Useful SSH/SCP Commands

This post was translated from Korean into English by AI.

SSH / SCP commands are most often used when working with remote servers. Here are a few useful commands worth knowing.

Below, local machine refers to the computer on which you are running the command.
Below, remote server refers to another computer that you want to control through the local machine.

Connecting to a Remote Server

ssh [username]@[hostname] -p [sshport]
ssh unknownpgr@my-webserver.server.io -p 1234

Running a Specific Command on a Remote Server

ssh [username]@[hostname] -p [sshport] command
ssh unknownpgr@192.168.0.2 -p 22 make

This runs the given command on the remote server.

Forwarding a Port to a Specific Port on a Remote Server

As you can see in the examples below, the -N option is included. This option prevents a Bash shell from being opened. It is useful when you do not need a Bash shell, such as when forwarding ports.

ssh -N -L [localport]:[destserver]:[destport] [jumpserver]
ssh -N -L 9876:inta.server.com:80 public.server.com

Running the example above connects port 9876 on localhost to port 80 on inta.server.com through the public.server.com server. This is useful when a secure connection is required. For example, code-server also recommends connecting to code-server with a command like the following.

ssh -N -L 8080:127.0.0.1:8080 <instance-ip> # After doing this, open localhost:8080 in your browser.

Forwarding a Port from a Remote Server to the Local Machine

ssh -R [remoteport]:[host]:[hostport] [remote]
ssh -R 8080:localhost:5000 remote.server.com
ssh -R 8080:www.google.com:80 remote.server.com

This option can be a little confusing. More precisely, it works as follows.

It makes the remoteport port on the remote server connect through the local machine to hostport on the host server.

Therefore, the second example connects port 8080 on remote.server.com to port 5000 on the local machine, while the third example connects port 8080 on remote.server.com through the local machine to port 80 on www.google.com. Additional options can be used to accept connections on various interfaces, but the default is localhost. In other words, opening remote.server.com:8080 in my web browser will not work, but running curl localhost:8080 on the remote server will connect through the local machine to the desired destination server.

Transferring a File from the Local Machine to a Remote Server

scp [local-file-path] [username]@[host]:[remote-file-path]
scp ~/file.txt unknownpgr@remote.server.com:"~/remote-path"

This places the file at local-file-path on the local machine into the remote-file-path directory on the host remote server. Running the second example saves the ~/file.txt file from the local machine in the ~/remote-path directory on the remote.server.com server.

Transferring a Directory from the Local Machine to a Remote Server

scp -r [local-folder] [user]@[host]:[remote-dir]

This is almost identical to the command above, except that it copies an entire directory rather than a single file.

Transferring a File from a Remote Server to the Local Machine

scp [user]@[host]:[remote-file] [local-dir]

This is also exactly the same as transferring from the local machine to the remote server, except that the order is reversed. It moves remote-file from the host remote server to local-dir on the local machine. Likewise, adding the -r option lets you transfer an entire directory.