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How to avoid multiple SSH connections on data transfer?

When transferring multiple files, it can be problematic to use a separate SSH connection for each transfer operation. The network firewall can block a large amount of independent simultaneous SSH connections. There are different options to avoid multiple SSH connections:

Use rsync or use scp with multiple files:

rsync -avhzP local_folder/ username@host:remote_folder

rsync only copies new or changed files, this will reserve transfer bandwith.

scp -r local_folder/ username@host:remote_folder

will copy local_folder recursively

Use tar-container to transfer less files

Creating a tar file and transfer it can be much faster compared to transferring all files separately:

tar -cf tar.file local_folder

The tar file creation, transmission and extraction process can also be done on the fly:

tar -c local_folder/ | ssh username@host \
'cd remote_folder; tar -x'

Use shared SSH connection

Shared SSH connections allow usage of the same connection multiple times:

Open master connection:

ssh -M -S /tmp/ssh_mux_%h_%p_%r username@host

Reuse connection:

ssh -S /tmp/ssh_mux_%h_%p_%r username@host

A shared connection can also be used when using scp:

scp -o 'ControlPath /tmp/ssh_mux_%h_%p_%r' \
local_folder username@host:remote_folder