Linux Commands

Question 1

Check OS version

Answer 1

cat /etc/redhat-release

rpm -q centos-release

Question 2

vi tips - moving the cursor

V - selects entire lines
v - selects range of text

Answer 2

:set number | v - copy
:set nonumber | p -paste
0 - move cursor to start of line | x - cut+paste
:0 - first line
$ - move cursor to end of line
:$ - last line
w - next word
b - preceding word

Question 3

toggle between the last two directories

Answer 3

cd -

Question 4

Use dirs, pushd and popd

to manipulate directory stack

Answer 4

dirs
pushd
popd

Question 5

vi tips II

% Find matching () { or } d Delete
^l Redraw screen dd Delete line
^r Refresh screen c Change
z Current line at top y Yank lines to buffer
z- Current line at bottom C Change rest of line
^e Scroll down one line D Delete rest of line
^y Scroll up one line s Substitute character
`` Previous context S Substitute lines
H Home window line J Join lines
L Last window line x Delete after
M Middle window line X Delete before
+ Next line Y Yank current line
hjkl Cursor movement: p Put back lines
left/down/up/right P Put before
0 Beginning of line > Shift line right
f Find forward u Undo last change
F Find backward U Restore current line

Answer 5

ZZ Exit, saving changes t Up to forward Q Enter ex mode T Back up to End of insert | Go to columnExecute ex command w,W Forward one word
:! Shell command b,B Back one word
^g Show filename/size e,E End of word
^f Forward one screen ^h Erase last character
^b Back one screen ^w Erase last word
^d Forward half screen ^? Interrupt
^u Backward half screen ~ Toggle character case
G Go to line a Append after
/ Search forward for i,I Insert before
? Search backward for A Append at end of line
n Repeat last search o Open line below
N Reverse last search O Open line above
]]fGOTO
Next section/function r Replace character
[[ Previous section/function R Replace characters

Question 6

vi Options:

autoindent Automatic line indentation
autowrite Write before quit
ignorecase Ignore case in searches
number Display line numbers
showmatch Show matches to ) and } as typed
terse Quiet mode
wrapscan Wraparound in searches
wrapmargin Automatic line splitting

Answer 6

q Quit set Enable option
q! Quit, discard changes set no Disable option
r Read in file set all Show all options
sh Invoke shell
vi Vi mode
wq Write and quit
w Write file
w! Overwrite file
/Emilee Tellez

Question 7

verify syslog is installed

Answer 7

rpm -qa | grep syslog

Question 8

verify rsyslog service is set to start

Answer 8

chkconfig rsyslog –list

chkconfig rsyslog –level 2345 on

Question 9

ls - no details

Answer 9

ls -a
ls -A (no implicit “.” or “..”)
ls -aF (classify ex. “/”)

Question 10

ls group directories first

Answer 10

ls –group-directories-first

Question 11

check running level

Answer 11

runlevel

Question 12

change running level

Answer 12

init 3 (0 - 6)

Question 13

GRUB abbreviation

Answer 13

Grand Unified Bootloader

Question 14

grubby –update-kernel=ALL –args=”…”

Answer 14

grubby –update-kernel=ALL –args=”video=hyperv_fb:1024x768”

Question 15

check listening ports with netstat

Answer 15

netstat -ant (all TCP ports numeric list)

Question 16

check listening ports with list open files

Answer 16

lsof -i :8080 (ex port 8080vi /etc/rsysl)

Question 17

restart network service

Answer 17

service network restart

Question 18

Hyper-v install cdrom module

Answer 18

insmod /lib/modules/$(uname -r)/kernel/drivers/ata/ata_piix.ko
lsmod | grep piix
rmmod …

Question 19

The file contains gateway?!? and host info

Answer 19

/etc/sysconfig/network

Question 20

ifconfig add/delete secondary (subinterface) interface

Answer 20

ifconfig eth0:0 10.10.20.218 netmask 255.255.255.0 up

ifconfig eth0:0 del 10.10.20.218

Question 21

ip address add

Answer 21

ip address add 192.168.99.37/24 dev eth0

you can add more than one IP (the additional become secondary)

Question 22

add a permanent secondary IP

Answer 22

cp the existing ifg-ethx
them edit it, removing the gateway and changing the name:
DEVICE=eth0:1
BOOTPROTO=static
ONBOOT=yes
IPADDR=10.1.1.2
NETMASK=255.255.255.0

Question 23

List all processes

Display tree

Answer 23

ps aux | less
-A all processes
a all proc on term (+ other users)
x —||— (w/o controlling ttys)

pstree

pgrep firefox get process ID by name

Question 24

kill

Answer 24

kill PID             (simply kill a PID)
kill -KILL           (bypass the program & send to OS kernel)

kill -l list signals
kill -0 -HUP (restart daemon w Hang-Up signal)
kill -9 -KILL

Question 25

grep (case insensitive)

Answer 25

grep -i