RHCE "Cheat Sheet"

This document attempts to provide answers to all study points on the RHCE and RHCT Exam Preparation Guide in a single-page (and thus, printable) format. This is not a “brain dump” or an attempt to cheat the RH302 exam in any way. These are just my self-study notes. Use them at your own risk.

:!:
Note: Study points last updated on 2009-08-11. This list may become out
of date without notice (especially after I pass the test ;-) ).

Testing Environment with Sun VirtualBox

install guest additions:

yum install gcc kernel-devel
sh /media/VBOXADDITIONS*/VBoxLinuxAdditions-x86.run
reboot

Prerequisite skills for RHCT and RHCE

Candidates should possess the following skills, as they may be
necessary in order to fulfill requirements of the RHCT and RHCE exams:

use
standard command line tools (e.g., ls, cp, mv, rm, tail, cat, etc.) to
create, remove, view, and investigate files and directories

use grep, sed, and awk to process text streams and files

use a terminal-based text editor, such as vim or nano, to modify text files

use input/output redirection

operator	description
>	redirect STDOUT to a file
2>	redirect STDERR to a file
&>	redirect all output to a file
2>&1	redirect all output to a pipe

use » to append instead of overwrite

understand basic principles of TCP/IP networking, including IP addresses, netmasks, and gateways for IPv4 and IPv6

use su to switch user accounts

<span class="kw2">su</span> - <span class="sy0"><</span>user<span class="sy0">></span>

use passwd to set passwords

<span class="kw2">passwd</span> <span class="sy0"><</span>user<span class="sy0">></span>

use tar, gzip, and bzip2

<span class="co0"># compress (tar/gzip)</span><br /><span class="kw2">tar</span> cvzf <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span>.tgz <span class="sy0"><</span>directory<span class="sy0">></span><br /> <br /><span class="co0"># extract (tar/gzip)</span><br /><span class="kw2">tar</span> xvzf <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span>.tgz<br /> <br /><span class="co0"># compress (tar/bzip)</span><br /><span class="kw2">tar</span> cvjf <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span>.tbz <span class="sy0"><</span>directory<span class="sy0">></span><br /> <br /><span class="co0"># extract (tar/bzip)</span><br /><span class="kw2">tar</span> xvjf <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span>.tbz

configure an email client on Red Hat Enterprise Linux

<span class="kw3">echo</span> <span class="st0">"message"</span> | mail <span class="sy0"><</span>email<span class="sy0">></span> <span class="re5">-s</span> <span class="st0">"subject"</span><br />mail <span class="sy0"><</span>email<span class="sy0">></span> <span class="re5">-s</span> <span class="st0">"subject"</span> <span class="sy0"><</span> <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span>

use text and/or graphical browser to access HTTP/HTTPS URLs

elinks
lynx

use lftp to access FTP URLs

RHCT skills

Troubleshooting and System Maintenance

RHCTs should be able to:

boot systems into different run levels for troubleshooting and system maintenance

append the desired runlevel to grub's kernel line:

1-5 runs appropriate rc and init scripts
single only runs rc.sysinit
emergency skips all rc and init scripts

diagnose and correct misconfigured networking

check /etc/sysconfig/network
check /etc/sysconfig/network-scripts/ifcfg-<interface>
service network restart
chkconfig network on
ifconfig
ping <localhost ip>
netstat -r
ping <default gateway>
ping 4.2.2.2

redhat network config tool:

system-config-network

diagnose and correct hostname resolution problems

check /etc/nsswitch.conf
check /etc/resolv.conf
check /etc/hosts
dig @<dns server> google.com

redhat network config tool:

system-config-network

configure the X Window System and a desktop environment

install x:

yum groupinstall <span class="st0">"x window system"</span>

init respawns /etc/X11/prefdm -nodaemon to keep x running in runlevel 5
startx to start manually

xfs is supposedly required for x windows (even though i can run x fine without it…):

service xfs on<br />chkconfig xfs on

x environment config:

/etc/sysconfig/desktop
/etc/X11/xinit/xinitrc
/etc/X11/xinit/Xclients
~/.xinitrc
~./Xclients

redhat display config tool:

system-config-display <span class="br0">[</span>--reconfig<span class="br0">]</span>

install gnome desktop:

yum groupinstall <span class="st0">"gnome desktop environment"</span>

switchdesk allows you to change your desktop environment:

yum <span class="kw2">install</span> switchdesk<br />switchdesk

if switchdesk is not available, edit /etc/sysconfig/desktop:

<span class="re2">DISPLAYMANAGER</span>=<span class="sy0"><</span>GNOME|KDE|XDM<span class="sy0">></span><br /><span class="re2">DESKTOP</span>=<span class="sy0"><</span>GNOME|KDE<span class="sy0">></span>

add new partitions, filesystems, and swap to existing systems

partitions

manage partitions:

fdisk <span class="sy0"><</span>device<span class="sy0">></span><br />partprobe

filesystems

make filesystems:

mkfs.<span class="sy0"><</span>ext2|ext3<span class="sy0">></span>

label filesystems:

e2label <span class="sy0"><</span>partition<span class="sy0">></span> <span class="sy0"><</span>label<span class="sy0">></span><br />blkid

manage filesystem settings:

tune2fs <span class="sy0"><</span>partition<span class="sy0">></span><br />dumpe2fs <span class="sy0"><</span>partition<span class="sy0">></span>

swap

note that it's possible to create a swap file instead of a partition:

<span class="kw2">dd</span> <span class="re2"><span class="kw1">if</span></span>=<span class="sy0">/</span>dev<span class="sy0">/</span>zero <span class="re2">of</span>=<span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span> <span class="re2">bs</span>=<span class="nu0">1024</span> <span class="re2">count</span>=<span class="sy0"><</span><span class="kw2">size</span><span class="sy0">></span>

format the file/partition:

mkswap <span class="sy0"><</span>partition|<span class="kw2">file</span><span class="sy0">></span><br /><span class="kw2">nano</span> <span class="re5">-w</span> <span class="sy0">/</span>etc<span class="sy0">/</span>fstab<br />swapon <span class="re5">-va</span><br /><span class="kw2">cat</span> <span class="sy0">/</span>proc<span class="sy0">/</span>swaps

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

check for full filesystems, quotas

Installation and Configuration

RHCTs must be able to:

perform network OS installation

at boot prompt:

linux askmethod

implement a custom partitioning scheme

configure printing

printing support is provided by cups:

service cups start<br />chkconfig cups on

redhat printer config tool:

system-config-printer

web config tool:

http://localhost:631<br />

printing via command line:

<span class="co0"># print</span><br /><span class="kw2">lpr</span> <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span><br /><span class="co0"># view print queue</span><br />lpq<br /><span class="co0"># remove print job</span><br />lprm <span class="sy0"><</span>job number<span class="sy0">></span>

configure the scheduling of tasks using cron and at

cron

make sure vixie cron is installed and running:

yum <span class="kw2">install</span> vixie-cron<br />service crond start<br />chkconfig crond on

if /etc/cron.allow exists, only these users are allowed (/etc/cron.deny is ignored)
if /etc/cron.allow does not exist, everyone allowed except users in /etc/cron.deny
if neither exists, only root allowed
empty /etc/cron.deny means all users allowed (default)

edit your cron jobs:

crontab <span class="re5">-e</span>

crontab format:

<minute> <hour> <day of month> <month> <day of week> <command><br />

:!: /etc/crontab has additional user field before command.

at/batch

make sure at is installed and running:

yum <span class="kw2">install</span> at<br />service atd start<br />chkconfig atd on

if /etc/at.allow exists, only these users are allowed (/etc/at.deny is ignored)
if /etc/at.allow does not exist, everyone allowed except users in /etc/at.deny
if neither exists, only root allowed
empty /etc/at.deny means all users allowed (default)

<span class="co0"># add jobs</span><br />at now + <span class="nu0">1</span> hour<br />at<span class="sy0">></span> <span class="sy0"><</span><span class="kw3">command</span><span class="sy0">></span><br /> <br />at 09:00 <span class="nu0">2009</span>-07-<span class="nu0">23</span><br />at<span class="sy0">></span> <span class="sy0"><</span><span class="kw3">command</span><span class="sy0">></span><br /> <br />batch<br />at<span class="sy0">></span> <span class="sy0"><</span><span class="kw3">command</span><span class="sy0">></span>

<span class="co0"># list jobs</span><br />atq

remove <span class="kw3">jobs</span><br />atrm <span class="sy0"><</span>job<span class="sy0">></span>

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

redhat config tools:

system-config-authentication<br />authconfig-tui

required packages for nis:

yum <span class="kw2">install</span> ypbind portmap

required packages for ldap:

yum <span class="kw2">install</span> nss-ldap openldap

configure autofs

make sure the autofs service is running:

service autofs start<br />chkconfig autofs on

ensure the following line in /etc/nsswitch.conf:

automount: files nis

define an autofs-controlled mountpoint called test by adding the following to /etc/auto.master:

<span class="sy0">/</span><span class="kw3">test</span> <span class="sy0">/</span>etc<span class="sy0">/</span>auto.test

create /etc/auto.test:

blah example.com:<span class="sy0">/</span>pub<span class="sy0">/</span>something<br /><span class="sy0">*</span> example:<span class="sy0">/</span>home<span class="sy0">/&</span>

local /test/blah ⇒ remote example.com:/pub/something
local /test/user ⇒ remote example:/home/user ( this method can be used to automount home directories)

test automounting:

<span class="kw2">ls</span> <span class="sy0">/</span><span class="kw3">test</span><span class="sy0">/</span>blah<br /><span class="kw2">ls</span> <span class="sy0">/</span><span class="kw3">test</span><span class="sy0">/</span>user<br /> <br /><span class="co0"># redhat defaults</span><br /><span class="kw2">ls</span> <span class="sy0">/</span>net<span class="sy0">/<</span><span class="kw2">hostname</span><span class="sy0">></span><br /><span class="kw2">ls</span> <span class="sy0">/</span>misc<span class="sy0">/</span><span class="kw3">cd</span>

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

redhat user/group config tool:

system-config-users

users

/etc/passwd file format:

username:password:uid:gid:gecos:homedir:shell<br />

/etc/shadow file format:

username:password:lastpwchange:minpwchange:maxpwage:pwchangewarn:inactive:expire<br />

command line user management:

useradd <span class="sy0"><</span>user<span class="sy0">></span><br />usermod <span class="sy0"><</span>user<span class="sy0">></span><br />chage <span class="sy0"><</span>user<span class="sy0">></span><br />userdel <span class="sy0"><</span>user<span class="sy0">></span><br />pwck

default account expiration settings in /etc/login.defs

groups

/etc/group file format:

groupname:password:gid:members<br />

command line group management:

<span class="kw2">groups</span> <span class="sy0"><</span>user<span class="sy0">></span><br />groupadd <span class="sy0"><</span>user<span class="sy0">></span><br />groupmod <span class="sy0"><</span>user<span class="sy0">></span><br />groupdel <span class="sy0"><</span>user<span class="sy0">></span> <br />grpck

quotas

install quota package

yum <span class="kw2">install</span> quota

add fs options to /etc/fstab:

usrquota,grpquota

remount device

<span class="kw2">mount</span> <span class="re5">-o</span> remount <span class="sy0"><</span><span class="kw2">mount</span> point<span class="sy0">></span>

init quota database:

quotacheck <span class="re5">-cugm</span> <span class="sy0"><</span>device<span class="sy0">></span>

enable/disable quotas

quotaon <span class="sy0"><</span>device<span class="sy0">></span><br />quotaoff <span class="sy0"><</span>device<span class="sy0">></span>

edit quotas

edquota <span class="re5">-u</span> <span class="sy0"><</span>user<span class="sy0">></span><br />edquota <span class="re5">-g</span> <span class="sy0"><</span>group<span class="sy0">></span>

edit grace time

edquota <span class="re5">-ut</span> <span class="sy0"><</span>user<span class="sy0">></span><br />edquota <span class="re5">-gt</span> <span class="sy0"><</span>group<span class="sy0">></span>

check/report quotas

quota <span class="sy0"><</span>user<span class="sy0">></span><br />repquota <span class="re5">-aug</span>

Access Control Lists

install acl package

yum <span class="kw2">install</span> acl

add fs options to /etc/fstab:

acl

remount device:

<span class="kw2">mount</span> <span class="re5">-o</span> remount <span class="sy0"><</span><span class="kw2">mount</span> point<span class="sy0">></span>

manage acls:

<span class="co0"># set acls</span><br />setfacl <span class="re5">-m</span> <span class="br0">[</span>d:<span class="br0">]</span>u:<span class="sy0"><</span>user<span class="sy0">></span>:<span class="sy0"><</span>r|<span class="kw2">w</span>|x|-<span class="sy0">></span> <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span><br />setfacl <span class="re5">-m</span> <span class="br0">[</span>d:<span class="br0">]</span>g:<span class="sy0"><</span>group<span class="sy0">></span>:<span class="sy0"><</span>r|<span class="kw2">w</span>|x|-<span class="sy0">></span> <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span><br /> <br /><span class="co0"># get acls</span><br />getfacl <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span><br /> <br /><span class="co0"># remove acls</span><br />setfacl <span class="re5">-x</span> u:<span class="sy0"><</span>user<span class="sy0">></span> <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span><br />setfacl <span class="re5">-x</span> g:<span class="sy0"><</span>user<span class="sy0">></span> <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span><br />setfacl <span class="re5">--remove-all</span> <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span><br />setfacl <span class="re5">--remove-default</span> <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span>

configure filesystem permissions for collaboration

create new group
add users to group
chown folder to root.<group>
chmod folder to 2770 (g+s)

install and update packages using rpm

<span class="co0"># install</span><br />rpm <span class="re5">-ivh</span> <span class="sy0"><</span>package<span class="sy0">></span>.rpm<br /> <br /><span class="co0"># update</span><br />rpm <span class="re5">-Uvh</span> <span class="sy0"><</span>package<span class="sy0">></span>.rpm<br /> <br /><span class="co0"># freshen </span><br />rpm <span class="re5">-Fvh</span> <span class="sy0"><</span>package<span class="sy0">></span>.rpm<br /> <br /><span class="co0"># remove</span><br />rpm <span class="re5">-e</span> <span class="sy0"><</span>package<span class="sy0">></span><br /> <br /><span class="co0"># query by file name</span><br />rpm <span class="re5">-qf</span> <span class="sy0"><</span>full path of <span class="kw2">file</span><span class="sy0">></span><br /> <br /><span class="co0"># verify a file</span><br />rpm <span class="re5">-Vf</span> <span class="sy0">></span> <span class="sy0"><</span>full path of <span class="kw2">file</span><span class="sy0">></span><br /> <br /><span class="co0"># verify status of all packages</span><br />rpm <span class="re5">-Va</span> <span class="sy0">></span> <span class="sy0">/</span>tmp<span class="sy0">/</span>rpmverify

:!: while inside the rescue environment, use the –root option to specify the real location of your root file system (e.g. –root=/mnt/sysimage).

properly update the kernel package

always do an install (i.e. rpm -ivh <kernel package>) rather than an update
check /boot/grub/grub.conf for proper configuration

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

yum config goes in /etc/yum.repos.d/

[id]<br />name=my repo<br />baseurl=http://example.com/centos/<br />enabled=1<br />

modify the system bootloader

production config is in /boot/grub/grub.conf
see examples in /usr/share/doc/grub-*/menu.lst

implement software RAID at install-time and run-time

to start, we need at least two devices/partitions of type “linux raid autodetect” (use fdisk to set partition type to “fd”)

create raid device:

mdadm <span class="re5">--create</span> <span class="sy0">/</span>dev<span class="sy0">/</span>md0 --<span class="re2">level</span>=<span class="sy0"><</span>0|<span class="nu0">1</span>|<span class="nu0">4</span>|<span class="nu0">5</span>|<span class="nu0">6</span>|<span class="nu0">10</span><span class="sy0">></span> --raid-<span class="re2">devices</span>=<span class="sy0"><</span>num<span class="sy0">></span> <span class="sy0"><</span>device list<span class="sy0">></span>

fail disk in array:

mdadm <span class="sy0">/</span>dev<span class="sy0">/</span>md0 <span class="re5">-f</span> <span class="sy0"><</span>device<span class="sy0">></span>

remove disk from array:

mdadm <span class="sy0">/</span>dev<span class="sy0">/</span>md0 <span class="re5">-r</span> <span class="sy0"><</span>device<span class="sy0">></span>

add disk to array:

mdadm <span class="sy0">/</span>dev<span class="sy0">/</span>md0 <span class="re5">-a</span> <span class="sy0"><</span>device<span class="sy0">></span>

stop array:

mdadm <span class="re5">--stop</span> <span class="sy0">/</span>dev<span class="sy0">/</span>md0

check raid status:

mdadm <span class="re5">--detail</span> <span class="sy0">/</span>dev<span class="sy0">/</span>md0

<span class="kw2">cat</span> <span class="sy0">/</span>proc<span class="sy0">/</span>mdstat

format works as usual:

mkfs.ext3 <span class="sy0">/</span>dev<span class="sy0">/</span>md0

:!: don't forget to configure /etc/fstab appropriately.

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

config is in /etc/sysctl.conf

<span class="co0"># search through parameters</span><br />sysctl <span class="re5">-a</span> | <span class="kw2">grep</span> <span class="sy0"><</span>whatever<span class="sy0">></span><br /><span class="co0"># apply changes from config file immediately</span><br />sysctl <span class="re5">-p</span>

use scripting to automate system maintenance tasks

configure NTP for time synchronization with a higher-stratum server

redhat config tool:

system-config-date<br />

config is in /etc/ntp.conf

synchronization configuration example:

server 0.pool.ntp.org<br />server 1.pool.ntp.org<br />server 2.pool.ntp.org<br />

apply changes:

service ntpd restart<br />chkconfig ntpd on<br />

verify changes:

ntpq <span class="re5">-p</span>

RHCE skills

Troubleshooting and System Maintenance

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

use the rescue environment provided by first installation CD

linux rescue

when working in non-chrooted rescue mode:
- mount /dev/hdc /mnt/source (to access install files on the cd/dvd)
- rpm commands should use the –root=/mnt/sysimage option

manually make /dev and /proc available in chrooted mode:

<span class="kw2">mount</span> <span class="re5">-o</span> <span class="kw3">bind</span> <span class="sy0">/</span>dev <span class="sy0">/</span>mnt<span class="sy0">/</span>sysimage<span class="sy0">/</span>dev<br /><span class="kw2">mount</span> <span class="re5">-o</span> <span class="kw3">bind</span> <span class="sy0">/</span>proc <span class="sy0">/</span>mnt<span class="sy0">/</span>sysimage<span class="sy0">/</span>proc

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

check in order:

mbr
/boot/grub/grub.conf
/etc/fstab
/etc/inittab
/etc/rc.d/rc.sysinit
/etc/rc.d/rc*.d
/etc/rc.d/init.d/*
/etc/rc.d/rc.local

grub errors

in general, use the last line before the error message to see where grub error'd out
to find correct value for root option, type find /grub/stage1 at the grub command line ( remember that all file names in grub.conf are relative to the root option)
check for missing files in kernel and/or initrd lines

kernel errors

missing/corrupt initrd file results in: kernel panic - not syncing: vfs: unable to mount root fs on unknown-block
invalid root parameter for kernel results in: setuproot: error mounting /proc: No such file or directory

reinstall grub to mbr:

grub-install <span class="sy0"><</span>device<span class="sy0">></span>

recreate initrd:

mkinitrd <span class="sy0"><</span>filename<span class="sy0">></span> <span class="sy0"><</span>kernel version<span class="sy0">></span>

fix corrupt filesystem:

fsck <span class="sy0"><</span>partition<span class="sy0">></span>

if fsck is unable to locate a superblock, you can specify an alternative one:

dumpe2fs <span class="sy0"><</span>partition<span class="sy0">></span><br />fsck <span class="re5">-b</span> <span class="sy0"><</span>block<span class="co0">#> <partition></span>

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

see what's listening on what port:

<span class="kw2">netstat</span> <span class="re5">-ntaupe</span>

add, remove, and resize logical volumes

redhat lvm config tool:

yum <span class="kw2">install</span> system-config-lvm<br />system-config-lvm

create physical volume:

pvcreate <span class="sy0"><</span>device<span class="sy0">></span>

create volume group:

vgcreate <span class="sy0"><</span>name<span class="sy0">></span> <span class="sy0"><</span>pv device<span class="sy0">></span> <span class="br0">[</span>pv device<span class="br0">]</span>

extend volume group:

vgextend <span class="sy0"><</span>name<span class="sy0">></span> <span class="sy0"><</span>pv device<span class="sy0">></span>

create logical volume:

lvcreate <span class="re5">--size</span> <span class="sy0"><</span><span class="kw2">size</span><span class="sy0">></span>M <span class="re5">--name</span> <span class="sy0"><</span>lv name<span class="sy0">></span> <span class="sy0"><</span>vg name<span class="sy0">></span>

extend logical volume:

lvextend <span class="re5">--size</span> <span class="sy0"><</span><span class="kw2">size</span><span class="sy0">></span>M <span class="sy0"><</span>device<span class="sy0">></span><br />resize2fs <span class="sy0"><</span>device<span class="sy0">></span>

shrink logical volume:

resize2fs <span class="sy0"><</span>device<span class="sy0">></span> <span class="sy0"><</span><span class="kw2">size</span><span class="sy0">></span>M<br />lvreduce <span class="re5">--size</span> <span class="sy0"><</span><span class="kw2">size</span><span class="sy0">></span>M <span class="sy0"><</span>device<span class="sy0">></span>

remove logical volume:

lvremove <span class="sy0"><</span>device<span class="sy0">></span>

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

enable/disable selinux in /etc/sysconfig/selinux:

SELINUX=enforcing<br />SELINUXTYPE=targeted<br />

install selinux troubleshooter:

yum <span class="kw2">install</span> setroubleshoot<br />service setroubleshoot start<br />chkconfig setroubleshoot on

install selinux management tool:

yum <span class="kw2">install</span> policycoreutils-gui

list selinux errors:

sealert <span class="re5">-a</span> <span class="sy0">/</span>var<span class="sy0">/</span>log<span class="sy0">/</span>audit<span class="sy0">/</span>audit.log | <span class="kw2">less</span>

launch gui browser:

sealert <span class="re5">-b</span>

list selinux booleans:

getsebool <span class="re5">-a</span>

set selinux boolean:

setsebool <span class="re5">-P</span> <span class="sy0"><</span>boolean<span class="sy0">></span> = <span class="sy0"><</span>0|<span class="nu0">1</span><span class="sy0">></span>

list security contexts:

<span class="kw2">ls</span> <span class="re5">-Z</span> <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span>

change security contexts:

<span class="co0"># using reference (copy contexts from existing known-good file)</span><br />chcon <span class="re5">-R</span> <span class="re5">--reference</span> <span class="sy0"><</span>old <span class="kw2">file</span><span class="sy0">></span> <span class="sy0"><</span>new <span class="kw2">file</span><span class="sy0">></span><br /> <br /><span class="co0"># manual</span><br />chcon <span class="re5">-R</span> <span class="re5">-u</span> <span class="sy0"><</span>user<span class="sy0">></span> <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span><br />chcon <span class="re5">-R</span> <span class="re5">-t</span> <span class="sy0"><</span><span class="kw3">type</span><span class="sy0">></span> <span class="sy0"><</span><span class="kw2">file</span><span class="sy0">></span>

Installation and Configuration

RHCEs must demonstrate the RHCT-level skills listed above, and they
must be capable of configuring the following network services. For each
of these services, RHCEs must be able to:

install the packages needed to provide the service
configure SELinux to support the service
configure the service to start when the system is booted
configure the service for basic operation
Configure host-based and user-based security for the service

HTTP/HTTPS

install

yum <span class="kw2">install</span> httpd mod_ssl

selinux

make new DocumentRoot match default DocumentRoot ( :!: this applies to any directory that apache will serve files from):

chcon <span class="re5">-R</span> <span class="re5">--reference</span> <span class="sy0">/</span>var<span class="sy0">/</span>www <span class="sy0">/</span>www

start at boot

chkconfig httpd on

basic config

requirements for ~user/ directories:
- UserDir directive
- chmod 701 the user's home directory
- change security context on the user's UserDir

requirements for .htaccess file usage:
- AllowOverride All directive

requirements for name-based virtual hosts:
- NameVirtualHost *:80 and NameVirtualHost *:443 directives
- each virtual host requires appropriate ServerName and ServerAlias directives
- a single virtual host cannot span multiple ports (i.e. 80 and 443). two separate VirtualHost *:<port> sections are needed to do this.

self-signed ssl cert:

<span class="kw3">cd</span> <span class="sy0">/</span>etc<span class="sy0">/</span>pki<span class="sy0">/</span>tls<span class="sy0">/</span>certs<br /><span class="kw2">rm</span> localhost.crt<br /><span class="kw2">make</span> testcert

check virtual host config:

httpd <span class="re5">-D</span> DUMP_VHOSTS

host-based security

firewall config:

protocol	ports
tcp	80, 443

hosts are allowed by default and must be explicitly denied:

<Directory /var/www/html>     <br />     Order deny,allow<br />     Deny from 192.168.0.0/255.255.255.0<br />     Deny from badguys.example.com<br /></Directory><br />

hosts are denied by default and must be explicitly allowed:

<Directory /var/www/html>     <br />     Order allow,deny<br />     Allow from 192.168.0.0/255.255.255.0<br />     Allow from goodguys.example.com<br /></Directory><br />

user-based security

create web password file:

htpasswd <span class="re5">-c</span> <span class="sy0">/</span>etc<span class="sy0">/</span>httpd<span class="sy0">/</span>webusers testuser1<br />htpasswd <span class="sy0">/</span>etc<span class="sy0">/</span>httpd<span class="sy0">/</span>webusers testuser2

create web group file (/etc/httpd/webgroups):

testgroup: testuser1 testuser2

allow access by group:

<Directory /var/www/html>     <br />     AuthType Basic<br />     AuthName "top secret area"<br />     AuthUserFile /etc/httpd/webusers<br />     AuthGroupFile /etc/httpd/webgroups<br />     Require group testgroup<br /></Directory><br />

verify service functionality

test http/https:

elinks <span class="sy0"><</span>http|https<span class="sy0">></span>:<span class="sy0">//<</span><span class="kw2">hostname</span><span class="sy0">>/</span><span class="br0">[</span>path<span class="br0">]</span>

SMB

install

yum <span class="kw2">install</span> samba samba-client

selinux

allow samba to share home directories:

setsebool <span class="re5">-P</span> <span class="re2">samba_enable_home_dirs</span>=<span class="nu0">1</span>

mark a directory as sharable with samba:

chcon <span class="re5">-R</span> <span class="re5">-T</span> samba_share_t <span class="sy0"><</span>directory<span class="sy0">></span>

start at boot

chkconfig smb on

basic config

redhat samba config tool:

yum <span class="kw2">install</span> system-config-samba<br />system-config-samba

set workgroup/domain:

workgroup = <workgroup><br />

security modes:

# connections check local pwdb (default)<br />security = user<br /><br /># member server on a domain, uses pwdb on a dc<br />security = domain<br />workgroup = EXAMPLE<br /><br /># member server on an ad domain using kerberos, uses pwdb on a dc<br />security = ads<br />realm = EXAMPLE.COM<br />password server = kerberos.example.com<br /><br /># used when samba was not capable of being a domain member server (DO NOT USE)<br />security = server<br />encrypt passwords = yes<br />password server = <netbios name of dc><br /><br /># each share requires a password (DO NOT USE)<br />security = share<br />

share options:

[<share name>]<br /># path for share<br />path = <path> <br /><br /># share is visible <br />browseable = <yes|no><br /><br /># rw enabled<br />writeable = <yes|no><br /><br /># this is a shared printer<br />printable = <yes|no><br /><br /># all users connecting to this share use <group> as their primary group<br />group = <group name><br />

join domain:

net rpc <span class="kw2">join</span> <span class="re5">-U</span> root

fstab example:

<span class="sy0">//<</span><span class="kw2">hostname</span><span class="sy0">>/<</span>share<span class="sy0">></span> <span class="sy0"><</span>mountpoint<span class="sy0">></span>    cifs    <span class="re2">user</span>=<span class="sy0"><</span>username<span class="sy0">></span>,<span class="re2">pass</span>=<span class="sy0"><</span>password<span class="sy0">></span>    0 0

:!: mount.cifs and umount.cifs need to be chmod'ed u+s in order to be used by non-root users

host-based security

firewall config:

protocol	ports
tcp	139, 445
udp	137, 138

hosts allow/deny can be used per-server or per-share:

hosts allow = 127.0.0.1 192.168.2.0/24 192.168.3.0/24<br />hosts deny = 0.0.0.0/0<br />

user-based security

account maintenance:

<span class="co0"># add account (local linux account must exist first, or be translated via /etc/samba/smbusers):</span><br />smbpasswd <span class="re5">-a</span> <span class="sy0"><</span>username<span class="sy0">></span><br /> <br /><span class="co0"># enable/disable account:</span><br />smbpasswd <span class="re5">-e</span> <span class="sy0"><</span>username<span class="sy0">></span><br />smbpasswd <span class="re5">-d</span> <span class="sy0"><</span>username<span class="sy0">></span><br /> <br /><span class="co0"># remove account:</span><br />smbpasswd <span class="re5">-x</span> <span class="sy0"><</span>username<span class="sy0">></span>

:!: service smb reload may be needed after account changes

share access:

valid users = <user1> @<group1><br />

share access is also controlled by unix file permissions

verify service functionality

list shares:

smbclient <span class="re5">-L</span> <span class="sy0"><</span><span class="kw2">hostname</span><span class="sy0">></span> <span class="re5">-U</span> <span class="sy0"><</span>username<span class="sy0">></span>

browse shares:

smbclient <span class="sy0">//<</span><span class="kw2">hostname</span><span class="sy0">>/<</span>share<span class="sy0">></span> <span class="re5">-U</span> <span class="sy0"><</span>username<span class="sy0">></span>

test allow/deny statements for a host:

testparm <span class="sy0">/</span>etc<span class="sy0">/</span>samba<span class="sy0">/</span>smb.conf <span class="sy0"><</span><span class="kw2">hostname</span><span class="sy0">></span> <span class="sy0"><</span>ip address<span class="sy0">></span>

NFS

install

yum <span class="kw2">install</span> portmap nfs-utils

start at boot

chkconfig portmap on<br />chkconfig nfs on<br />chkconfig nfslock on<br />chkconfig netfs on

basic config

redhat config tool:

yum <span class="kw2">install</span> system-config-nfs<br />system-config-nfs

format of /etc/exports:

<mountpoint> <host>(<options>) [<host>(<options>) ...]<br />

activate new exports:

<span class="sy0">/</span>etc<span class="sy0">/</span>init.d<span class="sy0">/</span>nfs restart

host-based security

:!: edit /etc/sysconfig/nfs and restart nfs to set static ports

firewall config:

<span class="co0"># see ports </span><br />rpcinfo <span class="re5">-p</span>

host based security is intrinsic to the format of the exports file

user-based security

use standard file permissions

verify service functionality

list exports:

showmount -e <host><br />

FTP

install

yum <span class="kw2">install</span> vsftpd

selinux

allow local users to log in and cd into home directories:

setsebool <span class="re5">-P</span> <span class="re2">ftp_home_dir</span>=<span class="nu0">1</span>

start at boot

chkconfig vsftpd on

basic config

host-based security

use ipchains with -[!]s option

firewall config:

protocol	ports
tcp	21

:!: ftp data transfers will not work unless ip_conntrack_ftp is added to IPTABLES_MODULES in /etc/sysconfig/iptables-config

tcp_wrappers example:

vsftpd : 192.168.0.<br />

user-based security

allow/deny controlled via /etc/vsftpd/user_list ( users in /etc/vsftpd/ftpusers are always denied via pam)
default allow/deny is configured by userlist_deny statement in vsftpd.conf

verify service functionality

test ftp:

<span class="kw2">ftp</span> <span class="sy0"><</span>server<span class="sy0">></span>

Web proxy

install

yum <span class="kw2">install</span> squid

selinux

allow squid to connect to the network (this is recommended, but was not needed in my testing):

setsebool <span class="re5">-P</span> <span class="re2">squid_connect_any</span>=<span class="nu0">1</span>

start at boot

chkconfig squid on

host-based security

firewall config:

protocol	ports
tcp	3128

allow access from local networks:

acl our_networks src 192.168.1.0/24 192.168.2.0/23<br />http_access allow our_networks<br />

user-based security

FIXME

verify service functionality

test proxy:

<span class="re2">HTTP_PROXY</span>=<span class="sy0"><</span>server<span class="sy0">></span>:<span class="nu0">3128</span> elinks

SMTP

install

yum <span class="kw2">install</span> postfix<br />alternatives <span class="re5">--config</span> mta<br />service <span class="kw2">sendmail</span> stop

start at boot

chkconfig postfix on

basic config

listen on public interfaces:

inet_interfaces = all<br />

specify all destination hostnames/domains:

mydestination = <hostname1>, <hostname2>, ...<br />

specify origin domain:

myorigin = $mydomain<br />

local aliases in /etc/aliases ( :!: dont forget to run newaliases to apply changes):

<alias>: <user1>[, user2]<br />

virtual aliases in /etc/postfix/virtual ( :!: dont forget to run postmap /etc/postfix/virtual to apply changes):

<virtual alias>: <user><br />

enable virtual aliases:

virtual_alias_maps = hash:/etc/postfix/virtual<br />

outbound address rewriting in /etc/postfix/generic ( :!: dont forget to run postmap /etc/postfix/generic to apply changes):

<outbound alias>: <user><br />

enable outbound aliases:

smtp_generic_maps = hash:/etc/postfix/generic<br />

host-based security

use ipchains with -[!]s option

firewall config:

protocol	ports
tcp	25

user-based security

FIXME use smtp auth?

verify service functionality

test smtp:

telnet <span class="sy0"><</span>server<span class="sy0">></span> <span class="nu0">25</span>

IMAP, IMAPS, and POP3

install

yum <span class="kw2">install</span> dovecot

start at boot

chkconfig dovecot on

basic config

enable protocols:

protocols = <protocol list><br />

create custom ssl cert:

nano -w /etc/pki/dovecot/dovecot-openssl.cnf<br />/usr/share/doc/dovecot-*/examples/mkcert.sh<br />service dovecot restart<br />

host-based security

use ipchains with -[!]s option

protocol	ports
tcp	143, 110, 995, 993

user-based security

use pam_listfile in /etc/pam.d/dovecot

verify service functionality

test mailbox acess:

mutt <span class="re5">-f</span> <span class="sy0"><</span>imap|imaps|pop|pops<span class="sy0">></span>:<span class="sy0">//<</span>user<span class="sy0">>@<</span>server<span class="sy0">></span>

SSH

install

yum <span class="kw2">install</span> openssh-server

start at boot

chkconfig sshd on

user-based security

allow/deny user access:

AllowUsers user1 user2 user3@example.com<br />DenyUsers user4 user5 user6@example.com<br />

host-based security

use ipchains with -[!]s option

firewall config:

protocol	ports
tcp	22

tcp_wrappers example:

sshd : 192.168.0.<br />

verify service functionality

test logging in:

<span class="kw2">ssh</span> <span class="sy0"><</span>user<span class="sy0">>@<</span>server<span class="sy0">></span>

DNS (caching name server, slave name server)

install

yum <span class="kw2">install</span> bind-chroot caching-nameserver

start at boot

chkconfig named on

basic config

copy sample config:

<span class="kw2">cp</span> <span class="re5">-a</span> <span class="sy0">/</span>var<span class="sy0">/</span>named<span class="sy0">/</span><span class="kw2">chroot</span><span class="sy0">/</span>etc<span class="sy0">/</span>named.caching-nameserver.conf <span class="sy0">/</span>var<span class="sy0">/</span>named<span class="sy0">/</span><span class="kw2">chroot</span><span class="sy0">/</span>etc<span class="sy0">/</span>named.conf

caching-only nameserver:

edit listen-on directives (comment out to listen on all interfaces)
edit allow-query directives (comment out allow queries from everyone)
edit match-clients and match-destinations directives to allow recursive queries from other hosts

slave nameserver:

get slave example from /usr/share/doc/bind-*/sample/etc/named.conf

host-based security

firewall config:

protocol	ports
tcp	53
udp	53

allow-query example:

allow-query { 192.168.0.0/16; localnets; };<br />

user-based security

N/A

verify service functionality

test query:

dig <span class="sy0">@<</span>server<span class="sy0">></span> <span class="sy0"><</span>domain<span class="sy0">></span>

test zone transfer:

dig <span class="sy0">@<</span>server<span class="sy0">></span> <span class="sy0"><</span>domain<span class="sy0">></span> axfr

NTP

install

yum <span class="kw2">install</span> ntp

start at boot

chkconfig ntpd on

host-based security

firewall config:

protocol	ports
udp	123

allow other servers to sync with us:

restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap<br />

user-based security

N/A

verify service functionality

show peers:

ntpq <span class="re5">-p</span>

RHCEs must also be able to:

configure hands-free installation using Kickstart

yum <span class="kw2">install</span> system-config-kickstart

make installation tree available
create kickstart file (use system-config-kickstart to create ks.cfg) and validate (using ksvalidator)
validate kickstart file
make kickstart file available
- bootable diskette (place in top level directory)
- bootable cdrom (place in top level directory)
- network (http, ftp, nfs)
use bootable media and supply appropriate kernel parameter

<span class="re2">ks</span>=floppy:<span class="sy0">/</span>ks.cfg<br /><span class="re2">ks</span>=cdrom:<span class="sy0">/</span>ks.cfg<br /><span class="re2">ks</span>=http:<span class="sy0">//</span>example.com<span class="sy0">/</span>ks.cfg<br /><span class="re2">ks</span>=nfs:example.com:<span class="sy0">/</span>ks.cfg

implement logical volumes at install-time

use iptables to implement packet filtering and/or NAT

:!: do not
use system-config-securitylevel, as it will overwrite your custom
iptables rules. the following method seems to be the best way to go:

make changes in /etc/sysconfig/iptables
run /etc/init.d/iptables restart to apply changes

packet filtering

packet filtering example:

<span class="re5">-A</span> <span class="sy0"><</span>chain<span class="sy0">></span> <span class="re5">-p</span> <span class="sy0"><</span>tcp<span class="sy0">/</span>udp<span class="sy0">></span> <span class="re5">-m</span> <span class="sy0"><</span>tcp<span class="sy0">/</span>udp<span class="sy0">></span> <span class="br0">[</span>-s<span class="br0">[</span><span class="sy0">!</span><span class="br0">]</span> <span class="sy0"><</span><span class="kw3">source</span> address<span class="sy0">></span><span class="br0">]</span> <span class="re5">--dport</span> <span class="sy0"><</span>destination port<span class="sy0">></span> <span class="re5">-j</span> ACCEPT

NAT

enable ip forwarding in /etc/sysctl.conf:

net.ipv4.ip_forward = 1<br />

to test from another machine:

ip route replace default via <span class="sy0"><</span>ip address<span class="sy0">></span>

inbound dnat:

iptables <span class="re5">-t</span> nat <span class="re5">-A</span> PREROUTING <span class="re5">-p</span> <span class="sy0"><</span>tcp<span class="sy0">/</span>udp<span class="sy0">></span> <span class="re5">--dport</span> <span class="sy0"><</span>destination port<span class="sy0">></span> <span class="re5">-j</span> DNAT <span class="re5">--to-dest</span> <span class="sy0"><</span>private server<span class="sy0">></span>:<span class="sy0"><</span>port<span class="sy0">></span>

outbound dnat:

iptables <span class="re5">-t</span> nat <span class="re5">-A</span> OUTPUT <span class="re5">-p</span> <span class="sy0"><</span>tcp<span class="sy0">/</span>udp<span class="sy0">></span> <span class="re5">--dport</span> <span class="sy0"><</span>destination port<span class="sy0">></span> <span class="re5">-j</span> DNAT <span class="re5">--to-dest</span> <span class="sy0"><</span>private server<span class="sy0">></span>:<span class="sy0"><</span>port<span class="sy0">></span>

masquerading:

iptables <span class="re5">-t</span> nat <span class="re5">-A</span> POSTROUTING <span class="re5">-o</span> <span class="sy0"><</span>outbound interface<span class="sy0">></span> <span class="re5">-j</span> MASQUERADE

snat:

iptables <span class="re5">-t</span> nat <span class="re5">-A</span> POSTROUTING <span class="re5">-j</span> SNAT <span class="re5">--to-source</span> <span class="sy0"><</span>public server<span class="sy0">></span>:<span class="sy0"><</span>port<span class="sy0">></span>

FIXME

use PAM to implement user-level restrictions

module documentation

/usr/share/doc/pam-*/txts

module configuration

/etc/pam.d
/etc/security

<module interface> <control flag> <module name> <module arguments><br />

module interface	description
auth	user authentication (e.g. verifies password, set group membership or kerberos tickets, etc.)
account	verifies that access is allowed (e.g. expired account?, check group membership, etc.)
password	handles password changes
session	manages user sessions (e.g. mount home dir, create mailbox, logging, etc.)

control flag	description
required	must pass, continue testing on failure
requisite	must pass, stop testing on failure
sufficient	failure is ignored, but if passing so far, return success at this point
optional	pass or failure is irrelevant
include	include another file

pam_listfile.so example

allow/deny users if listed in /etc/special:

auth required pam_listfile.so onerr=success item=user sense=<allow|deny> file=/etc/special<br />

Additional Notes

tcp_wrappers

file format:

<daemon list> : <client list> [except <client list>] [: <option>]<br />

search order:

/etc/hosts.allow
/etc/hosts.deny
allow by default

:!: searching stops on first match

Troubleshooting

unable to log in

password wrong or expired?
account locked?
shell set to /sbin/nologin, /bin/false, etc.?
root user and PermitRootLogin no in /etc/ssh/sshd_config?
root user and terminal not listed in /etc/securetty?
non-root user and /etc/nologin exists?
check pam_listfile restrictions

Credit: http://conigliaro.org/wiki/rhce

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