Mosh, short for Mobile Shell, is a terminal application designed to connect to a server remotely over the internet. It can function similarly to SSH but comes with enhanced capabilities compared to the traditional Secure Shell.

Developed initially by Keith Winstein for Unix-like systems, Mosh is distributed under the GNU GPL v3 license and offers more flexibility in certain scenarios than SSH.

Key Features of Mosh

1. Enables roaming support during remote sessions.
2. Compatible with major UNIX-based platforms including Linux, FreeBSD, Solaris, Mac OS X, and Android.
3. Works well under unstable or fluctuating network conditions.
4. Offers smart local echo functionality.
5. Supports line editing of typed commands locally.
6. Optimized for performance on Wi-Fi, mobile networks, and long-distance connections.
7. Maintains connection even when IP addresses change, thanks to its use of UDP instead of TCP (used by SSH). UDP allows continued connectivity where TCP might drop the session upon reconnection or IP change.
8. Keeps sessions active across extended idle periods.
9. Eliminates network delay by showing keystrokes and deletions instantly.
10. Uses familiar SSH-style login syntax.
11. Equipped with mechanisms to manage packet loss effectively.

Installing Mosh on Linux Systems

For Debian, Ubuntu, and Linux Mint users, installing Mosh is straightforward using the apt package manager:

<code># apt-get update 
# apt-get install mosh</code>

On RHEL, CentOS, and Fedora distributions, you need to enable the EPEL repository before installing via yum:

<code># yum update
# yum install mosh</code>

For Fedora 22 , use the dnf package manager:

<code># dnf install mosh</code>

Other Linux distributions can use their respective package managers as follows:

<code># pacman -S mosh         [On Arch/Manjaro Linux]
$ sudo zypper in mosh    [On OpenSuse]
# emerge net-misc/mosh   [On Gentoo]</code>

Using Mosh: Basic Commands

1. To establish a connection to a remote Linux system using Mosh:

<code>$ mosh [email?protected]</code>

Note: In this example, a connection error occurred because the required port was blocked on the remote CentOS 7 system. A temporary workaround used was:

<code># systemctl stop firewalld    [on Remote Server]</code>

However, it's better practice to adjust firewall settings to allow specific ports rather than disabling the firewall entirely.

2. If your SSH service runs on a non-standard port such as 70, specify it using the ‘-p’ option along with the ssh command:

<code>$ mosh [email?protected] --ssh="ssh -p 70"</code>

3. To check the current version of Mosh installed:

<code>$ mosh --version</code>

4. To terminate a Mosh session, simply type:

<code>$ exit</code>

5. View all available Mosh options using:

<code>$ mosh --help</code>

Drawbacks of Using Mosh

1. Requires allowing UDP traffic, which isn’t needed for SSH.
2. Utilizes dynamic UDP ports between 60000-61000, with one port assigned per connection.
3. Default port usage may pose security issues in enterprise environments.
4. IPv6 connections are supported, but seamless roaming on IPv6 is not.
5. Does not support scrollback functionality.
6. No built-in support for X11 forwarding.
7. Lacks support for ssh-agent forwarding.

Final Thoughts

Despite some limitations—particularly around security and configuration requirements—Mosh is a powerful tool that enhances remote access experiences, especially for those frequently switching networks or dealing with intermittent connectivity. It's readily available in most Linux repositories, making it easy to test. For any Linux user who regularly uses SSH, trying out Mosh could be beneficial—it’s definitely worth exploring.

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