SSH Cheat Sheet

This page designed to help beginners starting out with SSH by providing a usable “SSH cheat sheet” full of common commands.

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 root@172.17.0.8 date
SSH with verbose ouptut	ssh -vvv -p 2702 root@45.33.87.74 date 2>&1
Setup ssh tunnel for your web browsing	sshuttle -r kubo@10.92.21.17 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

1.2 SSH tunnel & ssh proxy

Name	Summary
SSH port forward to a local port	ssh -N -i <ssh-keyfile> -f root@54.179.178.214 -L *:18085:localhost:8085 -n /bin/bash
Reverse port forward to remote server	ssh -R *:40099:localhost:22 root@54.179.178.214, ssh -p 40099 root@54.179.178.214
Setup ssh tunnel for your web browsing	sshuttle -r kubo@10.92.21.17 30.0.0.0/16 192.168.111.0/24 192.168.150.0/24 192.167.0.0/24

1.3 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

1.4 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 SSH files

Name	Summary
Generate a new key pair	ssh-keygen, ssh-keygen -C "your_email@example.com" -t rsa
Generate key pair without interaction	ssh-keygen -t rsa -f /tmp/sshkey -N "" -q
Add passphrase protection to ssh keyfile	ssh-keygen -p -f id_rsa
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

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 root@123.57.240.189