# Tramp #
I often find myself editing files in terminals on remote machines, and I really need to add [Tramp] to my muscle memory. Tramp is an Emacs package (installed by default?) for editing remote files via ssh. It allows you to open files with urls like this: `/ssh:user@host#port:/path/to/file`.
Note: I use `ssh` instead of `scp` (used in all of the examples) because the webpage says it’s faster and also because it supports the `#port` piece while `scp` does not. Also, the `user@` and `#port` pieces are optional. So feel free to use the minimum: `/ssh:host:/path/to/file`.
[Tramp]: http://www.emacswiki.org/emacs/TrampMode
## sudo, too ##
Even better, have you ever opened a root-owned file in an editor, made some changes, only to have the editor tell you that the file is read-only because you didn’t use sudo? For example, if you opened `/etc/root_owned_file` using Emacs, write the buffer to a “new” file, ^X^W, using this tramp-enabled file path: `/sudo::/etc/root_owned_file`. Emacs doesn’t know that you’re writing to the same file. It will open the file using tramp and sudo, save your changes, and replace your non-sudo buffer with the new one.
# OpenSSH ControlMaster #
The biggest problem I’ve had using Tramp mode, though, is latency. If your connection isn’t local, and you have the **good** habit of constantly saving, the delays can be annoying or at least jarring. On the EmacsWiki Tramp page, [there’s a hint][ControlMaster] about using the ControlMaster option in OpenSSH. With ControlMaster set, you simply open a regular ssh session to your remote host, and OpenSSH will use that already established connection for all of your future file access.
[ControlMaster]: http://archive09.linux.com/feature/54498
## Enabling it ##
Just put the following in `~/.ssh/config`:
Host *
ControlMaster auto
ControlPath ~/.ssh/master-%r@%h:%p
That’s it! Your welcome. Enjoy your better life. Here’s the effect in action on a local machine:
$ ./time_ssh_access.py
0.36 0.34 0.33 0.36 0.31 0.27 0.33 0.34 0.35 0.35
Average: 0.334
# ControlMaster added to ~/.ssh/config and a new terminal opened
$ ./time_ssh_access.py
0.02 0.02 0.04 0.02 0.02 0.04 0.01 0.02 0.02 0.02
Average: 0.023
That’s a 93% improvement. On a remote machine, times went from 0.861 down to 0.161 for an 81% improvement.
### time_ssh_access.py ###
Here’s the script used for testing. It uses the [_sh_][sh_module] python module which is so awesome it deserves its own blog post.
#!/usr/bin/env python -u
from sh import time
host = 'machine.local'
response = 'machine'
total = 0.0
for x in xrange(10):
output = time('ssh', host, 'hostname')
if output.exit_code != 0 or output.stdout.strip() != response:
print('Failed')
break
times = output.stderr.split()
# You may need to adjust this line depending on your version of the _time_ command.
index = times.index('real') - 1
print times[index],
total += float(times[index])
print
print 'Average: {}'.format(total/10.0)
[sh_module]: https://github.com/amoffat/sh
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