Copying files and port forwarding

Transfer files with scp, sftp and rsync, then forward ports through an SSH connection.

Copy files with scp

scp report.pdf ana@server.example.com:/home/ana/        # upload
scp ana@server.example.com:/var/log/app.log .            # download to current dir
scp -r project/ ana@server.example.com:/home/ana/        # a whole directory
scp -P 2222 file.txt ana@server.example.com:~            # custom port: uppercase P

sftp and rsync

• sftp ana@server.example.com opens an interactive session with ls, get, put and cd.
• rsync -avz -e ssh project/ ana@server.example.com:/home/ana/project/ copies only what changed, so repeated transfers are fast. Mind the trailing slash: project/ copies the contents, project copies the folder itself.

Local port forwarding (-L)

A tunnel carries traffic for another service inside your SSH connection. Suppose a database listens only on localhost of a remote server. This makes it reachable on your laptop:

ssh -L 5433:localhost:5432 ana@db.example.com

Read it as -L local_port:destination_host:destination_port. Connections to localhost:5433 on your machine travel through SSH and come out on the server, which connects to localhost:5432 as seen from the server. Add -N to open the tunnel without a shell.

Remote (-R) and dynamic (-D) forwarding

• -R 8080:localhost:3000 exposes a service on your machine through a port on the server. It is the reverse of -L.
• -D 1080 starts a local SOCKS proxy. Point a browser at localhost:1080 and its traffic exits from the server.

CarefulTunnels punch holes through firewalls. Open them only for services you are allowed to reach, and close them when you finish.