Date: 2023-10-16

# Secure Shell (SSH) Client for R

#### 2023-10-16

## Installation

On Windows or MacOS you can install the binary package directly from CRAN:

    install.packages("ssh")

Installation from source requires `libssh` (which is not `libssh2`). On Debian or Ubuntu use libssh-dev:

    sudo apt-get install -y libssh-dev

On Fedora we need libssh-devel:

    sudo yum install libssh-devel

On CentOS / RHEL we install libssh-devel via EPEL:

    sudo yum install epel-release
    sudo yum install libssh-devel

On OS-X use libssh from Homebrew:

    brew install libssh

## Connecting to an SSH server

First create an ssh session by connecting to an SSH server.

    session <- ssh_connect("jeroen@dev.opencpu.org")
    print(session)

    <ssh session>
    jeroen@dev.opencpu.org:22 (connected)
    server: 90:eb:52:6b:ee:fc:de:f1:c0:66:6c:53:82:dd:ce:80:d3:85:1e:d8

Once established, a session is closed automatically by the garbage collector when the object goes out of scope or when R quits. You can also manually close it using `ssh_disconnect()` but this is not strictly needed.

## Authentication

The client attempts to use the following authentication methods (in this order) until one succeeds:

1. try key from `privkey` argument in `ssh_connect()` if specified
2. if ssh-agent is available, try private key from ssh-agent
3. try user key specified in `~/.ssh/config` or any of the default locations: `~/.ssh/id_ed25519`, `~/.ssh/id_ecdsa`, `~/.ssh/id_rsa`, or `.ssh/id_dsa`.
4. Try challenge-response password authentication (if permitted by the server)
5. Try plain password authentication (if permitted by the server)

To debug authentication set verbosity to at least level 2 or 3:

    session <- ssh_connect("jeroen@dev.opencpu.org", verbose = 2)

    ssh_socket_connect: Nonblocking connection socket: 7
    ssh_connect: Socket connecting, now waiting for the callbacks to work
    socket_callback_connected: Socket connection callback: 1 (0)
    ssh_client_connection_callback: SSH server banner: SSH-2.0-OpenSSH_7.2p2 Ubuntu-4ubuntu2.4
    ssh_analyze_banner: Analyzing banner: SSH-2.0-OpenSSH_7.2p2 Ubuntu-4ubuntu2.4
    ssh_analyze_banner: We are talking to an OpenSSH client version: 7.2 (70200)
    ssh_packet_dh_reply: Received SSH_KEXDH_REPLY
    ssh_client_curve25519_reply: SSH_MSG_NEWKEYS sent
    ssh_packet_newkeys: Received SSH_MSG_NEWKEYS
    ssh_packet_newkeys: Signature verified and valid
    ssh_packet_userauth_failure: Access denied. Authentication that can continue: publickey
    ssh_packet_userauth_failure: Access denied. Authentication that can continue: publickey
    ssh_agent_get_ident_count: Answer type: 12, expected answer: 12
    ssh_userauth_publickey_auto: Successfully authenticated using /Users/jeroen/.ssh/id_rsa

Tools for setting up and debugging your ssh keys are provided via the `credentials` package.

    ssh_key_info()

    $key
    [1] "/Users/jeroen/.ssh/id_ed25519"

    $pubkey
    [1] "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAILGN+5tybmwKhcxvnwPSKlrp39Ni1gMD0UhV4gCxHg/x"

## Execute Script or Command

Run a command or script on the host and block while it runs. By default stdout and stderr are steamed directly back to the client. This function returns the exit status of the remote command (hence it does not automatically error for an unsuccessful exit status).

    out <- ssh_exec_wait(session, command = 'whoami')

    jeroen

    print(out)

    [1] 0

You can also run a script that consists of multiple commands.

    ssh_exec_wait(session, command = c(
      'curl -O https://cran.r-project.org/src/contrib/Archive/jsonlite/jsonlite_1.4.tar.gz',
      'R CMD check jsonlite_1.4.tar.gz',
      'rm -f jsonlite_1.4.tar.gz'
    ))

      % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                     Dload  Upload   Total   Spent    Left  Speed
    100 1071k  100 1071k    0     0   654k      0  0:00:01  0:00:01 --:--:--  654k
    * using log directory '/home/jeroen/jsonlite.Rcheck'
    * using R version 3.4.3 (2017-11-30)
    * using platform: x86_64-pc-linux-gnu (64-bit)
    * using session charset: ASCII
    * checking for file 'jsonlite/DESCRIPTION' ... OK
    * this is package 'jsonlite' version '1.4'
    * checking package namespace information ... OK
    * checking package dependencies ...
    ...

### Capturing output

The `ssh_exec_internal()` is a convenient wrapper for `ssh_exec_wait()` which buffers the output steams and returns them as a raw vector. Also it raises an error by default when the remote command was not successful.

    out <- ssh_exec_internal(session, "R -e 'rnorm(10)'")
    print(out$status)

    [1] 0

    cat(rawToChar(out$stdout))

    R version 4.1.2 (2021-11-01) -- "Bird Hippie"
    Copyright (C) 2021 The R Foundation for Statistical Computing
    Platform: x86_64-pc-linux-gnu (64-bit)

    R is free software and comes with ABSOLUTELY NO WARRANTY.
    You are welcome to redistribute it under certain conditions.
    Type 'license()' or 'licence()' for distribution details.

      Natural language support but running in an English locale

    R is a collaborative project with many contributors.
    Type 'contributors()' for more information and
    'citation()' on how to cite R or R packages in publications.

    Type 'demo()' for some demos, 'help()' for on-line help, or
    'help.start()' for an HTML browser interface to help.
    Type 'q()' to quit R.

    > rnorm(10)
     [1] -0.3837970  0.9754719  0.9999716 -0.2634097  0.1845797 -0.5664418
     [7]  0.6975547 -0.2063897 -0.7263869  2.3826802
    >
    >

This function is very useful if you are running a remote command and want to use it’s output as if you had executed it locally.

### Using sudo

Note that the exec functions are non interactive so they cannot prompt for a sudo password. A trick is to use `-S` which reads the password from stdin:

    command <- 'echo "mypassword!" | sudo -s -S apt-get update -y'
    out <- ssh_exec_wait(session, command)

Be very careful with hardcoding passwords!

## Transfer Files via SCP

Upload and download files via SCP. Directories are automatically traversed as in `scp -r`.

    # Upload a file to the server
    file_path <- R.home("COPYING")
    scp_upload(session, file_path)

    # Download the file back and verify it is the same
    scp_download(session, "COPYING", to = tempdir())
    tools::md5sum(file_path)
    tools::md5sum(file.path(tempdir(), "COPYING"))

## Hosting a Tunnel

Opens a port on your machine and tunnel all traffic to a custom target host via the SSH server.

    ssh_tunnel(session, port = 5555, target = "ds043942.mongolab.com:43942")

This function blocks while the tunnel is active. Use the tunnel by connecting to `localhost:5555` from a separate process. The tunnel can only be used once and will automatically be closed when the client disconnects.

## Disconnecting

When you are done with the session you should disconnect:

    ssh_disconnect(session)

If you forgot to disconnect, the garbage collector will do so for you (with a warning).