How to remotely connect to a Linux machine using a smartphone?

Sometimes, life can be really tough for a system admin. Flexible timings are part of the job description for any System admin. Imagine, you are on a vacation and all you have is your smartphone with you and you get the call: "There's something wrong with the web server! , your life can get really miserable.
With an SSH client on your Android device, you can check the status of your servers and IoT devices during times when you are on the go and required to check on your server for its status or performance.

• ConnectBot
• Termius
• Get Console 
• Juice SSH
• Mobile SSH

Following are some of the available apps for Android and iPhone(iOS) users that can be used to connect to Linux machine

ConnectBot 

Platform:  Android
Google Play store: https://play.google.com/store/apps/details?id=org.connectbot&hl=en

ConnectBot is a secure shell client for the Android platform. Its ultimate goal is to create a secure connection through which you can use a shell on a remote machine and transfer files back and forth to your phone. If you are looking for a free app with customization option, ConnectBot has all the basic features you’d expect from a good SSH client.
ConnectBot gives you a wide range of options like SSH authentication agent, compression, etc. while creating an SSH host.
The app comes with special keys that let you access control keys, arrow keys, function keys, etc.  Other features of ConnectBot include persistent connection, post login automation scripts, ability to manage public keys, etc. Simply put, ConnectBot has all the basic features you’d expect from a good SSH client.

Termius 

Platform: Android | iOS
Google Play store: https://play.google.com/store/apps/details?id=com.server.auditor.ssh.client
Mac App Store: https://itunes.apple.com/in/app/termius-ssh-client/id1176074088?mt=12

Termius is more than an SSH client - it's a complete command-line solution. With Termius, you can securely access Linux or IoT devices from your Android or iOS mobile device. It is Mosh-compatible, providing excellent reliability on high-latency constantly changing connections.
The user interface is pretty minimal and using the app is also very simple. All you have to do is enter the SSH command to log into your server and start managing your server, Raspberry Pi, Docker container, or any other service or machine. It has a built-in SFTP client so as to make it easy to manage, download, and upload files and directories on your server.
Using this app you can also work the other way round by accessing your Android device from a local terminal. What makes Termius really special is the support for multiple cryptographic algorithms like built-in key generator, support importing putty keys, support for two-factor authentication, dynamic port forwarding, ability to group hosts, etc.

Get Console  

Platform:  iOS
Mac App Store: https://itunes.apple.com/us/app/get-console/id412067943?mt=8

Get Console is a powerful and complete terminal app that provides physical serial console access to the network and other equipment as well as SSHv2, Telnet, Scripting, TFTP Server, full Logging, integration with Dropbox, iCloud and instant Screen Sharing. Please read below for Full information.
With Get Console, you can easily share your iPad/iPhones terminal window or get access of remote server to provide remote access to your console sessions - useful for remote support, teaching or for Disaster Recovery.

JuiceSSH   

Platform:  Android
Google Play store: https://play.google.com/store/apps/details?id=com.sonelli.juicessh

JuiceSSH claims to be the #1 free SSH client for Android users with sleek, minimal and packed with loads of feature. This app is an awesome SSH, mosh and telnet client which you can install and control and manage the Linux system from any Android device on the fly.
With JuiceSSH you can set identities for various connections. While creating an SSH connection, you can configure it to run a specific script at login. This feature is very useful when you always do that same thing after logging into your machine. It also provides local Android terminal support, third-party plugins, multiple themes, support for external keyboard, ability to copy and paste between sessions, RSA key generator, key forwarding, compression for slow connections, ability run multiple SSH connections in the background, etc.

Mobile SSH  

Platform: Android | iOS
Google Play Store: https://play.google.com/store/apps/details?id=mobileSSH.feng.gao&hl=en
Mac App Store: https://itunes.apple.com/app/id1156707581

Mobile SSH is a free SSH client that is designed based on OpenSSH and Putty. The app is very basic, has no settings or configuration options, and its user interface is not its strong suit. However, the app supports multiple SSH sessions and RSA key authentication. Just add your SSH details, tap on the connect button and you are good to go.
If you are just looking for a simple SSH client that gets the job done in a pinch then Mobile SSH is a good choice.