system administration with emacs

When performing system administration tasks, one often needs to edit files owned by root.

For both security and safety reasons, it's a good idea to do as little as possible as root (or with root privileges). For that reason, you probably don't want to run Emacs as 'root', because it's simply too powerful. I often see people use vi (usually, vim) instead – but since it allows you to do just about anything as well (like running shell commands), that's not much of an improvement.

Now, a while back we discussed editing files owned by root with tramp – you can use emacs with your normal user-account, and use sudo to write the root-owned file. That makes it much harder to screw things up.

Another reason people use vi for little editing jobs is because its startup time is significantly shorter than the startup time for a new emacs instance. For that, however, we have emacs daemon.

Combining tramp and emacs daemon and a shell function:

# edit file with root privs
function E() {
         emacsclient -c -a emacs "/sudo:root@localhost:$1"
}               

Now, we can very quickly edit any file owned by root using 'E' --

$ E /etc/hosts

So, if you prefer emacs, there's little reason to use vi, even for editing system files – although I have to admit that it takes time to evict 'sudo vi <system file>' from my muscle memory.

Update reader Yi Wang mentions that, in fact, we can make this a bit more general using sudoedit; so, instead of using Tramp, we can use:

# edit file with root privs
alias E="SUDO_EDITOR=\"emacsclient -c -a emacs\" sudoedit"   

This works also without absolute paths.

package management revisited

Ages ago we discussed ELPA, the emacs packaging system. It allows you to
browse through an online repository of emacs packages and install, uninstall
and upgrade them, all from within the emacs comfort zone (menu:
Options/Manage Emacs Packages).

Emacs 24.1 (a pretest is available) will include a version of ELPA --
package.el; the version included with emacs 24 supports multiple
archives. The official archive is the one provided by GNU, then there is
the current one for ELPA, but there's now a third one available: Marmalade.

Marmelade ('Spreadable Elisp') offers a very easy way for developers to
make their packages available to emacs users, and an even easier way for
users to test out interesting packages.

To use all available package repositories (GNU, ELPA and Marmalade), add
the following snippet to your .emacs:

(setq package-archives '(("ELPA" . "http://tromey.com/elpa/") 
                          ("gnu" . "http://elpa.gnu.org/packages/")
                          ("marmalade" . "http://marmalade-repo.org/packages/")))

This works out-of-the-box for Emacs 24; for Emacs 23, you'll need the newer
package.el, which you can get from the emacs 24 repo (if necessary, remove
the old package.el first).

Currently, there are 870 packages listed in the three repositories – a lot of
toys to play with! In fact, it is already getting quite hard to find what
you're looking for; a bit more structured way (maybe using categories) would
be useful. Also, a bit more information than the one-line description would
be very useful.

Nevertheless, it's a great addition to emacs, which will make it much easier
to play with packages – without even having to read the installation
instructions.

quick note-taking with deft and org-mode

Emacs must be gathering a lot of enthusiasts lately; there's hardly a week where I don't discover some new gem. Recently, I discovered deft. And apparently, I wasn't the only one.

So what is it deft good for? Well, often I want to jot down some quick thing during a meeting or a telephone-call. Of course, I don't want to think about file names or anything else distracting me from my task, just get me that note already! In addition, at some later time, I want to be able to quickly search through the notes I made.

For MacOS, there's a program called Notational Velocity which does this. But really - it sounds like a typical task for emacs - wouldn't it be nice to have an emacs package that does roughly the same?

And that is what deft does - enable you to quickly write notes, and retrieving them later. The author has an excellent introduction on his website, so my job is very easy :) deft is not part of org-mode, but they can work together seamlessly. Here's my set-up:

;; http://jblevins.org/projects/deft/
(when (require 'deft nil 'noerror) 
   (setq
      deft-extension "org"
      deft-directory "~/Org/deft/"
      deft-text-mode 'org-mode)
   (global-set-key (kbd "<f9>") 'deft))

This blob goes in my .emacs. Note, the first line ensures that emacs starts without errors, even when I run on a system without deft. Apart from that, I make deft use org files for note taking, which makes it all very familiar.

All notes are saved ~/Org/deft - you can set it to something else of course. A Dropbox-folder seems to be a popular choice for synchronizing between machines.

Finally, the last line binds F9 to deft-mode. So, when I need a quick note, I can type F9 C-c C-n and start writing.

finding just about anything

Buffer-switching is one of those things I do all the time in Emacs. And it should be quick and efficient, or it will break my 'flow'. There are many ways to customize the buffer switching experience, and we already discussed quite a few of those here: using Ctrl-Tab, iswitchb/ido, ibuffer, the lusty explorer and others.

Some of those packages - ido and lusty-explorer - do not solely focus on buffer-switching - they also let you open files using the same user interface. But why stop at files and buffers - wouldn't it be nice if we could quickly find just about anything quickly?

Indeed that would be nice - and there's a way to do just that - using the aptly named anything package. I was always a bit put off by this package due to the screenshots (see link), but once I got over that, I've become a very happy user.

Anyhow, what can anything find? I mentioned buffers and files, but it can also find bookmarks, recently used files, any file on your system (using locate), man-pages, info-pages, emacs-function/variables, FIXME-comments, org-headlines, bbdb-contacts, google-suggests… and a million other things. It can probably find your car keys, too.

Installation is pretty straightforward, using the git-repository:

git clone git://repo.or.cz/anything-config.git

Then, go into the just-cloned directory and execute make. After that, add to your .emacs (or ~/.emacs.d/init.el):

;; path-to-anything is the path which has the 'anything' we just cloned
(add-to-list 'load-path "path-to-anything")
(require 'anything-config)

This will add a menu with various anything-commands, and a bunch of key-bindings, starting with F5. Play around a bit with it, it's nice. The results are shown in a little temporary buffer, and pressing Tab will let you do (search-type dependent) actions on the matches - for example ediff two buffers.

Of course, the real fun starts when we super-charge some of the normal emacs functions with anything-based ones. Let's look at buffer switching. Let's create an anything-based version, and assign it to C-x b, the good-old switch-to-buffer.

The thing to consider is that while anything can find just about anything, you (well, I) usually only want to search for a certain set of things; when I want to switch to another buffer, I don't want to match man-pages. Luckily, anything allows for making nifty function which use certain subsets of the search sources. So for buffer switching, I have:

(global-set-key (kbd "C-x b")
  (lambda() (interactive)
    (anything
     :prompt "Switch to: "
     :candidate-number-limit 10                 ;; up to 10 of each 
     :sources
     '( anything-c-source-buffers               ;; buffers 
        anything-c-source-recentf               ;; recent files 
        anything-c-source-bookmarks             ;; bookmarks
        anything-c-source-files-in-current-dir+ ;; current dir
        anything-c-source-locate))))            ;; use 'locate'

This will search in buffers, then in my recent-files, then in my bookmarks, the files in the current directory, and finally check with the locate tool. That last one is pretty neat, and finally gives me something back for the countless times I've wondered why the hard disk is grinding – indeed, it was locate, updating its database.

Then, I've defined another binding for searching general documentation on my system; I've put it under C-c I. This looks look something like the following:

(global-set-key (kbd "C-c I")  ;; i -> info
  (lambda () (interactive)
    (anything
      :prompt "Info about: "
      :candidate-number-limit 3
      :sources
      '( anything-c-source-info-libc             ;; glibc docs
         anything-c-source-man-pages             ;; man pages
         anything-c-source-info-emacs))))        ;; emacs 

These are sources I query quite regularly; there are many more to be found - for most packages with info-pages there's a corresponding anything-c-source-info-...; there's a list in anything-config.el.

Now, those are my general documentation sources; in specific modes, I have specialized information sources; for example, for elisp-mode:

(add-hook 'emacs-lisp-mode-hook
  (lambda()
  ;; other stuff...
  ;; ...
  ;; put useful info under C-c i
    (local-set-key (kbd "C-c i")
      (lambda() (interactive)
        (anything
          :prompt "Info about: "
          :candidate-number-limit 5
          :sources
          '( anything-c-source-emacs-functions
             anything-c-source-emacs-variables
             anything-c-source-info-elisp
             anything-c-source-emacs-commands
             anything-c-source-emacs-source-defun
             anything-c-source-emacs-lisp-expectations
             anything-c-source-emacs-lisp-toplevels
             anything-c-source-emacs-functions-with-abbrevs
             anything-c-source-info-emacs))))

This post just scratches the surface of what is possible – so go and experiment :) One interesting thing is to add your own sources; I played a bit with that already,

There are many things in anything I did not cover yet. First, there are many more sources to search - and it's pretty easy to write your own – see the EmacsWiki-page.

customizing the mode-line

The mode-line is the emacs 'status bar', the bar just above the minibuffer that shows various pieces of information, such as the buffer name, the major mode, maybe the current line number, some indicators for active minor modes, and so on. As I'm looking at it, it starts with 1<U:**- (which is: input-method: latin-1-alt-postfix, buffer-coding-system: utf8-unix, line-ending: unix-style, buffer is writable and buffer is modified – the tooltips help).
As with just about anything in emacs, the mode-line can be customized just the way you like. I give some example below, not because I think it is necessarily the best way, but just to give you a bit of an example to start with when making your own best-mode-line-ever.
I'm not going through all the details of the example, but let me highlight a few things that make it a bit easier to understand.
First of all, the mode-line can be customized by setting the variable mode-line-format; this variable becomes buffer-local automatically when changed, so if you want to set it for all buffers, you'll need to use setq-default in your .emacs (or equivalent). The format is quite similar to the one for frame-title-format, which we discussed in setting the frame title a while back.
mode-line-format is a list of items which are evaluated, and put together as a string which then ends up as the mode-line contents. These properties can be any string. The following types of items can be used:

• First, normal strings are just shown as-is;
• Then, there are some special format parameters which will be replaced with their value in the mode-line, from the Emacs-documentation:

  %b -- print buffer name.      %f -- print visited file name.
  %F -- print frame name.
  %* -- print %, * or hyphen.   %+ -- print *, % or hyphen.
        %& is like %*, but ignore read-only-ness.
        % means buffer is read-only and * means it is modified.
        For a modified read-only buffer, %* gives % and %+ gives *.
  %s -- print process status.   %l -- print the current line number.
  %c -- print the current column number (this makes editing slower).
        To make the column number update correctly in all cases,
        `column-number-mode' must be non-nil.
  %i -- print the size of the buffer.
  %I -- like %i, but use k, M, G, etc., to abbreviate.
  %p -- print percent of buffer above top of window, or Top, Bot or All.
  %P -- print percent of buffer above bottom of window, perhaps plus Top,
        or print Bottom or All.
  %n -- print Narrow if appropriate.
  %t -- visited file is text or binary (if OS supports this distinction).
  %z -- print mnemonics of keyboard, terminal, and buffer coding systems.
  %Z -- like %z, but including the end-of-line format.
  %e -- print error message about full memory.
  %@ -- print @ or hyphen.  @ means that default-directory is on a
        remote machine.
  %[ -- print one [ for each recursive editing level.  %] similar.
  %% -- print %.   %- -- print infinitely many dashes.
Decimal digits after the % specify field width to which to pad.

• Forms of the type (:eval ...) are evaluated each time the mode-line is drawn (just like the '%'-parameters) ; so, if you have a value that changes of the course your emacs session, you should use (:eval ...). For example, for your emacs-uptime you could use (:eval (emacs-uptime "%hh")); while the emacs-PID does not change, so simply you could simply use (format "PID:%d").
  The format parameter mentioned above are of evaluated each time as well. Note that you have to be a bit careful with evaluations - don't do too heavy operations there, and be careful the updates don't recurse.
  
• There are many others which I won't go into now - please check the Elisp reference. It's a rather baroque format…

Now, let's put this all together in an example (tested with emacs 23 and 24). As I said, this is for demonstration purposes only; but hopefully it gives you some inspiration. A lot of the 'magic' (colors, tooltips, faces) happens with the propertize function; again, the Elisp documentation can tell you a lot more about that. I'm (ab)using the various font-lock-faces to have colors that blend in nicely with your current theme.
And it has a limitation still, namely that it does not react to mouse clicks; how to that, I will discuss in some future article.

;; use setq-default to set it for /all/ modes
(setq mode-line-format
  (list
    ;; the buffer name; the file name as a tool tip
    '(:eval (propertize "%b " 'face 'font-lock-keyword-face
        'help-echo (buffer-file-name)))

    ;; line and column
    "(" ;; '%02' to set to 2 chars at least; prevents flickering
      (propertize "%02l" 'face 'font-lock-type-face) ","
      (propertize "%02c" 'face 'font-lock-type-face) 
    ") "

    ;; relative position, size of file
    "["
    (propertize "%p" 'face 'font-lock-constant-face) ;; % above top
    "/"
    (propertize "%I" 'face 'font-lock-constant-face) ;; size
    "] "

    ;; the current major mode for the buffer.
    "["

    '(:eval (propertize "%m" 'face 'font-lock-string-face
              'help-echo buffer-file-coding-system))
    "] "


    "[" ;; insert vs overwrite mode, input-method in a tooltip
    '(:eval (propertize (if overwrite-mode "Ovr" "Ins")
              'face 'font-lock-preprocessor-face
              'help-echo (concat "Buffer is in "
                           (if overwrite-mode "overwrite" "insert") " mode")))

    ;; was this buffer modified since the last save?
    '(:eval (when (buffer-modified-p)
              (concat ","  (propertize "Mod"
                             'face 'font-lock-warning-face
                             'help-echo "Buffer has been modified"))))

    ;; is this buffer read-only?
    '(:eval (when buffer-read-only
              (concat ","  (propertize "RO"
                             'face 'font-lock-type-face
                             'help-echo "Buffer is read-only"))))  
    "] "

    ;; add the time, with the date and the emacs uptime in the tooltip
    '(:eval (propertize (format-time-string "%H:%M")
              'help-echo
              (concat (format-time-string "%c; ")
                      (emacs-uptime "Uptime:%hh"))))
    " --"
    ;; i don't want to see minor-modes; but if you want, uncomment this:
    ;; minor-mode-alist  ;; list of minor modes
    "%-" ;; fill with '-'
    ))

Have fun playing with this!

toward balanced and colorful delimiters

Emacs has the very useful feature of blinking the corresponding left "(" when you type its partner ")" (and the same for other delimiters like "[]", "{}" etc., depending on the mode). This is very useful for programming, especially for languages like Lisp and Scheme and the like.


Further help can come from tools like autopair or paredit – although the latter is a bit too much bondage & discipline for me, many people love it.
Anyway, recently I discovered a new helper in the quest for balance in delimited universe: rainbow-delimiters. With this package, the delimiters all get different colors based on their nesting level. It works wonderfully well.
Installation is straightforward:

• download rainbow-delimiters and put it in your load-path
• add something like the following in your .emacs:

(when (require 'rainbow-delimiters nil 'noerror) 
  (add-hook 'scheme-mode-hook 'rainbow-delimiters-mode))

That's it – of course you'll need to do the equivalent for modes where you'd like to enable it. See the screenshot below – maybe a bit too colorful for some people, but I like it and I have found it actually useful to see the corresponding delimiters without having to move the cursor over them.

I already added some nice Zenburn colors for this to the Zenburn theme for Emacs-24, as can be seen in the screenshot.

porting the zenburn theme to emacs 24

Just a small note: I already mentioned the zenburn color theme a couple of times. I have now ported the full (big) set of customizations to the emacs-24 format – find it at github; so if you run emacs 24 (the development version) and enjoy zenburn like me, you can give it try. Suggestions, additions are welcome.

Note, there seems to be a limitation with the :inherit-attribute for themes – in practice it means that some aspects of the theme may not work if a package sets the face before the theme does. Therefore, best to load the theme early from your .emacs or init.el; or alternatively visit the theme file (zenburn-theme.el in this case) and evaluate the buffer.