious memory.

     

4. Configuring Packages that have to be selected.
   • Desktop Environments - NONE

   • Applications

     • Editors
   • Development - NONE

   • Servers

     • DNS Name Server
     • Mail Server
     • Server Configuration Tools
     • Web Server - only following Packages
       • crypto-utils
       • dlstcache
       • mod_ssl
       • php-5
       • php-mysql

   • Base System

     • Base
   • Virtualization - NONE
   • Clustering - NONE
   • Cluster Storage - NONE
   • Languages - NONE (English is the default, it is not in the list)
5. After installation is completed and server reboots Setup Agent will appear
   • Authentication

   • Firewall Configuration
     

     • Disable SELinux here or put it in Permissive mode

       If you think you need SELinux then keep it. You can find more information how to configure SELinux on CentOS Wiki site

     • Customize

       • Enable SSH, WWW, SMTP
         
   • Network configuration - configure DNS to your specs
   • System services - configure startup services here
     • NetworkManager - OFF
     • acpid - ON
     • anacron - ON
     • apmd - ON
     • atd - ON
     • auditd - ON
     • autofs - OFF
     • avahi-daemon - ON
     • avahi-dnsconfd - OFF
     • bluetooth - OFF
     • conman - OFF
     • cpuspeed - ON
     • crond - ON
     • cups - OFF
     • dc_client - OFF
     • dc_server - OFF
     • dnsmasq - OFF
     • dovecot - ON
     • dund - OFF
     • firstboot - ON
     • gpm - ON
     • haldaemon - OFF
     • hidd - OFF
     • httpd - ON
     • ibmasm - OFF
     • ip6tables - ON
     • iptables - ON
     • irda - OFF
     • irqbalance - OFF
     • kudzu - OFF
     • lvm2-monitor - OFF
     • mcstrans - OFF (enable ONLY if SELinux is ON)
     • mdmonitor - OFF (enabled ONLY if RAID is used)
     • mdmpd - OFF
     • messagebus - ON
     • microcode_ctl - ON
     • multipathd - OFF
     • named - OFF
     • netconsole - OFF
     • netfs - OFF
     • netplugd - OFF
     • network - ON
     • nfs - OFF
     • nfslock - OFF
     • nscd - OFF
     • oddjobd - OFF
     • pand - OFF
     • pcscd - OFF
     • portmap - ON
     • psacct - OFF
     • rawdevices - OFF
     • rdist - OFF
     • readahead_early - ON
     • readahead_later - OFF
     • restoredcond - OFF (enabled only if SELinux is ON)
     • rpcgssd - ON
     • rpcidmapd - ON
     • rpcsvcgssd - OFF
     • saslauthd - ON
     • sendmail - ON
     • smartd - OFF
     • smb - OFF
     • spamassasin - OFF
     • squid - OFF
     • sshd - ON
     • syslog - ON
     • tcsd - OFF
     • tux - OFF
     • winbind - OFF
     • wpa_supplicant - OFF
     • ypbind - OFF
     • yum-updatesd - ON



6. Login as ROOT
   Open /etc/sysctl.conf for editing with your favourite editor
   

   vim /etc/sysctl.conf

   
   And add this line to the bottom of the file
   

   # Cache Pressure
   vm.vfs_cache_pressure = 10000
   

    
   Reboot your machine 
   

   reboot

    

   References

   About CentOS

   • http://wiki.centos.org/Manuals/ReleaseNotes/CentOS4.8
   • http://wiki.centos.org/Manuals/ReleaseNotes/CentOS5.5

   CentOS 4 Minimal

   • http://anchorite.org/blog/2006/11/13/minimal-services-on-centos-44-mini-howto/

   Settings-up LAMP server with CentOS

   • http://www.phpvs.net/articles/blakes-centos-lamp-server-guide-single-page/

   Caching Problems

   • http://rackerhacker.com/2008/12/03/reducing-inode-and-dentry-caches-to-keep-oom-killer-at-bay/

   About Linux Services

   • http://linux.die.net/man/1/
   • http://www.hscripts.com/tutorials/linux-services/