centos6-very-minimal

What is it ?

A script / documentation to get a very minimal CentOS 6 x86_64 install to run in VirtualBox.

It's a just a base to build on.

Rules

Here are some rules :

• no IPV6
• no SELinux, no firewall
• no specific hardware drivers (we run it in VirtualBox)
• we keep yum and a "not broken" rpm database
• just ssh access
• no "VirtualBox guest additions"
• no NFS
• no RPC

Howto

First stage

Install a standard CentOS x86_64 minimal distribution with (for example) : CentOS-6.3-x86_64-minimal.iso.

Then :

# Install latest updates
yum -y upgrade

# Clean cache
yum clean all

# Reboot
reboot

Starting point :

• 214 packages
• around 80 MB of used memory
• 870 MB of used disk space

Second stage

# No SELinux
cp -pf /etc/sysconfig/selinux /etc/sysconfig/selinux.orig
cat /etc/sysconfig/selinux.orig |sed 's/^SELINUX=.*$/SELINUX=disabled/g' >/etc/sysconfig/selinux

# No IPV6
# (some ideas stolen on http://wiki.centos.org/FAQ/CentOS6)
cp -pf /etc/sysctl.conf /etc/sysctl.conf.orig
echo "net.ipv6.conf.all.disable_ipv6 = 1" >>/etc/sysctl.conf
echo "net.ipv6.conf.default.disable_ipv6 = 1" >>/etc/sysctl.conf
cp -pf /etc/hosts /etc/hosts.orig
cat /etc/hosts.orig |grep -v localhost6 >/etc/hosts
cp -pf /etc/ssh/sshd_config /etc/ssh/sshd_config.orig
cat /etc/ssh/sshd_config |sed 's/#AddressFamily any/AddressFamily inet/g' |sed 's/#ListenAddress 0.0.0.0/ListenAddress 0.0.0.0/g' >/etc/ssh/sshd_config

# Disable some services
for SERVICE in auditd fcoe iptables ip6tables iscsi iscsid lldpad lvm2-monitor netfs nfslock rpcbind rpcidmapd rpcgssd; do
    chkconfig ${SERVICE} off
done

# Remove some packages
cat >/tmp/packages_to_remove <<EOF
aic94xx-firmware
bfa-firmware
kernel-firmware
ql2100-firmware
ql2200-firmware
ql23xx-firmware
ql2400-firmware
ql2500-firmware
iptables-ipv6
nfs-utils
nfs-utils-lib
iscsi-initiator-utils
device-mapper-multipath-libs
device-mapper-multipath
audit
checkpolicy
selinux-policy
selinux-policy-targeted
policycoreutils
device-mapper
cryptsetup-luks
cryptsetup-luks-libs
device-mapper-event
device-mapper-event-libs
device-mapper-libs
kpartx
lvm2
lvm2-libs
EOF
yum remove `cat /tmp/packages_to_remove |xargs`

# Clean cache
yum clean all

# Reboot
reboot

Conclusion

Very minimal list of processes (with an open ssh connection) :

[root@centos6 ~]# ps -ef |wc -l
63

[root@centos6 ~]# pstree
init─┬─dhclient
     ├─login───bash
     ├─6*[mingetty]
     ├─rsyslogd───3*[{rsyslogd}]
     ├─sshd───sshd───bash───pstree
     └─udevd───2*[udevd]

Less than 50 MB of used memory :

[root@centos6 ~]# free |grep buffers
             total       used       free     shared    buffers     cached
-/+ buffers/cache:      49684     971012

810 MB of used disk space :

[root@centos6 ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              40G  809M   38G   3% /
tmpfs                 499M     0  499M   0% /dev/shm

A GOOD FOUNDATION TO BUILD ON !

License (New BSD)

Copyright (c) 2012, Fabien MARTY <fabien.marty@gmail.com>
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.
    * Neither the name of the <organization> nor the
      names of its contributors may be used to endorse or promote products
      derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.