Monday, August 24, 2015

Mosh Shell – A SSH Based Client for Connecting Remote Unix/Linux Systems

Mosh, which stands for Mobile Shell is a command-line application which is used for connecting to the server from a client computer, over the Internet. It can be used as SSH and contains more feature than Secure Shell. It is an application similar to SSH, but with additional features. The application is written originally by Keith Winstein for Unix like operating system and released under GNU GPL v3.
Mosh Shell SSH Client
Mosh Shell SSH Client

Features of Mosh

  1. It is a remote terminal application that supports roaming.
  2. Available for all major UNIX-like OS viz., Linux, FreeBSD, Solaris, Mac OS X and Android.
  3. Intermittent Connectivity supported.
  4. Provides intelligent local echo.
  5. Line editing of user keystrokes supported.
  6. Responsive design and Robust Nature over wifi, cellular and long-distance links.
  7. Remain Connected even when IP changes. It usages UDP in place of TCP (used by SSH). TCP time out when connect is reset or new IP assigned but UDP keeps the connection open.
  8. The Connection remains intact when you resume the session after a long time.
  9. No network lag. Shows users typed key and deletions immediately without network lag.
  10. Same old method to login as it was in SSH.
  11. Mechanism to handle packet loss.

Installation of Mosh Shell in Linux

On DebianUbuntu and Mint alike systems, you can easily install the Mosh package with the help of apt-get package manager as shown.
# apt-get update 
# apt-get install mosh
On RHEL/CentOS/Fedora based distributions, you need to turn on third party repository called EPEL, in order to install mosh from this repository using yum package manager as shown.
# yum update
# yum install mosh
On Fedora 22+ version, you need to use dnf package manager to install mosh as shown.
# dnf install mosh

How do I use Mosh Shell?

1. Let’s try to login into remote Linux server using mosh shell.
$ mosh root@
Mosh Shell Remote Connection
Mosh Shell Remote Connection
Note: Did you see I got an error in connecting since the port was not open in my remote CentOS 7 box. A quick but not recommended solution I performed was:
# systemctl stop firewalld    [on Remote Server]
The preferred way is to open a port and update firewall rules. And then connect to mosh on a predefined port. For in-depth details on firewalld you may like to visit this post.
  1. How to Configure Firewalld
2. Let’s assume that the default SSH port 22 was changed to port 70, in this case you can define custom port with the help of ‘-p‘ switch with mosh.
$ mosh -p 70 root@
3. Check the version of installed Mosh.
$ mosh --version
Check Mosh Version
Check Mosh Version
4. You can close mosh session type ‘exit‘ on the prompt.
$ exit
5. Mosh supports a lot of options, which you may see as:
$ mosh --help
Mosh Shell Options
Mosh Shell Options

Cons of Mosh Shell

  1. Mosh requires additional prerequisite for example, allow direct connection via UDP, which was not required by SSH.
  2. Dynamic port allocation in the range of 60000-61000. The first open fort is allocated. It requires one port per connection.
  3. Default port allocation is a serious security concern, especially in production.
  4. IPv6 connections supported, but roaming on IPv6 not supported.
  5. Scrollback not supported.
  6. No X11 forwarding supported.
  7. No support for ssh-agent forwarding.


Mosh is a nice small utility which is available for download in the repository of most of the Linux Distributions. Though it has a few discrepancies specially security concern and additional requirement it’s features like remaining connected even while roaming is its plus point. My recommendation is Every Linux-er who deals with SSH should try this application and mind it, Mosh is worth a try.

Mhddfs – Combine Several Smaller Partition into One Large Virtual Storage

Let’s assume that you have 30GB of movies and you have 3 drives each 20 GB in size. So how will you store?
Obviously you can split your videos in two or three different volumes and store them on the drive manually. This certainly is not a good idea, it is an exhaustive work which requires manual intervention and a lots of your time.
Another solution is to create a RAID array of disk. The RAID has always remained notorious for loss of storage reliability and usable disk space. Another solution is mhddfs.
Combine Multiple Partitions in Linux
Mhddfs – Combine Multiple Partitions in Linux
mhddfs is a driver for Linux that combines several mount points into one virtual disk. It is a fuse based driver, which provides a easy solution for large data storage. It combines all small file systems to create a single big virtual filesystem which contains every particle of its member filesystem including files and free spaces.

Why you need Mhddfs?

All your storage devices creates a single virtual pool and it can be mounted right at the boot. This small utility takes care of, which drive is full and which is empty and to write data to what drive, intelligently. Once you create virtual drives successfully, you can share your virtual filesystem using SAMBA. Your client will always see a huge drive and lots of free space.

Features of Mhddfs

  1. Get attributes of the file system and system information.
  2. Set attributes of the file system.
  3. Create, Read, Remove and write Directories and files.
  4. Support for file locks and Hardlinks on single device.
Pros of mhddfsCons of mhddfs
 Perfect for home users.mhddfs driver is not built in the Linux Kernel
 Simple to run. Required lots of processing power during runtime
 No evidence of Data loss No redundancy solution.
 Do not split the file. Hardlinks moving not supported
 Add new files to the combined virtual filesystem. 
 Manage the location where these files are saved. 
  Extended file attributes 

Installation of Mhddfs in Linux

On Debian and portable to alike systems, you can install mhddfs package using following command.
# apt-get update && apt-get install mhddfs
Install Mhddfs on Debian based Systems
Install Mhddfs on Debian based Systems
On RHEL/CentOS Linux systems, you need to turn on epel-repository and then execute the below command to install mhddfs package.
# yum install mhddfs
On Fedora 22+ systems, you may get it by dnf package manger as shown below.
# dnf install mhddfs
Install Mhddfs on Fedora
Install Mhddfs on Fedora
If incase, mhddfs package isn’t available from epel repository, then you need to resolve following dependencies to install and compile it from source as shown below.
  1. FUSE header files
  2. GCC
  3. libc6 header files
  4. uthash header files
  5. libattr1 header files (optional)
Next, download the latest source package simply as suggested below and compile it.
# wget
# tar -zxvf mhddfs*.tar.gz
# cd mhddfs-0.1.39/
# make
You should be able to see binary mhddfs in the current directory. Move it to /usr/bin/ and /usr/local/bin/ as root.
# cp mhddfs /usr/bin/ 
# cp mhddfs /usr/local/bin/
All set, mhddfs is ready to be used.

How do I use Mhddfs?

1. Lets see all the HDD mounted to my system currently.
$ df -h
Check Mounted Devices
Sample Output
Filesystem      Size  Used Avail Use% Mounted on

/dev/sda1       511M  132K  511M   1% /boot/efi
/dev/sda2       451G   92G  336G  22% /
/dev/sdb1       1.9T  161G  1.7T   9% /media/avi/BD9B-5FCE
/dev/sdc1       555M  555M     0 100% /media/avi/Debian 8.1.0 M-A 1
Notice the ‘Mount Point‘ name here, which we will be using later.
2. Create a directory /mnt/virtual_hdd where all these all file system will be grouped together as,
# mkdir /mnt/virtual_hdd
3. And then mount all the file-systems. Either as root or as a user who is a member of FUSE group.
# mhddfs /boot/efi, /, /media/avi/BD9B-5FCE/, /media/avi/Debian\ 8.1.0\ M-A\ 1/ /mnt/virtual_hdd  -o allow_other
Mount All File System in Linux
Mount All File System in Linux
Note: We are used mount Point names here of all the HDDs. Obviously the mount point in your case will be different. Also notice “-o allow_other” option makes this Virtual file system visible to all others and not only the person who created it.
4. Now run “df -h” see all the filesystems. It should contain the one you created just now.
$ df -h
Verify Virtual File System Mount
Verify Virtual File System Mount
You can perform all the option to the Virtual File System you created as you would have done to a Mounted Drive.
5. To create this Virtual File system on every system boot, you should add the below line of code (in your case it should be different, depending upon your mount point), at the end of /etc/fstab file as root.
mhddfs# /boot/efi, /, /media/avi/BD9B-5FCE/, /media/avi/Debian\ 8.1.0\ M-A\ 1/ /mnt/virtual_hdd fuse defaults,allow_other 0 0
6. If at any point of time you want to add/remove a new drive to Virtual_hdd, you may mount a new drive, copy the contents of mount point /mnt/virtual_hddun-mount the volume, Eject the Drive you want to remove and/or mount the new drive you want to include, Mount the overall filesystem under Virtual_hdd using mhddfscommand and you should be done.

How do I Un-Mount Virtual_hdd?

Unmounting virtual_hdd is as easy as,
# umount /mnt/virtual_hdd
Unmount Virtual Filesystem
Unmount Virtual Filesystem
Notice it is umount and not unmount. A lot of user type it wrong.