Basic unix commands

Question 1

create a tar archive file tecmint-14-09-12.tar for a directory /home/tecmint in current working directory

Answer 1

tar -cvf tecmint-14-09-12.tar /home/tecmint

-cvf options specified? no? then rate 2

Question 2

create a compressed MyImages-14-09-12.tar.gz file for the directory /home/MyImages

Answer 2

tar -cvzf MyImages-14-09-12.tar.gz /home/MyImages

right extension of tar file, no-rate 3

Question 3

create a Phpfiles-org.tar.bz2 file for a directory /home/php

Answer 3

tar -cvfj Phpfiles-org.tar.bz2 /home/php

options specified? no? then rate 2
right extension of tar file, no-rate 3

Question 4

untar the file public_html-14-09-12.tar in present working directory

Answer 4

tar -xvf public_html-14-09-12.tar

options specified? no? then rate 2
if said untar instead of tar -x, rate 1

Question 5

Uncompress tar.gz archive file in different working directory /etc/psswd -the absolute path

Answer 5

tar -xvf public_html-14-09-12.tar.gz -C /etc/psswd

options specified? no? then rate 2
if said untar instead of tar -x, rate 1
right extension of tar file, no-rate 3

Question 6

Uncompress highly compressed tar.bz2 file

Answer 6

tar -xvf public_html-14-09-12.tar.bz2

options specified? no? then rate 2
if said untar instead of tar -x, rate 1
right extension of tar file, no-rate 3
no j in the options during uncompress-note this

Question 7

list the content of uploadprogress.tar file.

Answer 7

tar -tvf uploadprogress.tar

options specified? no? then rate 2

Question 8

list the content of tar.gz file

Answer 8

tar -tvf uploadprogress.tar.gz

options specified? no? then rate 2
right extension of tar file, no-rate 3

Question 9

list the content of tar.bz2 file

Answer 9

tar -tvf uploadprogress.tar.bz2

options specified? no? then rate 2
right extension of tar file, no-rate 3

Question 10

extract a single file called cleanfiles.sh from cleanfiles.sh.tar

Answer 10

tar -xvf cleanfiles.sh.tar cleanfiles.sh

command arguments in same order or not? no -rate 3
options specified? no? then rate 2

Question 11

extract a single file tecmintbackup.xml from tecmintbackup.tar.gz archive file

Answer 11

tar -zxvf tecmintbackup.tar.gz tecmintbackup.xml

command arguments(not options) in same order or not? no -rate 3
options specified? no? then rate 2

Question 12

extract a single file called index.php from the file Phpfiles-org.tar.bz2

Answer 12

tar -jxvf Phpfiles-org.tar.bz2 index.php

command arguments(not options) in same order or not? no -rate 3
options specified? no? then rate 2
j and respective z options are required here

Question 13

extract or untar multiple files from the tar, tar.gz and tar.bz2 archive file

Answer 13

tar -jxvf Phpfiles-org.tar.bz2 “file1.xml”,” file2.xml”
tar -zxvf tecmintbackup.tar.gz “file1.xml”,” file2.xml”
tar -xvf cleanfiles.sh.tar “index.php” , “k2.php”

options specified? no? then rate 2
command arguments(not options) in same order or not? no -rate 2

Question 14

extract a group of all files whose pattern begins with .php from a tar, tar.gz and tar.bz2 archive file

Answer 14

tar -jxvf Phpfiles-org.tar.bz2 –wildcards ‘.php’
tar -zxvf tecmintbackup.tar.gz –wildcards ‘.php’
tar -xvf cleanfiles.sh.tar –wildcards ‘*.php’

options specified? no? then rate 2
command arguments(not options) in same order or not? no -rate 2
quotations and regex not correct, rate 3

Question 15

add file xyz.txt and directory php to existing tecmint-14-09-12.tar archive file

Answer 15

tar -rvf tecmint-14-09-12.tar xyz.txt
tar -rvf tecmint-14-09-12.tar php

options specified? no? then rate 2
command arguments(not options) in same order or not? no -rate 2
quotations and regex not correct, rate 3
didnt identify which option for append, rate 1

Question 16

add files or directories to an existing compressed tar.gz and tar.bz2 archive file

Answer 16

tar -rvf tecmint-14-09-12.tar.gz xyz.txt
tar -rvf tecmint-14-09-12.tar.bz2 php

options specified? no? then rate 2
command arguments(not options) in same order or not? no -rate 2
quotations and regex not correct, rate 3
didnt identify which option for append, rate 1

Question 17

check the size of any tar, tar.gz and tar.bz2 archive file

Answer 17

tar -czvf tecmint-14-09-12.tar.gz xyz.txt | wc -c
tar -cjvf tecmint-14-09-12.tar.bz2 php | wc -c

options specified? no? then rate 2
command arguments(not options) in same order or not? no -rate 2
quotations and regex not correct, rate 3
didnt identify which option for size check , rate 1

Question 18

see the actual content of that tar file

Answer 18

tar -tvf actualcontent.tar

options specified? no? then rate 2
right extension of tar file, no-rate 3
didn’t understand the question , rate 1
didn’t remember the right option, rate 1

Question 19

create tar file in Unix with just specified contents

Answer 19

tar -cvf equitytrading.tar equity currency

command arguments(not options) in same order or not? no -rate 2
didn't understand the question , rate 1

Question 20

view contents of gzip tar file

Answer 20

tar -ztvf trading.tgz

options specified? no? then rate 2

Question 21

know the size of tar file before creating it

Answer 21

tar -cf - * | wc -c

didn’t understand the question , rate 1
options specified? no? then rate 2

Question 22

How To Uncompress A Tar.Gz In Another Directory

Answer 22

tar xzf archive.tar.gz -C /destination

didn’t understand the question , rate 1
options specified? no? then rate 2

Question 23

Using tar -xzvf filename.tar.gz doesn’t extract the file. it is gives this error:

gzip: stdin: not in gzip format
tar: Child returned status 1
tar: Error exit delayed from previous errors

Answer 23

If file filename.tar.gz gives this message: POSIX tar archive, the archive is a tar, not a GZip archive.

Unpack a tar without the z, it is for gzipped (compressed), only:

mv filename.tar.gz filename.tar # optional
tar xvf filename.tar

didn’t understand the question , rate 1
options specified? no? then rate 2
don’t remember the solution, rate 3

Question 24

How to check if a Unix .tar.gz file is a valid file without uncompressing?

Answer 24

What about just getting a listing of the tarball and throw away the output, rather than decompressing the file?

tar -tzf my_tar.tar.gz >/dev/null

This test in no way implies integrity of the data. Because it was designed as a tape archival utility most implementations of tar will allow multiple copies of the same file!

Question 25

How do I tar a directory of files and folders without including the directory itself?

Answer 25

$ mkdir my_directory
$ touch my_directory/file1
$ touch my_directory/file2
$ touch my_directory/.hiddenfile1
$ touch my_directory/.hiddenfile2
$ cd my_directory/ && tar -zcvf ../my_dir.tgz * && cd ..
./
./file1
./file2
./.hiddenfile1
./.hiddenfile2
$ tar ztf my_dir.tgz
./
./file1
./file2
./.hiddenfile1
./.hiddenfile2

Question 26

What is the difference between tar and zip? What are the use cases for each?

Answer 26

tar in itself just bundles files together, while zip applies compression as well.

Usually you use gzip along with tar to compress the resulting tarball, thus achieving similar results as with zip

Question 27

How can you untar more than one file at a time?

Answer 27

find -iname *.tar -exec tar -xvf {} \

if can’t think of exec or xargs, rate 1

Question 28

Untar a file in current directory or in a specified directory

Answer 28

tar xvfj file.tar
tar xvfj file.tar -C path of file in directoy

didn’t understand the question , rate 1
options specified? no? then rate 2
don’t remember the solution, rate 3

Question 29

list only for the mentioned text or image from archived file.

Answer 29

tar tvf file.tar | grep “text to find”
tar tvf file.tar | grep “filename.file extension”

don’t remember the command to use, rate 1
didn’t understand the question , rate 1

–wilcards can’t be used?

Question 30

views the archived files along with their details like the file name that’s archived in the given tar file

Answer 30

tar tvf file.tar filename

don’t remember the argument to use at the end, rate 1
didn’t understand the question , rate 1

Question 31

Viewing the Archive file.tar

Answer 31

tar tvf file.tar

don’t remember the argument to use at the end, rate 1
didn’t understand the question , rate 1

Question 32

Creating an uncompressed archive using tar command

Answer 32

tar cvf archive_name.tar dirname/

don’t remember the options to use , rate 1
didn’t understand the question , rate 1

Question 33

make a tar file out of two specific files file1, file2 in a specified directory

Answer 33

$ ls
abc  def
$ tar cvf compressed.tar abc def
abc
def
$ ls
abc  compressed.tar  def

if dont know that passing specified filenames is an option to tar only them, rate 1

Question 34

Listing an uncompressed archive using tar command

Answer 34

tar tvf archive_name.tar

didn’t understand the question , rate 1
don’t know listing imples option t, rate 1

Question 35

Listing a compressed archive using tar command

Answer 35

tar tvfz archive_name.tar.gz
tar tvfj archive_name.tar.bz2

didn’t understand the question , rate 1
don’t know listing imples option t, rate 1
don’t know what compressed archive imples option t, rate 1

Question 36

You cannot add file or directory to a compressed archive. If you try to do so, you will get “tar: Cannot update compressed archives” error

Answer 36

do u know this very well?

Question 37

estimates the tar file size ( in KB ) before you create the tar file

Answer 37

tar -cf - /directory/to/archive/ | wc -c

Question 38

Find all the files whose name is tecmint.txt in a current working directory

Answer 38

find -name techmint.txt /path/to/current/working/dir
shouldn’t be your answer

The right answer is
find . -name techmint.txt

-name option if not specified, rate 1
if doesnt strike that . = current working dir, rate 1
command arguments(not options) in same order or not? no -rate 2

Question 39

Find all the files under /home directory with name tecmint.txt

Answer 39

find /home -name techmint.txt

if not specified the full file name with extensions, rate 3

Question 40

Find all the files whose name is tecmint.txt and contains both capital and small letters in /home directory.

Answer 40

find /home -iname techmint.txt

if not specified the full file name with extensions, rate 3
if not specified the i letter before name , rate 1

Question 41

Find all directories whose name is Tecmint in / directory.

Answer 41

find / -name Techmint

The question implies that techmint is the name for multiple directories, if dont understand this -rate 2
if any quotations are added, rate 4 coz its plain-no quotations

Question 42

Find all php files whose name is tecmint.php in a current working directory

Answer 42

find . -type f -name techmint.php

if missed the type -f option-it could bring in directories with such name too(possible)- rate 2
If don’t watch out that the question only asked for files and not the directories- rate 1

Question 43

Find all php files in a directory

Answer 43

find /path/to/dir -type f -name “*.php”

If don’t understand that its a wildcard or regex -rate 2
if don’t put it in “”, rate 2
if don’t put along with the -name option, rate 1

Question 44

Find all the files whose permissions are 777

Answer 44

find . -type f -perm 0777 -print

if don’t know that / means check all dirs in current dir, rate 1
if are specific that you want to print to std out like screen, rate 5

Question 45

Find all the files without permission 777

Answer 45

find . -type f ! -perm 0777 -print

if don’t know that ! means a negation before an option, rate 1

Question 46

Find all the SGID bit files whose permissions set to 644

Answer 46

find . -type f -perm 2644

if the first bit is set to 2 , sgid bit is set-dont know this rate 1

Question 47

Find all the Sticky Bit set files whose permission are 551

Answer 47

find . -type f -perm 1551

if the first bit is set to 1 , sticky bit is set-dont know this rate 1

Question 48

Find all SUID set files

Answer 48

find . -type f -perm /u=s

if don’t remember that -perm option is used, rate 1
if don’t remember the argument to -perm userid set bit which is /u=s(set suid), rate 1

Question 49

Find all SGID set files.

Answer 49

find . -type f -perm /g=s

if don’t remember that -perm option is used, rate 1
if don’t remember the argument to -perm userid set bit which is /g=s(set sgid), rate 1

Question 50

Find all Read Only files

Answer 50

find . -perm /u=r

if don’t remember that -perm option is used, rate 1
if don’t remember the argument to -perm userid set bit which is /u(user)=r(read), rate 1

Question 51

Find all Executable files

Answer 51

find . -perm /u=x

if don’t remember that -perm option is used, rate 1
if don’t remember the argument to -perm userid set bit which is /a(any user or all )=x(execute), rate 1,
use /u(user)=x rate 3

Question 52

Find all 777 permission files and set permissions to 644

Answer 52

find . -perm 0777 -exec chmod 0644 {} /;

If don’t remember that -perm option is used, rate 1
if don’t remember that -exec option is used, rate 1
if don’t remember that {} ‘; syntax is at the end of -exec option, rate 1
If don’t remember that -chmod option is used to set permissions, rate 1

Question 53

Find all 777 permission directories and set permissions to 755

Answer 53

find . -type d-perm 0777 -exec chmod 0644 {} /;

if don’t note that the permissions are to be set for directories, rate 1
If don’t remember that -chmod option is used to set permissions, rate 1
If don’t remember that -perm option is used, rate 1
if don’t remember that -exec option is used, rate 1
if don’t remember that {} ‘; syntax is at the end of -exec option, rate 1

Question 54

find a single file called tecmint.txt and remove it

Answer 54

find . -name techmint.txt -exec rm -rf {} /;

If don’t remember that -rm option for deleting or removing, rate 1
If don’t remember that -perm option is used, rate 1
if don’t remember that -exec option is used, rate 1
if don’t remember that {} ‘; syntax is at the end of -exec option, rate 1

Question 55

find and remove multiple files such as .mp3

Answer 55

find . -name “*.txt” -exec rm-rf {} /;

if don’t remember multiple files with a pattern has to be in “ “, rate 1

Question 56

find all empty files under certain path

Answer 56

find . -type f -empty

if don’t remember , -empty is an option , rate 1

Question 57

find all empty directories under certain path

Answer 57

find . -type d -empty

if don’t remember , -empty is an option , rate 1
if don’t notice the question is on directories , and use -type d , rate 1

Question 58

To find all hidden files

Answer 58

find . -type f -name “ .*”

if don’t remember that . is the pattern of the hidden file start-rate 1

Question 59

find all or single file called tecmint.txt under / root directory of owner root

Answer 59

find / -type f -user root -name techmint,txt

if don’t remember that the option is -user ,rate 1
if the options are in wrong order, rate 3
if dont rememeber / corresponds to root dir, rate 1

Question 60

find all files that belongs to user Tecmint under /home directory

Answer 60

find /home -user Techmint -type f

if added any extra options like -name , rate 1
if the options are in wrong order, rate 3

Question 61

find all files that belongs to group Developer under /home directory

Answer 61

find /home -group developer -type f

If don’t remember that the option is -group ,rate 1
if added any extra options like -name , rate 1
if the options are in wrong order, rate 3

Question 62

find all .txt files of user Tecmint under /home directory

Answer 62

find /home -type f -iname “*.txt” -user Techmint

if don’t remember that the option is -user ,rate 1
if the options are in wrong order, rate 3
if dont rememeber / corresponds to root dir, rate 1

Question 63

find all the files which are modified 50 days back

Answer 63

find . -type f -mtime 50

if don’t remember that the option is -mtime ,rate 1
if have any + or - sign , rate 3,since asked just precise 50 days

Question 64

find all the files which are accessed 50 days back

Answer 64

find . -type f -atime 50

if don’t remember that the option is -atime ,rate 1
if have any + or - sign , rate 3 ,since asked just precise 50 days

Question 65

nd all the files which are modified more than 50 days back and less than 100 days

Answer 65

find . -type f -mtime +50 -mtime -100

If don’t remember that the option is -mtime ,rate 1
If don’t remember that the option is -mtime should be used two times to specify range ,rate 1
f don’t remember that the option is -mtime arguments have +, - signs ,rate 1

Question 66

find all the files which are changed in last 1 hour

Answer 66

find . -type f -cmin 60

if confused with cmin and mmin, rate 3
if don’t remember the cmin option, rate 1
if don’t remember the arguments are in minutes count, rate 1

Question 67

find all the files which are modified in last 1 hour

Answer 67

find . -type f -mmin 60

if confused with cmin and mmin, rate 3
if don’t remember the cmin option, rate 1
if don’t remember the arguments are in minutes count, rate 1

Question 68

find all the files which are accessed in last 1 hour

Answer 68

find . -type f -amin 60

if confused with cmin and mmin, rate 3
if don’t remember the cmin option, rate 1
if don’t remember the arguments are in minutes count, rate 1

Question 69

find all 50MB files

Answer 69

find / -type f -size 50M

if don’t remember the -size option, rate 1
if don’t remember the option’s argument needs to specify the unit of size, rate 1

Question 70

find all the files which are greater than 50MB and less than 100MB

Answer 70

find / -type f -size +50M -size +100M

If don’t remember that the option is -size ,rate 1
If don’t remember that the option is -size should be used two times to specify range ,rate 1
f don’t remember that the option is -size arguments have +, - signs ,rate 1
if don’t remember the option’s argument needs to specify the unit of size, rate 1

Question 71

find all 100MB files and delete them using one single command

Answer 71

find / -type f -size 100M -exec rm -rf {} /;

if don’t remember the -size and -exec for deleting -rm, rate 1

Question 72

Find all .mp3 files with more than 10MB and delete them using one single command

Answer 72

find / -type f -name “*.mp3” -size +10M -exec rm -rf {} /;

Question 73

Symbol	
1	f	
2	d	
3	b	
4	c	
5	p	
6	l	
7	s

Answer 73

Type
Regular file
Directory file
Block file
Character file
Pipe file
Symbolic link file
Socket file.

Question 74

Search for all the files whose StickyBit is set

Answer 74

find / -perm /o=t

if dont know o means others and t is for sticky, rate 1

Question 75

Search for all the files whose owener permissions is read only

Answer 75

find / -perm /u=r

if don’t know u means owner and r is for read pnly , rate 1

Question 76

Search for all the files which have user, group and others with executable permissions

Answer 76

find / -perm /a=x

if don’t know a means owner, user and all others and x is for execution , rate 1

Question 77

want to get all the files which are created later this file creation newer.txt .

Answer 77

find / -newer newertxt

need to know that -newer is an option, rate 1 if no

Question 78

Search for files whose size is more than 10bytes

Answer 78

find / -type -f -size +10c

if don’t now that c is used for bytes notation of size in units, rate 1

Question 79

Search for files which are exactly 10kb in /opt folder

Answer 79

find /opt -type -f -size 10k

if don’t now that k is used for kilo bytes notation of size in units, rate 1

Question 80

find all the empty files in my system

Answer 80

find /opt -type -f -size 0k

if don’t now that k is used for kilo bytes notation of size in units for empty files too , rate 1

Question 81

Search for files which are more than 1GB size in /usr folde

Answer 81

find /opt -type -f -size +1G

if don’t now that G is used for giga bytes notation of size in units, rate 1

Question 82

Find all the files with SGID for the group sales and with size exactly 100MB with file name as pass.txt under /opt.

Answer 82

find /opt -size 100M -group sales -perm g+s -name pass.txt

Question 83

Find all the files which are more than 100MB and less than 1GB in size.

Answer 83

find / -size +100M -size -1G

if don’t know to put appropriate units near the -size’s argument, rate 2

Question 84

: find a file with passwd.txt in /var folder and long list this file for checking file properties

Answer 84

find /var -iname passwd.txt -exec ls -l {} ;

if dont remeber long listing option is for ls , rate 1

Question 85

Find all the files with name test.txt in /mnt and change the ownership of the files from Surendra to Narendra

Answer 85

find /mnt -type f -name test.txt -user Surendra -exec chown Narendra {} \;

if don’t remember that exec needs to be used, rate 1
if don’t remember that chown needs to used with exec to do modifications on the found files, rate 2
if added extra options with chown, rate 3

Question 86

finding a file with inode number

Answer 86

find /mnt -type f -inode 23

if don’t remember the inode number , then rate 2

Question 87

Find all the files with name test.sh in /abc folder and then grep if for word is there in that file or not

Answer 87

find /abc -type f -name test.sh -exec grep “for” {} \;

Question 88

Find all the files with name xyz.txt owned by Surendra in /var/ftp/pub and change the permissions to 775 to them.

Answer 88

find /var/ftp/pub -type f -name xyz.txt -user Surendra -exec chmod 775 { } \;

make sure you have included all the filter options, rate 4 if missed

Question 89

Find all the files with name temp.txt in /xyz folder and backup then compress them to send it for saving

Answer 89

find /xyz -type f -name temp.txt -exec tar -cvfz backup.tar.gz {} /;

any small obvious mistake , rate 1

Question 90

Find files with name abc.txt in /home directory and take backup of each file before modifying it

Answer 90

find /xyz -type f -name temp.txt -exec cp {} {}.bkf /;

If doesn’t strike to use cp command, rate 1
if don’t remember that cp follows w=by the current path of the file represented by {} in -exec command , rate 1
If don’t remember the cp syntax, rate 1

Question 91

Find all the files with executable permissions and display their checksum value

Answer 91

find /con -type f -perm /a=x -exec -md5sum {} \;

if don’‘t remember that md5sum is the command for the checksum, rate 1

Question 92

Find all the files with name abc.txt and owner as surendra then move them to /opt folder

Answer 92

find /com -type f -name abc.txt -user surendra -exec mv {] /opt/ \;

If doesn’t strike to use mv command, rate 1
if don’t remember that mv follows by {}. rate 1
the current path of the file represented by {} in -exec command , rate 1
If don’t remember the mv syntax, rate 1

Question 93

Find files with abc.txt name in /opt directory change the owner permissions from Surendra to Narendra and change the permissions to 775

Answer 93

find /com -type f -name abc.txt -user surendra -exec chown Narendra \; -exec chmod 775 \;

If you don’t remember that We can use this multiple -exec option more than two times, rate 2

Question 94

Find abc.txt file in /opt and /var folder at a time

Answer 94

find /opt /var -name abc.txt

If you don’t remember that two locations can be specified side by side, rate 2

Question 95

Search multiple locations but not in particular location. Find abc.txt file in /opt and /var folder at a time, Search in entire system expect /proc folder

Answer 95

find /opt /var -path /proc -prune -name abc.txt

if don’t remember this - The -path variable to define the path of a location. And -prune combined with -path will say not to descend in to the mention path /proc- rate 1

Question 96

search for abc.txt and hash.c file at a time

Answer 96

find /opt /var -name abc.txt -o -name hash.c

if don’t know that the -o should be followed by the specific previous option , rate 3
if don’t know h=that -o option should be used to find for something together, rate 1

Question 97

find two directories say opt and var how can i find them

Answer 97

find . -type d -name opt -o -type d-name var

if don’t understand the question, rate 1
if doesn’t strike that its type d option, rate 1

Question 98

Finding files only in the current directory not searching on subdirectories

Answer 98

find . -maxdepth 1 -type f -newer first_file

if don’t remember the maxdepth option, rate 1

Question 99

find all of the symbolic links in your home directory, and print the files your symbolic links points to

Answer 99

find . -type l -print0 | xargs -o ls -ld | awk ‘{print $10}’

10th field has the actual link pointing, remember if forgot, rate 3
if forgot about the awk syntax, rate 2
if forgot about symbolic links , rate 1

Question 100

always use find -print0 along with xargs -0 if you see slightest possibilities of file names containing space in UNIX or Linux

Answer 100

know this or not

Question 101

/bin for what

Answer 101

executable files

Question 102

/ for what

Answer 102

root dir

Question 103

/etc

Answer 103

config files

Question 104

/tmp for

Answer 104

only temporary files, they clear during boot time

Question 105

/opt for

Answer 105

installing software not bundled with os

Question 106

/var for

Answer 106

log files created by programs and applications

Question 107

/cdrom for

Answer 107

mount point for files on cdrom

Question 108

/media for

Answer 108

mount point for cdrom and dvd

Question 109

/srv for

Answer 109

web files, ftp server files /srv/ftp

Question 110

/opt/avg/bin

Answer 110

executable files

Question 111

/etc/opt/myapp

Answer 111

configuration files

Question 112

/var/opt/myapp

Answer 112

log files

Question 113

long listing of files and dir

Answer 113

ls -l

Question 114

long listing of hidden files

Answer 114

ls -la

Question 115

listing of only files not directories

Answer 115

ls -F

@ link
/ dir
* binary executables

Question 116

how to execute a binary execuatable file

Answer 116

./binaryfilename

Question 117

listing of files with time

Answer 117

ls -t

Question 118

listing of files recursively

Answer 118

ls -R

Question 119

listing of directories only

Answer 119

ls -d

Question 120

ls -R alternative is

Answer 120

tree

Question 121

listing of files in revers order, can this command be confused with anything elsr

Answer 121

ls -r

yes with ls -R which is a recursive listing not reverse listing

Question 122

directory structure

Answer 122

tree -d

tree - c to colorize output

Question 123

listing with colorized output

Answer 123

ls –color

Question 124

edit a file using editor

Answer 124

vi filename

Question 125

modes of vi

Answer 125

3

command, insert, line

Question 126

get into vi command mode by

Answer 126

ESC key

Question 127

get into vi insert mode by

Answer 127

i - to insert right at after the cursor

Question 128

in vi insert mode, to append right after cursor is

Answer 128

A

Question 129

in vi insert mode, to append at the beginning of the line is

Answer 129

a

Question 130

in vi insert mode, to insert at the beginning of the line is

Answer 130

I

Question 131

what are the navigation commands in command mode

Answer 131

h left j down k up l right

Question 132

how to get into line mode in vi

Answer 132

type : followed by the command

Question 133

to save writes in line mode

Answer 133

:w

Question 134

to force save writes in line mode

Answer 134

:w!

Question 135

to quit in line mode

Answer 135

:q

Question 136

to force quit in line mode

Answer 136

:q!

Question 137

to save writes and force quit, its alternative also in line mode

Answer 137

:wq! :x

Question 138

navigating through lines in line mode, to position cursor at line n

Answer 138

:n

Question 139

navigating through lines in line mode, to position cursor at the line end

Answer 139

:$

Question 140

navigating through lines in line mode, to turn on line numbers

Answer 140

:set nu

Question 141

navigating through lines in line mode, to turn off line numbers

Answer 141

:set nonu

Question 142

navigating the command mode, to delete a character

Answer 142

x

Question 143

navigating the command mode, to delete a word

Answer 143

dw

Question 144

navigating the command mode, to delete a line

Answer 144

dd

Question 145

navigating the command mode, to delete from current position

Answer 145

D

Question 146

navigating the command mode, to change current character

Answer 146

r

Question 147

navigating the command mode, to change current word

Answer 147

cw

Question 148

navigating the command mode, to change current line

Answer 148

cc

Question 149

navigating the command mode, to change from current position

Answer 149

C

Question 150

navigating the command mode, to change case of a charecter

Answer 150

~

Question 151

copy a word in command mode vi

Answer 151

yy

Question 152

in command mode vi , copy 3 words

Answer 152

y3w; y

Question 153

in command mode vi, paste the copied or deleted word

Answer 153

p

Question 154

in command mode vi, undo

Answer 154

u

Question 155

in command mode vi, redo

Answer 155

Cntrl+ R

Question 156

to search in vi, line mode- forward searching

Answer 156

/pattern ( n for next, N for previous match)

Question 157

to search in vi, line mode- backward searching

Answer 157

? n for next, N for previous match

Question 158

Display current running processes

Answer 158

ps

Question 159

Display current running processes not owned and running as you

Answer 159

ps -e

Question 160

Display the full format of the process

Answer 160

ps -f

Question 161

Display process running on root

Answer 161

ps -u root

Question 162

Display process details of process 123

Answer 162

ps -p 123

Question 163

Display process tree

Answer 163

ps -e –forest

pstree

Question 164

Interactive process view

Answer 164

top

Question 165

What are environment variables for

Answer 165

they specify storage location and has a name and a value, they affect the way programs behave

Question 166

the command to know all the environment variables

Answer 166

printenv

Question 167

List few names of environment variables

Answer 167

TZ,HOME,PATH

Question 168

another way than printenv to print the contents of environment variables are

Answer 168

echo $ENVIRONMENT VARIABLE NAME($HOME)

Question 169

Create an environment variable name VAR with a value -value

Answer 169

export VAR=’value’

Question 170

Update an environment variable EDITOR to vi

and TZ environemnt variable to ‘US/Pacific’

Answer 170

export EDITOR=”vi”

export TZ=”US/Pacific”

Question 171

Remove environment variable TZ to revert it’s value to default

Answer 171

unset TZ

Question 172

Does an unset and export command persist changes between logins?

Answer 172

No,

Question 173

How to persist changes in environment variables between logins

Answer 173

vi .bash_profile

insert mode, go to the end
export TZ="US?Pacific"
\:wq!
exit
login to shell
printenv TZ or echo $TZ

Question 174

what is the pager utility to print output upto the screen fit

Answer 174

pipe the output to less command

Question 175

How to tell if a particular program or an application is using a particular environment variables

Answer 175

man commandname will display the man pages with a section on environment variables

Question 176

command for background process

Answer 176

&

Question 177

what to do to kill a foreground process like:

sleep 300

Answer 177

Cntrl + C

Question 178

what to do to suspend a foreground process like:

sleep 300

Answer 178

Cntrl + Z

Question 179

How to foreground a background process

Answer 179

fg %jobid ;fg %3

Question 180

How to background a running foreground process

Answer 180

bg %jobid; bg (will background the latest process evoked)

Question 181

How to kill a job

Answer 181

kill %jobid; kill %3
kill pid; kill 103458
kill -TERM pid; kill -TERM 123
kill 15 123
kill -9 123 (9 kill signal)

Question 182

what is kill’s kill signal

Answer 182

9

Question 183

what is kill’s termination signal

Answer 183

15

Question 184

what is signal 15’s in kill, it’s also used interchangebaly

Answer 184

-TERM

Question 185

command to list all the jobs

Answer 185

jobs

Question 186

command to list job details of a job with id 1

Answer 186

jobs %1

Question 187

command to list the current job(recent /latest job id)

Answer 187

job %+

Question 188

command to list the previous job id

Answer 188

job %-

Question 189

what in unix helps to do time based job scheduling

Answer 189

cron services

Question 190

Tell more about cron services

Answer 190

cron job starts when the system boots,
it performs routine maintenance
and it automates a process

Question 191

syntax of thecrontab command

Answer 191

min hr dom month dow  /path/to/the/executable/file
min(0-59)
hr(0-23)
(dom= day of the month) (1-31)
(dow=day of the week)(0-6)

Question 192

schedule a cron job located at /opt/sales/bin/weekly-report every monday at 7 pm

Answer 192

min hr dom month dow

0 19 * * 1 /opt/sales/bin/weekly-report

Question 193

perform a half hourly check

Answer 193

0,30 * * * * /opt/sales/bin/weekly-report
*/2 * *  * * /opt/sales/bin/weekly-report

Question 194

perform a check every first 5 min of the hr

Answer 194

0-5 * * * * /opt/sales/bin/weekly-report

Question 195

Perform a cron job annually

Answer 195

0 0 1 1 * /opt/sales/bin/weekly-report

Question 196

Perform a cron job weekly

Answer 196

0 0 * * 0 path/to/the/executable/file

Question 197

Perform a cron job monthly

Answer 197

0 0 1 * * path/to/the/executable/file

Question 198

Perform a cron job daily

Answer 198

0 0 * * * path/to/the/executable/file

Question 199

Perform a cron job hourly

Answer 199

0 * * * * path/to/the/executable/file

Question 200

What command manipulates cron jobs

Answer 200

chrontab command

Question 201

command to install a cron job from file

Answer 201

crontab file

Question 202

command to list cron jobs

Answer 202

crontab -l

Question 203

command to edit cron job files

Answer 203

crontab -e (should open ur favrt editor: set an environment variable)

Question 204

command to remove all your cron jobs

Answer 204

crontab -r

Question 205

how to create a cron job

Answer 205

1) open a vi editor with the file name => vi my-cron
2) in insert mode type 07 **1 /opt/sales/bin/weekly-report
3) :wq!
4) install the file with crontab command => crontab my-cron
5) echo $ EDITOR
6) export EDITOR =vi
7) crontab -e to do any edits

Question 206

command as a way to start a session as another user is

Answer 206

su

Question 207

how to start a session as root user

Answer 207

su with no arguments

Question 208

execute a command by starting a session as a root user

Answer 208

su -C command; su -C ls -l

Question 209

command to know the what is the current user in our session

Answer 209

whoami

Question 210

how to stay with the same environment while switched as a user

Answer 210

su oracle ( with out - before the user name )

Question 211

how to change to the user’s environment while switched as a user

Answer 211

su - oracle (with the - and space followed by a username)

Question 212

command to switch user to obtain privileges and security of super user

Answer 212

sudo

Question 213

Does sudo prompts for a password?

Answer 213

yes

Question 214

list of available commands as superuser switching

Answer 214

sudo -l

Question 215

to execute a command as privileged user sqoop

Answer 215

sudo -u sqoop command

Question 216

to execute a command as privileged user sqoop and also switch to the users environment

Answer 216

sudo su - sqoop command

Question 217

command to start a shell as root

Answer 217

sudo -s

Question 218

command to start a shell as sqoop

Answer 218

sudo -u sqoop -s

Question 219

command to modify sudo configurations

Answer 219

sudo visudo

Question 220

command to copy files from one local machine to linux server

Answer 220

scp source destination

scp z.txt linuxserver(hostname):~ (~ shortcu for hoe dir)

Question 221

command to copy files from one local machine to linux server interactively

Answer 221

sftp linuxserver

pwd
ls

lpwd # local path to directory

lls # local list files

put z.txt

ls
rm z.txt

quit

Question 222

Transfer this z.txt file as different user: adminuser

Answer 222

scp z.txt adminuser@linuxserver:/home/adminstration

or

sftp adminuser@linuxserver

pwd
ls

lpwd # local path to directory

lls # local list files

put z.txt

ls
rm z.txt

quit

Question 223

command to find difference between contents of file 1 AND file 2

Answer 223

diff file1 file2

Question 224

explain the output of diff file1 file2 command : 3c3

Answer 224

file1lineno change - c file2lineno

Question 225

if the difference between two files is addition of txt at the 8th line then o.p of diff file1 file2 would be

Answer 225

4a4

Question 226

if the difference between two files is addition of txt at the 8th line then o.p of diff file1 file2 would be 4a4, Now to see what line was added and the diff the command woud be

Answer 226

sdiff file1 file2

or vimdiff file1 file2 (to view ffiles in two diffent windows)

symbol for differing lines
> lines exist only in 2nd file
< lines exist only in 1rst file

Question 227

To quit seeig both the file windows using vimdiff command then

Answer 227

:qa!

Question 228

To quit seeing both the file windows using vimdiff command then

Answer 228

:q

Question 229

Command to remove file

Answer 229

rm file

Question 230

command to reove directory

Answer 230

rm -r -dir

Question 231

command to copy a lift of files to /home

Answer 231

cp file1 file2 /home

Question 232

command to copy files into a dir that doesnot exist

Answer 232

cp -r file /newdir

Question 233

command to move or rename files

Answer 233

mv source destin

Question 234

command to sort file based on the field no

Answer 234

sort -k 10 # 10 is field no

Question 235

command to sort file in reverse order

Answer 235

sort -r

Question 236

command to sort file uniquely

Answer 236

sort -u

Question 237

command to know the disk space used by a file in kilobytes

Answer 237

du -k

Question 238

command to know the disk space used by a file in human readable format

Answer 238

du -h

Question 239

if u have to gzip a dir by checking it’s file usage on disk

Answer 239

du

then 
gzip
then check du
then tar gzip 
and view contents of the tar gzip file

Question 240

When you login you get “$” prompt, what is the prompt for root?

Answer 240

#

Question 241

Explain the difference between grep and egrep?

Answer 241

egrep is to search for multiple patterns with pattern having a pipe character

eg: egrep “PATTERN1|PATTERN2” FILE

grep is for searching patterns as a string, any special characters are needed to be escaped

eg: grep “PATTERN1|PATTERN2” FILE

Question 242

What are the mostcommon Linux command line tools for parsing files.

Answer 242

grep, egrep, sed, awk

Question 243

get a list of all email address with grep

Answer 243

$ grep -E -o “\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,6}\b” file.txt

Question 244

Parse a file and print all expressions that match a range between 0.0.0.0 and 999.999.999.999.

Answer 244

grep -E -o “([0-9]{1,3}[.]){3}[0-9]{1,3}” file.txt

Question 245

What is the port # for DNS, NTP and NFS?

Answer 245

53, 123 and 111/2049

Question 246

What is the configuration file name of DNS and where is it located?
/etc/named.conf

Answer 246

All configuration files are located in /etc directory and the name of the DNS configuration file is named.conf.

/etc/named.conf

Question 247

How many new directories will be created after running the following command
mkdir {a..c}{1..3}

Answer 247

9

Question 248

Your PC is configured with a DNS server address but not the default gateway. Can the PC access internet?

Answer 248

No

Question 249

Can you assign one static IP to 2 computers, if not then why?

Answer 249

No because it will create IP conflict

Question 250

You are trying to ping a server by hostname and you get an error message, “ping: unknown host …”. What could be the reason and how to solve the problem so you can ping it by hostname?

Answer 250

Check for /etc/hosts or DNS to see if it has hostname to IP entry

Question 251

Explain the difference between relative and absolute path?

Answer 251

Absolute path starts from / where relative path is your current directory

Question 252

List 3 different methods of adding user?

Answer 252

1) The adduser command automatically creates a home directory and sets the default group, shell, etc. To create a new standard user with the adduser command the syntax is as follows:
sudo adduser bob
2) Anytime you add a user, that user is added to the passwd file,You can edit the file directly or use the commands we will go over shortly - useradd roman
3) useradd bob
passwd

Question 253

What is the command to change file/directory ownership and group?

Answer 253

chown and chgrp

Question 254

List any 3 type of filesystem?

Answer 254

ext4,
NTFS
FAT

Question 255

What is /bin directory used for?

Answer 255

A user of an operating system can expect to find executable files in binary.

Question 256

How to change a user password?

Answer 256

passwd username

Question 257

How to logoff from the system?

Answer 257

exit

Question 258

Give any 3 examples of operating systems?

Answer 258

Windows, Linux and MAC

Question 259

List any 4 linux distributions?

Answer 259

Redhat, CentOS, Ubuntu and SUSE

Question 260

How to create a directory?

Answer 260

mkdir

Question 261

Where are the zone files located for DNS service?

Answer 261

/var/named/zonefiles

Question 262

How to check kernel version?

Answer 262

uname –a

Question 263

Which directory has all the configuration files?

Answer 263

/etc

Question 264

How to become root user from a regular user?

Answer 264

su –

Question 265

What is the purpose of having different network ports?

Answer 265

So the communication of each application goes through a dedicated port

Question 266

How to display first column of a file?

Answer 266

cat filename | awk ‘{print $1}’

Question 267

What is the name of DNS rpm package?

Answer 267

bind

Question 268

How to check a file’s permission?

Answer 268

ls –l

Question 269

What is the difference between “kill” and “kill -9” command?

Answer 269

kill will create a sigterm signal. kill -9 willforcefull kill the process

Question 270

You are troubleshooting an issue with Redhat support and they have asked you to send the contents of /etc directory. How and which method you will use to transfer the contents?

Answer 270

tar (compress) the entire /etc directory and sftp or scp

Question 271

What is root home directory?

Answer 271

/root

Question 272

How to check the computer name or host name in Linux?

Answer 272

hostname

Question 273

Which permission allows a user to run an executable with the permissions of the owner of that file?

Answer 273

First 3 bits should have x

Question 274

What is the command to untar a tarred file?

Answer 274

untar

Question 275

What is /proc directory used for?

Answer 275

1) provides a method of communication between kernel space and user space.
2) the process reporting utility ps uses the proc file system to obtain its data,
3) special filesystem in Unix-like operating systems that presents information about processes and other system information in a hierarchical file-like structure

Question 276

List 3 basic commands to navigate the filesystem?

Answer 276

cd, pwd and ls

Question 277

Which service/daemon should be running on the server that allows you to connect remotely?

Answer 277

sshd

Question 278

What is the purpose of firewall?

Answer 278

1) it provides a barrier to control network traffic both into and out of an organization’s Internet-connected network, or perhaps between different segments of an internal network.
2) companies can configure multiple firewalls inside their corporate network to essentially divide the network into multiple segments. That helps contain the damage should some form of worm or other malware be unleashed in any given segment.

Question 279

List any 3 IT components?

Answer 279

Hardware, OS and Applications

Question 280

What is the difference between memory, virtual memory and cache?

Answer 280

virtual memory: memory in db server or any virtual machine memory
cache: active memeory sits between cpu and memory
physical memory: memory

Question 281

Which directory has all the commands we use, e.g. ls, cd etc.?

Answer 281

/usr/bin or /bin

Question 282

Which of the following is a communication command?

Answer 282

o grep
o mail this one
o touch
o cd

Question 283

How to rename a file or directory?

Answer 283

mv

Question 284

How to change a hostname in Linux?

Answer 284

sudo nano /etc/hosts

sudo nano /etc/hostname

Question 285

How to check network interfaces in Linux?

Answer 285

ifconfig

Question 286

What command used most often to output all incoming logs in real time

Answer 286

“tail –f logfilename”

Question 287

How to sort a file in reverse order?

Answer 287

cat filename | sort –r

Question 288

What is the name of operating system that runs Unix?

Answer 288

Solaris, HP-UX etc

Question 289

List all byte sizes from smallest to largest?

Answer 289

bytes, kilobytes, megabytes,gigabytes,terabytes

Question 290

How to check the total number of partition in Linux?

Answer 290

fsdisk -l

Question 291

How to access a linux system from a linux system?

Answer 291

ssh

Question 292

What is the exact command syntax to list the 5th column of a file and cut the first 3 letters?

Answer 292

cat filename | awk ‘{print $5}’ | cut –c1-3

Question 293

What is /etc/hosts file used for?

Answer 293

To resolve hostnames with IP address

Question 294

List any 3 options of ‘df’ command and what they are used for?

Answer 294

df -h
df -x tmpfs to exclude certain filesytem types
df -t ext4 list only specific file system types
df -T To show the file system type pass the -T option

Question 295

What is the command to change file/directory permissions?

Answer 295

chmod

Question 296

What is the purpose of pipe (|)?

Answer 296

To combine multiple commands

Question 297

What is /etc directory used for?

Answer 297

For configuration files

Question 298

Which command is used to list files in a directory?

Answer 298

ls -l

Question 299

There is a command which gives you information about other commands, please explain that command and what is it used for?

Answer 299

man

Question 300

How to delete a file and a directory?

Answer 300

rm filename and rmdir dirname

Question 301

What is the difference between “tail” and “tail -10”?

Answer 301

None

Question 302

List 4 commands to display or read a file contents?

Answer 302

cat, more, less, vi

Question 303

Which command is used to read the top 5 lines of a file?

Answer 303

head -5 filename

Question 304

What are the different commands or methods to write to a file?

Answer 304

echo > filename and vi filename

Question 305

What is swap space and how to check swap space?

Answer 305

top command shows swap space,
swap space is the amount of memory reserved for a process which is equivalent to amount of memory assigned to the process by the kernel., when the physical memory passes its threshold then the swap space is activated,the inactive

Question 306

What is inode and how to find an inode of a file?

Answer 306

1) An inode is simply an internal data structure that Linux uses to store information about a filesystem object
2)
ls -id /path/to/dir

i = inode 
d= directory

Question 307

Which file to edit for kernel tuning?

Answer 307

1) /etc/sysctl.conf you can configure various Linux networking and system settings

Question 308

Name the command to find specific word from a file?

Answer 308

grep word filename

Question 309

You have scheduled a job using crontab but it does not run at the time you specified, what could be the reason and how would you troubleshoot?

Answer 309

Check your system time
Check your crontab entry
Check /var/log/messages

Question 310

How to check network interface MAC address?

Answer 310

ifconfig

Question 311

If I don’t want others to read my file1, how to do that?

Answer 311

Remove r from the last 3 bits of file permission

Question 312

What is the purpose of “uniq” and “sed” command?

Answer 312

1) uniq authors.txt, uniq command is of showing a count of occurrences, showing only repeated lines and ignoring characters and specific fields.
uniq -c authors.txt To output the number of occurrences of a line use the -c
uniq -d authors.txt This will output only lines that occur more than once and write the result to standard output
In summary the purpose of uniq is to parse data a

2) sed is a stream editor. A stream editor is used to perform basic text transformations on an input stream (a file or input from a pipeline).

for eg: 
the input file is 
Tom Westley Essex
Ravi Bopara Essex
Marcus Trescothick Somerset
Joe Root Yorkshire
Jonny Bairstow Yorkshire

uniq -f 2 -c cricketers.txt | sed ‘s/^\s*//’ | cut -d ‘ ‘ -f 1,4

2 Essex
1 Somerset
2 Yorkshire

To ignore fields in a comparison pass the -f option to uniq. This will run the comparison on the specified field and output the result to standard output.

^/s* zero or more occurences of space is replaced by1 single space “ “ to make a solid delimiter for cut command

The cut command in UNIX is a command line utility for cutting sections from each line of files and writing the result to standard output.

In summary, the sed and uniq command are for data transformation.

Question 313

Which command is used to list the contents of a directory in the most recent time and in reverse order, meaning the most updated file should be listed on the bottom?

Answer 313

ls –ltr

explanation:

ls -ltr :

• t option will sort the entries by modification date (with newest first)
• r will reverse the sorting order.

As -t will sort by modification time with newest first, -r will cause the reverse i.e. oldest entries will be shown first now.

Question 314

What is the difference between tar, gzip and gunzip?

Answer 314

Tar is a file archiving technique and it combines mulitple files to a single archive file

gzip is to compression technique to compress a file which has large file

gunzip is to decompress the compressed file that was compressed using the gzip technique

Question 315

How to view difference between two files?

Answer 315

diff file1 and file2

Question 316

Run a command that shows all lines except any lines starting with the character # in a file

Answer 316

grep -v “^#” filename

Question 317

What is the difference between .bash_profile and basharc

Answer 317

.bash_profile is executed when newly logged in to the shell session.

.basharc is executed when already logged in but opened a new trminal

Question 318

The difference between $ and # prompts on CLI

Answer 318

$ prompt is for users and # prompt is for root

Question 319

How to create a file

Answer 319

touch ,vi

Question 320

Default port number of DNS

Answer 320

53

Question 321

name of DNS package name

Answer 321

bind

Question 322

configuration file for DNS location

Answer 322

/etc/named.conf

Question 323

List 3 type of filesyste

Answer 323

ext3,ext4, xfs,fat,ntfs

Question 324

list any 4 unix flavors

Answer 324

fedora ubuntu redhat suse

Question 325

hw to find filetype of a file

Answer 325

file filename

Question 326

how to check files permission

Answer 326

ls -l

Question 327

command to find your current directory

Answer 327

pwd

Question 328

how to log off from linux system

Answer 328

exit

Question 329

how to check if a package is installed

Answer 329

for eg to check if DNS package is installed

rpm -qa | grep bind

Question 330

to check all previously typed commands

Answer 330

history

Question 331

how to check where passwd command is located

Answer 331

which passwd

Question 332

how to list all the commands

Answer 332

ls /usr/bin

Question 333

how to check ip and ac address

Answer 333

ifconfig -a

Question 334

How to count no. of lines in a file

Answer 334

wc -l filename

Question 335

where is the network time config file located

Answer 335

/etc/ntpd.conf

Question 336

how to reboot a linux system with init command

Answer 336

init 6

Question 337

when is the last comand used

Answer 337

to show last logged in users

Question 338

Can’t write to hard disk on the linux systems?

Answer 338

1) Run the df command to find out info about the total space and available space on a file system including partitions
2) Locate the filesystem that has unusually high usage
3) When the disk is full, du on the /var/logs and tar the files where the directory is large on du
4) compress the tar files either usng gzip or bzip technique.
5) Delete unwanted files using rm , and unwanted directories using rmdir
6) Move files to other systems or external hard disk

rsync –remove-source-files -azv /ftp/tmp/*.log /mnt/usbdisk/

rsync –remove-source-files -azv /ftp/tmp/*.log server2:/path/to/the destination/directory

7) find largest dir or files eating disk space on unix system

du -a /ftp/tmp | sort -n -r| head -n 10

8) locate those largest files and truncate the largest files on unix/linux

truncate -s 0 /ftpuser/ftp.log

9)find and remove large files that are open but have been deleted on unix

lsof -np | grep ‘deleted’

10) Check if you are running out of inodes, coz most likely when 1000’s of small files are created on a dir, the ifilesystem runs out of inodes.

To check this out we can use du -i /dirname/filename.ext

if 100 % of inodes are used, we need to find the unwanted files and delete them after transfering them to different server or mount point using rsync command

11) du -hs points to the biggest directory and points to what needs cleaning up

Question 339

Why getting disk full messages on the screen?

Answer 339

1) Run the df command to find out info about the total space and available space on a file system including partitions
2) Locate the filesystem that has unusually high usage
3) When the disk is full, du on the /var/logs and tar the files where the directory is large on du
4) compress the tar files either usng gzip or bzip technique.
5) Delete unwanted files using rm , and unwanted directories using rmdir
6) Move files to other systems or external hard disk

rsync –remove-source-files -azv /ftp/tmp/*.log /mnt/usbdisk/

rsync –remove-source-files -azv /ftp/tmp/*.log server2:/path/to/the destination/directory

7) find largest dir or files eating disk space on unix system

du -a /ftp/tmp | sort -n -r| head -n 10

8) locate those largest files and truncate the largest files on unix/linux

truncate -s 0 /ftpuser/ftp.log

9)find and remove large files that are open but have been deleted on unix

lsof -np | grep ‘deleted’

10) Check if you are running out of inodes, coz most likely when 1000’s of small files are created on a dir, the ifilesystem runs out of inodes.

To check this out we can use du -i /dirname/filename.ext

if 100 % of inodes are used, we need to find the unwanted files and delete them after transfering them to different server or mount point using rsync command

11) du -hs points to the biggest directory and points to what needs cleaning up

Question 340

how to solve full/corrupt or failed disk issues?

Answer 340

1) Run the df command to find out info about the total space and available space on a file system including partitions
2) Locate the filesystem that has unusually high usage
3) When the disk is full, du on the /var/logs and tar the files where the directory is large on du
4) compress the tar files either usng gzip or bzip technique.
5) Delete unwanted files using rm , and unwanted directories using rmdir
6) Move files to other systems or external hard disk

rsync –remove-source-files -azv /ftp/tmp/*.log /mnt/usbdisk/

rsync –remove-source-files -azv /ftp/tmp/*.log server2:/path/to/the destination/directory

7) find largest dir or files eating disk space on unix system

du -a /ftp/tmp | sort -n -r| head -n 10

8) locate those largest files and truncate the largest files on unix/linux

truncate -s 0 /ftpuser/ftp.log

9)find and remove large files that are open but have been deleted on unix

lsof -np | grep ‘deleted’

10) Check if you are running out of inodes, coz most likely when 1000’s of small files are created on a dir, the ifilesystem runs out of inodes.

To check this out we can use du -i /dirname/filename.ext

if 100 % of inodes are used, we need to find the unwanted files and delete them after transfering them to different server or mount point using rsync command

11) du -hs points to the biggest directory and points to what needs cleaning up

Question 341

One application is connected to 30 Databases using DB connect, there is also a pool limit user , and when that exceeds, the error is pooped us saying pool limit user exceeded or error establishing DB connection .How to trouble shoot it and what causes it ?

Answer 341

1) It happens when the query execution time exceeds the normal time
2) There will already by some shell scripts created by primary admin or system admin.
3) So, whenever the application is down, run the scripts
4) if the scripts don’t work, accelerate the issue either to the system admin or the server admin
5) Sometimes the script requires to pass arguments to the scripts, we can either go and edit certain part of the script using the vi editor

Question 342

How to pass arguments to the script just before execution?

Answer 342

./shellscript.sh argument1 argument2 argument3 2 “Newyork”

Question 343

How to know the total number of arguments specified to the script

Answer 343

$# wil output the number of arguments specified to the script

Question 344

What is shebang?

Answer 344

! /usr/bin/prl meaning it should execute using the interpreter specified on a first line

Shebang is a pound symbol followed by an exclamation #!

This syntx is used in scripts to indicate an interpreter for the execution under linux/unix os

for eg #!/bn/bash would mean the shell script should be executed with the bash interpreter

Question 345

what is the difference between sh script and ./script

Answer 345

1) Both are used to execute the script
2) Howewer sh scriptname will make it execute under sh
3) ./ could execute under bash/perl/sh/etc whatever interpreter specified in its shebang line

Question 346

How to tackle out of meory alert and why it occurs?

Answer 346

Each process is allocated some java heap size for eg 3gig has been alloted to one process

However a user has started downloading a 600 MB excel file and now the process is taking 4GB RAM , then that particular process throws out of memory exception, since it’s demanding more than what’s allocated to it.

The ways to troubleshoot this issue is:

1) If we have a shell script to auto-restart the process, we will go ahead and run it
2) If the process hangs, we will kill it or teminate it

Question 347

Some unexpected behavior on the server side may at times causes real resource outage issues. process crucial to your web application was killed as a result of out of memory situation. How do you troubleshoot it.

Answer 347

We have couple of options

1) Reduce amount ofmeory asked by the process
2) Disallow process to overcomit memory
3) Simply add more memory to the server configuration

> A useful memorymonitoring tool is the top command

> If your system memory gets used up to the extent that it can threathen the system stability, the out of memory killer will choose which process to terminate or eliminate and linux keeps a score for each running process for this purpose and it’s called oom score and this score is stored in the file /proc//oom_score

ps aux |grep processname will give the processid
cat /proc/pid/oom_score can give the score, higher the number more likely its can be eliminated.

> Now to change the overcommit mode if the system is at risk of running out of memory,
sudo sysctl -w um.overcomit_memory=2

2 meaning if system doesnt have meomry it will not overcommit
other options include
1 to always allow
0 estimate if we have enough RAM

Question 348

How to know what process runs on which port

Answer 348

sudo netstat -tunlp | grep 8080
t = tcp
u =udp
n= numerical display of addresses ,ip and ports
l=list only listening ports
p=show processid and name of the program to which the socket belongs

Question 349

List what files are being used by port 80

Answer 349

sudo lsof -i :80

Question 350

Find process nae associated with the pid

Answer 350

ps -p 2212 -o -comm=

or

ls -l /proc//exc

Question 351

display the working directory of a process with the pid 123

Answer 351

pwdx 123

Question 352

To understand what the command is about

Answer 352

whatis pwdx

Question 353

What is the difference between ssh and telnet

Answer 353

both are used to connect remotely to the other servers remotely

However, ssh is encrypted version of telnet -
telnet sends data in plain text, if the usecase is for fast protocol,telnet is the choice

if the usecase if for security, ssh is the choice-its a slow protocol due to encryption.

Question 354

Can you troubleshoot what may be causing a connection issue when trying to connect remotely ?

Answer 354

1) During establishing connections to other computers firewall issues may be encountered
2) So we need to make sure that port is open in the firewall to listen
3) So wen use telent command to test ports opened or closed on a remote server as follows:
telnet domainnameorIP port

eg. telnet adminuser@google.com 80

Due to security issues of transferring data in plain text most use ssh
4) We can use ping to know if the ip or port are active, but most likely this will be disabled

5) After port issue is established, another issue that can be causing this is ip restriction

ifconfig is to query network interface parameters, using this we can figure out if the ip address is resolved with the particular hostname

Question 355

The system is in trouble , how will you troubleshoot?

Answer 355

Will continuously monitor log files for errors, this way I can keep tabs on the live feed of data coming into the log file : var/log/messages
tail -f /var/log/messages

AND use Cntrl C to exit

Question 356

Which is the file where we an go and look for errors

Answer 356

/var/log/messages

Question 357

When it’s a really large file particularly because the system is on over the years, which command will u use to view the recently written data

Answer 357

I will not use cat command as it can potentially hang the system

I will use the tail -f /varlog/messages

Question 358

How to remove files older than 7 days by creating cronjob to run everynight

Answer 358

vi filename

0 0 * * * /bin/find -mtime +7 -exec rm -rf {} ;/

Question 359

How to list all the created users in the system and send the in a file

Answer 359

tar -cvf users.tar /etc/passwd | awk ‘{print $1}’ >file.ext
tar -cvf users.tar /etc/passwd | cut d ‘:’ -f 1 >file.ext
sftp file.ext server2:/destination/dir

Question 360

How would you create a file or how to print out the first column of the first field

Answer 360

touch or vi used to create a file,

awk and cut can be used to pront out the first column

Question 361

Someone needs data from a file which is really large but only need second column from a file ? how will u do thi

Answer 361

cut -d ‘ ‘ -f 2

Question 362

system is about to go down due to some emergency that happened, probably a hack, so it needs to be booted, how to broadcast a message to all the logged in users

Answer 362

wall -n “server is going down in 15 mins”

Question 363

How to create a user with no login access because there is an aplication that need a usr account but does not require access to login to a s/m

Answer 363

useradd -s /sbin/nologin username

then su username to check

Question 364

Schedule server reboot in 15 minutes

Answer 364

shutdown -r 15

Question 365

Schedule server reboot immediately

Answer 365

shutdown -r now

Question 366

Schedule server reboot at 11 pm

Answer 366

shutdown -r 23:00

Question 367

How to find disk usage by the largest directory

Answer 367

this can be troubleshooted by checking disk space pertaining to a particulr user or by particular directory and sub directories

pwd

/var
du -Sh | sort -n | less

S is for searching disk space for directories

Question 368

How to prevent users deleting other users files in a directory

Answer 368

This question is pointing towards special permissions that are called sticky bit

chmod 1777 hist/

Question 369

how to display the 10th line of a file only

Answer 369

cat filename | head -n 10 | tail -n 1

Question 370

the server got damaged as it got hacked , due to the amount of damage the whole server needs to be restored. How would you go about doing that?

Answer 370

There are two parts in this question: Vmware and physical server

1) If I am using VMware and ther is a complete copy of that disk, VM has a tool in it that captures the ystems state off a particular system or depending on which date it’s capturing from , you can completely redo the system from that particular date.

we can restore it from the system state if VMware has saved it to some kind of capture tool that captures the whole system and deploys that image for that system

2) If it’s the physical server , then only the data gets backedup , also some config files can be restored not all.

We can restore the entire OS just from the back up and use the data from the back up taped device

Config files are restored in /etc files

So to summarize , we create a new system, get all the data from the back up and throw them on your new system.

Question 371

To update packages in the server

Answer 371

yum update

Question 372

to remove the package

Answer 372

yum remove packagename

Question 373

Command to disable service

Answer 373

service servicename stop

Question 374

What is the difference between linux and unix

Answer 374

Unix was primarily developed with multi tasking and multi users in ind, unix cannot be installed on any hardware. Where as linux can be installed in almost many hardwares and supports may flavors of file system, whereas unix supports only fewer filesystems.

Question 375

What is linux

Answer 375

Linux is an operating system sits between hardware and users

Question 376

Difference between linux and windows

Answer 376

free not free
not user friendly userfreindly
very secure not so secure
very open to public can modify ur own changes Not an open surce os, cannot open the code or reveal to anyone
Best for multi tasking multi tasking requires high cpu and mem

Question 377

To list all the available ips or interfaces that u have on your system

Answer 377

ifconfig command is deprecated,

ip addr

Question 378

What is a filesystem.

Answer 378

A filesystem is something similar to your closet at your hoe. Think of each shelf with specific kind of storage. One folder has only programs or applications, another folder have only attaced devices, so it will be much easier for the operating system to access the files,

There are different types of filesystems:
1)ext3
ext4
FAT
NTFS
XFS

Question 379

what command to use to creata ultiple files in a directory

Answer 379

touch command
eg:
touch mart lisa tex

Question 380

what command to use to create multiple files in a directory

Answer 380

touch command
eg:
touch mart lisa tex

Question 381

what command to use to create multiple directories in a directory

Answer 381

mkdir dir1 dir2

Question 382

Tell me what kind of file starts with c

Answer 382

if any eboard of mouse is attaches, then that file starts with c

Question 383

Tell me what kind of file starts with p

Answer 383

named pipe file starts with p

Question 384

Tell me what kind of file starts with b

Answer 384

block device starts with b

Question 385

What are the commands to file diles and directories in a system

Answer 385

find and locate

Question 386

How to create files with one command using wildcards

Answer 386

touch abcd{1…9}-xyz

this will create 9 files
wildcards are to substitute for charecters

Question 387

touch abcd{1…9}-xyz will create how many files?

Answer 387

9 files

Question 388

wildacard used for the begining of the line and the end of the line

Answer 388

^ and $ respectively

Question 389

What is soft link and hard link?

Answer 389

it is related to inode.

Inode is a pointer of a file on the hard disk

Eevrytime we create a file, computer assisgns a number to the file and hard disk will associate that number to it and that number is called inode

Soft link is a link if when created will be removed if the filname of that link is removed or renamed

once created it looks for the inode through that file, so that creates a soft link, if removed the source file it removes the destination link

whereas for hard link, deleting or renaming the source file will not change the hard link, as if you have copied it

Question 390

What are the commands to create a hard link command

Answer 390

ln

Question 391

to create a soft link command

Answer 391

ln -s

Question 392

the reason why we creata soft link or hard link

Answer 392

to creata shortcut of the actual file, to have easy access instaed of doing a lot directory chnages or specifying the long path to the file

Question 393

Create a soft link to a file in /tmp dir where the file is in /home/hulk

and verify that the link got created

Answer 393

cd /tmp
ln -s /home/hulk

to check that the link got created ls -ltr command , at the botto of the output the file is seen

Question 394

Why do we get the error that failed to create a hard link

Answer 394

This happens when the hard link is created on the different partition. . For the hard link to work, it needs to be on the same partition.

Question 395

what are file permissions

Answer 395

Since unix is a multi user system. typically for protecting our environment where files could be viewed by other users, or unnecessarily modified or deleted by other users

Question 396

how to display directory or file permission , explain them

Answer 396

ls -l command,

the first 3 bits are for the user
the second three bits are for the group
the last three bits are for the other users of the system

Question 397

How to remove write permissions of a file for a group

Answer 397

chmod g-w filename

Question 398

How to remove read permissions to all users

Answer 398

chmod a-r filename

Question 399

How to grant both read and write permissions to user

Answer 399

chmod u+rw filename

Question 400

what is the meaning of x in the permissions bits of the direcotry

Answer 400

It certainly doesnot mean it is a script, what it means is we cannot cd into that directory

Question 401

commands to change the ownership of the files

Answer 401

chown and chgroup that an be changed from the root account

Question 402

let the root user own the filename

Answer 402

chown root filename

Question 403

let the root group own the filename

Answer 403

chgroup root filename

Question 404

what key completes the command on cli

Answer 404

hitting a tab key after the command completes the command

Question 405

to show commands that start with ch

Answer 405

type ch and press tab twice

Question 406

To bring the last command that you ran and the commands that were ran previous to it

Answer 406

up arrow key

Question 407

Give me the commands that you use to monitor the system

Answer 407

top 
free
df
dmesg
netstat 
iostat
cat proc/cpuinfo
cat proc/meminfo

Question 408

What does df report

Answer 408

df reports filesystem usage of disk

Question 409

If your system is dead or crashed, one of the things that you will look into it is

Answer 409

df command

Question 410

If you see 100 % usage with the df command output,then the next step is

Answer 410

to free up the disk space an, and the comand to help in this pursuit is du which will output the disk usage of the files and the directories

Question 411

The command to show you the output of the system related warnings , error messages , failures

Answer 411

It throws bunch of messages and bunch of information at you , and that command is
dmesg

If there are any issues with the memory it will report right here , if there is a memory leak, cpu that crashed or any mother board issue, anything related to system hardware will be related to that

Question 412

what command that displays whats coming in and whats coming out and how we are communicating with our system’s peripheral devices or system internal devices if it’s a disk or network

Answer 412

iostat

Question 413

Command to find out gateway information, command to find out my subnet mask and what interface it is going through

Answer 413

netstat -rnv

Question 414

what is free command used for

Answer 414

It gives you information about the virtual memory and the swap space which is a virtual memory utilization

Question 415

What is connected to the system, what is been disconnected , what is the process id and which process is it running and the name of the owner of the process

Answer 415

netstat

Question 416

to get all the cpu info- which file to look at

Answer 416

cat /proc/cpuinfo

Question 417

what is the log file that stores messages or errors during boot time

Answer 417

cat /proc/boot.log |more

Question 418

All the system resouce informations are stored into files, where are these files located?

Answer 418

/var/directory

Question 419

what is the log file that stores messages or errors during boot time

Answer 419

cat /var/boot.log |more

Question 420

whenever you schedule a job or process through a cron tab entry, that activity is recorded as a log into this file

Answer 420

cat /var/cron

Question 421

email out and email in is recorded in which log

Answer 421

/var/maillog

Question 422

when troubleshooting issues as to why you are not able to send emails

Answer 422

/var/maillogs

Question 423

real time recent logs on users loggin in and logging out

Answer 423

tail -f /var/secure

Question 424

everytie there is an issue with the machine, the first thinga an adinistrator does is

Answer 424

look into the /var

Question 425

This file has all the hardware information, all the software information, all the application information, all the process information, everything is logged into this log

Answer 425

/var/messages

Question 426

command to see how many lines does /var/messages file has

Answer 426

cat /var/messages | wc -l

Question 427

which command will give information about the OS and some kernel information

Answer 427

uname -a

Question 428

which command will give you the information about the processor memory and the hardware underneath the OS

Answer 428

dmidecode

Question 429

the first thing every time who ever logs into the system they should check they should run this command to know about which system they are in

Answer 429

uname -a

Question 430

To tell which server you are logged in the command would be

Answer 430

hostname

Question 431

how to disable ping

Answer 431

go to sysctl.conf

net.ipv4.icmp.ignore_echo_ignore_all = 1

that parameter 1 will disable the ping,
the parameter 0 will enable it

Question 432

explain diff fields in /etc/passwd

Answer 432

username uid groupid shellname uid gid home drectory

Question 433

how to know that a port is listening

Answer 433

netstat -tunlp | grep 22

Question 434

Which commadn to tell how long the system has been running

Answer 434

uptime

Question 435

wat command to show load average on the server

Answer 435

uptime

Question 436

Define system load average

Answer 436

average number of processes that are in runnable state or uninterrupted state

Question 437

Dispaly all lines in the files with line numbers

Answer 437

cat -n filename

Question 438

What is the command to list all the network interfaces

Answer 438

ifconfig

Question 439

How to make some congiguration on the network interface specified

Answer 439

go to /etc/sysconfig/network-scripts/ifcfg-empos3

Question 440

which command to run to find if certain package is installed

Answer 440

rpm -qa | grep packagename

rpm -qa | grep ntp

Question 441

How to find if DNS package is installed or not

Answer 441

rpm -qa | grep bind

Question 442

what is rpm command for

Answer 442

rpm command is a powerful package manager

Question 443

how to find total lines in a file without opening the file

Answer 443

wc -l filename

Question 444

shall we do cat on large files

Answer 444

no don’t do cat on large files

Question 445

How to find disk usage of the largest directory

Answer 445

du -Sh |sort -nr | head -n 10

Question 446

how to find all directories with name cong under root

Answer 446

find / -type d -name conf

Question 447

commadn to view all the currently logged in users

Answer 447

who

Question 448

what is SOS report

Answer 448

sos repor is a package of all the sysyem congifuration informations, all the processes and all the resources information packaged and send t redhat for support

Question 449

How to combine multiple files into one

Answer 449

cat file1 file2 file3 > file4

Question 450

The file is very large, compression is not the option, you need t chop the files to send them to another server or a third party vendor and the log file is huge
how to split single filesinto multiple files

Answer 450

split -l 300 filename childfile

Question 451

How to append data to an existing file

Answer 451

echo uk&raquo_space;filename

Question 452

To send a foreground running process to background the command is

Answer 452

cntrl Z

Question 453

To stop a background process

Answer 453

Cntrl C

Question 454

A process when initiated always attaches itself to the terminal from where it is initiated

Answer 454

know this?

Question 455

How to not interrupt a background process even after the terminal is closed?

Answer 455

nohup processname &

Question 456

How to set priority of a process,

Answer 456

nice is the command to set priority of a process, the nice value ranges from -19 to 20, lower the number more priority the task gets.

nice -n process command

Question 457

what is the command to start an applicationand stop an application

Answer 457

systemctl restart ntpd

d means daemon

Question 458

what does ntp application do

Answer 458

its a daemon and is a network time protocol that runs all the time and syncs your time with other clocks

Question 459

How to know the status of a service

Answer 459

systemctl status ntpd

Question 460

To stop a service or an application or a process

Answer 460

systemctl stop ntpd

Question 461

To startt an application whenever the system starts the command is

Answer 461

systemctl enable ntpd

this will start the ntpd daemon whenevr the system strts

Question 462

How do you know that a process is hung

Answer 462

top command that shows 99% of usage of mem and cp

Question 463

command to know no. of users currently logged into the system

Answer 463

uptime

Question 464

how to view all the commands available to you as a user

Answer 464

cd /usr/bin

ls -l

Question 465

Did you know that you need to sort before u pipe it to uniq command?

Answer 465

only then the uniq command works

sort | uniq

Question 466

To get the partition information on the disk

Answer 466

fdisk -l

Question 467

Steps to mount new disk to the system

Answer 467

1) add new disk
2) initialize the disk
3) Patition the disk
4) mount it to the different mount points

Question 468

what is the purpose of adding a new disk

Answer 468

when u run out of the disk space or if you have multiple applications may be one
partition is required for one application and other partiton is required for another application, that’s why we ask new disk

Question 469

what is the purpose of adding a new disk

Answer 469

when u run out of the disk space or if you have multiple applications may be one
partition is required for one application and other partition is required for another application, that’s why we ask new disk

Question 470

How to regular zip a directory

Answer 470

zip -r filename /path/to/dir/to/zip

Question 471

How to unzip a regular zipped file

Answer 471

unzip filename -d dire/where/to/unzip/into

Question 472

what is also another way to monitor cpu usage

Answer 472

sar -u

Question 473

how to monitor cpu usage of all cores

Answer 473

sar -p ALl

Question 474

How to monitor cpu usage of particular core

Answer 474

sar -p 4 (here 4 is the core number)

Question 475

How to monitor the memory free and used

Answer 475

sar -r

Question 476

which command shows memory usage ,cpu usage, cpu core usage, i/o statistics, block drivers,run query,load average,netwrok statisitcs

Answer 476

sar commadn with it’s different options

Question 477

How to monitor i/o statistics

Answer 477

sar -b

Question 478

How to get the historic statistics of the cu usage of 15th of this month

Answer 478

sar -u -f /varlog/sa/sa15

Question 479

which command to know the information on number of block drivers

Answer 479

sar -d

Question 480

which command to know the information on the run queue and the load average

Answer 480

sar -q

Question 481

which command to know the information on the network statistics

Answer 481

sar -n

Question 482

which command to show the cpu and i/o of all partitions

Answer 482

iostat

Question 483

to show only the cpu utilization bu tnot the partition i/o

Answer 483

iostat -c

Question 484

to show only the partition i/o not the cpu

Answer 484

iostat -d

Question 485

to show only the info a specified partition device name

Answer 485

iostat -p partition-device-name

Question 486

command to display when the system was last rebooted

Answer 486

last reboot

Question 487

command to displaywhen the system was last shutdown

Answer 487

last shutdown

Question 488

command to display who all logged in to the system on 3rd january 2 am this year

Answer 488

last -t 201801030300

Question 489

when did the username =cloudbreak last logged in?

Answer 489

last username

Question 490

list all the users currently logged into the system

Answer 490

who

Question 491

what is the number of users currently logged into the system

Answer 491

who -q

Question 492

when was the system last rebooted

Answer 492

who -b

Question 493

what are the processes spawned by the init

Answer 493

who -p

Question 494

what are the processes that are dead and their details

Answer 494

who -d

Question 495

command to compress a file

Answer 495

compress filename

Question 496

command to uncompress a filename

Answer 496

compress -rv filename

Question 497

command to know the amount of disk space util

Answer 497

df

Question 498

command to know the dis space take up by a specified file say filename

Answer 498

du -a filename

Question 499

You noticed that one of the Linux servers has no disk space left, how would you troubleshoot that issue

Answer 499

add more disk, create a new partition and link the new partition to an existing file-system

Question 500

How to check Redhat version release?

Answer 500

uname -a

Question 501

What is the difference between TCP and UDP?

Answer 501

TCP and UDP are protocols used for sending bits of data — known as packets — over the Internet.
The main difference between TCP and UDP is connection; TCP is connection oriented and UDP is connectionless.

TCP is all about reliability—packets sent with TCP are tracked so no data is lost or corrupted in transit

UDP is used when speed is desirable and error correction isn’t necessary. For example, UDP is frequently used for live broadcasts and online games

Question 502

To view the lined between 5 through 10 on file.txt

Answer 502

sed -n ‘5,10p’ file.txt

Question 503

to print the entire file except a certain range. To exclude lines 20 through 35 from myfile.txt, do:

Answer 503

sed ‘20,35d ‘file.txt’

Question 504

it’s possible that you’re interested in set of non-consecutive lines, or in more than one range. Let’s display lines 5-7 and 10-13 from myfile.txt:

Answer 504

sed -n -e ‘5-7p’ -e ‘10-13p’ myfile.txt

Question 505

To replace every instance of the word version with story in myfile.txt, do:

Answer 505

sed ‘s/version/story/g’ myfile.txt

Question 506

To replace every instance of the word version with story in myfile.txt, is this command in order to ignore character case

Answer 506

sed ‘s/version/story/gi’ myfile.txt

Question 507

replace multiple blank spaces with a single space

Answer 507

sed ‘s/ */ /g’ myfile.txt

Question 508

If you’re interested in replacing words only within a line range (30 through 40, for example), you can do

Answer 508

sed ‘30,40 s/version/story/g’ myfile.txt

Question 509

Sometimes configuration files are loaded with comments. While this is certainly useful, it may be helpful to display only the configuration directives sometimes if you want to view them all at a glance.

To remove empty lines or those beginning with # from the Apache configuration file, do

Answer 509

sed ‘/^##/|^$/|*#/d’ myfile.txt

Question 510

in regular expresion ^$ represnts what

Answer 510

blank lines

Question 511

To replace a word beginning with uppercase or lowercase with another word, we can also use

Answer 511

sed ‘s/[zZ]ip/rar/g’ file.txt

Question 512

the pattern to search for is Jul 2 at the beginning of each line

Answer 512

sed -n ‘/^ Jul 2/p’ file.txt

Question 513

we can also insert spaces (blank lines) for each non-empty line in a file. To insert one blank line every other line in LICENSE, a plain text file

Answer 513

sed G file.txt

Question 514

To insert two blank lines, for each non-empty line in a file. do

Answer 514

sed ‘G;G’ file.txt

Question 515

replace all instances of this or This (ignoring case) with that in myfile.txt, and we will save the original file as myfile.txt.orig.

Answer 515

sed -i ‘.orig’ ‘s/this/that/gi’ myfile.txt

Question 516

you have a file containing full names in the format First name, Last name. To adequately process the file, you may want to switch Last name and First name

Answer 516

sed ‘s/^(.)\,(.)/$/2\,/1’ fil.txt

Question 517

we may want to replace start with stop only if the word services is found in the same line. In that scenario, here’s what will happen:

Answer 517

sed ‘/services/ s/start/stop/gi’ file.txt

Question 518

Performing two or more substitutions at once

Answer 518

sed ‘s/this/that/gi;s/him/her/gi’ file.txt

Question 519

What is a zombie process?

Answer 519

To understand what a zombie process is and what causes zombie processes to appear, you’ll need to understand a bit about how processes work on Linux.

When a process dies on Linux, it isn’t all removed from memory immediately — its process descriptor stays in memory (the process descriptor only takes a tiny amount of memory). The process’s status becomes EXIT_ZOMBIE and the process’s parent is notified that its child process has died with the SIGCHLD signal. The parent process is then supposed to execute the wait() system call to read the dead process’s exit status and other information. This allows the parent process to get information from the dead process. After wait() is called, the zombie process is completely removed from memory.

This normally happens very quickly, so you won’t see zombie processes accumulating on your system. However, if a parent process isn’t programmed properly and never calls wait(), its zombie children will stick around in memory until they’re cleaned up.

Utilities like GNOME System Monitor, the top command, and the ps command display zombie processes.

Question 520

How do you search for a pattern/word in a file and then replace it in an entire file?

Answer 520

sed ‘s/patter/replcer/gi’ filename

Question 521

Explain the purpose of “touch” command?

Answer 521

To create an empty file

Question 522

If a command hangs, how to stop it and get the prompt back?

Answer 522

Ctrl C

Question 523

Which command is used to count words or lines?

Answer 523

wc

Question 524

How to check the number of users logged in?

Answer 524

who

Question 525

What is the command to view the calendar of 2011?

Answer 525

cal 2011

Question 526

Which command is used to view disk space?

Answer 526

df –h

Question 527

How to create a new group in Linux?

Answer 527

groupadd

Question 528

What is the command to send a message to everyone who is logged into the system?

Answer 528

wall

Question 529

Which command is used to check total number of disks?

Answer 529

fdisk –l

Question 530

What does the following command line do?

ps -ef | awk ‘{print $1}’ | sort | uniq

Answer 530

print all the processes and only print the first column of all running processes and sort them and remove duplicates

Question 531

. You get a call that when a user goes to www.yourwebsite.com it fails and gets an error, how do you troubleshoot?

Answer 531

Check for user internet
Check to see if user computer has DNS for hostname lookup
Check to see if the server is up that is running that website
Check to see if the server’s web service is running
Check for DNS availability which is resolving that website

Question 532

109. List 4 different directories in /?

Answer 532

/etc, /bin, /tmp, /home

Question 533

What is the output of the following command: $tail -10 filename | head -1

Answer 533

It will show the first line from the last 10 lines of a file

Question 534

What are the different fields in /etc/passwd file?

Answer 534

username passwword uid group name group id fullname of the user user home directory user terminall login

Question 535

113. What is the difference between “hostname” and “uname” commands?

Answer 535

Hostname will give you system name and uname will give you OS information

Question 536

How to check system load?

Answer 536

top and uptime command

Question 537

How to schedule jobs?

Answer 537

crontab

Question 538

What is the 3rd field when setting up crontab?

Answer 538

Day of the month

Question 539

117. What is the command to create a new user?

Answer 539

useradd

Question 540

118. What is the “init #” for system reboot?

Answer 540

6

Question 541

119. How to restart a service?

Answer 541

systemctl restart servicename

Question 542

120. How to shutdown a system?

shutdown or init 0

Answer 542

shutdown or init 0

Question 543

How to shutdown a system?

shutdown or init 0

Answer 543

shutdown or init 0

Question 544

What is “ftp” command used for?

Answer 544

To transfer files from one computer to another

Question 545

123. How to delete a package in Linux?

Answer 545

rpm –e packagename

Question 546

124. What is the file name where user password information is saved?

Answer 546

/etc/shadow

Question 547

125. Which command you would use to find the location of chmod command?

Answer 547

which chmod

Question 548

1. Which command is used to check if the other computer is online?

Answer 548

ping othercomputer

Question 549

Please explain about LAN, MAN and WAN

Answer 549

A LAN (Local Area Network) is a group of computers and the network devices connected together usually within the same building. By definition, the connections must be high-speed and relatively inexpensive (e.g. token ring or Ethernet). A “LAN Connection” is a high-speed connection to a LAN. See “What is a LAN (local area network)?” below.

A MAN (Metropolitan Area Network) is a larger network that usually spans several buildings in the same city or town.

A WAN (Wide Area Network) is, in comparison, not restricted to a geographical location, although it might be confined within the bounds of a state or a country. A WAN connects several LANs, and may be limited to an enterprise (a corporation or an organization) or accessible to the public. The technology is high-speed, and is relatively expensive. The Internet is an example of a worldwide public WAN.

Question 550

How to list hidden files in a directory?

Answer 550

ls –la

Question 551

1. What is the difference between telnet and ssh?

Answer 551

ssh is secure where telnet is not

Question 552

1. How to run a calculator on Linux and exit out of it?

Answer 552

bc and quit

Question 553

131. List any 4 commands to monitor system?

Answer 553

top, df –h, iostat, dmesg

Question 554

1. You are notified that your server is down, list the steps you will take to troubleshoot?

Answer 554

Check the system physically
Login through system console
Ping the system
Reboot or boot if possible

Question 555

1. What is difference between static and DHCP IP?

Answer 555

A Static IP address is a dedicated IP address that has been assigned to you. This is an IP address that is used by you every time you log in to network and need an IP address. DHCP or Dynamic is an IP address that will automatically be chosen for you from a pool of IP addresses that are assigned in the DHCP scope available on your network. Think Static as permanent and DHCP as temporary.

Question 556

134. How to write in vi editor mode?

Answer 556

i = insert, a = insert in next space, o = insert in new line

Question 557

135. What is the difference between “crontab” and “at” jobs?

Answer 557

crontab is for repetitive jobs where at is for one time job

Question 558

1. What is “dmidecode” command used for?

Answer 558

To get system information

Question 559

1. What is the location of system logs? E.g. messages

Answer 559

/var/log directory

Question 560

140. How to setup an alias and what is it used for?

Answer 560

alias aliasname=”command”

It is used to created short-cuts for long commands

Question 561

what is the purpose of netstat

Answer 561

Netstat is a common command line TCP/IP networking utility available in most versions of Windows, Linux, UNIX and other operating systems. Netstat provides information and statistics about protocols in use and current TCP/IP network connections.

netstat (network statistics) is a command line tool for monitoring network connections both incoming and outgoing as well as viewing routing tables, interface statistics etc. netstat is available on all Unix-like Operating Systems and also available on Windows OS as well

Question 562

What is nslookup used for

Answer 562

to resolve dns to obtain dns or ip addreses mapping for any other specific dns record

Question 563

142. What are terminal control keys, list any 3?

Answer 563

Crtl C, D and Z, tab and up arrow

Question 564

143. Which command(s) you would run if you need to find out how many processes are running on your system?

Answer 564

ps -ef |awk ‘{print $1}’ |sort |uniq|wc -l or simply

ps -ef |wc -l

Question 565

1. What are the different types of shells?

Answer 565

sh, bash, ksh, csh etc.

Question 566

1. How to delete a line when in vi editor mode?

Answer 566

dd

Question 567

146. Which is the core of the operating system?

Answer 567

a) Shell
b) Kernel«
c) Commands
d) Script

Question 568

147. Which among the following interacts directly with system hardware?

Answer 568

a) Shell
b) Commands
c) Kernel«
d) Applications

Question 569

148. How to save and quit from vi editor?

Answer 569

Shift ZZ or :wq!

Question 570

149. What is the difference between a process and daemon?

Answer 570

A daemon is just a term for a process that runs continuously and usually is not attached to a terminal

Question 571

1. What is the process or daemon name for NTP?

Answer 571

ntpd

Question 572

151. What are a few commands you would run if your system is running slow?

Answer 572

top, iostat, df –h, netstat etc.

Question 573

152. How to install a package in Redhat Linux?

Answer 573

yum install packagename

Question 574

1. What is the difference between “ifconfig” and “ipconfig” commands?
   i

Answer 574

ifconfig for Linux and ipconfig for Windows

Question 575

154. What is the first line written in a shell script?

Answer 575

Define shell

e.g. #!/bin/bash

Question 576

155. Where is the network (Ethernet) file located, please provide exact directory location and file name?

Answer 576

/etc/sysconfig/network-scripts/ifcfg-nic

Question 577

1. Why do we use “last” command?

To see who has logged in the system whether active or logged off

Answer 577

To see who has logged in the system whether active or logged off

Question 578

158. To view your command history, which command is used and how to run a specific command?

Answer 578

history and history #

Question 579

193. What is the difference between domain and nameserver?

Answer 579

The server or usually called as web server is an actual place where your website files are hosted. … The domain name is a pointer to an IP address which hosts a server. Think of it as the difference between the street address “Example Street 42” (the domain name) and the house on that address (the server).

Question 580

197. How to check scheduled jobs?

Answer 580

crontab –l

Question 581

198. How to check system memory and CPU usage?

Answer 581

free and top

Question 582

199. Which utility could you use to repair the corrupted file system?

Answer 582

fsck

Question 583

1. What is the command to make a service start at boot?

Answer 583

systemctl enable servicename

Question 584

1. How to combine 2 files into 1? E.g. you 3 lines in file “A” and 5 lines in file “B”, which command syntax to use that will combine into one file of 3+5 = 8 lines

Answer 584

cat fileA&raquo_space; fileB

Question 585

1. What is echo command used for?

Answer 585

To output to a screen

Question 586

1. Which file to modify to allow users to run root commands

Answer 586

/etc/sudoers

Question 587

1. Your system crashed and being restarted, but a message appears, indicating that the operating system cannot be found. What is the most likely cause of the problem?

Answer 587

The /boot file is most likely corrupted