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Useful SSH and SCP commands and config

SSH and SCP are really powerful commands. In this entry I quickly explain them and show nice usage cases and configurations.

SSH

Easily put, SSH connects to another machine via terminal: ssh [user]@[ip, domain or hostName] -p [port]

  • Execute commands in another machine through SSH, all in one command, so it can be used in scripts:ssh -t [connexionParams] "bash command 1; bash command 2; ...". If one of the commands usesudo, it will prompt for the user/pass for the user to add it, in a way as you would expect.

SCP copies files from one machine to another by using SSH.

  • SCP takes 2 SSH commands as parameters. The first ssh is the origin (where you copy) and the second the destination (where you paste): scp [sshCommand1]:[pathWhereFileIs] [sshCommand2]:[destinationDirectoryOrFile]. Note the usage of :to separate between ssh command and path. Example: scp [email protected]:relativePath/to/foo's/home [email protected]:/abs/path.

  • If you want to copy or paste to the actual machine we are using, just avoid a ssh command: scp [email protected]:/file1 ~/destination/path/in/my/computer.

  • SCP accepts the same parameters as ssh, which transmits to ssh. However be careful when, for example, setting a port, as will set the port to both ssh's.

  • You can copy multiple files/dirs with -R: scp -R ssh1:dir1 ssh2:dir2

  • Copy the contents of a file from machine 1 to our clipboard: scp [ssh1]:file /dev/stdout | pbcopy. Note that bcopyis in macOS, just change it for your clipboard.

  • Paste in multiple machines: scp [ssh1]:[file1] [ssh2]:[file2] [ssh3]:[file3]...It will copy from ssh1 to ssh2 ... sshN.

SSH config

If you SSH often, do usea config. Seriously, it will simplify your life.

Write in the file ~/.ssh/config:

Host foo
    HostName www.foo.com # It can be an IP too.
    User dogo # Optional. If you don't add it it will prompt for it
    Port 2222 # Optional. by default 22

And connect as ssh foo or use scp foo:file1 ....

Don't check or save host keys

This is useful if connecting to computers that often change but share the same IP, and you know the connection won't be compromised (man in the middle attack and those things).

Host foo
        StrictHostKeyChecking no
        UserKnownHostsFile=/dev/null

Use wildcards and precedence to target multiple PCs

For example, the following says: "For host foo, connect through a specific IP with user foobar. Don't check for host keys on computers from my local network and always, if I don't specify the contrary, login with the user_dogo_".

Host foo
    HostName 192.168.1.10
    User foobar
Host 192.168.1.*
    StrictHostKeyChecking no
    UserKnownHostsFile=/dev/null
Host *
    User dogo

SSH to machine and use it's localhost

For example to connect to a local server.

Host foo
    HostName foo.com
    LocalForward 8080 localhost:80

So, if after performing ssh to_foo_ I go to my pc and write in the browser localhost:8080, it will connect to the_foo's_80 port. foo will understand that this is a_local_ connection, so it will allow you even if foo blocks extraneous (ex: firewall) from accessing the port 80.

There are more tricks on-line and I encourage you to man ssh, man scp, and man ssh_config. They are well documented.