1 SSH CheatSheet

• PDF Link: cheatsheet-ssh-A4.pdf, Category: tools
• Blog URL: https://cheatsheet.dennyzhang.com/cheatsheet-ssh-A4
• Related posts: Tmux/Tmate Cheatsheet, #denny-cheatsheets

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1.1 SSH general

Name	Summary
ssh without input password	sshpass -p '<your-passwd>' ssh <username>@<ssh_host>, brew install sshpass
Install sshd server	apt-get install openssh, apt-get install openssh-server
Restart sshd server	service sshd restart, systemctl reload sshd.service
Run ssh command	ssh -o StrictHostKeyChecking=no -p 2702 [email protected] date
SSH with verbose ouptut	ssh -vvv -p 2702 [email protected] date 2>&1
Setup ssh tunnel for your web browsing	sshuttle -r [email protected] 30.0.0.0/16 192.168.150.0/24 -e ...
SSH passwordless login	ssh-copy-id <username>@<ssh_host>, Or manually update ~/.ssh/authorized_keys
Remove an entry from known_hosts file	ssh-keygen -f ~/.ssh/known_hosts -R github.com
Diff local file with remote one	diff local_file.txt <(ssh <username>@<ssh_host> 'cat remote_file.txt')
Diff two remote ssh files	diff <(ssh user@remote_host 'cat file1.txt') <(ssh user2@remote_host2 'cat file2.txt')
Upload with timestamps/permissions kept	scp -rp /tmp/abc/ ec2-user@<ssh-host>:/root/
SSH agent load key	exec ssh-agent bash && ssh-add /tmp/id_rsa, ssh-add
SSH list all loaded key	ssh-add -l
SSH agent create and load key	exec ssh-agent bash && ssh-keygen, ssh-add
Emacs read remote file with tramp	emacs /ssh:<username>@<ssh_host>:/path/to/file
Generate a new key pair	ssh-keygen, ssh-keygen -C "[email protected]" -t rsa
Generate key pair without interaction	ssh-keygen -t rsa -f /tmp/sshkey -N "" -q

1.2 SSH Advanced

Name	Summary
Add passphrase protection to ssh keyfile	ssh-keygen -p -f id_rsa
configure SSH to avoid trying all identity files	ssh -o IdentitiesOnly=yes -i id1.key [email protected]
Convert OpenSSL format to SSH-RSA format	ssh-keygen -f my_ssh.pub -i
Critical ssh files/folders	~/.ssh/authorized_keys, ~/.ssh/config, ~/.ssh/known_hosts
SSH config file	/etc/ssh/ssh_config, /etc/ssh/sshd_config
SSH key file permission	chmod 600 ~/.ssh/id_rsa
SSH folder permission	chmod 700 ~/.ssh, chown -R $USER:$USER ~/.ssh
Authorized_keys file permission	chmod 644 ~/.ssh/authorized_keys
Mute Warning: Permanently added	ssh -o LogLevel=error

1.3 SSH tunnel & ssh proxy

Name	Summary
SSH port forward to a local port	ssh -N -i <ssh-keyfile> -f [email protected] -L *:18085:localhost:8085 -n /bin/bash
Reverse port forward to remote server	ssh -R *:40099:localhost:22 [email protected], ssh -p 40099 [email protected]
Setup ssh tunnel for your web browsing	sshuttle -r [email protected] 30.0.0.0/16 192.168.111.0/24 192.168.150.0/24 192.167.0.0/24

1.4 SSH security

Name	Summary
Disable ssh by password	sed -i 's/PasswordAuthentication yes/PasswordAuthentication no/g' /etc/ssh/sshd_config
Disable root login	sed -i 's/^PermitRootLogin yes/#PermitRootLogin yes/' /etc/ssh/sshd_config
Enable/Disable SSH Host Key Checking	StrictHostKeyChecking yes change ~/.ssh/config
Protect SSH server from brute force attacks	fail2ban command line tool

1.5 SCP

Name	Summary
Download a remote folder	scp -r ec2-user@<ssh-host>:/home/letsencrypt-20180825 ./
Upload a file	scp -i <ssh-keyfile> /tmp/hosts ec2-user@<ssh-host>:/root/
Upload a folder	scp -r /tmp/abc/ ec2-user@<ssh-host>:/root/
Upload with timestamps/permissions kept	scp -rp /tmp/abc/ ec2-user@<ssh-host>:/root/
Mount remote directory as local folder	sshfs name@server:/path/remote_folder /path/local_folder

1.6 Parse ssh log file

Name	Command
Events of ssh down	grep -R "ssh.*Received signal 15" /var/log/auth.log
Events of ssh up	grep -R "sshd.*Server listening" /var/log/auth.log
Events of ssh failed login	grep -R "sshd.*Failed password for invalid user" /var/log/auth.log
Events of ssh break-in attemp	grep -R "sshd.*POSSIBLE BREAK-IN ATTEMPT!" /var/log/auth.log
Events of ssh port scap	grep -R "sshd.*Bad protocol version identification" /var/log/auth.log
Events of ssh login by public key	grep -R "sshd.*Accepted publickey for" /var/log/auth.log
Events of ssh login by password	grep -R "sshd.*Accepted password for" /var/log/auth.log
Events of ssh logout event	grep -R "sshd.*pam_unix(sshd:session): session closed for" /var/log/auth.log

1.7 SSH tools

Name	Summary
Export local env to Internet	ngrok.com
Reverse ssh proxy	sshuttle
SSH by auto input password	sshpass sshpass -p “$PASSWORD” ssh -o StrictHostKeyChecking=no $username@$ssh_ip=

1.8 Scripts

• Inject local key to remote ssh server server

cat ~/.ssh/id_rsa.pub | ssh $username@$ssh_hostk "cat - >> ~/.ssh/authorized_keys"

ssh $username@$ssh_hostk "cat ~/.ssh/authorized_keys"

• SSH Config file

Host sandbox
     HostName 192.168.50.10
     StrictHostKeyChecking no
     User root

Host 192.168.1.*
   StrictHostKeyChecking no
   Port 32882
   UserKnownHostsFile=/dev/null
   IdentityFile ~/.ssh/id_rsa

• Use expect to run ssh command with credential auto input

#!/usr/bin/expect
set timeout 20
set command "cat /etc/hosts"
set user "vagrant"
set password "vagrant"
set ip "192.168.50.10"
spawn ssh -o stricthostkeychecking=no $user@$ip "$command"
expect "*password:*"
send "$password\r"
expect eof;

• ssh reverse tunnel

# https://www.howtoforge.com/reverse-ssh-tunneling

autossh -M 40000 -p 2702 -i /home/denny/al -fN \
    -o "PubkeyAuthentication=yes" \
    -o "StrictHostKeyChecking=false" -o "PasswordAuthentication=no" \
    -o "ServerAliveInterval 60" -o "ServerAliveCountMax 3" \
    -R 123.57.240.189:29995:localhost:22 [email protected]

1.9 More Resources

License: Code is licensed under MIT License.

https://neverendingsecurity.wordpress.com/2015/04/07/ssh-cheatsheet/

http://patrickward.com/cheatsheets/2015/02/16/ssh-cheatsheet/

https://bitrot.sh/cheatsheet/13-12-2017-ssh-cheatsheet/

https://gist.github.com/CodyKochmann/166833b3b31cdb936d69

http://pentestmonkey.net/cheat-sheet/ssh-cheat-sheet

https://www.thegeekstuff.com/2008/11/3-steps-to-perform-ssh-login-without-password-using-ssh-keygen-ssh-copy-id