RHEL4 vs RHEL5

Major differences between RHEL4 & RHEL5
1.Virtualization added in RHEL5
2.Package installation method changed to YUM(Yellow-dog Updater Modifier) in RHEL5
3.Redhat Clustring added in RHEL5
4.RHEL5 now supports unlimited RAM and Hard disk
5.Now varients in RHEL5 are
* Red Hat Enterprise Linux Advanced Platform (former AS)
* Red Hat Enterprise Linux (former ES) (limited to 2 CPU-s)
* Red Hat Enterprise Linux Desktop with Workstation and Multi-OS option
* Red Hat Enterprise Linux Desktop with Workstation option (former WS)
* Red Hat Enterprise Linux Desktop with Multi-OS option
* Red Hat Enterprise Linux Desktop (former Desktop)

Where as in RHEL4
* Red Hat Enterprise Linux AS for mission-critical/enterprise computer systems
* Red Hat Enterprise Linux ES for supported network servers
* Red Hat Enterprise Linux WS for technical power-user desktops or high- performance computing
* Red Hat Desktop ΓÇô for multiple deployments of single-user desktops

Minor differences
1.Newer kernel(2.6.18)
2.Newer softwares packages
3.Office removed from Server edition
4.More Hardware support
5.By default netconfig command is not there, we have to install it manually
6.SELinux improved a lot in RHEL5
7.We have to provide key at the time of installation so that we can choose to install most of the packages such as Clustring/Virtualization.
8.Some of the commands changed like in LVM

References
https://www.redhat.com/docs/manuals/enterprise/RHEL-5-manual/release-notes/package-changes.html
http://en.wikipedia.org/wiki/Red_Hat_Enterprise_Linux

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How To Open Big Size File Using VI Editor?

How to Open/edit large files using VI?
Ans : Some time you will get message like file is too large to open with VI editor or some sort of other error messages like. 

For Example : Warning: Tmp file too large
 
This doesn't mean that you don't have enough space to open the file in /var/tmp (this is default VI editor temp location). This is because VI is having limitation in opening big files which is more than 9070000 character or file of size 2GB.
This is a warning message you get from vi (i.e. the ex family of editors) that it can not track your changes in the temporary files, the editor maintains during an edit session. So when ever using VI editor remember following things(These are from VI editor manual).

1.If the editor crashes (i.e. system halts, or accidental process termination), a preserve file cannot be created and you will not be able to recover your changes via the recover feature(vi -r filename is used to recover a file from .swp file).

2.In addition, while editing a very large files and vi fails to come up in visual mode, do not write this file (:w) since it may be truncated/crashed. You should quit (:q!) and open the file with csplit utility to divide the big file into smaller smaller files and edit(I dont suggest this as it is very much advanced to normal users).

3.To open files less than 2GB use following procedure
Step1 : Just execute vi command with out any file
#vi

Step2 :
In the command mode,
type :set directory="any directory with enough free space"

Step3 :
Now open the file using
:e "file name"
And start editing it. Once you are done you can save and exit(:wq).
Through this way we can avaoid vi crashing.
Some utilities which is used to view large files are.
a.cat filename more
b.tail filename
c.head filename
d.more filename
e.less filename

To open a file at desired line
head -n filname tail -1

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Some interview topics

If you are preparing for interviews for linux admin jobs you should be familiar with below concepts..

1) Port number of different servers {cat /etc/services}
2) Linux Installation(through FTP,HTTP,NFS)
3) Boot process
4) Diff b/w ext3 and ext2
5) RAID LEVELS and Selection of raid
6) backup methods
7) Package management such as Yum server
8) Kernel Tuning
9) IPTABLES
10) TCP WRAPPERS
11) DIFFERENT RUN LEVELS
12) USER AND GROUP MANAGEMENT
13) QUOTA SETTING(user and group)
14) DIFF B/W CRON AND AT
15) BASIC SHELL SCRIPTING
16) Troubleshooting different issues.
17) Tell me why we should hire you?
18) DAILY ACTIVITES IN YOUR CURRENT COMPANY
19) RECENTLY SOLVED CRITICAL ISSUE
20) LVM (Very Imp)
21) vertias Volume manager
22) cluster basic like HAD , GAB , LLT , HEARTBEAT , CONFIG FILES , RESOURSE , SERVICE GROUPS etc
23 ) kernel panic troubleshooting
24) Process management
25)Configuration part of NFS , NIS , Samba , DHCP , DNS,Apache, Sendmail etc.

26)Remote administration experience.

And many more depending on your job profile. You should know each topics what you mentioned in your resume . If you are not sure about anything , dont mention in your resume and your resume should reflect your skills.

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