sshd – the SSH Server Daemon

If you take a look at the process listing on almost any Linux or Unix host it is very likely that you find the sshd process - an SSH server (or a daemon as they are also called). A newcomer to process listings and the operating system may find such unknown processes suspect, but in this case there is nothing to worry about. Quite the contrary. This page explains what sshd is, and why it is important.

sshd - What is it?

So what is the sshd process and what does it do in the system?

sshd is the SSH daemon - the SSH server - that listens to the network for incoming requests from SSH clients. sshd runs with root privileges and usually binds to the TCP/IP port 22. The daemon is typically started during the host boot process, and is used for providing secure remote connectivity to the operating system for various administrative tasks.

The figure below presents a sample process listing of a Linux host with the sshd daemon visible.

The sshd process running in a Linux host

Note that sshd (often) runs with the privileges of the host’s root user (the “superuser”). This observation highlights the relative importance of SSH in a system – since the SSH server process runs with the elevated privileges of root user, it has total and unrestricted visibility inside the system. This means that the requirements for software quality and security for SSH server implementations are considerably higher than for most software.

What does sshd do?

sshd does the extremely important job of providing a secure, authenticated, and protected way of remotely accessing the host it runs in - from anywhere in the network. Without an SSH server, the only way to access the host’s operating system securely would be to be physically in the same space as the host. sshd allows secure remote login and file transfer without the risk of credential or password theft by network snooping.

Where to get an SSH Server?

SSH server software is available from specialized security software vendors, such as SSH Communications Security. SSH Communications Security serves demanding customers with an SSH Client and Server offering that covers commercially relevant Linux and Unix operating systems, as well as important business OSs such as the IBM zOS and Microsoft Windows operating systems.

For Linux and some Unix plaftfroms SSH Servers are also available from the OpenSSH project and its porting partners.

Is sshd available for Windows?

Yes, sshd (or SSH Server) is also available for the Windows operating system. In the Windows case, the same functionality is usually referred to as the “SSH Server” or “SSH Windows Server”, but the functionality and the use cases are very similar.

Commercial SSH Windows Server implementations are available from a number of SSH vendors – the leading Windows SSH Server is Tectia SSH Server for Windows from SSH Communications Security.