rhce cheat sheet

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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 This list may become out of date without notice (especially after I pass the test ). updated by Dino Conti on 2010-06-25 Table of Contents RHCE "Cheat Sheet"............................................................................................................................1 Testing Environment with Sun VirtualBox......................................................................................4 Prerequisite skills for RHCT and RHCE......................................................................................... 4 use standard command line tools (e.g., ls, cp, mv, rm, tail, cat, etc.) to create, remove, view, and investigate files and directories............................................................................................ 4 use grep, sed, and awk to process text streams and files.............................................................4 use a terminal-based text editor, such as vim or nano, to modify text files................................ 4 use input/output redirection........................................................................................................ 4 understand basic principles of TCP/IP networking, including IP addresses, netmasks, and gateways for IPv4 and IPv6........................................................................................................ 5 use su to switch user accounts.....................................................................................................5 use passwd to set passwords....................................................................................................... 5 use tar, gzip, and bzip2................................................................................................................5 configure an email client on Red Hat Enterprise Linux..............................................................5 use text and/or graphical browser to access HTTP/HTTPS URLs............................................. 5 use lftp to access FTP URLs....................................................................................................... 5 HELP in RHEL5......................................................................................................................... 5 RHCT skills..................................................................................................................................... 6 Troubleshooting and System Maintenance................................................................................. 6 boot systems into different run levels for troubleshooting and system maintenance.............6 diagnose and correct misconfigured networking....................................................................6 diagnose and correct hostname resolution problems..............................................................6 configure the X Window System and a desktop environment............................................... 6 add new partitions, filesystems, and swap to existing systems.............................................. 7 partitions............................................................................................................................ 7 filesystems......................................................................................................................... 7 swap................................................................................................................................... 8 use standard command-line tools to analyze problems and configure system.......................8 Installation and Configuration.................................................................................................... 8 perform network OS installation............................................................................................ 8 implement a custom partitioning scheme............................................................................... 8 configure printing...................................................................................................................8 configure the scheduling of tasks using cron and at...............................................................9 cron.................................................................................................................................... 9 at/batch...............................................................................................................................9 attach system to a network directory service, such as NIS or LDAP...................................10 configure autofs....................................................................................................................10

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Page 1: RHCE Cheat Sheet

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 ).

updated by Dino Conti on 2010-06-25

Table of ContentsRHCE "Cheat Sheet"............................................................................................................................1

Testing Environment with Sun VirtualBox......................................................................................4Prerequisite skills for RHCT and RHCE.........................................................................................4

use standard command line tools (e.g., ls, cp, mv, rm, tail, cat, etc.) to create, remove, view, and investigate files and directories............................................................................................4use grep, sed, and awk to process text streams and files.............................................................4use a terminal-based text editor, such as vim or nano, to modify text files................................4use input/output redirection........................................................................................................4understand basic principles of TCP/IP networking, including IP addresses, netmasks, and gateways for IPv4 and IPv6........................................................................................................5use su to switch user accounts.....................................................................................................5use passwd to set passwords.......................................................................................................5use tar, gzip, and bzip2................................................................................................................5configure an email client on Red Hat Enterprise Linux..............................................................5use text and/or graphical browser to access HTTP/HTTPS URLs.............................................5use lftp to access FTP URLs.......................................................................................................5HELP in RHEL5.........................................................................................................................5

RHCT skills.....................................................................................................................................6Troubleshooting and System Maintenance.................................................................................6

boot systems into different run levels for troubleshooting and system maintenance.............6diagnose and correct misconfigured networking....................................................................6diagnose and correct hostname resolution problems..............................................................6configure the X Window System and a desktop environment...............................................6add new partitions, filesystems, and swap to existing systems..............................................7

partitions............................................................................................................................7filesystems.........................................................................................................................7swap...................................................................................................................................8

use standard command-line tools to analyze problems and configure system.......................8Installation and Configuration....................................................................................................8

perform network OS installation............................................................................................8implement a custom partitioning scheme...............................................................................8configure printing...................................................................................................................8configure the scheduling of tasks using cron and at...............................................................9

cron....................................................................................................................................9at/batch...............................................................................................................................9

attach system to a network directory service, such as NIS or LDAP...................................10configure autofs....................................................................................................................10

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add and manage users, groups, quotas, and File Access Control Lists................................10users......................................................................................................................................11groups...................................................................................................................................11

quotas...............................................................................................................................11Access Control Lists........................................................................................................12

configure filesystem permissions for collaboration.............................................................12install and update packages using rpm.................................................................................12properly update the kernel package......................................................................................13configure the system to update/install packages from remote repositories using yum or pup..............................................................................................................................................13

create yum repository from installation DVD.................................................................13modify the system bootloader..............................................................................................14implement software RAID at install-time and run-time.......................................................14use /proc/sys and sysctl to modify and set kernel run-time parameters...............................14use scripting to automate system maintenance tasks............................................................15configure NTP for time synchronization with a higher-stratum server................................15

RHCE skills...................................................................................................................................15Troubleshooting and System Maintenance...............................................................................15

use the rescue environment provided by first installation CD.............................................15diagnose and correct boot failures arising from bootloader, module, and filesystem errors15

grub errors........................................................................................................................16kernel errors.....................................................................................................................16

diagnose and correct problems with network services (see Installation and Configuration below for a list of these services).........................................................................................16add, remove, and resize logical volumes..............................................................................17diagnose and correct networking services problems where SELinux contexts are interfering with proper operation...........................................................................................................17

Installation and Configuration..................................................................................................18HTTP/HTTPS.......................................................................................................................19

install...............................................................................................................................19selinux..............................................................................................................................19start at boot......................................................................................................................19basic config......................................................................................................................19host-based security...........................................................................................................20user-based security...........................................................................................................20verify service functionality..............................................................................................20

SMB......................................................................................................................................20install...............................................................................................................................20selinux..............................................................................................................................21start at boot......................................................................................................................21basic config......................................................................................................................21host-based security...........................................................................................................22user-based security...........................................................................................................22verify service functionality..............................................................................................22

NFS.......................................................................................................................................23install...............................................................................................................................23start at boot......................................................................................................................23basic config......................................................................................................................23host-based security...........................................................................................................23user-based security...........................................................................................................23verify service functionality..............................................................................................23

FTP.......................................................................................................................................24

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install...............................................................................................................................24selinux..............................................................................................................................24start at boot......................................................................................................................24basic config......................................................................................................................24host-based security...........................................................................................................24user-based security...........................................................................................................24verify service functionality..............................................................................................24

Web proxy............................................................................................................................24install...............................................................................................................................24selinux..............................................................................................................................24start at boot......................................................................................................................25host-based security...........................................................................................................25parental control with blocklist.........................................................................................25user-based security...........................................................................................................25verify service functionality..............................................................................................25

SMTP....................................................................................................................................26to enable masquerading in sendmail................................................................................26install...............................................................................................................................27start at boot......................................................................................................................27basic config......................................................................................................................27host-based security...........................................................................................................28user-based security...........................................................................................................28verify service functionality..............................................................................................28

IMAP, IMAPS, and POP3....................................................................................................28install...............................................................................................................................28start at boot......................................................................................................................28basic config......................................................................................................................28create custom ssl cert: .....................................................................................................28host-based security...........................................................................................................28user-based security...........................................................................................................29verify service functionality..............................................................................................29

SSH.......................................................................................................................................29install...............................................................................................................................29start at boot......................................................................................................................29Generate Public / Private key pair...................................................................................29user-based security...........................................................................................................29host-based security...........................................................................................................29verify service functionality..............................................................................................29

DNS (caching name server, slave name server)...................................................................30install...............................................................................................................................30start at boot......................................................................................................................30basic config......................................................................................................................30host-based security...........................................................................................................31user-based security...........................................................................................................31verify service functionality..............................................................................................31

NTP......................................................................................................................................31install...............................................................................................................................31start at boot......................................................................................................................31host-based security...........................................................................................................31user-based security...........................................................................................................31verify service functionality..............................................................................................31

configure hands-free installation using Kickstart.................................................................32

Page 4: RHCE Cheat Sheet

implement logical volumes at install-time...........................................................................32use iptables to implement packet filtering and/or NAT........................................................32

packet filtering.................................................................................................................32NAT.................................................................................................................................32setup for router to internet...............................................................................................33

use PAM to implement user-level restrictions......................................................................33module documentation.....................................................................................................33module configuration.......................................................................................................33pam_listfile.so example...................................................................................................34

Additional Notes............................................................................................................................34tcp_wrappers.............................................................................................................................34Troubleshooting........................................................................................................................34

unable to log in.....................................................................................................................34

Testing Environment with Sun VirtualBoxinstall guest additions:

yum install gcc kernel-develsh /media/VBOXADDITIONS*/VBoxLinuxAdditions-x86.runreboot

Prerequisite skills for RHCT and RHCECandidates 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

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

use su to switch user accountssu - <user>

use passwd to set passwordspasswd <user>

use tar, gzip, and bzip2# compress (tar/gzip)tar cvzf <file>.tgz <directory>

# extract (tar/gzip)tar xvzf <file>.tgz

# compress (tar/bzip)tar cvjf <file>.tbz <directory>

# extract (tar/bzip)tar xvjf <file>.tbz

configure an email client on Red Hat Enterprise Linuxecho "message" | mail <email> -s "subject"mail <email> -s "subject" < <file>

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

• elinks• lynx

use lftp to access FTP URLs

HELP in RHEL5man <command>

man -k <command> search for specific word in manuals

makewhatis create manuals database

command --info

/usr/share/doc/<service or package> installed documentation

/usr/share/doc/Deployment-Guide all the manual

Page 6: RHCE Cheat Sheet

System > Documentation > Deployment Guide

elinks /var/www/manual/ Apache Documentation

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

1. check /etc/sysconfig/network2. check /etc/sysconfig/network-scripts/ifcfg-<interface>3. service network restart4. chkconfig network on5. ifconfig6. ping <localhost ip>7. netstat -r8. ping <default gateway>9. ping 4.2.2.2

redhat network config tool:

system-config-network

diagnose and correct hostname resolution problems

1. check /etc/nsswitch.conf2. check /etc/resolv.conf3. check /etc/hosts4. 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 "x window system"

• 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…):

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service xfs onchkconfig 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 [--reconfig]

install gnome desktop:

yum groupinstall "gnome desktop environment"

switchdesk allows you to change your desktop environment:

yum install switchdeskswitchdesk

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

DISPLAYMANAGER=<GNOME|KDE|XDM>DESKTOP=<GNOME|KDE>

add new partitions, filesystems, and swap to existing systems

partitions

manage partitions:

fdisk <device>n new partitionm menup print partition tablet toggle partition typed delete partition w write changes to diskq quit

partprobe make kernel aware of new partitions

( try also partprobe /dev/sda )

filesystems

make filesystems:

mkfs.<ext2|ext3> mkfs -t ext3 /dev/sda5

mkfs -t ext3 -L home-drive /dev/sda5

label filesystems:

e2label <partition> <label>blkid list UUID and Labels of partitions

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manage filesystem settings:

tune2fs <partition>dumpe2fs <partition>

mkdir /test

mount -t ext3 /dev/sda5 /test

mount -o acl /dev/sda5 /test mount with ACL support user created filesystems

edit /etc/fstab to make mount permanent

/dev/sda5 /test ext3 defaults 0 0

check fstab with mount -a command

if recovering /etc/fstab during recovery operation you need to mount read/write:

mount -o remount,rw /

swap

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

dd if=/dev/zero of=<file> bs=1024 count=<size>

format the file/partition:

mkswap <partition|file>nano -w /etc/fstabswapon -vacat /proc/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 startchkconfig cups on

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redhat printer config tool: system-config-printer

web config tool: http://localhost:631

printing via command line:

# printlpr <file># view print queuelpq# remove print joblprm <job number>

configure the scheduling of tasks using cron and at

cron

make sure vixie cron is installed and running:

yum install vixie-cronservice crond startchkconfig crond on

1. if /etc/cron.allow exists, only these users are allowed (/etc/cron.deny is ignored)2. if /etc/cron.allow does not exist, everyone allowed except users in /etc/cron.deny3. if neither exists, only root allowed4. empty /etc/cron.deny means all users allowed (default)

edit your cron jobs:

crontab -e

crontab format:

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

24 13 * * * /home/user/script

/etc/crontab has additional user field before command.

at/batch

make sure at is installed and running:

yum install atservice atd startchkconfig atd on

1. if /etc/at.allow exists, only these users are allowed (/etc/at.deny is ignored)2. if /etc/at.allow does not exist, everyone allowed except users in /etc/at.deny3. if neither exists, only root allowed4. empty /etc/at.deny means all users allowed (default)

# add jobsat now + 1 hourat> <command>

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at 09:00 2009-07-23at> <command>

batchat> <command>

# list jobsatq

remove jobsatrm <job>

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

redhat config tools: system-config-authentication

authconfig-tui

required packages for nis: yum install ypbind portmap

required packages for ldap: yum install nss-ldap openldap

configure autofs

make sure the autofs service is running:

service autofs startchkconfig 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:

/test /etc/auto.test

create /etc/auto.test:

blah example.com:/pub/something* example:/home/&

1. local /test/blah remote ⇒ example.com:/pub/something2. local /test/user remote ⇒ example:/home/user ( this method can be used to automount

home directories)

test automounting:

ls /test/blahls /test/user

# redhat defaultsls /net/<hostname>ls /misc/cd

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

redhat user/group config tool: system-config-users

Page 11: RHCE Cheat Sheet

users

/etc/passwd file format:

username:password:uid:gid:gecos:homedir:shell

/etc/shadow file format:

username:password:lastpwchange:minpwchange:maxpwage:pwchangewarn:inactive:expire

command line user management:

useradd <user>usermod <user>usermod -aG accounts <username> add user to group and keep all

other group memberships

chage <user>chage -M 30 user set password to expire in 30 days

userdel <user>pwck

• default account expiration settings in /etc/login.defs

groups

/etc/group file format:

groupname:password:gid:members

command line group management:

groups <user>groupadd <user>groupmod <user>groupdel <user> grpck

gpasswd -a group <user>

quotas

install quota package :

yum install quota

add fs options to /etc/fstab:

usrquota,grpquota

remount device

mount -o remount <mount point>

init quota database:

quotacheck -cugm <device>

enable/disable quotas

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quotaon <device>quotaoff <device>

edit quotas

edquota -u <user>edquota -g <group>

edit grace time

edquota -ut <user>edquota -gt <group>

check/report quotas

quota <user>repquota -aug

Access Control Lists

install acl package

yum install acl

add fs options to /etc/fstab:

acl

remount device:

mount -o remount,acl <mount point>

manage acls:

# set aclssetfacl -m [d:]u:<user>:<r|w|x|-> <file>setfacl -m [d:]g:<group>:<r|w|x|-> <file>

setfacl -m u:user:--- /shared/to/secret-file remove all access to file

# get aclsgetfacl <file>

# remove aclssetfacl -x u:<user> <file>setfacl -x g:<user> <file>setfacl --remove-all <file>setfacl --remove-default <file>

configure filesystem permissions for collaboration

1. create new group2. add users to group3. chown folder to root.<group>4. chmod folder to 2770 (g+s) this is also required for Samba Group shares

install and update packages using rpm

# installrpm -ivh <package>.rpm

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# updaterpm -Uvh <package>.rpm

# freshen rpm -Fvh <package>.rpm

# removerpm -e <package>

# query by file namerpm -qf <full path to file>

# verify a filerpm -Vf > <full path of file>

# verify status of all packagesrpm -Va > /tmp/rpmverify

rpm -qi package get info on installed package

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

1. always do an install (i.e. rpm -ivh <kernel package>) rather than an update2. 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]name=my repobaseurl=http://example.com/centos/enabled=1

create yum repository from installation DVD

umount /media/RHEL_5.4\ i386\ DVD/

[root@mail ~]# mkdir /mnt/cdrom

[root@mail ~]# mount /dev/cdrom /mnt/cdrom/

mount: block device /dev/cdrom is write-protected, mounting read-only

[root@mail ~]# cd /mnt/cdrom/Server/repodata

[root@mail yum.repos.d]# cat rhel-cd.repo

[rhel-cd] name=Red Hat Enterprise Linux $releasever - $basearch - Debug baseurl=file:/mnt/cdrom/Server/ #baseurl=file:///media/RHEL_5.4\ i386\ DVD/Server/

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enabled=1 gpgcheck=0 #gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release

yum search nmap

system-config-packages ( this will now display package groups available during installation )

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 --create /dev/md0 --level=<0|1|4|5|6|10> --raid-devices=<num> <device list>

fail disk in array:

mdadm /dev/md0 -f <device>

remove disk from array:

mdadm /dev/md0 -r <device>

add disk to array:

mdadm /dev/md0 -a <device>

stop array:

mdadm --stop /dev/md0

check raid status:

mdadm --detail /dev/md0

cat /proc/mdstat

format works as usual:

mkfs.ext3 /dev/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

# search through parameterssysctl -a | grep <whatever># apply changes from config file immediately

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sysctl -p

use scripting to automate system maintenance tasks

configure NTP for time synchronization with a higher-stratum server

redhat config tool:

system-config-date

• config is in /etc/ntp.conf

synchronization configuration example:

server 0.pool.ntp.orgserver 1.pool.ntp.orgserver 2.pool.ntp.org

apply changes:

service ntpd restartchkconfig ntpd on

verify changes:

ntpq -p

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:

mount -o bind /dev /mnt/sysimage/devmount -o bind /proc /mnt/sysimage/proc

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

check in order:

1. mbr2. /boot/grub/grub.conf3. /etc/fstab4. /etc/inittab5. /etc/rc.d/rc.sysinit6. /etc/rc.d/rc*.d

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7. /etc/rc.d/init.d/*8. /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 <device>

or

grubgrub> find /grub/stage1grub> root (hd0,0)grub> setup (hd0)grub> quit

to password protect grub :

grub-md5-crypt to create md5 password hash

copy and paste this into /boot/grub/grub.conf ( 2 options – protect editing of GRUB during boot or protect selection of kernel image – for testing )

recreate initrd:

mkinitrd <filename> <kernel version>

fix corrupt filesystem:

fsck <partition>

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

dumpe2fs <partition>fsck -b <block#> <partition>

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:

netstat -ntaupe

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add, remove, and resize logical volumes

redhat lvm config tool:

yum install system-config-lvmsystem-config-lvm

create physical volume:

pvcreate <device>

create volume group:

vgcreate <name> <pv device> [pv device]

extend volume group:

vgextend <name> <pv device>

create logical volume:

lvcreate --size <size>M --name <lv name> <vg name>

extend logical volume:

lvextend --size <size>M <device>resize2fs <device>

shrink logical volume:

resize2fs <device> <size>Mlvreduce --size <size>M <device>

remove logical volume:

lvremove <device>

lvm vgchange -ay activate lvm Volume Groups in Rescue Modelvm lvs use these commands to check lvm in rescue mode

lvm vgslvm pvslvm vgsanlvm pvscanlvm lvscan

mkdir /mnt/sysimage

mount /dev/VolGroup00/LogVol00 /mnt/sysimage mount root partitionmount /dev/sda1 /mnt/sysimage/boot mount boot partition

from here you can resize LVM partitions or reinstall grub

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

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

SELINUX=enforcingSELINUXTYPE=targeted

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install selinux troubleshooter:

yum install setroubleshootservice setroubleshoot startchkconfig setroubleshoot on

install selinux management tool:

yum install policycoreutils-gui

list selinux errors:

sealert -a /var/log/audit/audit.log | less

launch gui browser:

sealert -b

list selinux booleans:

getsebool -a

set selinux boolean:

setsebool -P <boolean> = <0|1> make persistent SELinux changes

(check ftp, nfs, http, smb for such problems )

list security contexts:

ls -Z <file>

change security contexts:

# using reference (copy contexts from existing known-good file)chcon -R --reference <old file> <new file>

# manualchcon -R -u <user> <file>chcon -R -t <type> <file>

use semanage fcontext to survive a relabel of filesystem ( especially when changing SELinux from ON to OFF to ON )

semanage fcontext -a -t public_content_t '/www/data/html(/.*)?'

restorecon -vvFR /www/data/html restore default context

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

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HTTP/HTTPS

install

yum install httpd mod_ssl httpd-manual

selinux

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

chcon -R --reference /var/www /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:

cd /etc/pki/tls/certsrm localhost.crtmake testcert.pem

edit /etc/httpd/conf.d/ssl.conf

change following lines to point to new certificate :

SSLCertificateFile /etc/pki/tls/certs/dino.pem #SSLCertificateFile /etc/pki/tls/certs/localhost.crt

# Server Private Key: # If the key is not combined with the certificate, use this # directive to point at the key file. Keep in mind that if # you've both a RSA and a DSA private key you can configure # both in parallel (to also allow the use of DSA ciphers, etc.) SSLCertificateKeyFile /etc/pki/tls/certs/dino.pem #SSLCertificateKeyFile /etc/pki/tls/private/localhost.key

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check virtual host config:

httpd -D 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> Order deny,allow Deny from 192.168.0.0/255.255.255.0 Deny from badguys.example.com</Directory>

hosts are denied by default and must be explicitly allowed:

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

user-based security

create web password file:

htpasswd -c /etc/httpd/webusers testuser1htpasswd /etc/httpd/webusers testuser2

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

testgroup: testuser1 testuser2

allow access by group:

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

verify service functionality

test http/https:

elinks <http|https>://<hostname>/[path]

SMB

install

yum install samba samba-client

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selinux

allow samba to share home directories:

setsebool -P samba_enable_home_dirs=1

mark a directory as shareble with samba:

chcon -R -T samba_share_t <directory>

start at boot

chkconfig smb on

basic config

redhat samba config tool:

yum install system-config-sambasystem-config-samba

set workgroup/domain:

workgroup = <workgroup>

security modes:

# connections check local pwdb (default)security = user

# member server on a domain, uses pwdb on a dcsecurity = domainworkgroup = EXAMPLE

# member server on an ad domain using kerberos, uses pwdb on a dcsecurity = adsrealm = EXAMPLE.COMpassword server = kerberos.example.com

# used when samba was not capable of being a domain member server (DO NOT USE)security = serverencrypt passwords = yespassword server = <netbios name of dc>

# each share requires a password (DO NOT USE)security = share

share options:

[<share name>]# path for sharepath = <path>

# share is visible browseable = <yes|no>

# rw enabledwriteable = <yes|no>

# this is a shared printerprintable = <yes|no>

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# all users connecting to this share use <group> as their primary groupgroup = <group name>

join domain:

net rpc join -U root

mount -t cifs 192.168.0.200:shared-folder /mnt/share -o user=<user>

fstab example:

//<hostname>/<share> <mountpoint> cifs user=<username>,pass=<password> 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 = 127.0.0.1 192.168.2.0/24 192.168.3.0/24hosts deny = 0.0.0.0/0

user-based security

account maintenance:

# add account (local linux account must exist first, or be translated via /etc/samba/smbusers):smbpasswd -a <username>

# enable/disable account:smbpasswd -e <username>smbpasswd -d <username>

# remove account:smbpasswd -x <username>

service smb reload may be needed after account changes

share access:

valid users = <user1> @<group1>

• share access is also controlled by unix file permissions

verify service functionality

list shares:

smbclient -L <hostname> -U <username>

browse shares:

smbclient //<hostname>/<share> -U <username>

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test allow/deny statements for a host:

testparm /etc/samba/smb.conf <hostname> <ip address>

NFS

install

yum install portmap nfs-utils

start at boot

chkconfig portmap onchkconfig nfs onchkconfig nfslock onchkconfig netfs on

basic config

redhat config tool:

yum install system-config-nfssystem-config-nfs

format of /etc/exports:

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

activate new exports:

/etc/init.d/nfs restart

host-based security

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

firewall config:

# see ports rpcinfo -p

open ports 111, 2049 and rpc ports defined in /etc/sysconfig/nfs

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>

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FTP

install

yum install vsftpd

selinux

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

setsebool -P ftp_home_dir=1

start at boot

chkconfig vsftpd on

basic config

host-based security

• use iptables 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.

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:

ftp <server>

Web proxy

install

yum install squid

selinux

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

setsebool -P squid_connect_any=1

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start at boot

chkconfig squid on

host-based security

firewall config:

protocol ports tcp 3128

Edit /etc/squid/squid.conf

visible_hostname www.quake.lan

allow access from local networks:

acl our_networks src 192.168.1.0/24 192.168.2.0/23http_access allow our_networks

parental control with blocklist

acl our_networks src 192.168.1.0/24 192.168.2.0/23acl block-sites dstdomain .yahoo.com .hotmail.com acl block-words url_regex sex cunt penis movieshttp_access deny block-sites http_access deny block-words http_access allow our_networks

user-based security

Install ncsa_auth

htpasswd /etc/squid/passwd username create username / password file

Edit /etc/squid/squid.conf

auth_param basic program /usr/lib/squid/ncsa_auth /etc/squid/passwdauth_param basic children 5auth_param basic realm Squid proxy-caching web serverauth_param basic credentialsttl 2 hoursauth_param basic casesensitive off

acl ncsa_users proxy_auth REQUIREDhttp_access allow ncsa_users

verify service functionality

test proxy:

HTTP_PROXY=<server>:3128 elinks

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SMTP

Using Sendmail

yum install sendmail sendmail-cf

edit /etc/mail/sendmail.mc

dnl DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl

LOCAL_DOMAIN(`example.com')dnl

build new sendmail.cf :

make -C /etc/mail

edit /etc/mail/access

Connect:192.168.0 RELAY allow relay from local LAN

edit /etc/mail/local-host-names

example.com domains hosted on our server

quake.lan

edit /etc/mail/virtualusertable

[email protected] [email protected] virtual users mappings

/etc/aliases

root: admin aliases to other accounts

tony: mark

run newaliases to build new file

to enable masquerading in sendmail

edit /etc/mail/sendmail.mc

MASQUERADE_AS(`mydomain.com')dnl

FEATURE(masquerade_envelope)dnl

FEATURE(masquerade_entire_domain)dnl

MASQUERADE_DOMAIN(localhost)dnl

MASQUERADE_DOMAIN(localhost.localdomain)dnl

MASQUERADE_DOMAIN(mydomainalias.com)dnl

MASQUERADE_DOMAIN(mydomain.lan)dnl

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MAILER(smtp)dnl

MAILER(procmail)dnl

rebuild sendmail.cf file ( make -C /etc/mail )

check mail passing through : /var/log/maillog

check /var/spool/mail to see mailboxes

install

yum install postfixalternatives --config mtaservice sendmail stop

start at boot

chkconfig postfix on

basic config

listen on public interfaces:

inet_interfaces = all

specify all destination hostnames/domains:

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

specify origin domain:

myorigin = $mydomain

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

<alias>: <user1>[, user2]

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

<virtual alias>: <user>

enable virtual aliases:

virtual_alias_maps = hash:/etc/postfix/virtual

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

<outbound alias>: <user>

enable outbound aliases:

smtp_generic_maps = hash:/etc/postfix/generic

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host-based security

• use iptables with -[!]s option

firewall config:

protocol ports tcp 25

user-based security

use smtp auth?

verify service functionality

test smtp:

telnet <server> 25

IMAP, IMAPS, and POP3

install

yum install dovecot

start at boot

chkconfig dovecot on

basic config

enable protocols:

protocols = imap imaps pop3 pop3s

create custom ssl cert:

nano -w /etc/pki/dovecot/dovecot-openssl.cnf/usr/share/doc/dovecot-*/examples/mkcert.shservice dovecot restart

or

mv /etc/pki/dovecot/certs/dovecot.pem /etc/pki/dovecot/certs/dovecot.pem.origmv /etc/pki/dovecot/private/dovecot.pem /etc/pki/dovecot/private/dovecot.pem.origcd /etc/pki/tls/certs/make dovecot.pemcp dovecot.pem /etc/pki/dovecot/certs/cp dovecot.pem /etc/pki/dovecot/private/

host-based security

use iptables with -[!]s option

protocol ports tcp 143, 110, 995, 993

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-A RH-Firewall-1-INPUT -p tcp -m tcp -s 192.168.0.0/24 --dport 143 -j ACCEPT-A RH-Firewall-1-INPUT -p tcp -m tcp -s 192.168.0.0/24 --dport 25 -j ACCEPT

user-based security

use pam_listfile in /etc/pam.d/dovecot

verify service functionality

test mailbox acess:

mutt -f <imap|imaps|pop|pops>://<user>@<server>

SSH

install

yum install openssh-server

start at boot

chkconfig sshd on

Generate Public / Private key pair

ssh-keygen -t rsa create public / private keys for user

ssh-copy-id -i .ssh/id_rsa.pub server_IP send public key and install in server

ssh-keygen -p create password for ssh keys to be used

user-based security

allow/deny user access:

AllowUsers user1 user2 [email protected] user4 user5 [email protected]

host-based security

• use ipchains with -[!]s option

firewall config:

protocol ports tcp 22 tcp_wrappers example:

sshd : 192.168.0.

verify service functionality

test logging in:

ssh <user>@<server>

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DNS (caching name server, slave name server)

install

yum install bind-chroot caching-nameserver system-config-bind

start at boot

chkconfig named on

setup bind with system-config-bind

make sure there is no file /var/named/chroot/etc/named.conf

system-config-bind

this will ask to create new named.conf

Now start editing DNS Server options > right click on DNS Server > EDIT

add Forwarders > Ipv4 > 192.168.0.200

New > View > name: External > From ACL : anyto ACL : any

Once saved all other settings are migrated into the View.

Right click on DNS Server or View > Add Zone > Class : InternetOrigin Type : Forward quake.lanZone Type : master

go on quake.lan > right click > Add > A,MX,CNAME,PTR records

check DNS resolution with dig or nslookup

open IPTABLES ports 53 UDP and TCP.

basic config

copy sample config:

cp -a /var/named/chroot/etc/named.caching-nameserver.conf /var/named/chroot/etc/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

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host-based security

firewall config:

protocol ports tcp 53 udp 53 allow-query example:

allow-query { 192.168.0.0/16; localnets; };

user-based security

N/A

verify service functionality

test query:

dig @<server> <domain>

test zone transfer:

dig @<server> <domain> axfr

NTP

install

yum install 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

user-based security

N/A

verify service functionality

show peers:

ntpq -p

RHCEs must also be able to:

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configure hands-free installation using Kickstart

yum install system-config-kickstart

1. make installation tree available2. create kickstart file (use system-config-kickstart to create ks.cfg) and validate (using

ksvalidator)3. validate kickstart file4. make kickstart file available

• bootable diskette (place in top level directory)• bootable cdrom (place in top level directory)• network (http, ftp, nfs)

5. use bootable media and supply appropriate kernel parameter

ks=floppy:/ks.cfgks=cdrom:/ks.cfgks=http://example.com/ks.cfgks=nfs:example.com:/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:

1. make changes in /etc/sysconfig/iptables to load conntrack modules2. run /etc/init.d/iptables restart to apply changes

packet filtering

packet filtering example:

-A <chain> -p <tcp/udp> -m <tcp/udp> [-s[!] <source address>] --dport <destination port> -j ACCEPT

-A RH-Firewall-1-INPUT -p tcp -m tcp -s 192.168.0.0/24 --dport 631 -j ACCEPT

NAT

enable ip forwarding in /etc/sysctl.conf:

net.ipv4.ip_forward = 1

to test from another machine:

ip route replace default via <ip address>

inbound dnat:

iptables -t nat -A PREROUTING -p <tcp/udp> --dport <destination port> -j DNAT --to-dest <private server>:<port>

outbound dnat:

iptables -t nat -A OUTPUT -p <tcp/udp> --dport <destination port> -j DNAT --to-dest <private server>:<port>

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masquerading:

iptables -t nat -A POSTROUTING -o <outbound interface> -j MASQUERADE

snat:

iptables -t nat -A POSTROUTING -j SNAT --to-source <public server>:<port>

setup for router to internet

Check Deployment guide chapter for IPTABLES syntax

Setup RH Firewall with default settings using eth0 to Internet while eth1 to LAN.

vi /etc/sysct.conf and set net.ipv4.ip_forward = 1

add following rules from CLI:

iptables -A FORWARD -i eth1 -j ACCEPT

iptables -A FORWARD -o eth1 -j ACCEPT

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j DNAT --to 192.168.188.133:80

iptables-save > /etc/sysconfig/iptables

Add extra rules to the RH-FIREWALL-1 ACCEPT / DENY statements

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>

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

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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

Additional Notes

tcp_wrappers

file format:

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

search order:

1. /etc/hosts.allow2. /etc/hosts.deny3. 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