Tuesday, July 6, 2010

RHCT skills

Troubleshooting and System Maintenance

RHCTs should be able to:

1) boot systems into different run levels for troubleshooting and system maintenance

boot single to set root password, or fix mounting, or init problem

Q: Machine won't boot

A: modify /boot/grub/grub.conf

root (hd0,0)

A: Check files



A: Fix initrd

mkinitrd initrd-`uname -r`.img `uname -r`

Q: root password not known

A: 1) boot single (at grub screen, "a", "space", "1", enter),

2) passwd root

Items to study: grub, initrd,vmlinuz, inittab, rc.sysinit...

2) diagnose and correct misconfigured networking

system-config-network, or

vi /etc/sysconfig/network-scripts/ifcfg-eth0




vi /etc/sysconfig/network

3) diagnose and correct hostname resolution problems



4) configure the X Window System and a desktop environment

Remember X troubleshooting should be done from the command prompt, and

not within X.




Q: Boot to X

A: Set runlevel 5 in /etc/inittab

vi /etc/inittab





Q: X won't load

A: Check config files

A: system-config-display --reconfig

A: /tmp or /home is full

5) add new partitions, filesystems, and swap to existing systems

This one is a little hard to explain. It just takes some practice to understand.

Tools available:

fdisk /dev/hda

t / fd (raid)


mdadm -C /dev/md0 -l 5 -n 3 /dev/hda6 /dev/hda7 /dev/hda8

mke2fs -j /dev/md0

Q: mount something, such as: /dev/hda7 on /data

A: make directory, mount, modify /etc/fstab

1) mkdir /data

2) mount -t ext3 /dev/hda7 /data

3) vi /etc/fstab

/data /data ext3 defaults 1 2

view or change label:

e2label /dev/hda2

e2label /dev/vg0/data0 /data

6) use standard command-line tools to analyze problems and configure system

ls, cp, mv, rm, tail, cat, etc


Installation and Configuration

RHCTs must be able to:

1) perform network OS installation

Enter the nfs, or ftp server address and path

2) implement a custom partitioning scheme

Probably easiest during GUI install

3) configure printing

probably the easiest thing to do is use:




lpstat, lpq

reject disable

accept /usr/bin/enable

4) configure the scheduling of tasks using cron and at

Understand how cron fields work:

min hr month_day month weekday

copy script to /etc/cron.daily, /etc.cron.monthly, etc. or

Modify /etc/crontab: crontab -e

List cron jobs: crontab -l

Add an at job: at [-f file] TIME

View at queue: atq

Remove at jog: atrm job

5) attach system to a network directory service, such as NIS or LDAP

1) Install ypbind, portmap

2) system-config-authentication

check: Enable NIS Support, or Enable LDAP Support

click: Configure NIS..., or Configure LDAP...

3) configure firewall, if required

iptables -A INPUT -s -p tcp -m tcp --dport 835:837 -j ACCEPT

service iptables save



nisdomainname -y

genent services

getent passwd smith

rpcinfo -p






6) configure autofs


/home/guests /etc/auto.guests --timeout=60


* -rw,soft,intr server1:/home/guests/&

service autofs restart

chkconfig portmap on

chkconfig autofs on

7) add and manage users, groups, quotas, and File Access Control Lists

Q: Create group, add users, set primary group

A: Use groupadd, useradd, usermod

groupadd -g 1000 groupname

useradd username

usermod -G groupname username

(-G for primary group)


Q: Setup a 70kb hard block user quota for user tim on /home/tim:

A: Use a Hard Block user quota (or Soft depending on question).

1) modify /etc/fstab

change defaults to usrquota for /home

2) mount -o remount /home

3) quotacheck -cuf /home

4) quotaon /home

5) setquota -u tim 0 60 0 0 /home


5a) edquota tim

Disk quotas for user tim (uid 502):

Filesystem blocks soft hard inodes soft hard

/dev/hda5 16 0 0 8 0 0

6) repquota /home


quota tim

7) test

a) quota tim

b) su - tim

c) dd if=/dev/zero of=/home/tim/somefile bs=1024 count=70

d) ls -l

file should be less than 70 kilobytes

Quota Command to remember:

quotacheck -cuf /home

quotaon /home

edquota tim

quota tim

repquota /home

*** Lab: Set a user soft block quota of 1MB for user diskhog on /blackhole,

(or hard block, hard / soft inode). Know when to use each type of quota ***

Enable quotas:

quotacheck -cuf /blackhole

quotaon /blackhole

Set Quota:

block inode

h s h s

setquota -u diskhog 0 1024 0 0 /blackhole


edquota -u diskhog

Report on Quota for user or directory:

quota -u diskhog

repquota /blackhole




chage [options] username

password files:




8) configure filesystem permissions for collaboration

Q: Make user alex a member of sales with write permissions to /depts/sales

Q: Make user sales, hr, and web groups in /depts/


mkdir -p /depts/{sales,hr,web}

for GROUP in sales hr web;do chgrp $GROUP /depts/$GROUP;done

chmod 770 /depts/*

chmod g+s /depts/*

Test permissions as alex:

su - alex

9) install and update packages using rpm

You may have to mount a directory over nfs, or install directly from http://

rpm -Uvh filenamex.i386.rpm

rpm --import /usr/share/rhn/RPM-GPG-KEY

rpm -K /tmp/rpmversion.i386.rpm

10) properly update the kernel package

Just remember to use rpm -i, so the old kernel will still be there.

1) mkdir /server1

2) mount server1:/var/ftp/pub /server1

3) cd /server1/Redhat/RPMS

4) rpm -ivh kernel-*

5) vi /boot/grub/grub.conf


11) configure the system to update/install packages from remote repositories using yum or pup


12) modify the system bootloader


13) implement software RAID at install-time and run-time

fdisk /dev/hda

fd (raid)


mdadm -C /dev/md0 -l 5 -n 3 /dev/hda6 /dev/hda7 /dev/hda8

mke2fs -j /dev/md0



mdadm --detail /dev/md0


mdadm /dev/md0 -a /dev/sda1

14) use /proc/sys and sysctl to modify and set kernel run-time parameters

Q: turn on ip forwardarding

A: 1) vi /etc/sysctl.conf


2) sysctl -p


echo 1 > /proc/sys/net/ipv4/ip_forward

to view:

sysctl -a | grep ipv4

to find available options for ipv4:

ls /proc/sys/net/ipv4

15) use scripting to automate system maintenance tasks

Maybe put a script in /etc/cron.daily?

Login Shell Scripts






RHCE skills

Troubleshooting and System Maintenance

RHCEs must demonstrate the RHCT skills listed above, and should be able to:

1) use the rescue environment provided by first installation CD

linux rescue

2) diagnose and correct boot failures arising from bootloader, module, and filesystem errors



/etc/rc.d/rc adn /etc/rc.d/rc?.d






fsck /dev/hda

3) diagnose and correct problems with network services (see Installation and Configuration below for a list of these services)

4) add, remove, and resize logical volumes


Hint: use apropos quota, or just lvm to find commands.

Q: expand or shrink logical volume (RHCE)

A: Make sure there is enough space, and volume is online, use vgconvert if necessary

ext2online /dev/vg0/data0 120M

lvextend -L +100M /dev/vg0/data0

lvreduce -L 120M /dev/vg0/data0

vgdisplay -v vg0



Q: Create a logical volume

A: First create physical volume, then volume group, then logical volume

PV -> VG -> LV

pvcreate /dev/hda6 /dev/hda7 /dev/hda8

vgcreate vg0 /dev/hda6 /dev/hda7

lvcreate -L 50M -n data0 vg0

ext2online /dev/vg0/data0

lvextend -L +6M /dev/vg0/data0

resize2fs -L /dev/vg0/data0 40M

lvreduce -L 40M /dev/vg0/data0


5) diagnose and correct networking services problems where SELinux contexts are interfering with proper operation.



setenforce 1

check context with ls -Z

Q: Set up directory to use context of another directory

A: Use the other directory as a reference

chcon -R --reference /var/www/html /var/www/html/www1

Installation and Configuration

RHCEs must demonstrate the RHCT-level skills listed above, and they must be capable of configuring the following network services:


install httpd, check context with ls -Z

Q: Create a virtual host www1.example.com w/ subdirectory /var/www/html/www1


1) install httpd, modify /etc/httpd/conf/httpd.conf file

ServerName www1.example.com

DocumentRoot /var/www/html/www1

2) chcon -R --reference /var/www/html /var/www/html/www1

3) service httpd restart

4) chkconfig httpd on


service httpd configtest

2) SMB

Q: Configure Samba share /home/depts/legal

1) install samba

rpm -Uvh samba-* system-config-samba*(optional)

2) vi /etc/samba/smb.conf


path = /home/depts/legal

browseable = no

writeable = no

3) configure firewall

port 445, 137-139

3) NFS

Q: Export /data directory with nfs

The nfs server is an RPC service, and thus requires portmap

A: Modify /etc/exports, start nfs & portmap (make sure /data directory exists)

1) modify /etc/exports

/data *(sync,rw)

2) start services

service nfs start

service portmap start

chkconfig nfs on

chkconfig portmap on

3) verify config, & check mounts

exportfs -v

showmount -e localhost

rpcinfo -p localhost

4) restart

exportfs -r, or

service nfs reload

Q: Mount server1:/var/ftp/pub with nfs on /server1

1) mkdir /server1

2) vi /etc/fstab /server1 nfs soft,defaults 0 0

3) mount -a

* configure autofs


Q: Configure automount for nfs mount from nis domain on server1


1) mkdir /net

2) vi /etc/auto.master

# uncomment /net line

/net /etc/auto.net

3) start services

service portmap start

service autofs start

chkconfig autofs on

chkconfig portmap on

Q: Configure automount for nfs mount of /rhome directories from nis domain on server1

A: Create base directory

1) mkdir /rhome

2) vi /etc/auto.master

# copy and modify /misc line

/rhome /etc/auto.rhome

3) vi /etc/auto.rhome

* -rw,soft.intr server1:/home/guests/&

4) start services

service portmap start

service autofs start

chkconfig autofs on

chkconfig portmap on

4) FTP

Q: Configure ftp with /var/ftp/incoming directory


install vsftpd

1) rpm -Uvh vsftpd*

2) service vsftpd start

3) chkconfig vsftpd on

4) create incoming directory

cd /var/ftp

mkdir incoming

chown root:ftp fincoming

chmod 730 incoming

5) vi /etc/vsftpd/vsftpd.conf

uncomment the lines --






6) service vsftpd restart

7) configure firewall

iptables -A INPUT -s -p tcp --dport 21 -j ACCEPT

service iptables save

5) Web proxy

Q: Install a web proxy and allow a certain network to access it

A: Install & configure squid

1) install squid, and start the service

rpm -ivh --aid squid*

service squid start

chkconfig squid on

2) vi /etc/squid

acl example src

http_access allow example

3) service squid reload

4) Configure browser to test:

Edit / Preferences /General / Connection Settings

Manual proxy configuration / HTTP Proxy: localhost Port: 3128

Enable port in firewall, if required

iptables -A INPUT -s -p tcp --dport 3128 -j ACCEPT

service iptables save

Useful parameters:

http_port 3128

cache_mem 8 MB

cache_dir ufs /var/spool/squid 100 16 256

acl all src

http_access allow localhost

http_access deny all

hint: find out that port number is 3128

grep squid /etc/services


install sendmail, sendmail-cf, sendmail-doc (optional)

Q: Configure mail server to accept internet email

A: modify /etc/mail/sendmail.mc

1) cd /etc/mail

2) vi /etc/mail/sendmail.mc

search for 127.0, put dnl at the front of the line

3) make

or m4 sendmail.mc > sendmail.cf

service sendmail restart

Q: Mail alias

A: modify /etc/aliases, run newaliases

Q: Receive mail for DomainX.example.com

A: modify sendmail mc as above, and add domain to /etc/mail/local-host-names



mail -v root

mailq, mailq -Ac

sendmail -q

tail -f /var/log/maillog

7) IMAP, IMAPS, and POP3

Q: Configure for pop3 (or imap)

A: 1) install dovecot

2) vi /etc/dovcot.conf

protocols = pop3

3) service dovecot restart

4) chkconfig dovecot on


note: root is not permitted to login

echo "pop" | mail -s test student

telnet localhost 110

user student

pass student



retr 1


8) SSH



9) DNS (caching name server, slave name server)

Q: Setup a slave name server


1) install bind, bind-utils, and caching-nameserver

2) when configuring a slave name server, start with caching, and modify

3) vi /etc/named.conf

comment out dump-file section


zone "example.com" {

type slave;

masters { };

file "slaves/slave-example.com.zone";


4) vi 0.168.192.in-addr.arpa


zone "0.168.192.in-addr.arpa" {

type slave;

masters { };

file "slaves/0.168.192.zone";


To verify:


named-checkconf -t /var/named

named-checkzone example.com example.com.zone

5) start named, and make it start at boot

service named restart; tail -f /var/log/messages | grep named

chkconfig named on

Remember to check /etc/resolv.conf on all client machines.

10) NTP


For each of these services, RHCEs must be able to:

1) install the packages needed to provide the service

rpm -Uvh packagename.rpm, or

yum install packagename

2) configure SELinux to support the service


setenforce 1

check context with ls -Z

chcon -R --reference /var/www/html /var/www/html/www1

3) configure the service to start when the system is booted

chkconfig servicename on

4) configure the service for basic operation

different for each service

5) Configure host-based and user-based security for the service



RHCEs must also be able to:

1) configure hands-free installation using Kickstart

2) implement logical volumes at install-time

3) use iptables to implement packet filtering and/or NAT

iptables is usually configured to be as restrictive as possible, but this

may be difficult to implement in an exam environment. Read the instructions

carefully, and try to find the best way to implement it.

--- commands ---

iptables -L

iptables -F

service iptables save

service iptables restart

chkconfig iptables on

--- starting config ---

iptables -P INPUT DROP

iptables -A INPUT -i lo -j ACCEPT

iptables -A INPUT -m state --state ESTABLISHED, RELATED -j ACCEPT

--- sample file ---

cat /etc/sysconfig/iptables


:INPUT DROP [67:11217]


:OUTPUT ACCEPT [58:6450]

-A INPUT -s -p tcp -m tcp --dport 22 -j ACCEPT

-A INPUT -s -p tcp -m tcp --dport 22 -j ACCEPT

-A INPUT -i lo -j ACCEPT

-A INPUT -s -p tcp -m tcp --dport 22 -j ACCEPT

-A INPUT -s -p udp -m udp --sport 53 -j ACCEPT


-A INPUT -s -p tcp -m tcp --dport 22 -j ACCEPT

-A INPUT -s -p udp -m udp --dport 53 -j ACCEPT

-A INPUT -s -p tcp -m tcp --dport 445 -j ACCEPT

-A INPUT -s -p tcp -m tcp --dport 21 -j ACCEPT

-A INPUT -s -p tcp -m tcp --dport 2049 -j ACCEPT

-A INPUT -s -p udp -m udp --dport 2049 -j ACCEPT

-A INPUT -s -p tcp -m tcp --dport 25 -j ACCEPT

-A INPUT -s -p tcp -m tcp --dport 110 -j ACCEPT

-A INPUT -s -p tcp -m tcp --dport 80 -j ACCEPT

-A INPUT -s -p tcp -m tcp --dport 3128 -j ACCEPT

-A INPUT -s -p tcp -m tcp --dport 835:837 -j ACCEPT


4) use PAM to implement user-level restrictions