RHCE Preparation - System Configuration and Management

This is post 1 in a series of posts where I will be going through the objectives for the RHCE certifications. It builds on the initial post that has the objectives:

https://www.guldmyr.com/red-hat-certification-rhce-preparation/

It appears that the objectives have been updated, at least if you compare between my post above and https://www.redhat.com/training/courses/ex300/examobjective

for example build a simple rpm is installs one package is not in the list.

I bet there are many blogs about this topic. I'm doing this quite a lot for myself, but maybe somebody else finds these useful.

This post will be about the section 'System Configuration and Management'.

My setup: Core i7, 8GB RAM, Windows 7 x64, VMWare Workstation with CentOS installed.

Installing a fresh VM with 4 cores, 5GB RAM, virtualization and CentOS.

CentOS is a free clone of Red Hat, it's missing some stuff (satellite for example) but it does the job for learning. You can find it in many places, for example here: http://www.nic.funet.fi/pub/Linux/INSTALL/Centos/6/isos/x86_64/

IP Routing and NAT

The part "Routing / NAT" will be tricky, as I do not have a second computer that I could use for this. Maybe I can get something working inside the virtual machines though, but for now I think I will skip these two and get straight into the other ones.

Use /proc/sys and sysctl to modify and set kernel runtime parameters

Edit /etc/sysctl.conf

Or use sysctl -w to set it temporary

For example one is: vm.overcommit_ratio

You can then do either of these to view the current setting:

cat /proc/sys/vm/overcommit_ratio
sysctl vm.overcommit_ratio

To set it temporarily:

echo "60" > /proc/sys/vm/overcommit_ratio
sysctl -w vm.overcommit_ratio="50"

To set each time on boot:

echo "vm.overcommit_ratio = 50" >> /etc/sysctl.conf

Configure a system to authenticate using Kerberos

Waiting with this. Need to set up a KDC - kerberos service first.

Build a simple RPM that packages a single file

This appears to be a bit complicated - the details below are about as simple as this can be made. There is a lot more nifty things that you can do with an rpm.

Would be nice to have a guide of this in for example /usr/share/doc

yum install rpm-build
cd $HOME/rpmbuild
mkdir {BUILD,RPMS,SOURCES,SPECS,SRPMS}
mkdir GetIP
cd GetIP

The "program":

cat getip.sh
## !/bin/bash

wget -q <https://guldmyr.com/ip.php> -O/tmp/ip
cat /tmp/ip

chmod +x getip.sh

Make an archive and put it in the SOURCES DIR:

cd $HOME/rpmbuild
tar -cf GetIP.tar.gz GetIP
mv GetIP.tar.gz SOURCES/

Edit a spec-file (do this as a normal user instead of root, it will show the default entries):

cd SPECS
vi sample.spec

Make it look like this:

Name:GetIP
Version:1.0
Release:        1%{?dist}
Summary: Get an IP wooop

Group:  Development/Tools
License:        GPL
URL:            <https://guldmyr.com>
Source0:        %{name}.tar.gz
BuildRoot:      %(mktemp -ud %{_tmppath}/%{name}-%{version}-%{release}-XXXXXX)

BuildRequires:bash
Requires:bash

%description
Get an IP woop!

%prep
%setup -n GetIP

%build

%install
mkdir -p "$RPM_BUILD_ROOT/opt/GetIP"
cp -R * "$RPM_BUILD_ROOT/opt/GetIP"

%clean
rm -rf "$RPM_BUILD_ROOT"

%files
/opt/GetIP
%defattr(-,root,root,-)
%doc

%changelog

Then make an rpm:

rpmbuild -v -bb $HOME/rpmbuild/SPECS/sample.spec

Then as root:

cd /home/user/rpmbuild/RPMS/x86_64/
rpm -ivh GetIP-1.0-1.el6.x86_64.rpm

Then as normal user you can now execute the installed file:

/opt/getip/getip.sh

If you wonder about things - check this fairly unreadable blog post out.

Basically you want to use the $RPM_BUILD_ROOT in front of where you want to install the software. By default there are 'make', 'configure' and nothing in the 'require' entries. I removed the make, configured and just put 'bash' in the require entries, it seemed to do the trick though.

More info is also available on rpm.org - which recommend to use /usr/src/redhat for building packages.

Configure a system as an iSCSI initiator that persistently mounts an iSCSI target

Waiting with this. Need to set up an iSCSI target first.

Produce and deliver reports on system utilization (processor, memory, disk, and network)

sar -A

/etc/cron.d/sysstat

Use shell scripting to automate system maintenance tasks

Well, this can be a lot of things and is quite hard to prepare for.

But I think a 'for loop' is a good thing to know about and can help with a lot of system maintenance tasks.

an input file with usernames:

[martbhell@rhce ~]$ cat /tmp/userlist
bengt
goran

a scriptfile:

[root@rhce ~]# cat usersndirs.sh
## !/bin/sh

userlist=/tmp/userlist

for i in `cat $userlist`; do
echo useradd $i;
echo mkdir $i;
done

Remove the "echo" to create the users.

Of course, you could also use the 'newuser' command (interactive or send a file).

This happens a lot I think: You get an idea that "hey, I can do this with a script". But then a random amount of time later you find out that there is already a command that does this for you. That doesn't mean the time spent is a total waste, hopefully you learned something while doing it. Maybe your script even does a better job than the new one you found.

Configure a system to log to a remote system

syslog / rsyslog

man rsyslog.conf has an example for how to log to a remote machine

edit /etc/rsyslog.conf

add

To  forward  messages  to another host via UDP, prepend the hostname with the at sign ("@").  To forward it via plain tcp, prepend two at
signs ("@@"). To forward via RELP, prepend the string ":omrelp:" in front of the hostname.

Example:
*.* @@192.168.0.8

Set the IP to the machine that will be receiving the logs.

Configure a system to accept logging from a remote system

So this step you may want to do before the previous step (unless you already have a working syslogd server).

You edit /etc/rsyslog.conf

and uncomment the "reception" parts (don't forget firewall and restart service).

To test try to "su -" with the wrong password and then check in /var/log/secure on the loghost.

Create a private repository

"To create a private repository you should proceed as follows: - Install the createrepo software package - Create a directory where files can be shared (via FTP or HTTP) - Create a subdirectory called Packages and copy all packages to be published in Packages - run createrepo -v directory"