YUM Configuration

Features:
1. The ability to centralize packages (updates)

Installation & Setup:
1. Install 'createrepo*rpm'
2. Setup directory structure
a. /srv/www/Linuxtutorial.com/RH5/yum

3. Run 'createrepo /srv/www/Linuxtutorial.com/RH5/yum'

4. Publish the yum repository using HTTP

5. Configure yum client to use HTTP to fetch the RPMs
a. /etc/yum.conf
a1. ###Included as our first repository on the SUSE box###
[0001]
name=Linuxtutorialsuse1
baseurl=http://192.168.75.100/RH5/yum

Note: Ensure that about 3GBs are available for the yum respository


tar -cjvf yum_metadata.bz2 repodata

Yum Usage:
1. Search for packages
a. 'yum search gftp'

2. Install packages - Requires RedHat GPG Key for RPMs
rpm --import http://192.168.75.100/RH5/i386/RPM-GPG-KEY-redhat-release
a. 'yum -y install gftp'
b. 'yum -y install gftp dhcp' installs 2 packages

3. Remove Package
a. 'yum -y remove gftp'

RPM

Features:
1. Provides package management
a. Query
b. Install
c. Uninstall
d. Upgrade
e. Verify
2. Auto-verifies packages using GPG, MD5, SHA1SUMs
3. Automatically reports on unresolved dependencies

'rpm'

Query:
1. rpm -qa - dumps all installed packages
2. rpm -qa | wc -l - this dumps all packages and provides a count
3. rpm -qa | grep -i nano
4. rpm -qi nano - dumps info. about the 'nano' package as it's recorded in the local RPM database
5. rpm -qf /usr/bin/nano - dumps package membership info. for the 'nano' file
6. rpm -qpi http://192.168.75.100/RH5/i386/Server/dhcp-3.0.5-7.el5.i386.rpm - dumps info. about the uninstalled 'dhcp' package, which resides on the repository
7. rpm -ql package_name - returns all included files


Verify:
1. rpm -Va - verifies ALL packages on the system, returning info. only if there are discrepancies from the original installation

2. rpm -Vf /usr/bin/nano

Task: Change '/usr/bin/nano' then verify

SM5....T /usr/bin/nano

S(file size), M(mode or permissions), 5(MD5), T(mod time)
3. rpm -Vp nano


Install (Does NOT overwrite previous package):
Note: Use this method to install a new version of the kernel
1. rpm -ivh *.rpm
2. rpm -ivh http://192.168.75.100/RH5/i386/Server/dhcp-3.0.5-7.el5.i386.rpm



Upgrade (Installs or overwrites existing package):
1. rpm -Uvh *.rpm
2. rpm -Uvh http://192.168.75.100/RH5/i386/Server/dhcp-3.0.5-7.el5.i386.rpm

Freshen (Updates an existing package):
Note: Will NOT install the package, if it doesn't exist locally

1. rpm -Fvh *.rpm - freshens the current version of a package


Removal:
1. rpm -ev *.rpm - removes a pacakge
Note: removal process considers dependencies and will complain if the removal will break 1 or more packages. To get around this, use '--nodeps' option with 'rpm -ev --nodeps *.rpm'

2. rpm -ev gftp


Package Management GUI:
1. Add/Remove Software
2. system-config-packages

RAID

Features:
1. The ability to increase availability and reliability of data


Tasks:
1. Create a RAID-1 Device (/dev/md0..n)
a. fdisk /dev/sdb - to create usable raw partitions
b. partprobe /dev/sdb - to force a kernel update of the partition layout of the disk: /dev/sdb
b. mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb5 /dev/sdb6
c. cat /proc/mdstat - lists active RAID (md) information
d. mke2fs -j /dev/md0 - overlays a file system on the RAID device
e. mount /dev/md0 /raid1
f. update: /etc/fstab

Note: use 'mdadm --query /dev/md0' to get information about a RAID device


Note: You may create RAID volumes/devices on a single or on multiple disks
Ideally, your RAID volumes should span multiple physical disks to improve:
a. reliability
b. performance
c. availability

2. Remove the RAID-1 device
a. umount /dev/md0
b. mdadm --manage --stop /dev/md0

3. Create a RAID-5 Volume
a. fdisk /dev/sdb - to create a partition number 7
b. partprobe /dev/sdb - to update the kernel's view of the partition table
c. mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sdb5 /dev/sdb6 /dev/sdb7
d. watch cat /proc/mdstat - refreshes every 2 seconds
e. Overlay a file system: mke2fs -j /dev/md0
f. mount /dev/md0 /raid5
g. Test I/O to RAID-5 device
h. Update: /etc/fstab

Logical Volume Management (LVM)

Features:
1. Ability to create volume sets and stripe sets
2. LVM masks the underlying physical technology (ATA,ATAPI,IDE,SCSI,SATA,PATA,etc.)
3. LVM represents storage using a hierarchy:
a. Volume groups
a1. Physical volumes (/dev/sda2, /dev/sdb2, etc.)
b. Logical Volumes
b1. File systems
3. LVM physical volumes can be of various sizes
4. Ability to resize volumes on the fly

Note: Volume groups join: physical volumes (PVs) and Logical Volumes (LVs)


6 Steps to setup LVM:
1. Create LVM partitions via fdisk or parted
a. fdisk /dev/sda, /dev/sdb, /dev/sdc
b. n
c. p
d. +10G
e. t - change to type '8e' (LVM)
f. w
g. partprobe /dev/sda

2. Create Physical Volumes using 'pvcreate'
a. pvcreate /dev/sda3 /dev/sdb3 /dev/sdc3

3. Create Volume Groups using 'vgcreate'
a. vgcreate volgroup001 /dev/sda3 /dev/sdb3 /dev/sdc3
Note: Volume groups can be segmented into multiple logical volumes

4. Create one or more Logical Volumes
a. lvcreate -L 10GB -n logvolvar1 volgroup001
b. lvcreate -L 10GB -n logvolusr1 volgroup001

5. Create File system on logical volume(s)
a. mke2fs -j /dev/volgroup001/logvolvar1
b. mke2fs -j /dev/volgroup001/logvolusr1

6. Mount logical volume
a. mkdir /var1
b. mount /dev/volgroup001/logvolvar1 /var1
c. mkdir /usr1
d. mount /dev/volgroup001/logvolusr1 /usr1


Note: Be certain to update: /etc/fstab so that volumes are mounted when the system reboots

3-tiers of LVM display commands include:
a. pvdisplay - physical volumes - represent raw LVM partitions
b. vgdisplay - volume groups - aggregate physical volumes
c. lvdisplay - logical volumes - file systems - mount here


Rename of Logical Volume:
1. lvrename volume_group_name old new - used to rename volumes

Task: Rename 'logvolvar1' to 'logvolopt1'
a. lvrename volgroup001 logvolvar1 logvolopt1
Note: LVM is updated immediately, even while volume is mounted
However, you must remount the logical volume to see the changes
b. umount /var1 && mount /dev/mapper/volgroup001-logvolopt1 /opt1
c. Update /etc/fstab


Remove Logical Volume:
Task: Remove 'logvolusr1' from the logical volume pool
a. umount /usr1
b. lvremove /dev/mapper/volgroup001-logvolusr1
c. use 'lvdisplay' to confirm removal


Resize Logical Volume:
Task: Grow (resize) 'logvolopt1' to 20GB
a. lvresize -L 20GB /dev/volgroup001/logvolopt1
b. lvdisplay - to confirm new size of logical volume
c. df -h - will still reveal the current size
d. Resize the file system to update the INODE table on the logical volume to account for the new storage in 'logvolopt1'
'resize2fs -f -p /dev/volgroup001/logvolopt1'

Note: You may resize file systems online if the following are met:
1. 2.6x kernel series
2. MUST be formatted with ext3

Task: Shrink (resize) 'logvolopt1' to 15GB
a. lvresize -L 15GB /dev/volgroup001/logvolopt1
b. lvdisplay
c. df -h
d. resize2fs -f -p /dev/volgroup001/logvolopt1
Note: online shrinking is not supported
e. df -h

Note: Check disk utilization prior to shrinking to reduce the risk of losing data

LVM GUI Utility:
system-config-lvm

Create Swap based on File

Features:
1. The ability to provision swap space based on a file, similar to pagefile.sys in Windows NT, etc., if you have no available disk space to partition.

2. Doesn't waste partitions


Task:
1. Create 512MB swap file
a. dd if=/dev/zero of=/home1/swapfile1 bs=1024 count=524288
b. mkswap /home1/swapfile1 - overlays swap file system
c. swapon /home1/swapfile1 - makes swap space avaialable to the kernel

2. Ensure that when the system reboots, the swapfile is made avialable to the kernel
a. nano /etc/fstab - /home1/swapfile1 swap swap defaults 0 0


3. Create 2GB swap file
a. dd if=/dev/zero of=/home1/swapfile2 count=2G

Swap Partitions & Files

Features:
1. Extra, virtual RAM for the OS


Steps:
1. Identify current swap space
a. swapon -s - enumerates partitions and/or files, which constitute swap storage

b. free -m

2. Select target drive and provision swap partition
a. fdisk /dev/sdb
b. n
c. 2
d. 500
e. +512 (cylinder 562) - 63 cylinders are required for 512MB
f. t - change type
g. 82 - Linux Swap/Solaris
h. w - committ changes to disk

3. Create the swap file system on the raw partition: /dev/sdb2
a. mkswap /dev/sdb2

4. Enable swapping - publish the swap space to the kernel
a. swapon /dev/sdb2 - this enables swapping on /dev/sdb2

5. update /etc/fstab
a. /dev/sdb2 swap swap defaults 0 0

swapoff /dev/sdb2 - disables swapping on /dev/sdb2

Task:
1. Improve system performance by distributing swapping to /dev/sdb2
a. swapon /dev/sdb2
b. swapoff /dev/sda6
c. disable /dev/sda6 via /etc/fstab

Basic Provisioning of Partitions and File Systems

Features:
1. Ability to provision extra storage on-the-fly

Steps:
1. Identify available storage
a. 'fdisk -l' - returns connected storage

2. Create partitions on desired hard drive:
a. 'fdisk /dev/sdb' - interacts with /dev/sdb drive
b. 'n' - to add a new partition
c. 'p' - primary
d. '1' - start cylinder
e. '+4096M' - to indicate 4 Gigabytes
f. 'w' - to write the changes to the disk

Note: use 'partprobe partition (/dev/sdb1)' to force a write to a hard drive's partition table on a running system

Note: 'fdisk' creates raw partitions

3. Overlay (format) the raw partition with a file system
a. mke2fs -j /dev/sdb1 - this will write inodes to partition

4. Mount the file system in the Linux file system hierarchy:
a. mkdir /home1 && mount /dev/sdb1 /home1
b. mount OR df -h - either will reveal that /dev/sdb1 is mounted

Note: lost+found directory is created for each distinct file system

5. Configure '/home1' to auto-mount when the system boots
a. nano /etc/fstab and copy and modify the '/home' entry

Quotas

Features:
1. Limits disk usage (blocks or inodes)
2. Tied to file systems (set on a per file system basis)
3. Can be configured for users and groups

Steps to enable quota support:
1. Enable quota support per file system in: /etc/fstab
a. defaults,usrquota,grpquota
2. Remount the file system(s)
a. mount -o remount /
b. use 'mount' to confirm that 'usrquota,grpquota' support are enabled
3. Create quota database files and generate disk usage table
a. quotacheck -mcug / - this creates /aquota.user & /aquota.group
b. quotacheck -mavug
4. Assign quota policies
a. edquota username - set blocks/inodes soft_limits hard_limit
edquota student1 - sets quotas for user 'student1'
export EDITOR=nano - to have edquota default to 'nano' editor
5. Check quotas
a. quota username
quota student1

Note: place 'quotacheck -avug' in /etc/cron.*(hourly,daily)

6. Report on usage
a. repquota -a - this reports on usage

Note: The blocks are measured in 1K increments. i.e. 20000 blocks is roughly 20MB

Symlinks

Features:
1. Provides shortcuts to files (including directories)
2. Provides hard links to inode (file system) locations

Soft Links:
1. ln -s source_file target
a. ln -s ./regextest.pl lastscript.pl

Note: Soft links may span multiple file systems/hard drives
Note: Symlink count is NOT increased when using soft links

2. ln -s /home/Linuxtutorial/testRH5/regextest.pl . - this will symlink (soft) to the /boot file system

Note: With soft links, if you change the name or location of the source file, you will break ALL of the symlinks (soft)


Hard Links:
Features:
1. The ability to reference the same inode/hard drive location from multiple places within the same file system
a. ln source target
ln regextest.pl ./testhardregextest.pl - creates a hard link

File Types - Permissions - Symlinks

Features:
1. The ability to restrict/control access to files

Note: 10 bits represent permissions for files (including directories)

Note: use 'ls -l' to examine permissions or GUI application like 'Nautilus'

-rwxrwxr-x 1 linuxcbt linuxcbt 681 Jan 13 11:31 regextest.pl

1st bit = file type. '-' = file, 'd' = directory
2nd - 4th bits = owner's permissions
r = read = 4
w = write = 2
x = execute = 1
- = none = 0

5th - 7th bits = group owner's permissions
r = read = 4
w = write = 2
x = execute = 1
- = none = 0

8th - 10th bits = everyone (world)
r = read = 4
w = write = 2
x = execute = 1
- = none = 0

Task:
1. Manipulate file permissions using 'chmod'
a. chmod -x regextest.pl

-rw-rw-r-- 1 linuxcbt linuxcbt 681 Jan 13 11:31 regextest.pl
rw = 6 or 4+2 for owner
rw = 6 or 4+2 for group owner
r = 4 for everyone else (world)

Octal notation: 664 for file 'regexetest.pl'

chmod 664 regextest.pl - removes execution for ALL users
chmod 775 regextest.pl - enables execution for ALL users


2. Ensure that 'regextest.pl' is rw by owner and noone else
a. chmod 600 regextest.pl

Note: File will now be rw by owner (linuxcbt) and 'root'

3. Ensure that 'regextest.pl' is r by owner and noone else
a. chmod 400 regextest.pl && ls -l regextest.pl

Note: chmod supports string values, which represent octal values
chmod +/- x file
chmod +/- w file
chmod +/- r file

chmod +/- u+x file - updates owner's execute permissions on the file
chmod +/- o+x file - updates other's execute permissions on the file
chmod +/- g+x file - updates group's execute permissions on the file

chmod a+rwx = chmod 777


chown - permits changing of ownership of files
a. chown root regextest.pl - changes ownership to 'root'
b. chown linuxcbt:sales regextest.pl - changes owner and group to 'linuxcbt:sales'

Task:
Update 'regextest.pl' so that owner and group owner may modify the file

a. chmod 660 regextest.pl


SETUID:
Features:
1. ability to execute file as owner

chmod 4760 regextest.pl - this will ensure that the perl script always executes as the user 'linuxcbt'
-rwsrw---- 1 linuxcbt sales 787 Jan 28 16:08 regextest.pl

's' in the execute position means that the program will execute as that user


SETGID:
Features:
1. Ability to enforce permissions to a directory structure

mkdir /sales
chmod 2775 /sales

Create a file in the '/sales' directory as 'linuxcbt'
seq 1000000 > linuxcbt.1million.txt


chgrp:
Permits updating of group permissions


Sticky Bit:
Features:
1. Ability to ensure that users cannot delete others' files in a directory

drwxrwxrwt 23 root root 4096 Jan 28 15:05 /tmp/


/tmp - users cannot delete other user's files in '/tmp'

chmod 3777 /sales - ensures that /sales will not lose files from incorrect users

Task:
1. Set '/sales' using sticky bit and test
a. chmod 3777 /sales && ls -ld /sales OR chmod 777 /sales && chmod +t /sales

User/Group Management

Features:
1. The ability to control users and groups

Primary tools:
1. useradd - used to add users and modify group membership
2. system-config-users

Task:
1. Create a user named 'student1' using 'useradd'

Note: Default user settings derive from: /etc/login.defs
a. useradd student1
b. set password for user 'student1': passwd student1


Default User Accounts DB: /etc/passwd
student1:x:501:501::/home/student1:/bin/bash

username:shadow_reference:uid:gid:Description(GECOS):$HOME:$SHELL
Note: /etc/passwd is a world-readable file
Note: /etc/shadow now stores passwords in encrypted form
Note: /etc/shadow is NOT world-readable

Fields in /etc/shadow:
student1:$1$XSFMv2ru$lfTACjN.XxaxbHA0EkB4U0:13891:0:99999:7:::

1. username:
2. encrypted_password:
3. Days_since_Unix_epoch_password_was_changed (01/01/1970)
4. Days before password may be changed
5. Days after which the password MUST be changed
6. Days before password is to expire that user is warned
7. Days after password expires, that account is disabled
8. Days since Unix epoch, that account is disabled
9. Reserved field (currently unused)


2. Modify user 'student1' to have password expire after 45 days
a. usermod


Groups:
1. groupadd - adds new group
2. groups - lists groups on the system: /etc/group
/etc/group - maintains group membership information

Task: Create a 'sales' group and add 'linuxbbt' and 'student1' as members
1. groupadd sales
2. usermod -G sales linuxbbt
3. usermod -G sales student1

Note: 2 types of groups exist:
1. Primary - used by default for a user's permissions
2. Supplemental - used to determine effective permissions

Note: use 'id' to determine the group information of user
Note: Create a new shell session to realize new group membership information

userdel/groupdel are used to delete users and groups, respectively

System Utilities

Features:
1. Process listing
2. Free/available memory
3. Disk utilization


1. ps - process status/listing
a. ps -ef or ps -aux

2. top - combines, ps, uptime, free and updates regulary

3. uptime - returns useful system utilization information:
a. current time
b. uptime - days, hours and minutes
c. connected users
d. load averaged - 1,5,15 minute values

4. free - returns memory utilization
a. RAM
b. SWAP
free -m - for human readable format

5. df - returns disk partition/mount point information
a. df - returns info. using kilobytes
b. df -h - returns info. using megabytes/human readable (gigs/teray/etc.)

6. vmstat - reports on: processes, memory, paging, block I/O, traps, CPU activity

a. vmstat
b. vmstat -p /dev/hda1 - returns partitions stats for /dev/hda1 (/boot)

7. gnome-system-monitor - GUI, combining most system utilities
8. ls -ltr /proc
a. cat /proc/cpuinfo

9. kill PID - kills the process with a given PID
10. runlevel - returns runlevel information using 2 fields:
a. represents previous runlevel
b. represents current runlevel

Perl

Features:
1. Parses text
2. Executes programs
3. CGI - Web forms, etc.
4. Supports RegExes (Perl and POSIX)
5. etc.


Task:
1. Print 'Hello World' to STDOUT
a. perl -c helloworld.pl - checks the syntax of the script
b. perl helloworld.pl - executes the script
c. chmod +x helloworld.pl && ./helloworld.pl

2. Parse RegExes from the command line

Sed - Stream Editor

Features:
1. Faciliates automated text editing
2. Supports RegExes (POSIX)
3. Like Awk, supports scripting using '-F' option
4. Supports input via: STDIN, pipe, file

Usage:
1. sed [options] 'instruction[s]' file[s]
2. sed -n '1p' grep1.txt - prints the first line of the file
3. sed -n '1,5p' grep1.txt - prints the first 5 lines of the file
4. sed -n '$p' grep1.txt - prints the last line of the file
5. sed -n '1,3!p' grep1.txt - prints ALL but lines 1-3
6. sed -n '/linux/p' grep1.txt - prints lines with 'linux'
7. sed -e '/^$/d' grep1.txt - deletes blank lines from the document
8. sed -e '/^$/d' grep1.txt > sed1.txt - deletes blank lines from the document 'grep1.txt' and creates 'sed1.txt'

9. sed -ne 's/search/replace/p' sed1.txt
10. sed -ne 's/linux/unix/p' sed1.txt
11. sed -i.bak -e 's/3/4' sed1.txt - this backs up the original file and creates a new 'sed1.txt' with the modifications indicated in the command

Note: Generally, to create new files, use output redirection, instead of allowing sed to write to STDOUT

Note: Sed applies each instruction to each line

Awk

Features:
1. Field/Column processor
2. Supports egrep-compatible (POSIX) RegExes
3. Can return full lines like grep
4. Awk runs 3 steps:
a. BEGIN - optional
b. Body, where the main action(s) take place
c. END - optional
5. Multiple body actions can be executed by separating them using semicolons. e.g. '{ print $1; print $2 }'
6. Awk, auto-loops through input stream, regardless of the source of the stream. e.g. STDIN, Pipe, File


Usage:
1. awk '/optional_match/ { action }' file_name | Pipe
2. awk '{ print $1 }' grep1.txt

Note: Use single quotes with awk, to avoid shell interpolation of awk's variables

3. awk '{ print $1,$2 }' grep1.txt

Note: Default input and output field separators is whitespace

4. awk '/linux/ { print } ' grep1.txt - this will print ALL lines containing 'linux'

5. awk '{ if ($2 ~ /Linux/) print}' grep1.txt

6. awk '{ if ($2 ~ /8/) print }' /var/log/messages - this will print the entire line for log items for the 8th

7. awk '{ print $3 }' /var/log/messages | awk -F: '{ print $1}'

GREP

Features:
1. The ability to parse lines based on text and/or RegExes
2. Post-processor
3. Searches case-sensitively, by default
4. Searches for the text anywhere on the line


1. grep 'linux' grep1.txt
2. grep -i 'linux' grep1.txt - case-insensitive search
3. grep '^linux' grep1.txt - uses '^' anchor to anchor searches at the beginning of lines
4. grep -i '^linux' grep1.txt
5. grep -i 'linux$' grep1.txt - uses '$' anchor to anchor searches at the end of lines

Note: Anchors are RegEx characters (meta-characters). They're used to match at the beginning and end of lines

6. grep '[0-9]' grep1.txt - returns lines containing at least 1 number
7. grep '[a-z]' grep1.txt


8. rpm -qa | grep grep - searches the package database for programs named 'grep'

9. rpm -qa | grep -i xorg | wc -l - returns the number of pacakges with 'xorg' in their names

10. grep sshd messages
11. grep -v sshd messages - performs and inverted search (all but 'sshd' entries will be returned)
12. grep -v sshd messages | grep -v gconfd
13. grep -C 2 sshd messages - returns 2 lines, above and below matching line

Note: Most, if not all, Linux programs log linearly, which means one line after another, from the earliest to the current

Note: Use single or double quotes to specify RegExes
Also, execute 'grep' using 'egrep' when RegExes are being used

Tar, Gzip, Bzip2, Zip

Features:
1. Compression utilities (gzip, bzip2, zip)
2. File rollers (the ability to represent many files as one)


Gzip:
Includes:
1. gzip - compresses/decompresses files
2. gunzip - decompresses gzip files

Tasks:
1. compress '1million.txt' file using gzip
a. gzip -c 1million.txt > 1million.txt.gz

Note: gzip auto-dumps to STDOUT, by default

b. gzip -l 1million.txt.gz - returns status information
c. gunzip 1million.txt.gz - dumps to file, and removes compressed version
d. gzip -d 1million.txt.gz
e. zcat 1million.txt.gz - dumps the contents to STDOUT
f. less 1million.txt.gzip - dumps the contents of gzip files to STDOUT


Bzip2:

1. bzip2 -c 1million.txt > 1million.txt.bz2

Note: Bzip2 tends to outperform gzip on larger files
2. bunzip2 1million.txt.bz2
3. bzip2 -d 1million.txt.bz2
4. bzcat 1million.txt.bz2 - dumps contents to STDOUT
5. less 1million.txt.bz2 - also dumps the contents to STDOUT


Zip & unzip:
1. zip filename.zip path/ - general usage
2. zip 1million.txt.zip 1million.txt
Note: zip differs slight from gzip and bzip2 in that the destination file (resultant zip file) is specified before the source
3. unzip 1million.txt.zip


Tar & Gzip/Bzip2:

1. tar -cvf filename.tar path/ - creates a non-compressed archive
2. tar -cvf 1million.txt.tar 1million.txt
Note: tar, requires a small overhead for itself in each file

3. tar -czvf 1million.txt.tar.gz 1million.txt - creates, tar/gzip document
4. tar -cjvf 1million.txt.tar.bz2 1million.txt - creates, tar/bzip2 document
5. tar -tzvf

6. tar -cjvf 1million.txt.tar.bz2 1million.txt testRH5/- creates, tar/bzip2 document for the text file and 'testRH5' directory tree

Command Chaining

Features:
1. Permits the execution of multiple commands in sequence
2. Also permits execution based on the success or failure of a previous command

1. cat 123.txt ; ls -l - this runs first command, then second command without regards for exit status of the first command

2. cat 123.txt && ls -l - this runs second command, if first command is successful
3. cat 1234.txt && ls -l

4. cat 123.txt || ls -l - this runs second command, if first command fails


24. more|less - paginators, which display text one-page @ a time
1. more /etc/fstab
2. less 1thousand.txt

25. seq - echoes a sequence of numbers
a. seq 1000 > 1thousand.txt - creates a file with numbers 1-1000

26. su - switches users
a. su - with no options attempts to log in as 'root'

27. head - displays opening lines of text files
a. head /var/log/messages

28. tail - displays the closing lines of text files
a. tail /var/log/messages

29. wc - counts words and optionally lines of text files
a. wc -l /var/log/messages
b. wc -l 123.txt

30. file - determines file type
a. file /var/log/messages

Linux Redirection & Pipes

Features:
1. Ability to control input and output

Input redirection '<': 1. cat < 123.txt Note: Use input redirection when program does NOT default to file as input Output redirection '>':
1. cat 123.txt > onetwothree.txt
Note: Default nature is to:
1. Clobber the target file
2. Populate with information from input stream


Append redirection '>>':
1. cat 123.txt >> numbers.txt - creates 'numbers.txt' if it doesn't exist, or appends if it does

2. cat 456.txt >> numbers.txt


Pipes '|':
Features: Connects the output stream of one command to the input stream of a subsequent command

1. cat 123.txt | sort
2. cat 456.txt 123.txt | sort
3. cat 456.txt 123.txt | sort | grep 3

BASIC LINUX COMMANDS

1. tty - reveals the current terminal
2. whoami - reveals the currently logged-in user
3. which - reveals where in the search path a program is located
4. echo - prints to the screen
a. echo $PATH - dumps the current path to STDOUT
b. echo $PWD - dumps ths contents of the $PWD variable
c. echo $OLDPWD - dumps the most recently visited directory

5. set - prints and optionally sets shell variables
6. clear - clears the screen or terminal
7. reset - resets the screen buffer
8. history - reveals your command history
a. !690 - executes the 690th command in our history
b. command history is maintained on a per-user basis via:
~/.bash_history
~ = users's $HOME directory in the BASH shell
9. pwd - prints the working directory
10. cd - changes directory to desired directory
a. 'cd ' with no options changes to the $HOME directory
b. 'cd ~' changes to the $HOME directory
c. 'cd /' changes to the root of the file system
d. 'cd Desktop/' changes us to the relative directory 'Desktop'
e. 'cd ..' changes us one-level up in the directory tree
f. 'cd ../..' changes us two-levels up in the directory tree

11. Arrow keys (up and down) navigates through your command history
12. BASH supports tab completion:
a. type unique characters in the command and press 'Tab' key
13. You can copy and paste in GNOME terminal windows using:
a. left button to block
b. right button to paste OR Ctrl-Shift-v to paste

14. ls - lists files and directories
a. ls / - lists the contents of the '/' mount point
b. ls -l - lists the contents of a directory in long format:
Includes: permissions, links, ownership, size, date, name
c. ls -ld /etc - lists properties of the directory '/etc', NOT the contents of '/etc'
d. ls -ltr - sorts chronologically from older to newer (bottom)
e. ls --help - returns possible usage information
f. ls -a - reveals hidden files. e.g. '.bash_history'
Note: files/directories prefixed with '.' are hidden. e.g. '.bash_history'

15. cat - catenates files
a. cat 123.txt - dumps the contents of '123.txt' to STDOUT
b. cat 123.txt 456.txt dumps both files to STDOUT
c. cat 123.txt 456.txt > 123456.txt - creates new catenated file

16. mkdir - creates a new directory
a. mkdir testRH5 - creates a 'testRH5' directory

17. cp - copies files
a. cp 123.txt testRH5/
By default, 'cp' does NOT preserve the original modification time

b. cp -v 456.txt testRH5/

18. mv - moves files
a. mv 123456.txt testRH5/ - moves the file, preserving timestamp

19. rm - removes files/directories
a. rm 123.txt
b. rm -rf 456.txt - removes recursively and enforces

20. touch - creates blank file/updates timestamp
a. touch test.txt - will create a zero-byte file, if it doesn't exist
b. touch 123456.txt - will update the timestamp
c. touch -t 200801091530 123456.txt - changes timestamp

21. stat - reveals statistics of files
a. stat 123456.txt - reveals full attributes of the file

22. find - finds files using search patterns
a. find / -name 'fstab'
Note: 'find' can search for fields returned by the 'stat' command

23. alias - returns/sets aliases for commands
a. alias - dumps current aliases
b. alias copy='cp -v'

FTP INSTALLATION OF REDHAT LINUX 5

Steps:
1. Create FTP user account on FTP server
a. 'useradd -s /bin/false -d /srv/wwwlinux.com linuxinstall'
b. 'passwd linuxinstall'
2. Confirm FTP connectivity as the user 'linuxinstall'

3. Reboot server with 'boot.iso' CD and type 'linux askmethod'

Kickstart Configuration

It is an automated installation method to install Red Hat Linux
Features:
1. Hands-free, automated installation
2. Scripted installation
3. Script can be used on multiple systems

Note: 'system-config-kickstart' is NOT installed by default

Steps:
1. Open previously created 'anaconda-ks.cfg' file and modify
2. Define partitions accordingly
3. Confirm settings
4. Publish the 'ks.cfg' file to HTTP server
5. Install server using the following at the main menu:
'linux ks=http://192.168.75.100/ks.cfg'

Note: The following can be used to boot a kickstart installation:
1. boot.iso CD-ROM
2. First CD-ROM of the RH5 installation set
3. The DVD-ROM of the RH5 installation set
4. USB Pen/Stick - diskboot.img (use dd)

BASICS OF REDHAT LINUX 5

REDHAT LINUX 5 Features:

1. 2.6x kernel (2.6.18)
a. 'uname -a' returns OS/Kernel information
Note: 'uname -a' returns the following useful info:
1. OS - Linux
2. Fully Qualified Domain Name (FQDN)
3. Kernel version - 2.6.18...
a. 2.6 = major version
b. .18 = minor version
c. anything else after the minor version indicates that the kernel was patched by the distributor
4. Date and time that the kernel was compiled


2. Supports multiple versions:
a. Basic - Red Hat Enterprise Linux Server
a1. supports 2 physical (Socket) CPUs
a2. Up to 4 virtual guests

b. Advanced Platform
b1. supports unlimited physical CPUs
b2. supports unlimited virtual guests

Note: Virtualization limits pertain to the virtualization technology included with Red Hat Enterprise Linux. NOT third-party software (VMWare)


3. Supports the following platforms:
a. Intel 32/64-bits
b. AMD 32/64-bits
c. IBM - POWER and z-series, S/390

Note: Memory limitation is based on hardware


Note: Common uses of the various versions of RHEL
1. RHEL Basic Version
a. File & Print
b. Web server
c. Infrastructure server (DHCP, DNS, Proxy, etc.)

2. RHEL Advanced Version
a. Application server (Apache Tomcat, JBOSS, Weblogic, WebSphere, etc.)
b. Database server (MySQL, PostgreSQL, Oracle, Ingres, etc.)
c. Clustering