Next: GVFS based methods, Previous: Inline methods, Up: Configuration [Contents][Index]

### 4.3 External methods

External methods operate over multiple channels, using the remote shell connection for some actions while delegating file transfers to an external transfer program.

External methods save on the overhead of encoding and decoding of inline methods.

Since external methods have the overhead of opening a new channel, files smaller than tramp-copy-size-limit still use inline methods.

`rcp`—`rsh` and `rcp`

  This method uses the `rsh` and `rcp` commands to connect to the remote host and transfer files. This is the fastest access method available.

  The alternative method `remcp` uses the `remsh` and `rcp` commands.

`scp`—`ssh` and `scp`

  Using a combination of `ssh` to connect and `scp` to transfer is the most secure. While the performance is good, it is slower than the inline methods for smaller files. Though there is no overhead of encoding and decoding of the inline methods, `scp`’s cryptographic handshake negates those speed gains.

  `ssh`-based methods support ‘`-p`’ feature for specifying port numbers. For example, `host#42` passes ‘`-p 42`’ in the argument list to `ssh`, and ‘`-P 42`’ in the argument list to `scp`.

`rsync`—`ssh` and `rsync`

  `ssh` command to connect in combination with `rsync` command to transfer is similar to the `scp` method.

  `rsync` performs much better than `scp` when transferring files that exist on both hosts. However, this advantage is lost if the file exists only on one side of the connection.

  This method supports the ‘`-p`’ argument.

`scpx`—`ssh` and `scp`

  `scpx` is useful to avoid login shell questions. It is similar in performance to `scp`. `scpx` uses ‘`ssh -t -t host -l user /bin/sh`’ to open a connection.

  `sshx` is useful for Windows users when `ssh` triggers an error about allocating a pseudo tty. This happens due to missing shell prompts that confuses TRAMP.

  This method supports the ‘`-p`’ argument.

`pscp`—`plink` and `pscp`
`psftp`—`plink` and `psftp`

  These methods are similar to `scp` or `sftp`, but they use the `plink` command to connect to the remote host, and they use `pscp` or `psftp` for transferring the files. These programs are part of PuTTY, an SSH implementation for Windows.

  Check the ‘`Share SSH connections if possible`’ control for that session.

  These methods support the ‘`-P`’ argument.

`fcp`—`fsh` and `fcp`

  This method is similar to `scp`, but uses `fsh` to connect and `fcp` to transfer files. `fsh/fcp`, a front-end for `ssh`, reuse `ssh` session by submitting several commands. This avoids the startup overhead due to `scp`’s secure connection. Inline methods have similar benefits.

  The command used for this connection is: ‘`fsh host -l user /bin/sh -i`’

  `fsh` has no inline method since the multiplexing it offers is not useful for TRAMP. `fsh` connects to remote host and TRAMP keeps that one connection open.

`nc`—`telnet` and `nc`

  Using `telnet` to connect and `nc` to transfer files is sometimes the only combination suitable for accessing routers or NAS hosts. These dumb devices have severely restricted local shells, such as the `busybox` and do not host any other encode or decode programs.

`ftp`

  When TRAMP uses `ftp`, it forwards requests to whatever ftp program is specified by Ange-FTP. This external program must be capable of servicing requests from TRAMP.

`smb`—`smbclient`

  This non-native TRAMP method connects via the Server Message Block (SMB) networking protocol to hosts running file servers that are typically based on Samba or MS Windows.

  Using `smbclient` requires a few tweaks when working with TRAMP:

  The first directory in the localname must be a share name on the remote host.

  Since SMB shares end in the `$` character, TRAMP must use `$$` when specifying those shares to avoid environment variable substitutions.

  When TRAMP is not specific about the share name or uses the generic remote directory `/`, `smbclient` returns all available shares.

  Since SMB authentication is based on each SMB share, TRAMP prompts for a password even when accessing a different share on the same SMB host. This prompting can be suppressed by Password handling.

  To accommodate user name/domain name syntax required by MS Windows authorization, TRAMP provides for an extended syntax in `user%domain` format (where user is username, `%` is the percent symbol, and domain is the windows domain name). An example:

      /smb:daniel%BIZARRE@melancholia:/daniel$$/.emacs

  where user `daniel` connects as a domain user to the SMB host `melancholia` in the windows domain `BIZARRE` to edit `.emacs` located in the home directory (share `daniel$`).

  Alternatively, for local WINS users (as opposed to domain users), substitute the domain name with the name of the local host in UPPERCASE as shown here:

      /smb:daniel%MELANCHOLIA@melancholia:/daniel$$/.emacs

  where user `daniel` connects as local user to the SMB host `melancholia` in the local domain `MELANCHOLIA` to edit `.emacs` located in the home directory (share `daniel$`).

  The domain name and user name are optional for `smbclient` authentication. When user name is not specified, `smbclient` uses the anonymous user (without prompting for password). This behavior is unlike other TRAMP methods, where local user name is substituted.

  The `smb` method is unavailable if Emacs is run under a local user authentication context in MS Windows. However such users can still access remote files using UNC file names instead of TRAMP:

      //melancholia/daniel$$/.emacs

  UNC file name specification does not allow the specification of a different user name for authentication like the `smbclient` can.

`adb`

  This method uses Android Debug Bridge program for accessing Android devices. The Android Debug Bridge must be installed locally for TRAMP to work. Some GNU/Linux distributions provide Android Debug Bridge as an installation package. Alternatively, the program is installed as part of the Android SDK. TRAMP finds the `adb` program either via the `PATH` environment variable or the absolute path set in the variable tramp-adb-program.

  TRAMP connects to Android devices with `adb` only when the custom option `tramp-adb-connect-if-not-connected` is not `nil`. Otherwise, the connection must be established outside Emacs.

  TRAMP does not require a host name part of the remote file name when a single Android device is connected to `adb`. TRAMP instead uses `/adb::` as the default name. `adb devices` shows available host names.

  `adb` method normally does not need user name to authenticate on the Android device because it runs under the `adbd` process. But when a user name is specified, however, TRAMP applies an `su` in the syntax. When authentication does not succeed, especially on un-rooted Android devices, TRAMP displays login errors.

  For Android devices connected through TCP/IP, a port number can be specified using `device#42` host name syntax or TRAMP can use the default value as declared in `adb` command. Port numbers are not applicable to Android devices connected through USB.

Next: GVFS based methods, Previous: Inline methods, Up: Configuration [Contents][Index]