Install OpenSSH

Published on: 22nd Apr 2014

Updated on: 3rd Oct 2022

Why

SSH allows the server administrator to remote access the server and manage the server. If you are using a cloud server, SSH service should have already been installed and you may skip this section.

Here's how you install it

To check the SSH status, run the following command,
```
sudo systemctl status ssh 
```
To install SSH, run the following command,
```
sudo apt install ssh
```
To access to the remote server,
- With Windows OS, install PuTTy - key in your server IP address and press Enter. Key in your Ubuntu login ID & password.
  
  To download the PuTTy program, visit the following page,
  
  https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html
  - 03.Oct.2022: by installing PuTTy program, you will get the pscp.exe (for transferring file using SCP utility) and psftp.exe (for transferring file using SFTP protocol).
    
    For example, you want to copy a file from your Windows computer to Linux server,
```
cd "C:\Program Files\PuTTY"
.\pscp.exe -pw 123456 -P 22  "D:\temp\my-file.txt" myftpuserid@192.168.101.11:/home/myftpuserid
```
    Where:
    - -pw the user password.
    - -P is the SSH port.
    - myftpuserid is the user account for uploading the file.
    Make sure that the 'myftpuserid' has the permission to access the shell. To verify the user permission, run the following command,
```
sudo cat /etc/passwd | grep myftpuserid
```
    Notes: in case you want to write a program to upload the file (which gives you more control), you may want to research more on the node-ssh or ssh2 packages for Node.js.
- With Mac OS, run Terminal and execute ssh user@myhostname - then, key in your password.
To change the SSH port,
```
sudo nano /etc/ssh/sshd_config
```
Then, set the following
```
Port 10001
```
Notes: don't forget to open the port in the firewall (through ufw command).
To disable/enable the login with password
```
sudo nano /etc/ssh/sshd_config
```
Then, set 'yes' to enable and 'no' to disable.
```
PasswordAuthentication yes
```

Access the server with sftp

The following URL (step 1 to 3) shows you how to restrict an user from using SFTP (SSH will be disabled). In this case, the user may run FileZilla and upload/download files using SFTP protocol.

http://www.howtoforge.com/restricting-users-to-sftp-plus-setting-up-chrooted-ssh-sftp-debian-squeeze
To configure the SFTP access (without SSH access),
```
cd /etc/ssh
sudo nano sshd_config
```
Replaces the Subsystem with the following value,
```
Subsystem internal-sftp
```
Add the following lines to the bottom of the file where myftpuserid is the OS user ID and /home/myftpuserid is the user directory. Repeat the whole section for every user
```
Match User myftpuserid
    ChrootDirectory /home/myftpuserid
    AllowTCPForwarding no
    X11Forwarding no
    ForceCommand internal-sftp
```
Make sure that /home/myftpuserid is owned by root, update the access rights and then create a doc directory which is owned by myftpuserid. Finally, restart the service.
```
sudo chmod 700 /home/myftpuserid
sudo chown root:root /home/myftpuserid
sudo mkdir /home/myftpuserid/doc
sudo chown myftpuserid:myftpuserid /home/myftpuserid/doc
sudo service ssh restart
```
To restrict the user from access SFTP only (do this after you have added the user),
```
sudo nano /etc/passwd
```
Then, change the shell for the session:
```
/bin/sh
```
To
```
/usr/lib/openssh/sftp-server 
```

For how to open the port for SSH, please refers to: Configure firewall
For how to secure your server, please refers to: Hardening your server

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Author

Lau Hon Wan, software developer.

Install OpenSSH

Why

Here's how you install it

Access the server with sftp

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