Cat /etc/inittab or who –r

LVM Id: 8e

Ping remote server IP. (to check  alive or not)

Make sure remote server sshd service enabled

If everything is ok, login remote server ILO, open the remote console and check the status

nmap

Setfacl –m u:username:permission filename

Getfacl username (to check the user permissions)

Netstat –anultp service name or port number

Chkconfig –level 2 off

Hard Mount : After restarting the server keep on search nfs mount partition until found the device, if the device not found server not will not boot,.

Soft mount: if device not found it will skip

Rpm: need local rpm file and dependencies

Yum: need repository (collections of rpm) local or internet

du –sh <file/dir>

/tmp

Lsof

ps aux |grep “defunct” and ps aux |grep Z  to Kill: In order to kill these processes, you need to find the parent process first.

pstree –paul and find parent process id, use kill -9

rpm2cpio

Remount –o rw,remount

/et/passwd (!!)

/etc/hosts.deny à sshd: ALL except Node IP

Chage –l username

# pwunconv     (It creates the users according  /etc/passwd   file and deletes the  /etc/shadow   file)

# passwd     -x    -1    <user login name> How to put never expiry to a user?

# passwd     -x    -1    <user login name>

# fuser    -cu    (to see who are login)

#fuser    -ck    <user login name>(to kill the specified user)

# chkconfig <service  name>   on

# nmap   -p  22    <IP address of the remote host>    (to see the ssh is running or not on remote system)

Nmap servername portname

Hardware error, Kernel error

Lsof |wc –l (list of open files)

If more than 65k, open /etc/sysctl.conf increase the file.mx value and execute below command

Sysctl –p

Using /etc/ssh/sshd_congig

/tmp

fsck   <device or partition name>command we can check the integrity of the file system.

The before running the fsck command first unmount that partition and then run fsck command.

• Disk is full.
• Disk is failing or failed.
• File system corrupted or crashed.
• O/S is not recognizing the remote luns when scanning, …etc.,

The default run level command is /etc/inittab file in most Linux operating systems.

• May be there is no access to outside.
• May be outside is in a different network from the local.
• May be permission is denied for that system to access outside.
• If there is access, but router or modem or network switch or NIC may not be working to access the outside.

Permission check and disk space getting full

The ping command is used to determine connectivity between hosts on a network

$ ping google.com

Crontab –l –u rbtadmin

/boot/grub/grub.cong

.so

# ifconfig

There are Three types of class

• class A 1-126
• class B 128-191
• class c 192-221

:wq

# systemctl restart network

# useradd  linux

# passwd linux

# su linux

# cat /etc/passwd

# groupadd my group

# cat /etc/my group

#useradd  -d/root/abi abhi

The date command displays/sets the system date and time like this.

$ date

$ date –set=”8 JUN 2017 13:00:00”

It reflects the status of previous command

1. If 0 – Success
2. If Non-Zero – Not Success

It considers the script as a PHP script

YES

getenforce

Two ways

• echo “‘hi’”

1. echo \’hi\’

It’s the average of the usage of each CPU

It can be found with 4 commands

1. w
2. uptime

• top
• cat /proc/loadavg

pstree -pua

ps ax –forest

This command is the task manager of linux. We could able to find load average, memory usage, swap usage, total number of processes, CPU, Memory usage of each processes in sorted format.

It is shortcut of a big command, we can do this using the command ‘ln’

Eg: ln -s /usr/local/redis/bin/redis-cli /usr/bin/redis-cli

We can directly use the command redis-cli

All process identification is stored in this folder

• It will list all process id as folders /proc/12435
• It will show the command used by the process
• It will show the files used by the process
• Memory dump etc

Use ‘grep’ command

Eg: cat /proc/meminfo  | grep MemFree

Use command

who -Hu

Find it using ‘tty’ command or who command

Fix it by adding atleast the system binary path, so that basic command

export PATH=/sbin:/usr/bin:/usr/sbin

Use command

ip a

command &

semanage user -l

Edit /etc/selinux/config anf change the enforcement to disabled and reboot the server.

fdisk, parted

Yes, use LVM

LVM is a utility for dynamically extent or shrink a volume. ext3, ext4, it is not possible.

Once the above command is executed, the new volgroup will be available to use.

Then mount to a location like
mount /dev/mapper/VolGroup/pv /mnt

4

8e

rpm -qi <package>

It gives the package in which the provided binary associated.

ntpd -q

Firewall-cmd –list-ports

(firewall-cmd –zone external –permanent –add-forward-port port=25:proto=tcp:toaddr=10.10.1.80)

It will forward the inward traffic of SMTP to the IP mentioned.

kadmin, ktadd, authconfig, kinit

• Open /etc/rsyslog.conf and add the following line.
• *.* @@IP:514
• systemctl restart rsyslog

DocumentRoot

It defines the file to be considered as index file. Eg ‘DirectoryIndex index.php index.html’ : In this it will find index.php first when the URL is accessed, if this file is not available, it will search for index.html as index page.

• Passwd is used for setting the password for a System User.
• Htpasswd is used for setting the password for Apache Web User.

• For web files, httpd_sys_content_t is used
• For NFS mount files, httpd_use_nfs

apachectl

• apachectl -t : Checks Syntax
• apachectl start/stop/restart : For handling service

Use command : httpd -D DUMP_VHOSTS

Execute command : postconf -e inet_interfaces=all

Use : alternatives –config mta (mta is mail transfer agent)

Its is Pointer Record for reverse lookup : Inorder to get hostname if IP is queried.

• named-checkzone
• named-checkconf

dig @8.8.8.8 domainname

dig -x IP-Address

Use command : mysqldump -hHOST -uUSER -pPASSWORD DB_NAME > DB_NAME.sql

mysql -hHOST -uUSER -pPASSWORD DB_NAME < DB_NAME.sql (Create DB prior using ‘create database db_name’)

Use Init command : init 6 (6 option is for reboot in Linux Runlevels)

setgid

chmod g+s /usr/bin/wall

A.Both b and c

B.Parent directory

C.Sub directory

D None of above”]

A.Both b and c

A.cd /root

B.cd ..

C.cd /boot

D.cd /”]

B.cd ..

They are

A.pushd

B.Popd

C .both

D.none

C .both

A.Touch -t 201812190820 file

B.touch -t yyyymmddhrmin file

C.touch file

D.none”]

B.touch -t yyyymmddhrmin file

A.Rm -i

B.Rm -rf

C.Rm

D.none of above”]

A.Rm -i

A.cp -p

B.cp  -s

C.cp -d

D.none of above”]

A.cp -p

A.cat file reverse

B.concate file

C.tac file

D.none”]

C.tac file

A./

B./root

C./srv

D./proc”]

C./srv

A.ctrld

B.exit

C.logout

D.all of above”]

D.all of above

A.Ls – -color

B.Ugoa rwx

C.421 rwx

D.Chmod u=rwx,g+x file name.”]

A.Ls – -color

A.5

B 101

C.401

D.1001″]

B. 101

A.find /dirpath -mtime 15-20

B.find /dirpath -mtime +15 -mtime -20

C.find /dirpath |grep mtime 15-20

D.all”]

B.find /dirpath -mtime +15 -mtime -20

A.cat

B.more/less

C. head/tail

D.all”]

D.all

A.dfgp

B.hjkl

C.rpmn

D.none”]

B.hjkl

A.none

B.vimdiff

C.sdiff

D.all”]

D.all

A.-i

B. -c

C.-v

D..none of above.”]

B. -c

A.2>&1

B.2>

C. 1&2>

D.None”]

A.2>&1

Job in Monday will be”]

A.0

B.2

C.6

D.1″]

D.1

A.Setup user login environment similar as that of direct user

B.we need to use because it’s the only format to use su cmd

C.none of above

D.both a &b”]

A.Setup user login environment similar as that of direct user

A./Dev/null

B./Dev/tty

C./sbin

D./Mnt”]

B./Dev/tty

A.0

B.1-499

C.500 to 65534

D.only root user have uid’s”]

B.1-499

A.Hard link

B.Source file cannot be delated

C.Soft link

D.Destination file is independent of source file”]

A.Hard link

A.ext3

B.ext2

C.nfs

D.a&b”]

C.nfs

A.Master and superblock

B.Data and inode block

C.Both a&b

D.None

C.Both a&b

A.-d

B.-dv

C.-q

D.-ev”]

D.-ev

A .ture

B.False”]

A .ture

A .free -ram

B.free -m

C.none

D.both”]

B.free -m

A./etc/config

B./etc/sudoers

C./etc/proc

D./etc/visudo”]

B./etc/sudoers

A.Passed user

B.Passwd -x 99999 user

C.Psswwd -e user

D.None”]

B.Passwd -x 99999 user

A.scp filename user@server:/destination

B.winscp filename user@server:/destination

C.cp -v filename user@server:/destination

D.None”]

A.scp filename user@server:/destination

A.resize2fs ext

B.mkfs ext

C.pvcreate ext

D.lvcreate ext”]

B.mkfs ext

A./Var/log/messages

B./var/log/secure

C./var/log/auth.log

D./var/log/dmseg”]

C./var/log/auth.log

A.reboot

B.init 6

C.init 0

D.Both a&b”]

D.Both a&b

A./etc/config

B..ssh

C.ssh

D./etc/security”]

B..ssh

A.sed

B.pipe

C.export

D.cat”]

C.export

A.crontab

B.at cmd

C.both a and b

D.sudoers file”]

C.both a and b

A.time

B.server time

C.uptime

D.reboot time”]

C.uptime

chattr +i filename

A.Ifconfig

B.traceroute

C.netstat -m

D.all”]

D.all

A.nice

B.ps

C.renice

D.all of above”]

C.renice

A.top

B.ps

C.vmstat

D.only a b

E.all”]

E.all

A.fuser

B.vmstat

C.chroot

D.all”]

D.all

A.bootloader

B.Master boot record

C.Kernel

D.None of them.”]

B.Master boot record

A./etc/crontab

B./etc/config

C./etc/fstab

D.None”]

C./etc/fstab

A./Var/lib/

B./Var/lib/db/rpm

C./Var/rpm

D.Var/lib/rpm”]

D.Var/lib/rpm

A.sysctl kernal.host=Rakesh

B.sysctl kernal.hostname=Rakesh

C.both b and a”]

D.None

B.sysctl kernal.hostname=Rakesh

A.service iptables status

B.service network status

C.both of them

D.none of them.”]

A.service iptables status

A.smbpassword -a user

B.passwd user

C.sambapasswd user

D.None of them.”]

A.smbpassword -a user

A.to provide secure channel

B.no one can intercept the communication

C.authentication info are less secure.

D.a &b”]

D.a &b

A.subscription-manager –remove –serial=serial number

B.subscription-manager remove –serialnumber

C.subscription-manager remove –serial=serial number

D.none”]

C.subscription-manager remove –serial=serial number

• Ls –s <souce > <target>
• Ls <source> <target>

It will give 9 fileds file type, dir/file, file permissions, file owner, file group, file size, file access time, file name

By using lsof

Using ftp, sftp

Find . –type  f -size +100M

Grep –c “pattern” <fle_name?

Kill -9 , Kill -9 and kill -15 difference

Using sed

Sed –n 90 filename

SCP command stands for secure copy. It is used to copy/download data from one machine to another machine.

the telnet command is used to check the connectivity to other servers. It helps you to check whether you are able to talk to another server or now. Ex: telnet 192.0.0.1 22 where 22 is the port number.

A bastion host is also known as jump server. It is used to connect from one machine to another machine securely. Bastion hosts are used to connecting to private servers securely.

Some of the common text editors that are available in Linux are vi/vim, nano, subl, gedit, atom, emacs. Vi is the default editor that you have in Linux machines.

The different zip formats in Linux are zip, gzip and bzip.

cp command stands for copy and is used to copy data from one location to another. mv stands for the move and is used to move data from one location to another.

You can run a process in the background by pressing ctrl+z command.

chown stands for ‘change ownership’ and is used to change the ownership of a file or directory. Eg: chown username.username <filename>.

• A server is a tool which does the activity like storing, load balancing, running the application process ( Mobile/laptop which has more memory)
• whatever if accessible in the network, we may name that as differently, But all are servers only. Exam: routers, LDAP, switch, etc

• OS is supporting between the hardware and the user request in every Application. this will do backround processes
• hardware don’t understand what the user needs

• mkdir – create the directory
• cd – to go Path for directory
• rm,rf removing the directory or files
• scp – file moving from one server to another server

• using SSH, we can connect
• we have to keep the public k
• ey of A server to B server
• then we can connect A server from B server

• RAM
• ROM
• Cache

for an application (depends on the requirement ) needs below:

• Apache
• tomcat
• Database
• Load balancer
• SSO –  Single Sign-On
• LDAP

• After finding the IP address of an Application will search with that
• for that Subnet will help on that
• In this OSI model will come

physical,Data(MAC) ,network(IP), transport(TCP/UDP), Session, Presentation, Application

while finding the destination IP Address then it will go to many topics

• Firewall
• Types of networks (Private/Public)
• Routers
• Ports, SFTP,FTP,HTTP
• Ethernet
• ISP – Internet Service Provider
• Wi-Fi

In the destination server,via Apache, tomcat the request would be analyzed and based on the request that will reply to the user

nohup would be useful to run the process when the user logged off

free -m

/etc/passwd

/etc/groups

df -h

ifconfig

/etc/hosts

ssh

root

using SUDO

ps -ef

vi

grep

top

lsblk

ln -s

rm

chmod

useradd

mkdir

cat

touch

more

reboot

yum update -y

yum install -y httpd

srvctl start http

su – <username>

/tmp

generate the ssh keys and store it in .ssh/Authorizedkeys

Yes

cat test >> output.log

logfile

>

/etc/fstab

• whoami
• <OR>
• id

chown