Ssh
SSH
Best security practices
- The Best Ways to Secure Your SSH Server
- OpenSSH Security Hardening Guide for Linux
- 3 ways I configure SSH for privacy Change the default port, No more passwords, Decide who can log in.
- Top 20 OpenSSH Server Best Security Practices
- Use SSH public key based login
- Disable root user login
- Disable password based login
- Limit Users’ ssh access
- Disable Empty Passwords
- Use strong passwords and passphrase for ssh users/keys
- Firewall SSH TCP port # 22
- Change SSH Port and limit IP binding
- Use TCP wrappers (optional)
- Thwart SSH crackers/brute force attacks such as using fail2ban and DenyHosts software
- Rate-limit incoming traffic at TCP port # 22 (optional)
- Use port knocking (optional)
- Configure idle log out timeout interval
- Enable a warning banner for ssh users
- Disable .rhosts files (verification)
- Disable host-based authentication (verification)
- Patch OpenSSH and operating systems
- Chroot OpenSSH (Lock down users to their home directories)
- Disable OpenSSH server on client computer
- Bonus tips from Mozilla
Install OpenSSL
How to Install the latest OpenSSL version from Source on Linux
Install ssh client
sudo apt install openssh-client
firewall
How to open ssh port using ufw on Ubuntu/Debian Linux
sudo ufw allow ssh # OR sudo ufw allow 22/tcp
How to limit SSH connections with ufw
How to limit SSH (TCP port 22) connections with ufw on Ubuntu Linux
Configuration file ~/.ssh/config, avoid ssh connection timeout
- https://superuser.com/questions/98562/way-to-avoid-ssh-connection-timeout-freezing-of-gnome-terminal
- https://www.cyberciti.biz/faq/create-ssh-config-file-on-linux-unix/
- How to Troubleshoot/Debug SSH Connectivity Issues ssh -xvvv ServerName
- man ssh_config
- OpenSSH Config File Examples
Put the following in your ~/.ssh/config.
Host remotehost HostName remotehost.com Port 4242 User abcd IdentityFile "~/.ssh/id_rsa" ForwardX11 yes Compression yes TCPKeepAlive yes Host github.com User YourUserName IdentityFile ~/.ssh/YourGithubSSHKey
After that we can run ssh remotehost.
To enable it for all hosts use:
Host * ServerAliveInterval 240
Also make sure to run chmod 600 ~/.ssh/config
/etc/hosts
We can put some host name /etc/hosts as a shortcut to some IP address. After that we can run something like ssh ShortCutName
Change to a different port
$ sudo nano /etc/ssh/sshd_config # looking for the line containing port $ sudo service ssh restart # tested on Ubuntu 14.04
Remember to change the Router settings.
On the client PC, use ssh USERNAME@HOSTNAME -p NEWPORT for a connection.
For security reason, use the port < 1024 (privileged ports and can only be opened by root)
- Why putting SSH on port 2222 is a bad idea
- Here is a list of TCP and UDP port numbers.
ProxyJump, DynamicForward
How to Manage an SSH Config File in Windows and Linux
Avahi Daemon/Bonjour/Zeroconf
sudo apt-get install avahi-daemon
ipv6
- https://wiki.ubuntu.com/IPv6
- Check the file /proc/sys/net/ipv6/conf/all/disable_ipv6 to see if it is zero (0 means ipv6 is enabled).
- To query the ipv6 address on the server, the following command from the post How to get the IPv6 IP address in Linux only return one ipv6. Note the command ip -6 address or /sbin/ip -6 addr | grep inet6 will return too many ipv6 addresses.
# Ubuntu 22.04 on x64 ip -6 addr show scope global dynamic mngtmpaddr up|egrep -o '([0-9a-f:]+:+)+[0-9a-f]+' # Debian 12 on SBC ip -6 addr show scope global dynamic up|egrep -o '([0-9a-f:]+:+)+[0-9a-f]+'
- My ipv6 address looks like fdeb:2506:de09:4441:6604:3326:db42:d815
- Consecutive groups of zeros can be represented with a double colon (::). However, the double colon can only be used once in an address. This allows for shorter representations of address with long sequences of zeros. For example, 2001:0db8:0000:0000:0000:0000:0000:abcd can be written as 2001:0db8::abcd.
- The full ipv6 has a form of
- 128 bits,
- 8 groups and each group represents 16 bits,
- 32 digits where each digit actually represents four bits.
ssh alias
- Using linux's alias; eg put the following inside ~/.bashrc or ~/.zshrc
alias sshnocheck='ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no' alias scpnocheck='scp -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no' alias openports='sudo netstat -tulpn | grep LISTEN' alias checkport='sudo lsof -i -P -n | grep LISTEN'
With this trick, ssh and scp (scp alias_name:Downloads/myfile .) work perfectly.
Modify ~/.ssh/config
Host * ServerAliveInterval 120 ServerAliveCountMax 30 Host your-alias_name User username HostName remote.sshserver.com Port 50001 IdentifyFile ~/.ssh/id_file ServiceAliveInterval 120 Host work User abcde HostName work.workserver.com ServiceAliveCountMax 5 StrictHostKeyChecking yes
According to the man of ssh_config:
- ServerAliveCountMax: Sets the number of server alive messages (see below) which may be sent without ssh(1) receiving any messages back from the server. If this threshold is reached while server alive messages are being sent, ssh will disconnect from the server, terminating the session.
- ServerAliveInterval: Sets a timeout interval in seconds after which if no data has been received from the server, ssh(1) will send a message through the encrypted channel to request a response from the server. The default is 0, indicating that these messages will not be sent to the server.
Running commands on a remote host
ssh user@host 'COMMANDS' ssh user@host "command1; command2; command3" COMMANDS="command1; command2; command3" ssh user@host "$COMMANDS"
A practical example
#!/bin/bash IP_LIST="192.168.0.1 192.168.0.5 192.168.0.9" USER="test" for IP in $IP_LIST; do utime=$(ssh ${USER}@${IP} uptime | awk '{ print $3 }' ) echo $IP uptime: $utime done
How to Run a Local Shell Script on a Remote SSH Server
How to Run a Local Shell Script on a Remote SSH Server
Disable password log in
If we like to ask all users to use key-based to log in, we can modify the line
PasswordAuthentication no
in /etc/ssh/sshd_config and run sudo systemctl restart ssh.
Disable root log in
Modify /etc/ssh/sshd_config. Change this line:
#PermitRootLogin yes
to
PermitRootLogin no
and run /etc/init.d/sshd restart.
However, that line in my Ubuntu is
PermitRootLogin without-password
According to this post, “without-password” means password authentication is disabled for root.
ssh log files
- /var/log/syslog
- /var/log/auth.log (see who is trying to connect; check out http://ip-lookup.net/index.php to see their geolocation)
It is also helpful to check /etc/hosts.allow and /etc/hosts.deny for any possible wrong configuration.
Note that auth.log can show ssh security attacks. Am I compromised?
$ grep sshd /var/log/auth.log Feb 19 11:04:12 phenom sshd[16922]: Failed password for root from 92.62.131.23 port 49383 ssh2 Feb 19 11:04:12 phenom sshd[16922]: Received disconnect from 92.62.131.23: 11: Bye Bye [preauth] Feb 19 11:04:14 phenom sshd[16924]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=92.62.131.23 user=root Feb 19 11:04:36 phenom sshd[16998]: Invalid user enea from 113.160.227.93 Feb 19 11:04:36 phenom sshd[16998]: input_userauth_request: invalid user enea [preauth] Feb 19 11:04:37 phenom sshd[16998]: pam_unix(sshd:auth): check pass; user unknown Feb 19 11:04:37 phenom sshd[16998]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=113.160.227.93 Feb 19 11:04:39 phenom sshd[16998]: Failed password for invalid user enea from 113.160.227.93 port 36090 ssh2 Feb 19 11:04:39 phenom sshd[16998]: Connection closed by 113.160.227.93 [preauth] Feb 19 11:05:11 phenom sshd[17060]: refused connect from 58.218.198.170 (58.218.198.170) Feb 19 11:05:55 phenom sshd[17353]: refused connect from 58.218.198.170 (58.218.198.170) Feb 19 11:06:38 phenom sshd[17732]: refused connect from 58.218.198.170 (58.218.198.170) Feb 19 11:07:20 phenom sshd[17850]: refused connect from 58.218.198.170 (58.218.198.170) Feb 19 11:07:40 phenom sshd[17874]: refused connect from 221.194.47.221 (221.194.47.221) Feb 19 11:08:01 phenom sshd[17955]: refused connect from 58.218.198.170 (58.218.198.170) Feb 19 11:08:41 phenom sshd[18118]: refused connect from 58.218.198.170 (58.218.198.170) Feb 19 11:09:22 phenom sshd[18280]: refused connect from 58.218.198.170 (58.218.198.170) Feb 19 11:10:02 phenom sshd[18353]: Invalid user support from 103.89.89.223 Feb 19 11:10:02 phenom sshd[18353]: input_userauth_request: invalid user support [preauth] Feb 19 11:10:02 phenom sshd[18353]: pam_unix(sshd:auth): check pass; user unknown Feb 19 11:10:02 phenom sshd[18353]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.89.89.223 Feb 19 11:10:03 phenom sshd[18424]: refused connect from 58.218.198.170 (58.218.198.170) Feb 19 11:10:04 phenom sshd[18353]: Failed password for invalid user support from 103.89.89.223 port 54218 ssh2 Feb 19 11:10:05 phenom sshd[18353]: fatal: Read from socket failed: Connection reset by peer [preauth] Feb 19 11:10:07 phenom sshd[18425]: Did not receive identification string from 103.89.89.223 Feb 19 11:10:17 phenom sshd[18443]: Address 113.160.227.93 maps to static.vnpt.vn, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!
How to List Unsuccessful SSH Logins on Linux
How to List Unsuccessful SSH Logins on Linux
grep "Failed password" /var/log/auth.log # OR journalctl _SYSTEMD_UNIT=ssh.service | egrep "Failed|Failure"
DenyHosts
Note that denyhosts package is no longer available in Ubuntu 14.04, 16.04 now. We can install install from its source DenyHosts-2.6.tar.gz.
- How To Install DenyHosts on Ubuntu 16.04 LTS and https://www.cyberciti.biz/faq/how-to-install-denyhosts-intrusion-prevention-security-for-ssh-on-ubuntu/
- https://www.digitalocean.com/community/tutorials/how-to-install-denyhosts-on-ubuntu-12-04
- tecmint.com or howtoforge (installed from source)
- /etc/hosts.deny will records the IPs that are blocked. If the normal ssh connection failed (e.g. get a message ssh_exchange_identification: read: Connection reset by peer), check /etc/hosts.deny file to see if your IP is in it. One method is to add your IP to /var/lib/denyhosts/allowed-host file so your IP won't be blocked.
- Visualising SSH attacks with R
- A few minutes of run of denyhosts accumulates hundreds of IP in /etc/hosts.deny file. But I remove the service since I did not spend enough time to understand it.
Procedures: follow the README.txt file.
Fail2ban
- https://www.fail2ban.org/wiki/index.php/Main_Page
- How to Install and Configure Fail2ban on Ubuntu 20.04 tecadmin.net
- How to Install and Configure Fail2ban on Ubuntu 20.04 linuxize.com
- How to show banned IPs with Fail2ban client
- The best way to have a look at the full list of IPs that have been blocked would be to check the log file sudo zgrep 'Ban' /var/log/fail2ban.log*
- Each time after I run "sudo systemctl restart fail2ban", it will show [sshd] Restore Ban XX.XX.XX.XX in "tail -f /var/log/fail2ban.log".
- fail2ban has banned my Ip but I can still login using SSH. The key is to change the line "port = ssh" to "port = YOUR_SSHD_PORT_NUMBER". After I did that, "tail -f /var/log/fail2ban.log" is clean and previously banned IPs won't appear. Also the total failed is 0 from the output of "sudo fail2ban-client status sshd".
- How To Protect an Apache Server with Fail2Ban on Ubuntu 20.04
- How To Prevent SSH Brute Force Attacks Using Fail2ban In Linux
# Check the status $ /etc/init.d/fail2ban status $ sudo fail2ban-client status # show banned IPs $ sudo fail2ban-client status sshd Status for the jail: sshd |- Filter | |- Currently failed: 4 | |- Total failed: 10 | `- File list: /var/log/auth.log `- Actions |- Currently banned: 3 |- Total banned: 3 `- Banned IP list: 118.89.108.152 183.216.183.131 42.192.132.127 # manually unban an IP: fail2ban-client set <JAIL-NAME> unbanip <IP-ADDRESS> fail2ban-client set sshd unbanip <IP-ADDRESS> # manually ban an IP: fail2ban-client set <JAIL-NAME> banip <IP-ADDRESS> # Another way to list banned IPs sudo iptables -L -n # Real-time Monitor sudo tail -f /var/log/fail2ban.log
Log in history: last command
The following command also shows how long a user has been logged in.
last <username> | less
w/who can show who (and when) are currently logging in.
Generate a strong password
5 Ways To Generate A Random/Strong Password In Linux Terminal: pwgen, openssl, gpg, mkpasswd, makepasswd, ...
Put in your ~/.bashrc. See Top 20 OpenSSH Server Best Security Practices.
$ genpasswd() { local l=$1 [ "$l" == "" ] && l=20 tr -dc A-Za-z0-9_ < /dev/urandom | head -c ${l} | xargs } $ genpasswd 16
login banners/messages
https://kerneltalks.com/tips-tricks/how-to-configure-login-banners-in-linux/
There are two types of banners you can configure.
Banner message to display before user log in (configure in file of your choice eg. /etc/login.warn) Banner message to display after user successfully logged in (configure in /etc/motd)
Double dash
What Does ‐‐ (double dash) Mean In SSH Shell Command?
ssh -A: forwarding of the authentication agent connection
- https://serverfault.com/a/838194
- When is ssh -A insecure?
- Mentioned in 5 projects for Raspberry Pi at home
- What is SSH Agent Forwarding and How Do You Use It?
- VS Code on Biowulf
Two-factor authentication
- Setting up two-factor authentication on your Raspberry Pi
- How to Set Up Two-Factor Authentication for SSH in Linux
X11 forwarding
- How to Run Graphical X Apps Over SSH in Linux. You'll have to enable X11 forwarding on the remote server. /etc/ssh/sshd_config file.
- Mac connect to Linux
- https://unix.stackexchange.com/a/46748
- On Mac Mojave 10.14.6 (client side), I need to use -Y option (Enables trusted X11 forwarding) because "-X" does not work. The answer was found when I use "-v" option in ssh.
- The 'ForwardX11' option in ~/ssh/config file does not help.
- When I connect to my Linux machine, I can use display XXXX.png command to show the remote png file locally (display is part of imagemagick pack).
- Linux connect to Linux does not have a problem.
Bypass SSH password login (convenient for CVS, git etc)
- ssh-keygen -t rsa
- (make sure the remote server has .ssh directory)
- cat ~/.ssh/id_rsa.pub | ssh user@hostname 'cat >> .ssh/authorized_keys'
- ssh user@hostname
It helps with CVS log in too when the CVS works by using ssh protocol. Note that step 3 allows to run a shell command at a remote machine.
See https://help.github.com/articles/generating-ssh-keys also for similar instruction when work on github.
The ssh key can be copied to another a machine (pay attention to mode). Or let the new machine to create its own key pair and use ssh-copy-id to append the identity file to remote machine's ~/.ssh/authorized_keys file. See http://superuser.com/questions/332510/how-to-transfer-my-linux-ssh-keys-to-another-machine.
We can even have multiple ssh key on local machine by using <.ssh/config> file. See http://www.karan.org/blog/index.php/2009/08/25/multiple-ssh-private-keys.
Allow for a user
How to Enable/Disable SSH access for a particular user or user group in Linux
locale
-bash: warning: setlocale: LC_CTYPE: cannot change locale (UTF-8): No such file or directory Fix
SSH file server
How to create a personal file server with SSH on Linux
SSHFS: mount a remote file system over ssh
- https://en.wikipedia.org/wiki/SSHFS
- https://help.ubuntu.com/community/SSHFS (include an instruction to keep the connection alive)
- How to Install and Use SSHFS on Linux
- NAS Performance: NFS vs. SMB vs. SSHFS. NFS fastest in plaintext, SSHFS fastest in encryption. SMB always somewhat behind NFS.
- Mount a remote file system over ssh in file manager
From my testing, files in local and remote machines are automatically synchronized. Convenient and dangerous.
# Remote: only need to make sure openssh-server is installed # Local sudo apt install sshfs mkdir /local/dir sshfs user@ip:/remote/dir /local/dir # Unmount fusermount -u /local/dir
To make this more practical, make sure /etc/fstab is modified appropriately and the ssh key is copied to the remote server.
sudo nano /etc/fstab sshfs#[email protected]:/remote/dir /local/dir
sudo nano /etc/fuse.conf # uncomment user_allow_other sudo mkdir /media/roms sudo chown -R $USER:$USER /media/roms sshfs user@ip:/remote/roms /media/roms -o idmap=user,ro,allow_other
SSH server on Windows 10
ssh key
SSH key is useful if you want a password-less login to a remote system. Some useful resources:
- https://help.ubuntu.com/community/SSH/OpenSSH/Keys
- https://help.github.com/articles/generating-ssh-keys
- https://www.howtogeek.com/424510/how-to-create-and-install-ssh-keys-from-the-linux-shell/
Also there are different kinds of keys (see for example <~/.ssh/known_hosts file>): RSA, DSA and ECDSA (newer). They're keys generated using different encryption algorithms. See SSH key-type, rsa, dsa, ecdsa, are there easy answers for which to choose when?
The steps are
- Check if there is an existing key
ls -al ~/.ssh
- Create a new RSA key pair:
ssh-keygen -t rsa ssh-keygen -f ~/.ssh/personalid -C "bitbucket"
where the comment 'bitbucket' will appear at the end of <~/.ssh/personalid> file.
- Copy the public key to a remote host ([email protected]) over ssh. The current user (eg brb) and the remote user (eg git)have not any relationship (they most likely have different user names):
ssh-copy-id -i ~/.ssh/id_rsa.pub [email protected] # this will 'append' the key to the remote-host’s .ssh/authorized_key.
Or (may not work:()
cat ~/.ssh/id_rsa.pub | ssh [email protected] "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"
- Delete the authorized key. Open the text file '.ssh/authorized_keys' and remove the offending lines.
- Test if this is working by trying 'ssh [email protected]'.
- To disable the password for root login. Type sudo nano /etc/ssh/sshd_config
PermitRootLogin without-password
Then run the following to put the changes into effect:
reload ssh # Or service ssh restart
Default key file
Force SSH Client To Use Given Private Key ( identity file )
The default is ~/.ssh/identity for protocol version 1, and ~/.ssh/id_rsa and ~/.ssh/id_dsa for protocol version 2.
Multiple ssh keys and ssh-add; ssh-agent
<Method 1> If we want to use a specific key in ssh, use
ssh -i ~/.ssh/xxx_id_rsa [email protected]
<Method 2> Another way is to use ssh-add & ssh-agent to manager your keys. ssh-agent keeps your key in its memory and pulls it up whenever it is asked for it.
- What is SSH Agent Forwarding and How Do You Use It?
- https://www.ssh.com/ssh/add
- 5 Unix / Linux ssh-add Command Examples to Add SSH Key to Agent. ssh-add adds RSA or DSA identity files to the ssh agent. For ssh-add to work properly, the ssh-agent should be running (ps -ef | grep ssh-agent).
- How to Add SSH-Keys to SSH-Agent on Startup in MacOS Operating System
ssh-agent ssh-add -K ~/.ssh/id_rsa # add to keychain ssh-add -l
- Migrate SSH keys from Linux to Mac
$ ssh-keygen -f ~/.ssh/personalid -C "bitbucket" $ eval $(ssh-agent -s) # Ensure ssh-agent is enabled: $ ssh-add ~/.ssh/personalid # ssh-add program will ask you for your passphrase $ ssh-add -l # Display the entries loaded in ssh-agent
<Method 3> <~/.ssh/config> file.
- http://askubuntu.com/questions/269140/how-to-use-multiple-ssh-keys-with-different-accounts-and-hosts or http://nerderati.com/2011/03/17/simplify-your-life-with-an-ssh-config-file/
- Configure multiple SSH identities for bitbucket accounts
- Multiple SSH Keys settings for different github account
Windows OS
Set up SSH public key authentication in WinSCP.
- Use PuTTYgen to generate an rsa key.
- We only need to save the private key since PuTTYgen can load a private key (right click the key file and choose Edit with PuTTYgen) and show the public key value.
- The public key text box shown at the top of the PuTTYgen window is what we should copy to the server's ./ssh/authorized_keys file as instructed by the dialog.
- NOTE: the "Key comment" part does not affect the authentication. It is located at the end of the public key. It's helpful to change that to more meaningful words.
ssh key management
- Using privacyIDEA (howtoforge.com).
Copy ssh keys to another computer
# Copy $ ssh-copy-id -p 22 -i ~/.ssh/MyKey.pub [email protected] # Test $ ssh -p 22 -i ~/.ssh/MyKey [email protected]
http://askubuntu.com/questions/134975/copy-ssh-private-keys-to-another-computer
$ chown brb:brb ~/.ssh/id_rsa* $ chmod 600 ~/.ssh/id_rsa $ chmod 644 ~/.ssh/id_rsa.pub
If we do not change the permission correctly in <id_rsa>, we will get a warning: Unprotected private key file. Permissions 0664 for '/home/USERNAME/.ssh/id_rsa' are too open.
Preserve ssh keys when upgrading computers
- An article from bsdnewsletter.com.
- https://askubuntu.com/questions/17097/how-to-backup-restore-the-host-key-in-ssh-server
ls -l /etc/ssh/*key* > ~/key_list # optional mkdir ~/serverkeys && sudo cp -p /etc/ssh/*key* ~/serverkeys/ # back up, -p will preserve mode, ownership and timestamps sudo cp -p ~/serverkeys/*key* /etc/ssh # copy back ls -l /etc/ssh/*key* | diff - ~/key_list # optional
If diff produces no output, you're finished.
Pay attention to the permissions. All the /etc/ssh/* files should be owned by root:root, with 644 permissions except for those that end in *key, which should be 600.
udooer@udoo:~$ ls -l /etc/ssh/*key* total 32 -rw------- 1 root root 668 Dec 8 14:43 ssh_host_dsa_key -rw-r--r-- 1 root root 599 Dec 8 14:43 ssh_host_dsa_key.pub -rw------- 1 root root 227 Dec 8 14:43 ssh_host_ecdsa_key -rw-r--r-- 1 root root 171 Dec 8 14:43 ssh_host_ecdsa_key.pub -rw------- 1 root root 399 Dec 8 14:43 ssh_host_ed25519_key -rw-r--r-- 1 root root 91 Dec 8 14:43 ssh_host_ed25519_key.pub -rw------- 1 root root 1679 Dec 8 14:43 ssh_host_rsa_key -rw-r--r-- 1 root root 391 Dec 8 14:43 ssh_host_rsa_key.pub udooer@udoo:~$ cd /etc/ssh; sudo tar -czvf ~/Downloads/sshkeys.tar.gz *key* -rw------- root/root 668 2017-12-08 14:43 ssh_host_dsa_key -rw-r--r-- root/root 599 2017-12-08 14:43 ssh_host_dsa_key.pub -rw------- root/root 227 2017-12-08 14:43 ssh_host_ecdsa_key -rw-r--r-- root/root 171 2017-12-08 14:43 ssh_host_ecdsa_key.pub -rw------- root/root 399 2017-12-08 14:43 ssh_host_ed25519_key -rw-r--r-- root/root 91 2017-12-08 14:43 ssh_host_ed25519_key.pub -rw------- root/root 1679 2017-12-08 14:43 ssh_host_rsa_key -rw-r--r-- root/root 391 2017-12-08 14:43 ssh_host_rsa_key.pub udooer@udoo:~/$ cd /etc/ssh; sudo tar -xzvf ~/Downloads/sshkeys.tar.gz
Disable SSH host key checking
ssh -o UserKnownHostsFile=/dev/null \ -o StrictHostKeyChecking=no \ USERNAME@DOMAIN
To disable the checking for all hosts, in your ~/.ssh/config (if this file doesn't exist, just create it):
Host * StrictHostKeyChecking no
Or for certain domains https://superuser.com/a/433621
Host *.mydomain.com StrictHostKeyChecking no UserKnownHostsFile /dev/null User foo LogLevel QUIET
Handling the ssh key change when connecting to a remote machine
An article from cybercitz.biz.
- Method 1. Remove the key using ssh-keygen -R command.
$ ssh-keygen -R {server.name.com} $ ssh-keygen -R {ssh.server.ip.address} $ ssh-keygen -R server.example.com $ ssh-keygen -f "/home/$USERNAME/.ssh/known_hosts" -R "xxx.xxx.x.xx"
- Method 2. Add correct host key in /home/user/.ssh/known_hosts
- Method 3. Just delete the known_hosts file If you have only used one ssh server
- Method 4. Use ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no method. See Alias or Disable SSH host key checking.
What is tunnel
https://www.howtogeek.com/299845/why-is-a-network-tunnel-called-a-tunnel/. A tunnel provides a direct path that avoids some type of complexity you would otherwise have to deal with.
Cloudflare tunnel
See here.
awesome-tunneling
- awesome-tunneling
- Hosting Without The Need to Port Forward Using This Trick!
- Tunnelling services for exposing localhost to the web
- SSH Tunneling — Exposing local applications to the internet!!!
tunnel.pyjam.as
Tested it on Slax
First we install openssh server on slax so we can remote access it and copy/paste commands.
apt install openssh-server systemctl start sshd.service passwd # change root password
Testing tunnel.pyjam.as.
apt update apt install curl wireguard touch newfile python3 -m http.server # Serving http on 0.0.0.0 port 8000 (http://0.0.0.0:8000) # open a new terminal/tab curl https://tunnel.pyjam.as/8000 > tunnel.conf && wg-quick up ./tunnel.conf # access http://0.0.0.0/8000 on https://<unique_slug>.tunnel.pyjam.as/ # To stop your tunnel wg-quick down ./tunnel.conf
tailscale VPN
- How to Use Tailscale VPN to Access Your Home Assistant Server Remotely
- TailScale - Your Own Virtual Private Network by DB Tech
SSH Port forwarding
- Chapter 9 Port forward. SSH Mastery OpenSSH, PuTTY, Tunnels and Keys by Michael W. Lucas
- Using SSH port forwarding on Fedora
Verizon Quantum Gateway Router
User guide p98. Click 'Advanced' button first.
- Source port: Any (this is the key)
- Destination Ports: the port you want to use (connect from outside)
- Forward to Port: Same as incoming port or the port used in the local computer
'L'ocal port forwarding: view a certain port web page on a remote domain locally
- https://toic.org/blog/2010/ssh-port-forwarding/
- https://www.howtogeek.com/168145/how-to-use-ssh-tunneling/
- https://www.ssh.com/ssh/tunneling/example
This port forwarding involves three computers (local, remote/application server, host/secure shell server). If the remote is the same as the host, it will be reduced to involving 2 computers.
For example, we like to access home's router (192.168.1.1) information from an outsider computer. Suppose the host 'hostname' is one computer in the home network and it can be accessed from outside world.
Another example is if we want to use Jupyter running on a remote machine from local browser.
# ssh -L localPort:remoteIP:remotePort username@hostname ssh -L 8080:192.168.1.1:80 username@hostname ssh -L 8080:localhost:80 username@hostname # access http://hostname:80 using http://localhost:8080 ssh -i someKey.pem -L 443:127.0.0.1:8888 username@hostname
The -L option specifies local port forwarding. In this case, port 8080 on the local machine was forwarded to port 80 on the remote machine. For the duration of the SSH session, pointing your browser at http://localhost:8080/ would send you to http://192.168.1.1/ as if you are in the same local network of 'hostname'. We can try other ports like 1234 instead of 8080; it can be anything above 1024.
The reason it works is because the 'ssh' trick. In addition to being able to make yourself in the home network environment, the traffic on http://localhost:8080 is encrypted too.
Note that this forwarding uses port 8080 on the client rather than port 80. Binding to port 80 would require using root privileges every time we SSH.
To stop the ssh session, use ps -ef to find the process id and kill it.
Remote port forwarding (Reverse port forwarding)
- https://www.howtoforge.com/reverse-ssh-tunneling (use ssh option -f to detach ssh process from the tty, -N to not execute any command over ssh and option -i for key authentication)
- http://man.openbsd.org/ssh
- https://toic.org/blog/2009/reverse-ssh-port-forwarding/
- https://www.howtogeek.com/168145/how-to-use-ssh-tunneling/
This is most useful in situations where you have a machine which isn't publicly accessible from the internet, but you want others to be able to access a service on this machine. In this case, if you have SSH access to a remote machine which is publicly accessible on the internet, you can set up a reverse port forward on that remote machine to the local machine which is running the service.
ssh -R 8000:localhost:80 user@REMOTE_MACHINE
This will forward port 8000 on the remote machine to port 80 on the local machine. Using this method, if you browse to http://localhost on the remote machine, you will actually connected to a web server running on port 8000 of the local machine.
Example 2: Suppose you have two machine
- machine A (userA): under firewall. cannot be directly accessed (like corporate machines)
- machine B (userB): local machine (like home machines)
Our goal is to access machine A directly from machine B.
We can run the following on the machine A
# ssh -R remoteIP:remoteport:localIP:localport hostname # ssh -R remoteport:localIP:localport hostname ssh -R 2222:localhost:22 userB@machineB_IP ssh -i /path/to/priv/key/id_rsa -f -N -R 2222:localhost:22 userB@machineB_IP
Then we can access machine A from machine B by
ssh -p 2222 userA@localhost
If you want remote port forwarding configured every time you connect to a host, use the RemoteForward option in ssh_config .
LocalForward server-IP:server-port client-IP:client-port
'D'ynamic port forwarding, SOCKS proxy, bypass blocked websites from work computer
- http://www.panix.com/~ruari/censorship.html
- http://www.cyberciti.biz/faq/set-up-ssh-tunneling-on-a-linux-unix-bsd-server-to-bypass-nat/
- What Is a SOCKS Proxy and How Do You Use It?
- https://www.howtogeek.com/168145/how-to-use-ssh-tunneling/
ssh -D 4096 user@remoteip ssh -D 4096 -p 23 user@remoteip ssh -D 4096 -p 23 -f -N -q -C user@remoteip
This will require you to enter the password and leave you in the remote machine. If a nonstandard port is required, we can use -p option. -f is to fork process into background, -N means don't open a shell, -q means quiet and -C means compress data sent through tunnel. In order to close the connection, you need to find the process ID and kill it manually. You can use other port like 1080 (or something like 4321 which is also easy to remember too).
Now in the firefox, we need to go to Edit -> Preferences -> Advanced -> Network tab -> Settings... Check 'Manual proxy configuration' (The default is 'Use system proxy settings') and enter 'localhost' for SOCKS (SOCKS5 by default) Host and '4096' for the Port. Don't enter 'localhost' in the HTTP Proxy. Also check the option Proxy DNS when using SOCKS v5; otherwise someone on the network can see which site you are trying to get to even they are unable to see what you are seeing.
Open Google.com and search my ip to check if the change works.
Note that in addition to the Firefox, we can use
- Chrome or chromium
- SeaMonkey (seems better than Firefox since the form works better on 1024x600 resolution).
- Brave browser does not support proxy
On Windows, we can use Putty. In short, in the left-hand panel, navigate through Connection > SSH > Tunnels. Enter 4096 in the Source Port box and select the Dynamic radio button. Click Add and “D4096″ will appear in the Forwarded Ports list. The setting in the firefox end is the same. See also my Windows wiki page.
Linux journal also put a video on youtube. We can use http://www.ipligence.com/geolocation to check the current location. The port number is 1080 in the example. The example actually also use '-N' option which means no interaction; i.e. ssh -N -D 1080 user@remoteip. So we won't see anything after we type our password. Once we want to stop SOCK proxy, we just need to hit Ctr+C on terminal.
Backgrounding OpenSSH Forwarding
Use the -N flag to tell ssh to not run anything, including a terminal, on the remote server, and the -f flag to tell ssh to go into the background on the client.
ssh -fNL 2222:localhost:22 user@remotehost &
By backgrounding this command, you get your original terminal back.
tunnel a ssh connection through an intermediate server
- http://www.cyberciti.biz/faq/linux-unix-ssh-proxycommand-passing-through-one-host-gateway-server/
- https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Proxies_and_Jump_Hosts#Port_Forwarding_via_an_Intermediate_Host (more examples)
Simple method is (-t means Force tty/pseudo-terminal allocation).
$ ssh -t user1@domain1 ssh user2@domain2
Another method is to use ssh ProxyCommand to tunnel connections.
A third method is to
$ ssh -L 9999:host2:22 user1@host1 # leave this terminal # open a new terminal tab $ ssh -p 9999 user2@localhost
scp
file path with spaces (parentheses)
Use double quotes around the full path and a backslash to escape any space.
scp [email protected]:"web/tmp/Master\ File\ 18\ 10\ 13.xls" .
Use the 'Tab' key to get the full path used by Linux.
$ cd Calibre\ Library/calibre/Calibre-2\ days\ \(582\)/ $ exit ~/Downloads$ scp "taichimd:~/Calibre\ Library/calibre/Calibre-2\ days\ \(582\)/*.mobi" . # Use the path we understand does not work ~/Downloads$ scp "taichimd:~/Calibre Library/calibre/Calibre-2 days (582)/*.mobi" . bash: -c: line 0: syntax error near unexpected token `(' bash: -c: line 0: `scp -f ~/Calibre Library/calibre/Calibre-2 days (582)/*.mobi'
wildcard
You either need quotes, or a backslash before the star, but not both. And scp is not the one expanding it, the shell is. See How to use wildcards (*) when copying with scp?
scp [email protected]:/abc/def/*.txt . # no matches found: scp [email protected]:/abc/def/\*.txt . # macOS scp 'helix:/data/xxx/file_*.rda' .
Copy multiple files
scp or sftp copy multiple files with single command
From local to remote: use space character.
scp foo.txt bar.txt your_username@domain:
From remote to local: use escaped parentheses and comma sign.
scp your_username@domain:~/\{foo.txt,bar.txt\} .
Some uses double quotes around the files with the space character to separate files but it does not work when I try to copy files from remote(biowulf) to local(mac).
Recursive copying
Use -r parameter.
Preserve permissions and modes
Use -p parameter.
Disable SSH host key checking
See here. scp is supposed to take the same command line options as ssh. Add the following options to the scp command.
-o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null
scp files through one intermediate host
http://stackoverflow.com/questions/9139417/how-to-scp-with-a-second-remote-host
The following command is tested.
scp -o 'ProxyCommand ssh user@remote1 nc %h %p' user@remote2:path/to/file .
A second method which is useful for ssh and scp commands
$ ssh -L 9999:host2:22 user1@host1 # leave the terminal # Open a new terminal $ scp -P 9999 fileName user2@localhost:/path/to/dest/fileName # transfer from local to remote. Note: Upper P. $ scp -P 9999 user2@localhost:/path/to/source/fileName fileName # transfer from remote to local. Note: Upper P. # If we only want to use ssh $ ssh -p 9999 user2@localhost # Note: lower p.
scp with non-standard port: -P (capital)
Use -P argument.
scp -P 23 myfile user@remoteip:
scp without a password
Assume the ssh key has been copied to the remote computer
scp -p -P 22 -i ~/.ssh/MyKey [email protected]:MyFile .
- http://www.thegeekstuff.com/2008/06/perform-ssh-and-scp-without-entering-password-on-openssh/
- https://toic.org/blog/2008/ssh-basics/
Steps:
- Verify that local-host and remote-host is running openSSH (ssh -V)
- Generate key-pair on the local-host using ssh-keygen (Enter a passphrase here, do not leave it empty. A passphrase should be at least several words long, something you can easily remember. It's a bad idea to use a single word as a passphrase.)
- Install public key on the remote-host
- Give appropriate permission to the .ssh directory on the remote-host (chmod 755 ~/.ssh; chmod 644 ~/.ssh/authorized_keys)
- Login from the local-host to remote-host using the SSH key authentication to verify whether it works properly
- Start the SSH Agent on local-host to perform ssh and scp without having to enter the passphrase several times (ssh-agent $SHELL)
- Load the private key to the SSH agent on the local-host (ssh-add, need to enter the passphrase 1 time only)
- Perform SSH or SCP to remote-home from local-host without entering the password. It works for all remote machines containing the key from local-local.
Another option is to use ssh -i IDENTITY_FILE. See superuser.com.
ssh with password on the command line: sshpass
- Install sshpass utility. See https://serverfault.com/questions/241588/how-to-automate-ssh-login-with-password
- How to Use Encrypted Passwords in Shell Scripts on Linux. sshpass, gpg.
Rsync does use your ssh config
SCP user’s migration guide to rsync.
Some advantages of rsync over scp:
- In-flight compression
- Delta transfers
- Syncing