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.
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.
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.
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 is useful to avoid login shell questions. It is similar
in performance to scp. scpx uses ‘ssh -t -t -l
user -o RemoteCommand='/bin/sh -i' host’ to open a
connection. It supports changing the remote login shell
/bin/sh.
scpx is useful for MS 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.
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 MS Windows.
They support changing the remote login shell /bin/sh.
Check the ‘Share SSH connections if possible’ control for that session.
These methods support the ‘-P’ argument.
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.
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.
The sudoedit method allows to edit a file as a different user
on the local host. You could regard this as TRAMP’s
implementation of the sudoedit. Contrary to the
sudo method, all magic file name functions are implemented by
single sudo … commands. The purpose is to make
editing such a file as secure as possible; there must be no session
running in the Emacs background which could be attacked from inside
Emacs.
Consequently, external processes are not implemented.
The host name of such remote file names must represent the local host. Since the default value is already proper, it is recommended not to use any host name in the remote file name, like /sudoedit::/path/to/file or /sudoedit:user@:/path/to/file.
Like the sudo method, a sudoedit password expires after a predefined timeout.
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.
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 some SMB share names end in the $ character,
TRAMP must use $$ when specifying those shares to avoid
environment variable substitutions.
When TRAMP is not specific about the share name or uses the
generic remote directory /, smbclient returns all
available shares.
Since SMB authentication is based on each SMB share, TRAMP prompts for a password even when accessing a different share on the same SMB host. This prompting can be suppressed by Reusing passwords for several connections.
To accommodate user name/domain name syntax required by MS Windows
authorization, TRAMP provides for an extended syntax in
user%domain format (where user is the user name,
% is the percent symbol, and domain is the MS Windows
domain name). An example:
/smb:daniel%BIZARRE@melancholia:/daniel$$/.emacs
where user daniel connects as a domain user to the SMB host
melancholia in the MS 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.
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 user option tramp-adb-program.
TRAMP connects to Android devices with adb only when
the user 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, run in a shell outside Emacs, 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.