Q:1 What is the
default port & configuration file of SSH Server ?
Ans: 22 is
default port for ssh and ‘/etc/ssh/sshd_config’ is the configuration
file.
Q:2 How to
change the default ssh port in linux ?
Ans: To change
the port , first edit the file ‘ /etc/ssh/sshd_config ‘ , change the vaule of parameter ‘ port 22 ‘, now restart
the ssh service.
Q:3 What is the
configuration file of ssh client ?
Ans: ‘
/etc/ssh/ssh_config ‘ is configuration file for ssh client.
Q:4 What is SSH
port forwarding ?
Ans: SSH Port
Forwarding, sometimes called SSH Tunneling, which allows you to establish a
secure SSH session and then tunnel arbitrary TCP connections through it.
Tunnels can be created at any time, with almost no effort and no programming.
Syntax : ssh -L
localport:host:hostport user@ssh_server -N
where:
-L – port
forwarding parameters
localport –
local port (chose a port that is not in use by other service)
host – server
that has the port (hostport) that you want to forward
hostport –
remote port
-N – do not
execute a remote command, (you will not have the shell, see below)
user – user that
have ssh access to the ssh server (computer)
ssh_server – the
ssh server that will be used for forwarding/tunneling
Without the -N
option you will have not only the forwarding port but also the remote shell.
Q:5 How to
disable the root login in linux server ?
Ans: Open the
file ‘ /etc/ssh/sshd_config ‘ and chnage the paramenter ‘PermitRootLogin yes’
to ‘PermitRootLogin no’ & restart the ssh service.
Q:6 How to allow
only specific users to ssh your linux server ?
Ans: Open the
file ‘/etc/ssh/sshd_config’ and add the parameter ‘AllowUsers user1 user2′
& then restart the ssh server.
Q:7 How to
enable debugging in ssh command ?
Ans: To enable
debugging in ssh command use ‘-v’ option like ‘ssh root@www.linuxtechi.com -v’.
To increase the debugging level just increase the number of v’s.
Q:8 What is the
difference between ssh & Telnet ?
Ans: In ssh
communication between client & server is encrypted but in telnet
communication between the client & server is in plain text . We can also
say SSH uses a public key for authentication while Telnet does not use any
authentication.SSH adds a bit more overhead to the bandwidth compared to
Telnet.Default port of ssh is 22 and for telnet 23.
Q:9 What is use
of sshpass command in linux ?
Ans: sshpass is
a command which allows us to automatically supply password to the command
prompt so that automated scripts can be run as desired by users. sshpass
supplies password to ssh prompt using a dedicated tty , fooling ssh to believe
that a interactive user is supplying password.
Q:10 What is the
use of scp command ?
Ans: SCP stands
for Secure Copy ,it copies files between hosts over a network.
It uses ssh for data transfer &
uses the same authentication and provides the same security as ssh.
Unlike rcp, scp will ask for passwords or passphrases if they are needed for
authentication.
Q:11 What is the
use of blowfish options in scp command ?
Ans: Using
blowfish options in scp command , we can increase the speed, by default scp
uses the Triple-DES cipher to encrypt the data being copied.
Example : scp -c
blowfish /home/itstuff.txt root@mail.linuxtechi.com:/opt/
Q:12 How to
limit the bandwidth used by scp command ?
Ans: We can
limit the bandwidth used by the scp command using the -l option as shown in the
syntax.’#scp -l bandwidth_limit filename username@remote-host:/folder-name’ ,
where bandwidth_limit is numeric to be specified in kilobits per second.
Q:13 How to
enable passwordless ssh authentication in Linux ?
Ans: To
Implement passwordless or Keys based authentication we have to generate Public
and Private keys , Copy the Pubic keys to remote Linux servers either manually
or by ssh-copy-id command.ssh-copy-id command will automatically copy the
contents of id_rsa.pub file to ‘~/.ssh/authorized_keys’ file of remote linux
server.
Q:14 How to
check SSH server’s Version ?
Ans: Using the
command ‘ ssh -V ‘ we can find the ssh server’s version.
Q:15 How to Copy
the file “server.txt” from the local machine to a remote host using port 2751
in /opt folder.
Ans: scp -P 2751 /home/server.txt
root@mail.linuxtechi.com:/opt
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