3. Networking: ssh

Another network tool is ssh, which can be used to login to a remote system, execute commands remotely, and more.

First let's create a user account:

sudo useradd -m -s /bin/bash user01

echo user01:pass01 | sudo chpasswd

Let's login to it:

ssh user01@localhost

ls -al

exit

We can also use ssh to just run a command remotely:

ssh user01@localhost ls -al

ssh user01@localhost whoami

ssh user01@localhost ls .*

ssh user01@localhost 'ls .*'

Writing a password each time that we use ssh quickly becomes tedious. We can use keys instead, which is easier and more secure.

First let's generate a public/private key pair:
```
ssh-keygen --help
```
```
ssh-keygen -t ecdsa -q -N '' -f ~/.ssh/key1
```
The option -N '' makes it generate a key that does not have a passphrase.
```
ls -al ~/.ssh/key1*
```
```
cat ~/.ssh/key1
```
```
cat ~/.ssh/key1.pub
```
In order to be able to login to the server with this key, we need to send the public part of it to the server:
```
ssh-copy-id -i ~/.ssh/key1.pub user01@localhost
```
Now let's try to login using the private key as an identity file:
```
ssh -i ~/.ssh/key1 user01@localhost
```
```
ls -al
```
```
cat .ssh/authorized_keys
```
```
exit
```
```
cat ~/.ssh/key1.pub
```
You may notice that the public key has been appended to .ssh/authorized_keys on the server.

It gets even better. Let's add this configuration to ~/.ssh/config:
```
cat <<EOF >> ~/.ssh/config
Host server1
    HostName 127.0.0.1
    User user01
    IdentityFile ~/.ssh/key1
EOF
```
```
cat ~/.ssh/config
```
Now we can just use ssh with the name server1, without having to specify the hostname (or IP) of the server, the username, the identity file etc. It will get them automatically from the config file.
```
ssh server1
```
```
exit
```
```
ssh server1 whoami
```

Using scp, sftp, rsync etc.

All these tools use an SSH tunnel for a secure communication with the server. Now that we have an easy ssh access to the server, we can also use easily these tools:

touch foo.txt

scp foo.txt server1:

ssh server1 ls -l

ssh server1 touch bar.txt

ssh server1 ls -l

scp server1:bar.txt .

ls -l bar.txt

sftp:

sftp server1

ls

help

quit

rsync:

ls testdir

rsync -av testdir server1:

ssh server1 ls

ssh server1 ls testdir

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