CentOS System Administration

CentOS is the identical copy of RedHat Enterprise Server with no commercial support.  But you always could find good enough support from the CentOS Community: http://www.centos.org, http://wiki.centos.org/.

All experience that you got from CentOS can be easily applied on RedHat Enterprise.

Package Management with yum

CentOS is using PRM for packages.  yum is a great tool to manage all those packages: install, update, upgrade, dependence management, query, etc.

about rpm repositories

All repositories are configured under folder /etc/yum.repos.d.

Some popular repositories includes dag, automic, Centos-Testing, etc.

Atomic Rocket Turtle RPM Repository

quick tutorials: http://www.atomicorp.com/Tutorials/

quick installation and configuration:

wget -q -O - http://www.atomicorp.com/installers/atomic.sh | sh

DAG RPM Repository

Homepage: http://dag.wieers.com/rpm/

Installation and Configuration: http://dag.wieers.com/rpm/FAQ.php#B1

About mount and umount

How to attach extra volume to EC2 instance

 root # mkfs /dev/sdf
 root # mkdir /opt
 root # mount /dev/sdf /opt

A important file /etc/mtab and /etc/fstab. Adding the following lines:

# in file /etc/fstab
/dev/sdf   /opt2     ext2    defaults        0 0
# in file /etc/mtab
/dev/sdf /opt2 ext2 rw 0 0

File Permissions

This post has a very good explanation about File permission on Linux: http://www.tuxfiles.org/linuxhelp/filepermissions.html. Following are some examples:

 $ chmod g+w /path/to/file
# adding write permission to group for a file
 $ chmod u-w /path/to/file
# remove write permission from user for a file
 $ chmod o=x /path/to/file
# set execute permission to others for a file, onle execute permission