scala-ssh is a Scala library providing remote shell access via SSH. It builds on SSHJ to provide the following features:

• Remote execution of one or more shell commands
• Access to stdin, stdout, stderr and exitcode of remote shell commands
• Authentication via password, public key or agent
• Host key verification via known_hosts file or explicit fingerprint
• Convenient configuration of remote host properties via config file, resource or directly in code
• Scala-idiomatic API

The latest release is 0.11.1 and is built against Scala 2.12, 2.13 and 3. It is available from Maven Central. If you use SBT you can pull in the scala-ssh artifacts with:

libraryDependencies += "com.decodified" %% "scala-ssh" % "0.11.1"

SSHJ uses SLF4J for logging, so you might want to also add logback to your dependencies:

libraryDependencies += "ch.qos.logback" % "logback-classic" % "1.2.3"

The highest-level API element provided by scala-ssh is the SSH object. You use it like this:

SSH("example.com") { client =>
  for {
    result <- client.exec("ls -a")
  } println("Result:\n" + result.stdOutAsString())
}

This establishes an SSH connection to host example.com and gives you an SshClient instance that you can use to execute one or more commands on the host. SSH.apply has a second (optional) parameter of type HostConfigProvider, which is essentially a function returning a HostConfig instance for a given hostname. A HostConfig looks like this:

case class HostConfig(
  login: SshLogin,
  hostName: String = "",
  port: Int = 22,
  connectTimeout: Option[Int] = None,
  connectionTimeout: Option[Int] = None,
  commandTimeout: Option[Int] = None,
  enableCompression: Boolean = false,
  hostKeyVerifier: HostKeyVerifier = ...,
  sshjConfig: Config = ...
)

It provides all the details required for properly establishing an SSH connection. If you don't provide an explicit HostConfigProvider the default one will be used. For every hostname you pass to the SSH.apply method this default HostConfigProvider expects a file ~/.scala-ssh/{hostname}, which contains the properties of a HostConfig in a simple config file format (see below for details). The HostResourceConfig object gives you alternative HostConfigProvider implementations that read the host config from classpath resources.

If the file ~/.scala-ssh/{hostname} (or the classpath resource {hostname}) doesn't exist scala-ssh looks for more general files (or resources) in the following way:

1. As long as the first segment of the host name (up to the first .) contains one or more digits replace the rightmost of these with X and look for a respectively named file or resource. Repeat until no digits left.
2. Drop all characters up to (and including) the first . from the host name and look for a respectively named file or resource.
3. Repeat from 1. as long as there are characters left.

This means that for a host with name node42.tier1.example.com the following locations (either under ~/.scala-ssh/ or the classpath, depending on the HostConfigProvider) are tried:

1. node42.tier1.example.com
2. node4X.tier1.example.com
3. nodeXX.tier1.example.com
4. tier1.example.com
5. tierX.example.com
6. example.com
7. com

A host config file is a UTF8-encoded text file containing key = value pairs, one per line. Blank lines and lines starting with a # character are ignored. This is an example file:

# simple password-based config
login-type = password
username = bob
password = 123
command-timeout = 5000
enable-compression = yes

These key are defined:

login-type

required, can be either password or keyfile

host-name

optional, if not given the name of the config file is assumed to be the hostname

port

optional, the default value is 22

username

required

password

required for login-type password, ignored otherwise

keyfile

optionally specifies the location of the user keyfile to use with login-type keyfile, if not given the default files ~/.ssh/id_ed25519, ~/.ssh/id_rsa and ~/.ssh/id_dsa are tried, if the filename starts with a + the file is searched in addition to the default locations, if the filename starts with classpath: it is interpreted as the name of a classpath resource holding the private key, ignored for login-type password

passphrase

optionally specifies the passphrase for the keyfile, if not given the keyfile is assumed to be unencrypted, ignored for login-type password

connect-timeout

optionally specifies the number of milli-seconds that a connection request has to succeed in before triggering a timeout error, default value is 'no timeout'

connection-timeout

optionally specifies the number of milli-seconds that an idle connection is held open before being closed due due to idleness, default value is 'no timeout'

command-timeout

optionally specifies the number of milli-seconds that a pending response to an issued command is waited for before triggering a timeout error, default value is 'no timeout'

enable-compression

optionally adds zlib compression to preferred compression algorithms, there is no guarantee that it will be successfully negotiatied, requires jzlib on the classpath (see 'installation' chapter) above, default is 'no'

fingerprint

optionally specifies the fingerprint of the public host key to verify in standard SSH format (e.g. 4b:69:6c:72:6f:79:20:77:61:73:20:68:65:72:65:21), if not given the standard ~/.ssh/known_hosts or ~/.ssh/known_hosts2 files will be searched for a matching entry, fingerprint verification can be entirely disabled by setting fingerprint = any

Troubleshooting --------------

To use this library it might be necessary that you install the Java Cryptography Extension Policy Files from the JDK additional downloads section. Make sure they are installed, especially if you encounter exceptions like this:

net.schmizz.sshj.common.SSHRuntimeException: null

at net.schmizz.sshj.common.Buffer.readPublicKey(Buffer.java:432) ~[sshj-0.12.0.jar:na] at net.schmizz.sshj.transport.kex.AbstractDHG.next(AbstractDHG.java:108) ~[sshj-0.12.0.jar:na] at net.schmizz.sshj.transport.KeyExchanger.handle(KeyExchanger.java:352) ~[sshj-0.12.0.jar:na] at net.schmizz.sshj.transport.TransportImpl.handle(TransportImpl.java:487) ~[sshj-0.12.0.jar:na] at net.schmizz.sshj.transport.Decoder.decode(Decoder.java:107) ~[sshj-0.12.0.jar:na] at net.schmizz.sshj.transport.Decoder.received(Decoder.java:175) ~[sshj-0.12.0.jar:na] at net.schmizz.sshj.transport.Reader.run(Reader.java:61) ~[sshj-0.12.0.jar:na]

Caused by: java.security.GeneralSecurityException: java.security.spec.InvalidKeySpecException: key spec not recognised

at net.schmizz.sshj.common.KeyType$3.readPubKeyFromBuffer(KeyType.java:146) ~[sshj-0.12.0.jar:na] at net.schmizz.sshj.common.Buffer.readPublicKey(Buffer.java:430) ~[sshj-0.12.0.jar:na] ... 6 common frames omitted

Caused by: java.security.spec.InvalidKeySpecException: key spec not recognised

at org.bouncycastle.jcajce.provider.asymmetric.util.BaseKeyFactorySpi.engineGeneratePublic(Unknown Source) ~[bcprov-jdk15on-1.52.jar:1.52.0] at org.bouncycastle.jcajce.provider.asymmetric.ec.KeyFactorySpi.engineGeneratePublic(Unknown Source) ~[bcprov-jdk15on-1.52.jar:1.52.0] at java.security.KeyFactory.generatePublic(KeyFactory.java:334) ~[na:1.8.0_05] at net.schmizz.sshj.common.KeyType$3.readPubKeyFromBuffer(KeyType.java:144) ~[sshj-0.12.0.jar:na] ... 7 common frames omitted

Some of the tests needs a running SSH daemon and expects particular structure of ~/.scala-ssh. In case you want to run those tests locally there is prepared structure to run dockerized sbt and sshd. Running dockerized structure should work just by itself:

` scripts/local/dockerized-sbt.sh # and then in sbt: test`

Having sbt as a separate step make it easier to run changes iteratively in dockerized sbt.

scala-ssh is licensed under APL 2.0.

Feedback and contributions to the project, no matter what kind, are always very welcome. However, patches can only be accepted from their original author. Along with any patches, please state that the patch is your original work and that you license the work to the scala-ssh project under the project’s open source license.