tramp: Remote shell setup
4.16 Remote shell setup hints
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TRAMP checks for the availability of standard programs in the usual
locations. Common tactics include successively trying ‘test -e’,
‘/usr/bin/test -e’, and ‘/bin/test -e’. ‘ls -d’ is another approach.
But these approaches do not help with these new login patterns.
When TRAMP encounters two-factor logins or additional challenge
questions, such as entering birth date or security code or passphrase,
TRAMP needs a few more configuration steps to accommodate them.
The difference between a password prompt and a passphrase prompt is
that the password for completing the login while the passphrase is for
authorizing access to local authentication information, such as the ssh
key.
There is no one configuration to accommodate all the variations in
login security, especially not the exotic ones. However, TRAMP provides
a few tweaks to address the most common ones.
TRAMP-SHELL-PROMPT-PATTERN
‘tramp-shell-prompt-pattern’ is for remote login shell prompt,
which may not be the same as the local login shell prompt,
‘shell-prompt-pattern’. Since most hosts use identical prompts,
TRAMP sets a similar default value for both prompts.
TRAMP-PASSWORD-PROMPT-REGEXP
TRAMP-WRONG-PASSWD-REGEXP
TRAMP uses TRAMP-PASSWORD-PROMPT-REGEXP to distinguish between
prompts for passwords and prompts for passphrases. By default,
TRAMP-PASSWORD-PROMPT-REGEXP handles the detection in English
language environments. See a localization example below:
(setq
tramp-password-prompt-regexp
(concat
"^.*"
(regexp-opt
'("passphrase" "Passphrase"
;; English
"password" "Password"
;; Deutsch
"passwort" "Passwort"
;; Français
"mot de passe" "Mot de passe") t)
".*:\0? *"))
Similar localization may be necessary for handling wrong password
prompts, for which TRAMP uses TRAMP-WRONG-PASSWD-REGEXP.
‘tset’ and other questions
To suppress inappropriate prompts for terminal type, TRAMP sets the
‘TERM’ to ‘dumb’ before the remote login process begins via the
variable ‘tramp-terminal-type’. This will silence common ‘tset’
related prompts.
TRAMP’s strategy for handling such prompts (commonly triggered from
login scripts on remote hosts) is to set the environment variables
so that no prompts interrupt the shell initialization process.
An alternative approach is to configure TRAMP with strings that can
identify such questions using ‘tramp-actions-before-shell’.
Example:
(defconst my-tramp-prompt-regexp
(concat (regexp-opt '("Enter the birth date of your mother:") t)
"\\s-*")
"Regular expression matching my login prompt question.")
(defun my-tramp-action (proc vec)
"Enter \"19000101\" in order to give a correct answer."
(save-window-excursion
(with-current-buffer (tramp-get-connection-buffer vec)
(tramp-message vec 6 "\n%s" (buffer-string))
(tramp-send-string vec "19000101"))))
(add-to-list 'tramp-actions-before-shell
'(my-tramp-prompt-regexp my-tramp-action))
Conflicting names for users and variables in ‘.profile’
When a user name is the same as a variable name in a local file,
such as ‘.profile’, then TRAMP may send incorrect values for
environment variables. To avoid incorrect values, change the local
variable name to something different from the user name. For
example, if the user name is ‘FRUMPLE’, then change the variable
name to ‘FRUMPLE_DIR’.
Non-Bourne commands in ‘.profile’
When the remote host’s ‘.profile’ is also used for shells other
than Bourne shell, then some incompatible syntaxes for commands in
‘.profile’ may trigger errors in Bourne shell on the host and may
not complete client’s TRAMP connections.
One example of a Bourne shell incompatible syntax in ‘.profile’:
using ‘export FOO=bar’ instead of ‘FOO=bar; export FOO’. After
remote login, TRAMP will trigger an error during its execution of
‘/bin/sh’ on the remote host because Bourne shell does not
recognize the export command as entered in ‘.profile’.
Likewise, (‘~’) character in paths will cause errors because Bourne
shell does not do (‘~’) character expansions.
One approach to avoiding these incompatibilities is to make all
commands in ‘~/.shrc’ and ‘~/.profile’ Bourne shell compatible so
TRAMP can complete connections to that remote. To accommodate
using non-Bourne shells on that remote, use other shell-specific
config files. For example, bash can use ‘~/.bash_profile’ and
ignore ‘.profile’.
Interactive shell prompt
TRAMP redefines the remote shell prompt internally for robust
parsing. This redefinition affects the looks of a prompt in an
interactive remote shell through commands, such as ‘M-x shell’.
Such prompts, however, can be reset to something more readable and
recognizable using these TRAMP variables.
TRAMP sets the ‘INSIDE_EMACS’ variable in the startup script file
‘~/.emacs_SHELLNAME’.
‘SHELLNAME’ is ‘bash’ or equivalent shell names. Change it by
setting the environment variable ‘ESHELL’ in the ‘.emacs’ as
follows:
(setenv "ESHELL" "bash")
Then re-set the prompt string in ‘~/.emacs_SHELLNAME’ as follows:
# Reset the prompt for remote Tramp shells.
if [ "${INSIDE_EMACS/*tramp*/tramp}" == "tramp" ] ; then
PS1="[\u@\h \w]$ "
fi
(emacs)Interactive Shell.
‘busybox’ / ‘nc’
TRAMP’s ‘nc’ method uses the ‘nc’ command to install and execute a
listener as follows (see ‘tramp-methods’):
# nc -l -p 42
The above command-line syntax has changed with ‘busybox’ versions.
If ‘nc’ refuses the ‘-p’ parameter, then overwrite as follows:
(add-to-list
'tramp-connection-properties
`(,(regexp-quote "192.168.0.1") "remote-copy-args" (("-l") ("%r"))))
where ‘192.168.0.1’ is the remote host IP address (Predefined
connection information).
Info Catalog
tramp: Remote programs
tramp: Configuration
tramp: Android shell setup