SSH & SSHFS#

Author: Fu Yin
Update: July 26, 2022
Reading: 15 min

SSH (Secure Shell) is a network protocol that encrypts communication between two computers and supports various authentication mechanisms.

In practice, it is mainly used to ensure the security of remote login and remote communication. Any network service can be encrypted with this protocol.

Basic usage#

Use the -V parameter to check the version number

ssh -V

The following commands are used to log in to the server over SSH

ssh user@hostname

By default, SSH connects to port 22 of the server

ssh -p 22 -X user@hostname

-p: specifies the server port that the SSH client connects to
-X: opens the X window for forwarding (eg. X11)

Create SSH keys#

To create the keys, a preferred command is ssh-keygen. And ssh-keygen asks a series of questions and then writes a private key and a matching public key.

SSH keys are by default kept in the ~/.ssh directory. If you do not have a ~/.ssh directory, the ssh-keygen command creates it for you with the correct permissions. If an SSH key pair exists in the current location, those files are overwritten.

The following ssh-keygen command generates SSH RSA public and private key files by default in the ~/.ssh directory.

ssh-keygen -t rsa -C "fy21@rice.edu"

ssh-keygen: the program used to create the keys
-t rsa: type of key to create, in this case in the RSA format
-C "fy21@rice.edu": a comment appended to the end of the public key file to easily identify it. Normally an email address is used as the comment, but use whatever works best for your infrastructure.

The ~/.ssh directory has some personal key files and other files.

ls -l ~/.ssh
total 32
-rw-r--r--@ 1 yinfu  staff  1479 Jul 26 16:23 config
-rw-------  1 yinfu  staff  2602 Jul 20 22:53 id_rsa
-rw-r--r--  1 yinfu  staff   567 Jul 20 22:53 id_rsa.pub
-rw-------  1 yinfu  staff   749 Jul 20 23:02 known_hosts

config: the configuration file
id_rsa: the private key
id_rsa.pub: the public key
known_hosts: the public key’s fingerprint of existing SSH servers

Upload SSH keys#

The user public key is stored in the ~/.ssh/authorized_keys file on the server. Each public key occupies a line. If the file does not exist, you can manually create it.

The permission of the authorized_keys file must be set to 644, that is, only the file owner can write.

Manually Uploading a Public Key

User can edit the authorized_keys file manually and paste the public key into it, or can run the following command on the local computer.

cat ~/.ssh/id_rsa.pub | ssh user@host "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"
chmod 644 ~/.ssh/authorized_keys

ssh-copy-id

OpenSSH comes with the ssh-copy-id command to automatically copy the public key to the ~/. SSH /authorized_keys file on the remote server. If the ~/.ssh/authorized_keys file does not exist, the ssh-copy-id command automatically creates the file.

ssh-copy-id -i ~/.ssh/id_rsa.pub user@host

Note

ssh-copy-id adds the public key directly to the end of the authorized_keys file. If the end of the authorized_keys file is not a newline character, the new public key will be added to the end of the previous public key, and the two public keys will be linked together, making neither of them valid. Therefore, if the authorized_keys file already exists, make sure that the authorized_keys file ends with a newline character before using the ssh-copy-id command (assuming the file already exists).

Configure SSH config file#

Some main configuration commands of the SSH config file

Host: the alias name.
HostName: specifies the domain name or IP address.
User: specify the account name for remote login.
IdentityFile: specifies the private key file.
Port: indicates the SSH server Port that the specified client connects to.

My ~/.ssh/config configuration file

#####################################
# Rice -- Prof. Jonathan's group in NOTS
#####################################
Host nots
  HostName nots.rice.edu
  ForwardX11Trusted yes
  ForwardX11 yes
  User fy21
  IdentityFile /Users/yinfu/.ssh/id_rsa
  Port 22


#####################################
# USTC -- Prof. Junlun Li's group
#####################################
Host li
  HostName 222.195.76.240
  ForwardX11Trusted yes
  ForwardX11 yes
  User yinfu
  IdentityFile /Users/yinfu/.ssh/id_rsa
  Port 22


#####################################
# USTC -- Prof. Baoshan Wang's group
#####################################
Host core
  HostName 222.195.74.184
  ForwardX11Trusted yes
  ForwardX11 yes
  User yinf
  IdentityFile /Users/yinfu/.ssh/id_rsa
  Port 1010

Host m1
  HostName 222.195.74.184
  ForwardX11Trusted yes
  ForwardX11 yes
  User yinf
  IdentityFile /Users/yinfu/.ssh/id_rsa
  Port 1011

Host m2
  HostName 222.195.74.184
  ForwardX11Trusted yes
  ForwardX11 yes
  User yinf
  IdentityFile /Users/yinfu/.ssh/id_rsa
  Port 1012

Host m3
  HostName 222.195.74.184
  ForwardX11Trusted yes
  ForwardX11 yes
  User yinf
  IdentityFile /Users/yinfu/.ssh/id_rsa
  Port 1013

Host m4
  HostName 222.195.74.184
  ForwardX11Trusted yes
  ForwardX11 yes
  User yinf
  IdentityFile /Users/yinfu/.ssh/id_rsa
  Port 1014

Host crust
  HostName 222.195.74.184
  ForwardX11Trusted yes
  ForwardX11 yes
  User yinf
  IdentityFile /Users/yinfu/.ssh/id_rsa
  Port 1015


########################################
# SUSTech -- Prof. Xiaofei Chen's group
########################################
Host seislab2
  HostName 10.20.11.42
  ForwardX11Trusted yes
  ForwardX11 yes
  User yinfu
  IdentityFile /Users/yinfu/.ssh/id_rsa
  Port 22

SSHFS#

SSHFS is Secure Shell FileSystem, and it can mount a remote hard disk to the local Mac. SSHFS depends on FUSE on Mac, and the macFUSE allows you to extend macOS’s native file handling capabilities via third-party file systems.

Download macFUSE firstly, click macfuse-x.x.x.dmg to install.
Download SSHFS, click the X.dmg to install.

It can be used after the installation is complete, for example:

sshfs -o follow_symlinks -p 1012 yinf@222.195.74.184:/ /Users/yf/share1/
sshfs -o follow_symlinks fy21@nots.rice.edu:/ /Users/yinfu/share2/

Programming Notebook

SSH & SSHFS

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