If I do not install openssh when creating an ubuntu server, can someone still SSH into the server?
Solution 1:
Background:
-
OpenSSH is the premier connectivity tool for remote login with the SSH protocol, It encrypts all traffic to eliminate eavesdropping.
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The OpenSSH server component, sshd (ssh deamon), listens continuously for client connections from any of the client tools.
To your specific question:
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As far as i know and read on official ubuntu site https://ubuntu.com/server/docs/service-openssh sshd does not comes by default on ubuntu server.
-
To be sure that you do not have sshd installed, you can run this command
which sshd
. -
Furthemore you can check the default file of the
sshd
configuration/etc/ssh/sshd_config
which should not be found. -
You can also make sure that your server is not listening to
ssh
port by run the commandnetstat -tulpn4
.- note that the default port for
sshd
service is 22. - to be able to execute
netstat
command you have to installnet-tools
which can be installed bysudo apt install net-tools
- the output of executing
netstat -tulpn4
will be by this format:
- note that the default port for
(Not all processes could be identified, non-owned process info
will not be shown, you would have to be root to see it all.)
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 127.0.0.53:53 0.0.0.0:* LISTEN -
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN -
tcp 0 0 0.0.0.0:1122 0.0.0.0:* LISTEN -
tcp 0 0 0.0.0.0:3333 0.0.0.0:* LISTEN -
udp 0 0 127.0.0.53:53 0.0.0.0:* -
-
To avoid ssh access to your server you can:
-
not install sshd in the first place.
-
install and disable the sshd service by this command
systemctl disable sshd.service
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In Addition:
-
There are few more services that`s enabling shell connection to a server:
-
dropbear
- lightweight SSH server. -
telnet
- user interface to the TELNET protocol, The telnet command is used for interactive communication with another host using the TELNET protocol. - if you wanna make sure that your server is safe from any type of connection it is recommended to check that those services are disabled or uninstalled.
- Note that a configuration solution can also be found to secure the server.
- Finally, it is recommended to use the
netstat
tool and examine all the open ports on the server in order to detect security gaps and understand the server services.
-