Run a command over SSH with JSch

Question

I m trying to run a command over SSH with JSch  but JSch has virtually no documentation and the examples I ve found are terrible  For example  this one doesn t show code for handling the output stream  And  this one uses an ugly hack to know when to stop reading from the output stream

User · Answer

The example provided by Mykhaylo Adamovych is very thorough and exposes most of the major features of JSch. I packaged this code (with attribution, of course) into an open-source library called Remote Session. I added JavaDoc and custom exceptions, and I also provided a facility to specify custom session parameters (RemoteConfig).

One feature that Mykhaylo's code doesn't demonstrate is how to provide an "identity" for remote system interactions. This is critical if you're going to execute commands that require super-user access (i.e. - sudo). Remote Session adds this capability in its SessionHolder.newSession() implementation:

RemoteConfig remoteConfig = RemoteConfig.getConfig();
Path keyPath = remoteConfig.getKeyPath();

if (keyPath == null) {
    throw new RemoteCredentialsUnspecifiedException();
}

String keyPass = remoteConfig.getString(RemoteSettings.SSH_KEY_PASS.key());
if (keyPass != null) {
    Path pubPath = keyPath.resolveSibling(keyPath.getFileName() + ".pub");
    jsch.addIdentity(keyPath.toString(), pubPath.toString(), keyPass.getBytes());
} else {
    jsch.addIdentity(keyPath.toString());
}

Note that this behavior is bypassed if the remote system URL includes credentials.

Another feature that Remote Session demonstrates is how to provide a known-hosts file:

if ( ! remoteConfig.getBoolean(RemoteSettings.IGNORE_KNOWN_HOSTS.key())) {
    Path knownHosts = keyPath.resolveSibling("known_hosts");
    if (knownHosts.toFile().exists()) {
        jsch.setKnownHosts(knownHosts.toString());
    }
}

Remote Session also adds a ChannelStream class that encapsulates input/output operation for the channel attached to this session. This provides the ability to accumulate the output from the remote session until a specified prompt is received:

private boolean appendAndCheckFor(String prompt, StringBuilder input, Logger logger) throws InterruptedException, IOException {
    String recv = readChannel(false);
    if ( ! ((recv == null) || recv.isEmpty())) {
        input.append(recv);
        if (logger != null) {
            logger.debug(recv);
        }
        if (input.toString().contains(prompt)) {
            return false;
        }
    }
    return !channel.isClosed();
}

Nothing too complicated, but this can greatly simplify the implementation of interactive remote operations.

User · Answer

I am using JSCH since about 2000 and still find it a good library to use  I agree it is not documented well enough but the provided examples seem good enough to understand that is required in several minutes  and user friendly Swing  while this is quite original approach  allows to test the example quickly to make sure it actually works  It is not always true that every good project needs three times more documentation than the amount of code written  and even when such is present  this not always helps to write faster a working prototype of your concept

User · Answer

Note that Charity Leschinski s answer may have a bit of an issue when there is some delay in the response   eg  lparstat 1 5  returns one response line and works   lparstat 5 1  should return 5 lines  but only returns the first  I ve put the command output while inside another     I m sure there is a better way  I had to do this as a quick fix          while  commandOutput available    gt  0                while  readByte    0xffffffff                    outputBuffer append  char  readByte                   readByte   commandOutput read                              try  Thread sleep 1000    catch  Exception ee

User · Answer

This is a shameless plug  but I m just now writing some extensive Javadoc for JSch   Also  there is now a Manual in the JSch Wiki  written mainly by me      About the original question  there is not really an example for handling the streams  Reading writing a stream is done as always   But there simply can t be a sure way to know when one command in a shell has finished just from reading the shell s output  this is independent of the SSH protocol    If the shell is interactive  i e  it has a terminal attached  it will usually print a prompt  which you could try to recognize  But at least theoretically this prompt string could also occur in normal output from a command  If you want to be sure  open individual exec channels for each command instead of using a shell channel  The shell channel is mainly used for interactive use by a human user  I think

User · Answer

using ssh from java should not be as hard as jsch makes it  you might be better off with sshj

User · Answer

Usage   String remoteCommandOutput   exec  ssh   user pass host work dir path    ls -t   head -n1    String remoteShellOutput   shell  ssh   user pass host work dir path    ls    shell  ssh   user pass host work dir path    ls   System out   shell  ssh   user pass host   System in  System out   sftp  file  C  home file txt    ssh   user pass host home    sftp  ssh   user pass host home file txt    file  C  home      Implementation   import static com google common base Preconditions checkState  import static java lang Thread sleep  import static org apache commons io FilenameUtils getFullPath  import static org apache commons io FilenameUtils getName  import static org apache commons lang3 StringUtils trim   import com google common collect ImmutableMap  import com jcraft jsch Channel  import com jcraft jsch ChannelExec  import com jcraft jsch ChannelSftp  import com jcraft jsch ChannelShell  import com jcraft jsch JSch  import com jcraft jsch JSchException  import com jcraft jsch Session  import com jcraft jsch UIKeyboardInteractive  import com jcraft jsch UserInfo  import org apache commons io IOUtils  import org slf4j Logger  import org slf4j LoggerFactory   import java io BufferedOutputStream  import java io ByteArrayOutputStream  import java io Closeable  import java io File  import java io FileInputStream  import java io FileOutputStream  import java io IOException  import java io InputStream  import java io OutputStream  import java io PipedInputStream  import java io PipedOutputStream  import java io PrintWriter  import java net URI  import java util Map  import java util Properties   public final class SshUtils        private static final Logger LOG   LoggerFactory getLogger SshUtils class       private static final String SSH    ssh       private static final String FILE    file        private SshUtils                            lt pre gt          lt code gt         sftp  file  C  home file txt    ssh   user pass host home           sftp  ssh   user pass host home file txt    file  C  home            lt  code gt                 lt pre gt                 param fromUri                   file         param toUri                   directory             public static void sftp String fromUri  String toUri            URI from   URI create fromUri           URI to   URI create toUri            if  SSH equals to getScheme     amp  amp  FILE equals from getScheme                 upload from  to           else if  SSH equals from getScheme     amp  amp  FILE equals to getScheme                 download from  to           else             throw new IllegalArgumentException               private static void upload URI from  URI to            try  SessionHolder lt ChannelSftp gt  session   new SessionHolder lt  gt   sftp   to                   FileInputStream fis   new FileInputStream new File from                   LOG info  Uploading    -- gt       from  session getMaskedUri                 ChannelSftp channel   session getChannel                channel connect                channel cd to getPath                 channel put fis  getName from getPath                 catch  Exception e                throw new RuntimeException  Cannot upload file   e                        private static void download URI from  URI to            File out   new File new File to   getName from getPath              try  SessionHolder lt ChannelSftp gt  session   new SessionHolder lt  gt   sftp   from                   OutputStream os   new FileOutputStream out                   BufferedOutputStream bos   new BufferedOutputStream os                  LOG info  Downloading    -- gt       session getMaskedUri    to               ChannelSftp channel   session getChannel                channel connect                channel cd getFullPath from getPath                  channel get getName from getPath     bos              catch  Exception e                throw new RuntimeException  Cannot download file   e                                    lt pre gt          lt code gt         shell  ssh   user pass host   System in  System out           lt  code gt          lt  pre gt              public static void shell String connectUri  InputStream is  OutputStream os            try  SessionHolder lt ChannelShell gt  session   new SessionHolder lt  gt   shell   URI create connectUri                  shell session  is  os                                    lt pre gt          lt code gt         String remoteOutput   shell  ssh   user pass host work dir path    ls           lt  code gt          lt  pre gt              public static String shell String connectUri  String command            ByteArrayOutputStream baos   new ByteArrayOutputStream            try               shell connectUri  command  baos               return baos toString              catch  RuntimeException e                LOG warn baos toString                 throw e                                   lt pre gt          lt code gt         shell  ssh   user pass host work dir path    ls   System out          lt  code gt          lt  pre gt              public static void shell String connectUri  String script  OutputStream out            try  SessionHolder lt ChannelShell gt  session   new SessionHolder lt  gt   shell   URI create connectUri                    PipedOutputStream pipe   new PipedOutputStream                    PipedInputStream in   new PipedInputStream pipe                   PrintWriter pw   new PrintWriter pipe                  if  session getWorkDir      null                  pw println  cd     session getWorkDir                 pw println script               pw println  exit                pw flush                 shell session  in  out             catch  IOException e                throw new RuntimeException e                        private static void shell SessionHolder lt ChannelShell gt  session  InputStream is  OutputStream os            try               ChannelShell channel   session getChannel                channel setInputStream is  true               channel setOutputStream os  true                LOG info  Starting shell for     session getMaskedUri                 session execute                session assertExitStatus  Check shell output for error details               catch  InterruptedException   JSchException e                throw new RuntimeException  Cannot execute script   e                                    lt pre gt          lt code gt         System out println exec  ssh   user pass host work dir path    ls -t   head -n1             lt  code gt                  lt pre gt                  param connectUri         param command         return             public static String exec String connectUri  String command            try  SessionHolder lt ChannelExec gt  session   new SessionHolder lt  gt   exec   URI create connectUri                  String scriptToExecute   session getWorkDir      null                       command                        cd     session getWorkDir       n    command              return exec session  scriptToExecute                        private static String exec SessionHolder lt ChannelExec gt  session  String command            try  PipedOutputStream errPipe   new PipedOutputStream                    PipedInputStream errIs   new PipedInputStream errPipe                   InputStream is   session getChannel   getInputStream                   ChannelExec channel   session getChannel                channel setInputStream null               channel setErrStream errPipe               channel setCommand command                LOG info  Starting exec for     session getMaskedUri                 session execute                String output   IOUtils toString is               session assertExitStatus IOUtils toString errIs                 return trim output             catch  InterruptedException   JSchException   IOException e                throw new RuntimeException  Cannot execute command   e                        public static class SessionHolder lt C extends Channel gt  implements Closeable            private static final int DEFAULT CONNECT TIMEOUT   5000          private static final int DEFAULT PORT   22          private static final int TERMINAL HEIGHT   1000          private static final int TERMINAL WIDTH   1000          private static final int TERMINAL WIDTH IN PIXELS   1000          private static final int TERMINAL HEIGHT IN PIXELS   1000          private static final int DEFAULT WAIT TIMEOUT   100           private String channelType          private URI uri          private Session session          private C channel           public SessionHolder String channelType  URI uri                this channelType  uri  ImmutableMap of  StrictHostKeyChecking    no                        public SessionHolder String channelType  URI uri  Map lt String  String gt  props                this channelType   channelType              this uri   uri              this session   newSession props               this channel   newChannel session                      private Session newSession Map lt String  String gt  props                try                   Properties config   new Properties                    config putAll props                    JSch jsch   new JSch                    Session newSession   jsch getSession getUser    uri getHost    getPort                     newSession setPassword getPass                     newSession setUserInfo new User getUser    getPass                      newSession setDaemonThread true                   newSession setConfig config                   newSession connect DEFAULT CONNECT TIMEOUT                   return newSession                catch  JSchException e                    throw new RuntimeException  Cannot create session for     getMaskedUri    e                                     SuppressWarnings  unchecked           private C newChannel Session session                try                   Channel newChannel   session openChannel channelType                   if  newChannel instanceof ChannelShell                        ChannelShell channelShell    ChannelShell  newChannel                      channelShell setPtyType  ANSI   TERMINAL WIDTH  TERMINAL HEIGHT  TERMINAL WIDTH IN PIXELS  TERMINAL HEIGHT IN PIXELS                                     return  C  newChannel                catch  JSchException e                    throw new RuntimeException  Cannot create     channelType     channel for     getMaskedUri    e                                    public void assertExitStatus String failMessage                checkState channel getExitStatus      0   Exit status  s for  s n s   channel getExitStatus    getMaskedUri    failMessage                      public void execute   throws JSchException  InterruptedException               channel connect                channel start                while   channel isEOF                    sleep DEFAULT WAIT TIMEOUT                      public Session getSession                 return session                     public C getChannel                 return channel                      Override         public void close                 if  channel    null                  channel disconnect                if  session    null                  session disconnect                       public String getMaskedUri                 return uri toString   replaceFirst                                      public int getPort                 return uri getPort    lt  0   DEFAULT PORT   uri getPort                       public String getUser                 return uri getUserInfo   split      0                      public String getPass                 return uri getUserInfo   split      1                      public String getWorkDir                 return uri getPath                         private static class User implements UserInfo  UIKeyboardInteractive            private String user          private String pass           public User String user  String pass                this user   user              this pass   pass                      Override         public String getPassword                 return pass                      Override         public boolean promptYesNo String str                return false                      Override         public String getPassphrase                 return user                      Override         public boolean promptPassphrase String message                return true                      Override         public boolean promptPassword String message                return true                      Override         public void showMessage String message                   do nothing                     Override         public String   promptKeyboardInteractive String destination  String name  String instruction  String   prompt  boolean   echo                return null

User · Answer

The gritty terminal was written to use Jsch  but with better handling and vt102 emulation  You can take a look at the code there  We use it and it works just fine

User · Answer

I struggled for half a day to get JSCH to work without using the System in as the input stream to no avail  I tried Ganymed http   www ganymed ethz ch ssh2  and had it going in 5 minutes   All the examples seem to be aimed at one usage of the app and none of the examples showed what i needed  Ganymed s example Basic java Baaaboof Has everything i need

User · Answer

The following code example written in Java will allow you to execute any command on a foreign computer through SSH from within a java program   You will need to include the com jcraft jsch jar file             SSHManager           author cabbott      version 1 0        package cabbott net     import com jcraft jsch      import java io IOException    import java io InputStream    import java util logging Level    import java util logging Logger     public class SSHManager       private static final Logger LOGGER          Logger getLogger SSHManager class getName       private JSch jschSSHChannel    private String strUserName    private String strConnectionIP    private int intConnectionPort    private String strPassword    private Session sesConnection    private int intTimeOut     private void doCommonConstructorActions String userName          String password  String connectionIP  String knownHostsFileName           jschSSHChannel   new JSch          try                jschSSHChannel setKnownHosts knownHostsFileName               catch JSchException jschX                 logError jschX getMessage                  strUserName   userName       strPassword   password       strConnectionIP   connectionIP         public SSHManager String userName  String password        String connectionIP  String knownHostsFileName           doCommonConstructorActions userName  password                   connectionIP  knownHostsFileName        intConnectionPort   22       intTimeOut   60000         public SSHManager String userName  String password  String connectionIP        String knownHostsFileName  int connectionPort           doCommonConstructorActions userName  password  connectionIP           knownHostsFileName        intConnectionPort   connectionPort       intTimeOut   60000         public SSHManager String userName  String password  String connectionIP         String knownHostsFileName  int connectionPort  int timeOutMilliseconds           doCommonConstructorActions userName  password  connectionIP            knownHostsFileName        intConnectionPort   connectionPort       intTimeOut   timeOutMilliseconds         public String connect            String errorMessage   null        try                sesConnection   jschSSHChannel getSession strUserName               strConnectionIP  intConnectionPort           sesConnection setPassword strPassword              UNCOMMENT THIS FOR TESTING PURPOSES  BUT DO NOT USE IN PRODUCTION            sesConnection setConfig  StrictHostKeyChecking    no            sesConnection connect intTimeOut               catch JSchException jschX                 errorMessage   jschX getMessage                 return errorMessage         private String logError String errorMessage           if errorMessage    null                 LOGGER log Level SEVERE    0   1  -  2                 new Object   strConnectionIP  intConnectionPort  errorMessage                 return errorMessage         private String logWarning String warnMessage           if warnMessage    null                 LOGGER log Level WARNING    0   1  -  2                new Object   strConnectionIP  intConnectionPort  warnMessage                 return warnMessage         public String sendCommand String command           StringBuilder outputBuffer   new StringBuilder          try                Channel channel   sesConnection openChannel  exec              ChannelExec channel  setCommand command           InputStream commandOutput   channel getInputStream            channel connect            int readByte   commandOutput read             while readByte    0xffffffff                       outputBuffer append  char readByte              readByte   commandOutput read                       channel disconnect                catch IOException ioX                 logWarning ioX getMessage             return null              catch JSchException jschX                 logWarning jschX getMessage             return null               return outputBuffer toString           public void close            sesConnection disconnect               For testing                Test of sendCommand method  of class SSHManager             Test   public void testSendCommand            System out println  sendCommand                      YOU MUST CHANGE THE FOLLOWING         FILE NAME  A FILE IN THE DIRECTORY         USER  LOGIN USER NAME         PASSWORD  PASSWORD FOR THAT USER         HOST  IP ADDRESS OF THE SSH SERVER               String command    ls FILE NAME        String userName    USER        String password    PASSWORD        String connectionIP    HOST        SSHManager instance   new SSHManager userName  password  connectionIP            String errorMessage   instance connect          if errorMessage    null                 System out println errorMessage           fail                 String expResult    FILE NAME n           call sendCommand for each command and the output          without prompts  is returned      String result   instance sendCommand command           close only after all commands are sent      instance close         assertEquals expResult  result

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