plink

Plink: command-line connection utility Release 0.67 Usage: plink [options] [user@]host [command]        ("host" can also be a PuTTY saved session name) Options:   -V        print version information and exit   -pgpfp    print PGP key fingerprints and exit   -v        show verbose messages   -load sessname  Load settings from saved session   -ssh -telnet -rlogin -raw -serial             force use of a particular protocol   -P port   connect to specified port   -l user   connect with specified username   -batch    disable all interactive prompts   -sercfg configuration-string (e.g. 19200,8,n,1,X)             Specify the serial configuration (serial only) The following options only apply to SSH connections:   -pw passw login with specified password   -D [listen-IP:]listen-port             Dynamic SOCKS-based port forwarding   -L [listen-IP:]listen-port:host:port             Forward local port to remote address   -R [listen-IP:]listen-port:host:port             Forward remote port to local address   -X -x     enable / disable X11 forwarding   -A -a     enable / disable agent forwarding   -t -T     enable / disable pty allocation   -1 -2     force use of particular protocol version   -4 -6     force use of IPv4 or IPv6   -C        enable compression   -i key    private key file for user authentication   -noagent  disable use of Pageant   -agent    enable use of Pageant   -hostkey aa:bb:cc:...             manually specify a host key (may be repeated)   -m file   read remote command(s) from file   -s        remote command is an SSH subsystem (SSH-2 only)   -N        don't start a shell/command (SSH-2 only)   -nc host:port             open tunnel in place of session (SSH-2 only)   -sshlog file   -sshrawlog file             log protocol details to a file

7.2.2 Using Plink for automated connections

More typically Plink is used with the SSH protocol, to enable you to talk directly to a program running on the server. To do this you have to ensure Plink is using the SSH protocol. You can do this in several ways:

• • Use the -ssh option as described in section 7.2.1.

  • Set up a PuTTY saved session that describes the server you are connecting to, and that also specifies the protocol as SSH.

  • Set the Windows environment variable PLINK_PROTOCOL to the word ssh.

Usually Plink is not invoked directly by a user, but run automatically by another process. Therefore you typically do not want Plink to prompt you for a user name or a password.

Next, you are likely to need to avoid the various interactive prompts Plink can produce. You might be prompted to verify the host key of the server you're connecting to, to enter a user name, or to enter a password.

To avoid being prompted for the server host key when using Plink for an automated connection, you should first make a manual connection (using either of PuTTY or Plink) to the same server, verify the host key (see section 2.2 for more information), and select Yes to add the host key to the Registry. After that, Plink commands connecting to that server should not give a host key prompt unless the host key changes.

To avoid being prompted for a user name, you can:

• • Use the -l option to specify a user name on the command line. For example, plink login.example.com -l fred.

  • Set up a PuTTY saved session that describes the server you are connecting to, and that also specifies the username to log in as (see section 4.14.1).

To avoid being prompted for a password, you should almost certainly set up public-key authentication. (See chapter 8 for a general introduction to public-key authentication.) Again, you can do this in two ways:

• • Set up a PuTTY saved session that describes the server you are connecting to, and that also specifies a private key file (see section 4.21.8). For this to work without prompting, your private key will need to have no passphrase.

  • Store the private key in Pageant. See chapter 9 for further information.

Once you have done all this, you should be able to run a remote command on the SSH server machine and have it execute automatically with no prompting:

Z:\sysosd>plink login.example.com -l fred echo hello, world hello, world  Z:\sysosd>

Or, if you have set up a saved session with all the connection details:

Z:\sysosd>plink mysession echo hello, world hello, world  Z:\sysosd>

Then you can set up other programs to run this Plink command and talk to it as if it were a process on the server machine.

7.2.3 Plink command line options

Plink accepts all the general command line options supported by the PuTTY tools. See section 3.8.3 for a description of these options.

Plink also supports some of its own options. The following sections describe Plink's specific command-line options.

7.2.3.1 -batch: disable all interactive prompts

If you use the -batch option, Plink will never give an interactive prompt while establishing the connection. If the server's host key is invalid, for example (see section 2.2), then the connection will simply be abandoned instead of asking you what to do next.

This may help Plink's behaviour when it is used in automated scripts: using -batch, if something goes wrong at connection time, the batch job will fail rather than hang.

7.2.3.2 -s: remote command is SSH subsystem

If you specify the -s option, Plink passes the specified command as the name of an SSH ‘subsystem’ rather than an ordinary command line.

(This option is only meaningful with the SSH-2 protocol.)

7.3 Using Plink in batch files and scripts

Once you have set up Plink to be able to log in to a remote server without any interactive prompting (see section 7.2.2), you can use it for lots of scripting and batch purposes. For example, to start a backup on a remote machine, you might use a command like:

plink root@myserver /etc/backups/do-backup.sh

Or perhaps you want to fetch all system log lines relating to a particular web area:

plink mysession grep /~fred/ /var/log/httpd/access.log > fredlog

Any non-interactive command you could usefully run on the server command line, you can run in a batch file using Plink in this way.