(i) Remote administration means
administration of servers which are located in remotely.
(ii) Normally servers are placed in
datacenters like books arranged in a
rack.
(iii) These datacenters are normally located
in US, UK and Australia ... etc.,
(iv) Generally we login as normal user in
local systems and get the remote desktop or console using remote desktop tools like putty, VNC
server, ... etc.,
(v) If it is through remote desktop, we
can manage the servers using the GUI tools.
(vi) If it is
through putty, we can manage the serves using command line interface only. In
both ways we should give
server name or IP address, port no., user name and password.
2. What is SSH and explain it?
SSH is stands for
Secure Shell. It was designed and created to provide the best security
when accessing another computer remotely. Not only does it encrypt the session,
it also provides better authentication facilities.
On windows
systems install the putty software and through putty we can access the remote
system by configuring ssh.
SSh is protocol
which facilitates secured communication between two systems using Client-Server
architecture and allows users to login to the server host systems
remotely.
It is used to
connect to remote system and perform administrative task or jobs. By
default ssh takes password
authentication mechanism and its port no. is
22. Through ssh the data will be transferred in encrypted format.
3. What is telnet?
Telnet is a
mechanism to connect and to administrate the remote system from local system.
This is the oldest program which is available on most network capable operating
systems. Accessing a remote shell account through the telnet method is danger
because in that everything that you send or receive over that telnet session is
visible in plain text on your local network
and the local network of the machine you are connecting to.
So, anyone
can sniff the connection in-between can see our user
name, password, email and other messages that we read and command that we run.
For these reasons we need a more sophisticated program than telnet to connect
to a remote host.
4. What are the differences between Telnet and
SSH?
Telnet
SSH
(a) Through telnet we can connect the remote
system, but any network
hacker may see the
transferred data. And the
telnet port no. is 23.
(a) Through ssh also we can connect the remote
system, but nobody can
see the transferred data.
And the ssh port no.
is 22.
(b) Data will be transferred in non-encrypted format.
(b) Data will be transferred in encrypted format.
(c) We cannot trust this telnet connection.
(c) We can trust this ssh
connection.
(d) We cannot give the trusting in telnet.
(d) We can give the trusting in ssh.
(e) By snooping or sniffing technologies we can see
the data like system or
hostname, login name,
password and other data.
So, there is no
security.
(e) By snooping or sniffing technologies we cannot
see the data like system name or hostname, login
name, password and other data.
So, there is a security
(f) # telnet
(provide login name
and password)
(f) # ssh
(provide login name
and password)
5. In how many ways we can connect the
remote host through ssh?
Through ssh we can connect the remote host by two
methods.
(i) Command Line Interface (CLI).
Example
: # ssh (provide login name and password)
(ii) Graphical User Interface (GUI).
Example
: open VNS server window and provide
remote hostname, login name and password.
6. What are the requirements for ssh?
(i) Remote systems IP address.
(ii) Remote systems user name and password
(iii) A proper
network ie., our local and remote systems should be in the same network.
(iv) Open ssh
package to configure the ssh.
7. In how many ways we can connect the
remote system?
(i) telnet (ii) ssh
(iii) rlogin (iv)
rcp
(v) ftp (vi)
scp
(vii) sftp (viii)
tftp
8. What is the syntax for ssh?
# ssh -l
# ssh @
# ssh @
* After executing any of the above commands,
it may asks user name and password. Then type user name and
passwords to
connect the remote systems.
9. How to configure the ssh with
keybased authentication or explain the
ssh trusting?
(i) SSH
keybased authentication is used to access the remote system without
asking any passwords.
(ii) For that, first we have to generate
the public and private keys by executing
# ssh-keygen command on our system. Then the public and private keys are
generated in /home//.ssh location. ie., .ssh directory
in users home directory. And the keys are
id_rsa (private key) and id_rsa.pub (public key).
(iii) Then copy
the public key id_rsa.pub on the remote
system by executing the below command.
# ssh-copy-id -i
@
(iv) Go to remote system and check whether
the above key is copied or not by # cat
/home//.ssh/authorized_keys file.
And the private key should be in our system.
(v) Whenever we are trying to establish a
connection the public key on remote system should be matched with the private key on our system. otherwise
there is no connection is established.
(vi) If both
public and private keys are matched then connection will be established and
first time it will ask the password.
Once the connection is established, next time onwards it won't ask any
passwords.
# ssh
@ (first time it will asks the password)
(vii) The
authentication is done through the public and private keys, so this type of
authentication is called keybased
authentication.
10. How to prevent the remote login root user
or how to configure the ssh to
prevent the remote login for root?
(i) The location of the ssh
configuration file is /etc/ssh/sshd_config
(ii) Open the configuration file by #
vim /etc/ssh/sshd_config
-----> go to line no. 42
(in RHEL - 6) or
----->
go to line no. 48
(in RHEL - 7) PermitRootLogin yes
and uncomment that line and type as
" no " in place of " yes " andsave and exit this file.
(iii) Then
restart the or reload the sshd deamon by
# service
sshd restart (to
restart the sshd deamon or service in
RHEL - 6)
# systemctl restart sshd (to
restart the sshd deamon or service in RHEL - 7)
#
chkconfig sshd on (to
enable the sshd deamon at next reboot in RHEL - 6)
# systemctl
enable sshd (to
enable the sshd deamon at next reboot in RHEL - 7)
# service
sshd reload (to
reload the sshd deamon in RHEL - 6)
# systemctl
reload sshd (to reload
the sshd deamon in RHEL - 7)
(iv) Then no root user cannot access our
system remotely through ssh service.
11. How to allow the remote users to run
GUI commands through ssh?
(i) Open ssh configuration file by #
vim /etc/ssh/sshd_config
-----> go to line no. 109 in RHEL - 6 or
-----> go to line no. 117 in RHEL - 7 X11 Forwarding no
type as " yes
" in place of " no
" then save and exit this file.
* If it is
yes, then GUI commands can be
executed on the remote system.
* If it is no,
then GUI commands cannot be executed on the remote system.
(ii) Then restart the sshd service or
deamon to effect the above modification by
# service
sshd restart (to
restart the sshd deamon or service in
RHEL - 6)
# systemctl restart sshd (to
restart the sshd deamon or service in RHEL - 7)
# chkconfig sshd
on (to
enable the sshd deamon at next reboot in RHEL - 6)
# systemctl
enable sshd (to
enable the sshd deamon at next reboot in RHEL - 7)
# service
sshd reload (to
reload the sshd deamon in RHEL - 6)
# systemctl
reload sshd (to reload
the sshd deamon in RHEL - 7)
(iii) # gedit (to
open the gedit editor on remotely)
12. How to allow empty password through
ssh?
(i) Open the ssh configuration file
by #
vim /etc/ssh/sshd_config
-----> go to line no. 65 in RHEL - 6 or
----->
go to line no. 77 in RHEL - 7 PermitEmptyPassword no
type as " yes
" in place of "
no " then save and exit this
file.
* If it is
yes, then the remote system will
be allow the users with empty password ie., without password.
* If it is
no, then the remote system will
not be allow the users with empty passwords.
(ii) Then restart the sshd service or
deamon to effect the above modifications by
# service
sshd restart (to
restart the sshd deamon or service in
RHEL - 6)
# systemctl restart sshd (to
restart the sshd deamon or service in RHEL - 7)
# chkconfig sshd
on (to
enable the sshd deamon at next reboot in RHEL - 6)
# systemctl
enable sshd (to
enable the sshd deamon at next reboot in RHEL - 7)
# service
sshd reload (to
reload the sshd deamon in RHEL - 6)
# systemctl
reload sshd (to reload
the sshd deamon in RHEL - 7)
(iii) Now, the
users who are having empty passwords are also access the remote systems through
ssh.
13. How to prevent the password
authentication mechanism in ssh?
(i) Open the ssh configuration file
by #
vim /etc/ssh/sshd_config
-----> go to line no. 66 in RHEL - 6 or
-----> go to line no. 78 in RHEL - 7 PasswordAuthentication no
type as
" no " in place of "
yes " then save and exit this
file.
* If it is
yes, then the remote system will
ask the password.
* If it is
no, then the remote system will
not ask any type of passwords.
(ii) Then restart the sshd service or
deamon to effect the above modifications by
# service
sshd restart (to
restart the sshd deamon or service in
RHEL - 6)
# systemctl restart sshd (to
restart the sshd deamon or service in RHEL - 7)
# chkconfig sshd
on (to
enable the sshd deamon at next reboot in RHEL - 6)
# systemctl
enable sshd (to
enable the sshd deamon at next reboot in RHEL - 7)
# service
sshd reload (to
reload the sshd deamon in RHEL - 6)
# systemctl
reload sshd (to reload
the sshd deamon in RHEL - 7)
(iii) Now, we can
access the remote systems through ssh without Password Authentication
mechanism.
14. How to allow or
deny the uses or group to access the remote systems through ssh?
(i) If we want to allow or
deny the particular users then go to last line of the ssh configuration
file and type as
DenyUsers ...etc., (these users will be denied the ssh service)
AllowUsers ...etc., (these
users will be allowed the ssh service)
DenyGroup ...etc., (these group users will be denied the ssh
service)
AllowGroup ...etc., (these group users will be allowed the ssh
service)
(ii) Then restart the sshd service or
deamon to effect the above modifications by
# service
sshd restart (to
restart the sshd deamon or service in
RHEL - 6)
# systemctl restart sshd (to
restart the sshd deamon or service in RHEL - 7)
# chkconfig sshd
on (to
enable the sshd deamon at next reboot in RHEL - 6)
# systemctl
enable sshd (to
enable the sshd deamon at next reboot in RHEL - 7)
# service
sshd reload (to
reload the sshd deamon in RHEL - 6)
# systemctl
reload sshd (to reload
the sshd deamon in RHEL - 7)
15. How allow the specified no. of users
to access remote system at a time?
(i) Open the ssh configuration file
by #
vim /etc/ssh/sshd_config then go to
MaxAuthTries line and type as,
MaxAuthTries (type
any numeric value equal to Max. users to allowat a time in place of
, then save and exit this file)
(ii) Then restart the sshd service or
deamon to effect the above modifications by
# service
sshd restart (to
restart the sshd deamon or service in
RHEL - 6)
# systemctl restart sshd (to
restart the sshd deamon or service in RHEL - 7)
# chkconfig sshd
on (to
enable the sshd deamon at next reboot in RHEL - 6)
# systemctl
enable sshd (to
enable the sshd deamon at next reboot in RHEL - 7)
# service
sshd reload (to
reload the sshd deamon in RHEL - 6)
# systemctl
reload sshd (to reload
the sshd deamon in RHEL - 7)
16. How to allow or
deny the hosts or networks to use the ssh?
To deny IP addresses or
hostnames :
(i) Open
/etc/hosts.denyfile by #
vim /etc/hosts.deny and go to last line and type as,
sshd: >><IP address 3> ...etc., (to deny
IP 1, IP 2, IP 3, ...etc.,)
sshd: >><hostname 3> ...etc.,
sshd: *.example.com *.my133t.org ...etc., (to deny
all the hosts from these domains)
sshd: 192.168.0. 172.25.0.
...etc., (to deny
192.168.0 and 172.25.0
networks)
sshd:ALL
Except (to deny all the hosts
or IP addresses except the specified one in that network) and save & exit the file.
(ii) Then restart the sshd service or
deamon to effect the above modifications by
# service
sshd restart (to
restart the sshd deamon or service in
RHEL - 6)
# systemctl restart sshd (to
restart the sshd deamon or service in RHEL - 7)
# chkconfig sshd
on (to
enable the sshd deamon at next reboot in RHEL - 6)
# systemctl
enable sshd (to
enable the sshd deamon at next reboot in RHEL - 7)
# service
sshd reload (to
reload the sshd deamon in RHEL - 6)
# systemctl
reload sshd (to reload
the sshd deamon in RHEL - 7)
To allow IP addresses or
hostnames :
(i) Open
/etc/hosts.allow file
by # vim /etc/hosts.allow and go to last line and type as,
sshd: >><IP address 3> ...etc., (to allow
IP 1, IP 2, IP 3, ...etc.,)
sshd: >><hostname 3> ...etc.,
sshd: *.example.com *.my133t.org
...etc., (to allow all the hosts from
these domains)
sshd: 192.168.0. 172.25.0.
...etc., (to allow 192.168.0 and
172.25.0 networks)
sshd:ALL
Except (to allow all the hosts
or IP addresses except the specified one in that network) and save & exit the file.
(ii) Then restart the sshd service or
deamon to effect the above modifications by
# service
sshd restart (to
restart the sshd deamon or service in
RHEL - 6)
# systemctl restart sshd (to
restart the sshd deamon or service in RHEL - 7)
# chkconfig sshd
on (to
enable the sshd deamon at next reboot in RHEL - 6)
# systemctl
enable sshd (to
enable the sshd deamon at next reboot in RHEL - 7)
# service
sshd reload (to
reload the sshd deamon in RHEL - 6)
# systemctl
reload sshd (to reload
the sshd deamon in RHEL - 7)
17. How to check whether the ssh is
running or not on remote host?
# nmap -p
22 (to see the ssh is
running or not on remote system)
18. How to troubleshoot if the client has
complain that I am not accessing the server using ssh?
(i) First check the pinging of the
client system. If it is not pinging then check the IP address of the client
system. If client system and sever system
are in different domains or networks it will not ping. So, bring the client system into the network of the
server system. Check the network is working or not and also check whether the network cable is connected or not.
(ii) If both systems are pinging then
check whether the openssh package is
installed or not. If not installed then
install that package and configure ssh on the client system and restart the
sshd deamon.
(iii) Check the
client in /etc/hosts.deny files. If there is an entry of the client system in this file, then remove that entry
and restart the sshd deamon.
(iv) Finally open
the ssh configuration file by #
vim /etc/ssh/sshd_config and
see any client user name is present
or not and check other lines for client entries in this file, if present remove
those entries, save that file and
restart the sshd service.
(v) Finally check whether the client user
is there in the server or not, if not create the client user, assign the password share those details to
client. If user is there then check whether the client user's password is locked,
account expired and any other or not, if locked then remove the lock, if client
account is expired then activate
that account, assign the password and make the ssh trusting between client and
server systems.
19. How to copy the file from our system
to remote system?
# scp :
Example : ssh
/root/script1 192.168.1.1:/root/script1
(to copy /root/script1 file into 192.168.1.1 system)
* scp
means secured copy to copy the files or directories from local system to remote
system.
20. What is rsync and explain it?
rsync
is a very good program for backing up
or mirroring a directory tree of
files from one machine to another machine and for keeping the two machines " in
sync ". It is designed to speedup file transfer by coping the
differences between two files rather than coping an entire file every time.
If rsync is combined with ssh, it makes a great utility
to sync the data securely otherwise by sniffing any one can see our data ie.,
no security for our data.
21. A system is able to ping locally but not out site. Why?
(i) May be there is no access to outside.
(ii) May be outside is in different
network from the local.
(iii) May be permission is denied for that
system to access outside.
(iv) If there is access, but router or
modem or network switch or NIC may not be working to access the outside.
(v) May be outside is not available
temporarily.
22. A system is echoing the ping, but not
able to login via telnet. Why?
(i) Check telnet service is started or
not. If not started, start the telnet service.
(ii) May be telnet service is disabled, if
so, enable the telnet service.
(iii) May be telnet port is blocked, if so,
release that port no.
(iv) May be
telnet permission is denied, if so, change the permissions to allow the telnet
service.
(v) Check all the files whether the
telnet service is blocked or not, if blocked remove those entries.
23. How will you login or
start the system in what mode if you don't know the root password?
(i) If the user having sudo permissions,
then login as sudo user.
(ii) If no sudo permissions then boot with
CDROM in single user mode and start the system. Then provide the root password to root user if there is no
root password.
(iii) Even
though if it is not possible then
finally break the root password.
Other useful commands :
# telnet (to
connect the specified remote system through telnet)
# ssh (to
connect the specified remote system through ssh)
Username : xxxxxx
Password
: xxxxxxx
# ssh -l
(to
connect the remote system using user name)
Password
: xxxxxxx
# ssh 192.168.1.1
-l root (to
connect this remote system as root user)
# ssh root@192.168.1.1 (to connect this
remote system as root user)
# ssh root@server1.example.com (to connect
the server1 system in example.com domain)
# w (to
see all the users who are login to our system)
# w -f (to
see all the users who are login to our system with other details)
# ssh (if we not specified the user name, then it will ask the
current users password and search the current account in remote
system)
# cat /root/.ssh/known_hosts
(to see the ssh trusting remote hosts finger print information)
# ssh root@192.168.1.1 (to run a command on remote host
without login to that system)
# ssh root@192.168.1.1 -X (to
run GUI commands on the remote system because by default the ssh is configured
as command line interface, X is capital)
# lastb (to
see the login failed tries)
# last -x |grep
shutdown (to
see the date & time of the system's last shutdown)
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