What is network Entry procedure in WIMAX -interview question?

Go to the Section of Network entry and Initialization of wimax std 802.16d (page 167, section , 6.3.9)

The phases are :-

1. It scans the download channel and established synchronization with the BS (Base station)
2. Obtain the transmit parameter (from UCD message)
3. Perform ranging.
4. Negotiate basic capabilities.
5. Authorize SS and performs key exchange for privacy.
6. Perform registration.
7. Established IP connectivity.
8. Established TOD (time of Day)
9. Transfer operational parameters.
10. Setup connection .

The stages of 7, 8 and 9 are optional for SS . These phases are performed if the SS has indicated in the REG-REQ message that it is a managed SS.

Flag this message Unix Shell scripting opening for Bangalore

Dear Amaresh,

Hi,

IVitesse Technologies (ISO 9001-2000) is a leading provider of high-end, quality business technology solution and services with the traditional core competencies in the area of packaged solutions such as SAP, JD Edwards and Oracle E-Applications. IVitesse ensures that it's customers' IT environment deliver the high standards of availability and efficiency their business demands.

We have excellent job opening for Unix shell scripting profile for Bangalore location.


Experience:-5-6yrs

Job location:-Hyderabad



Job type:-Contract (3months) to hire

Description:- Develop UNIX shell Scripts to automate the deployment, administration, and monitoring of a large-scale UNIX environment
Gain deep application-level knowledge of the systems as well as contributing to their overall design
Work with Functional and development teams to enhance, document and improve UNIX scripting standards
Assist in the configuration/build-out of new deployments to facilitate our constant growth
Participate in a 24x7 on-call if needed
4-5 Years experience is Mandatory.
3+ years of experience in Unix Production Support with Unix Shell Scripting
Extensive UNIX shell scripting background
Strong troubleshooting and problem solving skills
Excellent written and verbal communication skills
Experience working with development and production operations
Experience with SAP, Control-M & Connect Direct desirable


Send your resume to :- sumita.baidya@ivitiesse.com

Ho will you detect SNMP crash or core dump ?

How will you detect or how to debug where the core dump occures?
Please follow the steps:-

GDB is the GNU debugger, which is a terminal-based debugger. DDD is a graphical (GUI) front end to GDB.

Normal invocation

The simplest way to run an application under GDB is like so:

$ gdb /usr/local/sbin/snmpd
(gdb) run -f -Lo

The '-f' is necessary to prevent snmpd from forking into the background, and '-Lo' tells snmpd to send log messages to STDOUT (i.e. print them in the GDB console window).

Libtool invocation

Net-SNMP uses libtool while building it's applications. This means that sometimes the applications in the source/build directory are not actually binaries, but shell scripts. The libtool script does some magic so that the applications will run using the shared libraries in the build directory, instead of any libraries installed on the system. To run an application with GDB, you have to run GDB through libtool, like so:

$ ./libtool gdb agent/snmpd
(gdb) run -f -Lo

Getting a backtrace (aka stack trace)

Once you have got an application running under GDB, you can easily get a backtrace, which will display the sequence of functions that were called to arrive at the point where the debugger is currently stopped.

(gdb) bt
#0  0x10153d78 in init_snmp(type=0x101bb140 "snmp") at snmp_api.c:854
#1  0x1000524c in main(argc=3, argv=0x7fe04636) at snmpd.c:910

If an application has crashed, often it will leave a core file. This core file can usually be loaded into GDB to get debugging information after the fact. Simply add the path to the core file after the path to the application when starting GDB.

$ gdb /usr/local/sbin/snmpd /tmp/core.70816

Often this will tell you why the application crashed (e.g. SIGSEGV, aka signal 11). You can then get a backtrace to send to one of the mailing lists for interpretation.

If testing snmpd (or another application) from within the source tree, you'll need to run gdb via libtool:

$ ./libtool gdb agent/snmpd /tmp/core.70816

Doubt in C programme

Dear all,

I have small doubt can anybody guide me how it's working and why?

It's give O/P as same code.
Please find the bellow code for your review.

int main()

{

char *s = "int main() { char *s = %c%s%c; printf(s,34, s, 34); ";

printf(s,34, s, 34);

}

Thanks,

-Amaresh

www.eOdissa.com

Debian dailuse commands

mkdir:-
----------------------
amaresh@eOdissa:~/Documents/Test$ mkdir --help
Usage: mkdir [OPTION] DIRECTORY...
Create the DIRECTORY(ies), if they do not already exist.

Mandatory arguments to long options are mandatory for short options too.
-m, --mode=MODE set file mode (as in chmod), not a=rwx - umask
-p, --parents no error if existing, make parent directories as needed
-v, --verbose print a message for each created directory
-Z, --context=CTX set the SELinux security context of each created
directory to CTX
--help display this help and exit
--version output version information and exit

cd - Change working directory:-
---------------------------------------------------------
cd - Change working directory,
cd :- will got respective dir
cd .. :- will go to one position dirctory to current dirctory
cd - :- will go to Old pwd from new pwd










http://www.oreillynet.com/linux/cmd/
http://ss64.com/bash/
http://www.pixelbeat.org/cmdline.html
http://www.debianhelp.co.uk/commands.htm
http://linux.about.com/od/commands/l/blcmdl8_ifconfi.htm
http://linux.about.com/od/lts_guide/a/gdelts47.htm

Different Linux command @faced in Interview

>chage :-
chage (1) - change user password expiry information

amaresh@eOdissa-desktop:~$ chage -l amaresh
Last password change : Jul 08, 2009
Password expires : never
Password inactive : never
Account expires : never
Minimum number of days between password change : 0
Maximum number of days between password change : 99999
Number of days of warning before password expires : 7

>seq:-
seq (1) - print a sequence of numbers

amaresh@eOdissa-desktop:~$ seq 1 4
1
2
3
4
amaresh@eOdissa-desktop:~$ seq 1 2 6
1
3
5
amaresh@eOdissa-desktop:~$ seq 6
1
2
3
4
5
6
amaresh@eOdissa-desktop:~$ seq 1 3 9
1
4
7

>vmstat :-
vmstat (8) - Report virtual memory statistics

usage: vmstat [-V] [-n] [delay [count]]
-V prints version.
-n causes the headers not to be reprinted regularly.
-a print inactive/active page stats.
-d prints disk statistics
-D prints disk table
-p prints disk partition statistics
-s prints vm table
-m prints slabinfo
-S unit size
delay is the delay between updates in seconds.
unit size k:1000 K:1024 m:1000000 M:1048576 (default is K)
count is the number of updates.

Q:What command do you use to get the information about disk statistics?
Ans:- vmstat -d

amaresh@eOdissa-desktop:~$ vmstat -d
disk- ------------reads------------ ------------writes----------- -----IO------
total merged sectors ms total merged sectors ms cur sec
ram0 0 0 0 0 0 0 0 0 0 0
ram1 0 0 0 0 0 0 0 0 0 0
ram2 0 0 0 0 0 0 0 0 0 0
ram3 0 0 0 0 0 0 0 0 0 0
ram4 0 0 0 0 0 0 0 0 0 0
ram5 0 0 0 0 0 0 0 0 0 0
ram6 0 0 0 0 0 0 0 0 0 0
ram7 0 0 0 0 0 0 0 0 0 0
ram8 0 0 0 0 0 0 0 0 0 0
ram9 0 0 0 0 0 0 0 0 0 0
ram10 0 0 0 0 0 0 0 0 0 0
ram11 0 0 0 0 0 0 0 0 0 0
ram12 0 0 0 0 0 0 0 0 0 0
ram13 0 0 0 0 0 0 0 0 0 0
ram14 0 0 0 0 0 0 0 0 0 0
ram15 0 0 0 0 0 0 0 0 0 0
sr0 0 0 0 0 0 0 0 0 0 0
sda 129824 12599 1675591 430108 108073 14333 979288 2993424 0 36


Q:What command do you use to get the information about disk table?
Ans:-vmstat -D

amaresh@eOdissa-desktop:~$ vmstat -D
18 disks
5 partitions
129824 total reads
12599 merged reads
1675591 read sectors
430108 milli reading
107383 writes
13450 merged writes
966704 written sectors
2990880 milli writing
0 inprogress IO
366 milli spent IO

Q:What command do you use to get the information about no of forking ?
Ans:- vmstat -f

amaresh@eOdissa-desktop:~$ vmstat -f
11008 forks


>What command do you use to create swap space?

Unix Interview questions (sed)

> remove first column of a space delimited txt
how to remove the first column of a space delimited txt file? there are 12+ columns... what is the cleanest way?

cut -d\ -f4-
OR
cat | cut -d\ -f4-
OR
sed -e 's/^[ \t]*//' filename

>delete 7th column in unix,

cut -f1-6,8- filename

>how to remove spaces in a string using sed.

`echo "$infilename" | sed 's/^ *//;s/ *$//`

>replace space or spaces in a line of a file with a single :

sed -e 's/\s/:/g'

>sed : remove whitespace

sed 's/ $//' file1.txt > file2.txt # Remove the last space at eol
sed 's/ *$//' file1.txt > file2.txt # Remove all spaces at eol

>To remove all whitespace (including tabs) from left to first word, enter:

cat | sed -e 's/^[ \t]*//'

Where,

* s/ : Substitute command ~ replacement for pattern (^[ \t]*) on each addressed line
* ^[ \t]* : Search pattern ( ^ - start of the line; [ \t]* match one or more blank spaces including tab)
* // : Replace (delete) all matched pattern

Some Network Linux Commands...

How will you get only TCP protocol status in a network?

Ans:- # netstat -t
O/P:-
root@eOdissa-desktop:/home/amaresh/Documents/Testing# netstat -t
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 eOdissa-desktop.l:59156 www-sf2p-a.facebook:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:59175 www-sf2p-a.facebook:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:57170 px-in-f83.google.co:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:45271 pv-in-f100.google.c:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:41356 a96-17-8-64.deploy.:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:52631 a96-17-8-48.deploy.:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:41932 ord-qs2-n24.panther:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:54438 px-in-f154.google.c:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:54442 px-in-f154.google.c:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:56950 a96-17-69-27.deploy:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:56949 a96-17-69-27.deploy:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:56948 a96-17-69-27.deploy:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:56947 a96-17-69-27.deploy:www ESTABLISHED
tcp 0 0 eOdissa-desktop.l:53859 221x247x49x219.ap:34580 ESTABLISHED

How will you get only UDP protocol status in a network ?
Ans:- # netstat -u
O/P:-
root@eOdissa-desktop:/home/amaresh/Documents/Testing# netstat -u
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State

How will you find only listening socket information?
Ans:- #netstat -l
O/P:-
root@eOdissa-desktop:/home/amaresh/Documents/Testing# netstat -r
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
192.168.152.128 * 255.255.255.128 U 0 0 0 tap0
192.168.1.0 * 255.255.255.0 U 0 0 0 eth0
link-local * 255.255.0.0 U 0 0 0 eth0
192.168.0.0 192.168.152.129 255.255.0.0 UG 0 0 0 tap0
172.16.0.0 192.168.152.129 255.240.0.0 UG 0 0 0 tap0
default 192.168.1.1 0.0.0.0 UG 0 0 0 eth0

How will you get the class of any IP ?
Ans:- ipcals ( install apt-get install ipcalc in debian linux)

O/P:-
root@eOdissa-desktop:/home/amaresh/Documents/Testing# ipcalc 192.168.1.143
Address: 192.168.1.143 11000000.10101000.00000001. 10001111
Netmask: 255.255.255.0 = 24 11111111.11111111.11111111. 00000000
Wildcard: 0.0.0.255 00000000.00000000.00000000. 11111111
=>
Network: 192.168.1.0/24 11000000.10101000.00000001. 00000000
HostMin: 192.168.1.1 11000000.10101000.00000001. 00000001
HostMax: 192.168.1.254 11000000.10101000.00000001. 11111110
Broadcast: 192.168.1.255 11000000.10101000.00000001. 11111111
Hosts/Net: 254 Class C, Private Internet

root@eOdissa-desktop:/home/amaresh/Documents/Testing#ipcalc 192.168.0.1 255.255.128.0 255.255.192.0
Address: 192.168.0.1 11000000.10101000.0 0000000.00000001
Netmask: 255.255.128.0 = 17 11111111.11111111.1 0000000.00000000
Wildcard: 0.0.127.255 00000000.00000000.0 1111111.11111111
=>
Network: 192.168.0.0/17 11000000.10101000.0 0000000.00000000
HostMin: 192.168.0.1 11000000.10101000.0 0000000.00000001
HostMax: 192.168.127.254 11000000.10101000.0 1111111.11111110
Broadcast: 192.168.127.255 11000000.10101000.0 1111111.11111111
Hosts/Net: 32766 Class C, Private Internet

Subnets after transition from /17 to /18

Netmask: 255.255.192.0 = 18 11111111.11111111.11 000000.00000000
Wildcard: 0.0.63.255 00000000.00000000.00 111111.11111111

1.
Network: 192.168.0.0/18 11000000.10101000.00 000000.00000000
HostMin: 192.168.0.1 11000000.10101000.00 000000.00000001
HostMax: 192.168.63.254 11000000.10101000.00 111111.11111110
Broadcast: 192.168.63.255 11000000.10101000.00 111111.11111111
Hosts/Net: 16382 Class C, Private Internet

2.
Network: 192.168.64.0/18 11000000.10101000.01 000000.00000000
HostMin: 192.168.64.1 11000000.10101000.01 000000.00000001
HostMax: 192.168.127.254 11000000.10101000.01 111111.11111110
Broadcast: 192.168.127.255 11000000.10101000.01 111111.11111111
Hosts/Net: 16382 Class C, Private Internet


Subnets: 2
Hosts: 32764

How will you monitor your LAN IP?
Ans:- iptraf (use apt-get install iptraf in debian linux)

How will you get your bandwidth usages of your interface by host ?
Ans:- iftop

Basic Unix commands for beginners!!

passwd

This command allows you to change your login password. You are prompted to enter your current password, and then prompted (twice) to enter your new password. On Linux systems (like haribol) passwords should exceed 6 characters in length, and contain at least one non-alphanumeric character (such as #, %, *, ^, [, or @ etc.)

cd

This command, as in DOS, changes directories. You can use .. to represent the directory above the current directory. You can use ~ to represent your root directory (also called your home or top directory). Example: cd maindir to move into the maindir directory, cd .. to move to the directory above, or cd ~ to move to your root directory.

pwd

This command tells you which directory you are currently working in. Your home directory is represented by the tilde ~ symbol. To go to your home directory from anywhere, type cd ~, however typing cd without the ~ also works on Linux systems.

ls

This gives you a listing of all files in a directory. You can't tell which are files and which are directories.

ls -F

This shows which files are normal files (they have no special symbols at the end), which are directories (they end in a / character), which are links (they end in a @ symbol) and which are executables (they end in a * character). These special symbols are NOT part of the file name.

ls -l

"Long" format. Gives more details about files and directories in the current directory.

ls -a

Lists "hidden" files in current directory (those starting with a . character).

ls -la

Options may usually be combined. This particular combination would list both hidden and unhidden files in the long format

mv

The "move" command is how you rename files. Example: mv oldfile.txt newfile.txt

cp

Allows you to copy one or more files. Example: cp myfile.c backup.c

rm

Deletes a file. BE CAREFUL!! There's no "undelete" command. Example: rm janfiles.*

cat

Sends the contents of a file to stdout (usually the display screen). The name comes from "concatenate." Example: cat index.html

more

Like cat but displays a file one page at a time. Example: more long_file.txt

wc

Counts the number of lines, words, and characters in a file. Example: wc essay.rtf

tail -n

Displays the last n lines of a file. Example: tail -5 myfile

head -n

Displays the first n lines of a file. Example: head -5 myfile

mkdir

Creates a new directory, located below the present directory. (Use pwd first to check where you are!) Example: mkdir new_dir

rmdir

Deletes a directory. Example: rmdir old_dir

man

The most important Unix command! It displays the manual pages for a chosen Unix command. Press [Enter] to advance one line, [Spacebar] to advance one page, and the [Q] key to quit and return to the Unix prompt. Example: man ls

man -k

Displays all Unix commands related to a given keyword. Example: man -k date will list all Unix commands whose man pages contain a reference to the word date.

date

Shows the current time and date.

logout

Terminates the current login session, (and returns you to your telnet client, if that is how you established the session originally).

---

I/O Redirection

<

Input redirection. This allows you to take input from a file rather than stdin. Example: tr a z

>

Output redirection. This allows you to send output to a file rather than stdout. Example: ls -l >listing

|

Pipe. This allows you to connect stdout from one command with stdin of another. Example: ls -la | more

File Compression:-

• • gzip filename --- compresses files, so that they take up much less space. Usually text files compress to about half their original size, but it depends very much on the size of the file and the nature of the contents. There are other tools for this purpose, too (e.g. compress), but gzip usually gives the highest compression rate. Gzip produces files with the ending '.gz' appended to the original filename.
  • gunzip filename --- uncompresses files compressed by gzip.
  • gzcat filename --- lets you look at a gzipped file without actually having to gunzip it (same as gunzip -c). You can even print it directly, using gzcat filename | lpr
• printing
  • lpr filename --- print. Use the -P option to specify the printer name if you want to use a printer other than your default printer. For example, if you want to print double-sided, use 'lpr -Pvalkyr-d', or if you're at CSLI, you may want to use 'lpr -Pcord115-d'. See 'help printers' for more information about printers and their locations.
  • lpq --- check out the printer queue, e.g. to get the number needed for removal, or to see how many other files will be printed before yours will come out
  • lprm jobnumber --- remove something from the printer queue. You can find the job number by using lpq. Theoretically you also have to specify a printer name, but this isn't necessary as long as you use your default printer in the department.
  • genscript --- converts plain text files into postscript for printing, and gives you some options for formatting. Consider making an alias like alias ecop 'genscript -2 -r \!* | lpr -h -Pvalkyr' to print two pages on one piece of paper.
  • dvips filename --- print .dvi files (i.e. files produced by LaTeX). You can use dviselect to print only selected pages.
    

Finding things

• ff --- find files anywhere on the system. This can be extremely useful if you've forgotten in which directory you put a file, but do remember the name. In fact, if you use ff -p you don't even need the full name, just the beginning. This can also be useful for finding other things on the system, e.g. documentation.
• grep string filename(s) --- looks for the string in the files. This can be useful a lot of purposes, e.g. finding the right file among many, figuring out which is the right version of something, and even doing serious corpus work. grep comes in several varieties (grep, egrep, and fgrep) and has a lot of very flexible options. Check out the man pages if this sounds good to you.

About other people

• w --- tells you who's logged in, and what they're doing. Especially useful: the 'idle' part. This allows you to see whether they're actually sitting there typing away at their keyboards right at the moment.
• who --- tells you who's logged on, and where they're coming from. Useful if you're looking for someone who's actually physically in the same building as you, or in some other particular location.
• finger username --- gives you lots of information about that user, e.g. when they last read their mail and whether they're logged in. Often people put other practical information, such as phone numbers and addresses, in a file called .plan. This information is also displayed by 'finger'.
• last -1 username --- tells you when the user last logged on and off and from where. Without any options, last will give you a list of everyone's logins.
• talk username --- lets you have a (typed) conversation with another user
• write username --- lets you exchange one-line messages with another user
• elm --- lets you send e-mail messages to people around the world (and, of course, read them). It's not the only mailer you can use, but the one we recommend.
  

About your (electronic) self

• whoami --- returns your username. Sounds useless, but isn't. You may need to find out who it is who forgot to log out somewhere, and make sure *you* have logged out.
• finger & .plan files
  of course you can finger yourself, too. That can be useful e.g. as a quick check whether you got new mail. Try to create a useful .plan file soon. Look at other people's .plan files for ideas. The file needs to be readable for everyone in order to be visible through 'finger'. Do 'chmod a+r .plan' if necessary. You should realize that this information is accessible from anywhere in the world, not just to other people on turing.
• passwd --- lets you change your password, which you should do regularly (at least once a year).
  
• ps -u yourusername --- lists your processes. Contains lots of information about them, including the process ID, which you need if you have to kill a process. Normally, when you have been kicked out of a dialin session or have otherwise managed to get yourself disconnected abruptly, this list will contain the processes you need to kill. Those may include the shell (tcsh or whatever you're using), and anything you were running, for example emacs or elm. Be careful not to kill your current shell - the one with the number closer to the one of the ps command you're currently running. But if it happens, don't panic. Just try again :) If you're using an X-display you may have to kill some X processes before you can start them again. These will show only when you use ps -efl, because they're root processes.
• kill PID --- kills (ends) the processes with the ID you gave. This works only for your own processes, of course. Get the ID by using ps. If the process doesn't 'die' properly, use the option -9. But attempt without that option first, because it doesn't give the process a chance to finish possibly important business before dying. You may need to kill processes for example if your modem connection was interrupted and you didn't get logged out properly, which sometimes happens.
• quota -v --- show what your disk quota is (i.e. how much space you have to store files), how much you're actually using, and in case you've exceeded your quota (which you'll be given an automatic warning about by the system) how much time you have left to sort them out (by deleting or gzipping some, or moving them to your own computer).
• du filename --- shows the disk usage of the files and directories in filename (without argument the current directory is used). du -s gives only a total.
• last yourusername --- lists your last logins. Can be a useful memory aid for when you were where, how long you've been working for, and keeping track of your phonebill if you're making a non-local phonecall for dialling in.

Connecting to the outside world

• nn --- allows you to read news. It will first let you read the news local to turing, and then the remote news. If you want to read only the local or remote news, you can use nnl or nnr, respectively. To learn more about nn type nn, then \tty{:man}, then \tty{=.*}, then \tty{Z}, then hit the space bar to step through the manual. Or look at the man page.
  
• rlogin hostname --- lets you connect to a remote host
• telnet hostname --- also lets you connect to a remote host. Use rlogin whenever possible.
• ftp hostname --- lets you download files from a remote host which is set up as an ftp-server. This is a common method for exchanging academic papers and drafts. If you need to make a paper of yours available in this way, you can (temporarily) put a copy in /user/ftp/pub/TMP. For more permanent solutions, ask Emma. The most important commands within ftp are get for getting files from the remote machine, and put for putting them there (mget and mput let you specify more than one file at once). Sounds straightforward, but be sure not to confuse the two, especially when your physical location doesn't correspond to the direction of the ftp connection you're making. ftp just overwrites files with the same filename. If you're transferring anything other than ASCII text, use binary mode.
• lynx --- lets you browse the web from an ordinary terminal. Of course you can see only the text, not the pictures. You can type any URL as an argument to the G command. When you're doing this from any Stanford host you can leave out the .stanford.edu part of the URL when connecting to Stanford URLs. Type H at any time to learn more about lynx, and Q to exit.

-----------------------------------------------------------------------------------------------------------------------------
Unix tutorials

There are a number of excellent Unix tutorials on the Web, including:

• Unix tutorial - NACSE http://www.nacse.org/demos/coping-with-unix/frames2.html
• A Basic Unix Tutorial http://www.isu.edu/departments/comcom/unix/workshop/unixindex.html
• UNIXhelp for users http://www.cit.gu.edu.au/services/UNIXhelp/
• UNIX help searchable index http://www.mcsr.olemiss.edu/cgi-bin/unixhelp_search
• FAQs for Unix - UAH/CS http://merlin.cs.uah.edu/resources/tutorials/faqunix.asp
• Jamming with UNIX http://www.acusd.edu/ac/help/?Jamming

Basic Shell Scripting Interview Questions!!!

1. How do you find out what’s your shell? - echo $SHELL
2. What’s the command to find out today’s date? - date
3. What’s the command to find out users on the system? - who
4. How do you find out the current directory you’re in? - pwd
5. How do you remove a file? - rm
6. How do you remove a - rm -rf
7. How do you find out your own username? - whoami
8. How do you send a mail message to somebody? - mail somebody@techinterviews.com -s ‘Your subject’ -c ‘cc@techinterviews.com‘
9. How do you count words, lines and characters in a file? - wc
10. How do you search for a string inside a given file? - grep string filename
11. How do you search for a string inside a directory? - grep string *
12. How do you search for a string in a directory with the subdirectories recursed? - grep -r string *
13. What are PIDs? - They are process IDs given to processes. A PID can vary from 0 to 65535.
14. How do you list currently running process? - ps
15. How do you stop a process? - kill pid
16. How do you find out about all running processes? - ps -ag
17. How do you stop all the processes, except the shell window? - kill 0
18. How do you fire a process in the background? - ./process-name &
19. How do you refer to the arguments passed to a shell script? - $1, $2 and so on. $0 is your script name.
20. What’s the conditional statement in shell scripting? - if {condition} then … fi
21. How do you do number comparison in shell scripts? - -eq, -ne, -lt, -le, -gt, -ge
22. How do you test for file properties in shell scripts? - -s filename tells you if the file is not empty, -f filename tells you whether the argument is a file, and not a directory, -d filename tests if the argument is a directory, and not a file, -w filename tests for writeability, -r filename tests for readability, -x filename tests for executability
23. How do you do Boolean logic operators in shell scripting? - ! tests for logical not, -a tests for logical and, and -o tests for logical or.
24. How do you find out the number of arguments passed to the shell script? - $#
25. What’s a way to do multilevel if-else’s in shell scripting? - if {condition} then {statement} elif {condition} {statement} fi
26. How do you write a for loop in shell? - for {variable name} in {list} do {statement} done
27. How do you write a while loop in shell? - while {condition} do {statement} done
28. How does a case statement look in shell scripts? - case {variable} in {possible-value-1}) {statement};; {possible-value-2}) {statement};; esac
29. How do you read keyboard input in shell scripts? - read {variable-name}
30. How do you define a function in a shell script? - function-name() { #some code here return }
31. How does getopts command work? - The parameters to your script can be passed as -n 15 -x 20. Inside the script, you can iterate through the getopts array as while getopts n:x option, and the variable $option contains the value of the entered option.

Basic Unix @sed Interview Questions!!!!

1. What is sed? - sed is stream editor, a Unix tool for working with streams of text data. See the awful truth about sed.
2. How do you substitute strings with sed? - Use ’s/old/new’ command, so sed ’s/hello/goodbye/’ would substitute the occurrence of the word hello to goodbye.
3. How do you inject text with sed? - & in the substitution string defines the pattern found in the search string. As an example, here’s us trying to find a word ‘hello’ and replacing it with ‘hello and how are you’:
   echo ‘hello there’ | sed ’s/^hello/& and how are you/’
4. Can I find several patterns and refer to them in the replacement string? - Yes, use (pattern) and then refer to your patterns as \1, \2, \3 and so on.
5. If the string is ‘old old old’ and I run ’s/old/new’, I get ‘new old old’ as the result. I need ‘new new new‘. - You forgot the global modifier, which would replace every occurrence of the pattern with the substitution. ’s/old/new/g‘ will work.
6. But I want ‘old old new’ from the previous example. - Just use the numeric modifier saying you want the third occurrence to be replaced. ’s/old/new/3‘ will work.
7. I wrote a rather complex sed script. How do I save and run it? - Assuming that your file is named myscript1.sed, you can invoke sed -f myscript1.sed.
8. How do I delete trailing whitespaces from each line? - sed ’s/[ \t]*$//’ Here we’re replacing any occurrence of a space or a tab with nothing. Check sed one-liners for more examples.
9. How do you print just a few first lines of the file? - sed 1q will give you just the first line, sed 10q the first 10 lines.
10. How do you replace a pattern only if it’s found, so that it’s executed faster? - Nest the replacement statement: sed ‘/old/ s/old/new/g’ file.txt

Unix Interview Questions and Answers!!!

1. You need to see the last fifteen lines of the files dog, cat and horse. What command should you use?
tail -15 dog cat horse
The tail utility displays the end of a file. The -15 tells tail to display the last fifteen lines of each specified file.
2. Who owns the data dictionary?
The SYS user owns the data dictionary. The SYS and SYSTEM users are created when the database is created.
3. You routinely compress old log files. You now need to examine a log from two months ago. In order to view its contents without first having to decompress it, use the _________ utility.
zcat
The zcat utility allows you to examine the contents of a compressed file much the same way that cat displays a file.
4. You suspect that you have two commands with the same name as the command is not producing the expected results. What command can you use to determine the location of the command being run?
which
The which command searches your path until it finds a command that matches the command you are looking for and displays its full path.
5. You locate a command in the /bin directory but do not know what it does. What command can you use to determine its purpose.
whatis
The whatis command displays a summary line from the man page for the specified command.
6. You wish to create a link to the /data directory in bob’s home directory so you issue the command ln /data /home/bob/datalink but the command fails. What option should you use in this command line to be successful.
Use the -F option
In order to create a link to a directory you must use the -F option.
7. When you issue the command ls -l, the first character of the resulting display represents the file’s ___________.
type
The first character of the permission block designates the type of file that is being displayed.
8. What utility can you use to show a dynamic listing of running processes? __________
top
The top utility shows a listing of all running processes that is dynamically updated.
9. Where is standard output usually directed?
to the screen or display
By default, your shell directs standard output to your screen or display.
10. You wish to restore the file memo.ben which was backed up in the tarfile MyBackup.tar. What command should you type?
tar xf MyBackup.tar memo.ben
This command uses the x switch to extract a file. Here the file memo.ben will be restored from the tarfile MyBackup.tar.
11. You need to view the contents of the tarfile called MyBackup.tar. What command would you use?
tar tf MyBackup.tar
The t switch tells tar to display the contents and the f modifier specifies which file to examine.
12. You want to create a compressed backup of the users’ home directories. What utility should you use?
tar
You can use the z modifier with tar to compress your archive at the same time as creating it.
13. What daemon is responsible for tracking events on your system?
syslogd
The syslogd daemon is responsible for tracking system information and saving it to specified log files.
14. You have a file called phonenos that is almost 4,000 lines long. What text filter can you use to split it into four pieces each 1,000 lines long?
split
The split text filter will divide files into equally sized pieces. The default length of each piece is 1,000 lines.
15. You would like to temporarily change your command line editor to be vi. What command should you type to change it?
set -o vi
The set command is used to assign environment variables. In this case, you are instructing your shell to assign vi as your command line editor. However, once you log off and log back in you will return to the previously defined command line editor.
16. What account is created when you install Linux?
root
Whenever you install Linux, only one user account is created. This is the superuser account also known as root.
17. What command should you use to check the number of files and disk space used and each user’s defined quotas?
repquota
The repquota command is used to get a report on the status of the quotas you have set including the amount of allocated space and amount of used space.



Thanks,
-Amar