SSH Protocols – Difference Between SFTP, SCP, and FISH

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I used to think SCP is a tool to copy files over SSH, and copying files over SSH is called SFTP, which is itself a synonym to FISH.

But now as I was looking for a Total Commander plugin to do this in Windows, I've noticed that on its page it says "Allows access to remote servers via secure FTP (FTP via SSH). Requires SSH2. This is NOT the same as SCP!".

If it's not the same then what am I misunderstanding?

Best Answer

SFTP isn't the FTP protocol over ssh, but an extension to the SSH protocol included in SSH2 (and some SSH1 implementations). SFTP is a file transfer protocol similar to FTP but uses the SSH protocol as the network protocol (and benefits from leaving SSH to handle the authentication and encryption).

SCP is only for transferring files, and can't do other things like list remote directories or removing files, which SFTP does do.

FISH appears to be yet another protocol that can use either SSH or RSH to transfer files.

UPDATE (2021/03/09): According to the release notes of OpenSSH 8.0/8.0p1 (2019-04-17):

The scp protocol is outdated, inflexible and not readily fixed. We recommend the use of more modern protocols like sftp and rsync for file transfer instead.

Related Solutions

SSHFS/SFTP – How to Fix Vim Hanging and Upload Issues Over SSHFS and SFTP

The sshfs FUSE filesystem is implemented by presenting a filesystem on top of sftp, the file transfer protocol. As a result, any file access such as editing with vi[m] requires the sshfs subsystem first to copy the file to a cache on the local filesystem. If the file is particularly large, or the network between your client and the server is particularly slow, it will take a measurable amount of time to transfer the file before it's accessible locally.

It's (very) broadly equivalent to the following (except it uses sftp instead of scp)

# Copy the remote file to a temporary local cache
scp -p remote:/path/to/file /tmp/file.tmp
checksum=$(cksum /tmp/file.tmp)

# Action on remote file is implemented by performing the action locally
vi /tmp/file.tmp

# Simplified; we would also need to handle local rm/mv -> remote rm/mv, etc.
[[ "$(cksum /tmp/file.tmp)" != "$checksum" ]] && scp -p /tmp/file.tmp remote:/path/to/file

As a consequence, you'll find that trying to run gcc locally will be measurably slower than just logging in to the remote server and running it there. To be honest I'm not overly surprised that "gcc crashes when trying to compile files on the remote fs". It shouldn't, of course, but then think about what's actually going on in the background...

Best Answer

Related Solutions

SSHFS/SFTP – How to Fix Vim Hanging and Upload Issues Over SSHFS and SFTP

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