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1 | \input texinfo @c -*-texinfo-*- |
2 | @c |
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3 | @c $Id: become.texi,v 1.6 2003/10/26 11:57:46 mdw Exp $ |
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4 | @c |
5 | @c Documentation for `become' |
6 | @c |
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7 | @c (c) 1998 EBI |
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8 | @c |
9 | |
10 | @c ----- Revision history --------------------------------------------------- |
11 | @c |
12 | @c $Log: become.texi,v $ |
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13 | @c Revision 1.6 2003/10/26 11:57:46 mdw |
14 | @c Fix key reloading core dumps. Change advice on keys. |
15 | @c |
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16 | @c Revision 1.5 2003/10/12 00:14:49 mdw |
17 | @c Major overhaul. Now uses DSA signatures rather than the bogus symmetric |
18 | @c encrypt-and-hope thing. Integrated with mLib and Catacomb. |
19 | @c |
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20 | @c Revision 1.4 1998/04/23 13:16:14 mdw |
21 | @c Include `texinice' to produce decent printed output. Add documentation |
22 | @c for new `bcquery' program. Various fixes, including spelling mistakes, |
23 | @c and some factual inaccuracies. |
24 | @c |
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25 | @c Revision 1.3 1998/01/20 14:37:43 mdw |
26 | @c Fix typo. Short form of `--preserve' should be `-e', not `-p'. |
27 | @c |
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28 | @c Revision 1.2 1998/01/12 16:41:31 mdw |
29 | @c Tidying for new release versions. Fix copyright date. |
30 | @c |
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31 | @c Revision 1.1 1997/09/18 11:16:34 mdw |
32 | @c Brand new Texinfo manual, with wider scope than the original LaTeX one. |
33 | @c |
34 | |
35 | @c ----- Standard boilerplate ----------------------------------------------- |
36 | |
37 | @c %**start of header |
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38 | @setfilename become.info |
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39 | @settitle Become |
40 | @setchapternewpage odd |
41 | @footnotestyle end |
42 | @paragraphindent 0 |
43 | @iftex |
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44 | @input texinice.tex |
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45 | @afourpaper |
46 | @c @parindent=0pt |
47 | @end iftex |
48 | @c %**end of header |
49 | |
50 | @c ----- Useful macros ------------------------------------------------------ |
51 | |
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52 | @set version 1.3 |
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53 | |
54 | @c ----- Copyright matters -------------------------------------------------- |
55 | |
56 | @c --- The `Info' version --- |
57 | |
58 | @ifinfo |
59 | |
60 | This file documents Become version @value{version}. |
61 | |
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62 | Copyright (c) 1998 European Bioinformatics Institute. |
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63 | |
64 | Permission is granted to make and distribute verbatim copies of this |
65 | manual provided the copyright notice and this permission notice are |
66 | preserved on all copies. |
67 | |
68 | @ignore |
69 | Permission is granted to process this file through TeX and print the |
70 | results, provided the printed document carries a copying permission |
71 | notice identical to this one except for the removal of this paragraph |
72 | (this paragraph not being relevant to the printed manual). |
73 | |
74 | @end ignore |
75 | Permission is granted to copy and distribute modified versions of this |
76 | manual under the conditions for verbatim copying, provided also that the |
77 | sections entitled `Copying' and `GNU General Public License' are |
78 | included exactly as in the original, and provided that the entire |
79 | resulting derived work is distributed under the terms of a permission |
80 | notice identical to this one. |
81 | |
82 | Permission is granted to copy and distribute translations of this manual |
83 | into another language, under the above conditions for modified versions, |
84 | except that this permission notice may be stated in a translation |
85 | approved by the European Bioinformatics Institute. |
86 | |
87 | @end ifinfo |
88 | |
89 | @c --- Printed title page --- |
90 | |
91 | @titlepage |
92 | |
93 | @title The Become program |
94 | @subtitle Become version @value{version} |
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95 | @author Mark Wooding @email{mdw@@ebi.ac.uk} |
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96 | @page |
97 | |
98 | @vskip 0pt plus 1filll |
99 | |
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100 | Copyright @copyright{} 1998 European Bioinformatics Institute. |
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101 | |
102 | Permission is granted to make and distribute verbatim copies of this |
103 | manual provided the copyright notice and this permission notice are |
104 | preserved on all copies. |
105 | |
106 | Permission is granted to copy and distribute modified versions of this |
107 | manual under the conditions for verbatim copying, provided also that the |
108 | sections entitled `Copying' and `GNU General Public License' are |
109 | included exactly as in the original, and provided that the entire |
110 | resulting derived work is distributed under the terms of a permission |
111 | notice identical to this one. |
112 | |
113 | Permission is granted to copy and distribute translations of this manual |
114 | into another language, under the above conditions for modified versions, |
115 | except that this permission notice may be stated in a translation |
116 | approved by the European Bioinformatics Institute. |
117 | |
118 | @end titlepage |
119 | |
120 | |
121 | @c -------------------------------------------------------------------------- |
122 | @ifinfo |
123 | @node Top, Copying, (dir), (dir) |
124 | @top Become |
125 | |
126 | |
127 | Become is a system for managing shared accounts. It allows users to |
128 | `become' other users in order to do useful work. It can be managed on a |
129 | central server (or a small number of central servers), or it can run |
130 | standalone. |
131 | |
132 | This file documents Become version @value{version}. |
133 | |
134 | @end ifinfo |
135 | |
136 | @menu |
137 | * Copying:: Your rights to distribute and modify |
138 | * Introduction:: A brief introduction to Become |
139 | * Becoming someone else:: How to become somebody else |
140 | * Administering Become:: How to maintain Become |
141 | * Invoking Become:: Reference to Become's command line options |
142 | |
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143 | @detailmenu |
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144 | --- The Detailed Node Listing --- |
145 | |
146 | Becoming someone else |
147 | |
148 | * Terminology:: Some important terms defined |
149 | * Environment:: Login styles and environment variables |
150 | * Group permissions:: How Become handles group permissions |
151 | * X authority:: Problems with X authority files |
152 | * Running commands:: Running commands other than a shell |
153 | |
154 | How Become sets up the environment |
155 | |
156 | * New environment variables:: Become adds some useful environment variables |
157 | * Login styles:: Choose how Become sets the environment |
158 | * Tweaking the environment:: Altering individual environment variables |
159 | * Removed variables:: Some environment variables aren't passed on |
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160 | |
161 | Login styles |
162 | |
163 | * The preserve style:: Preserve the current environment |
164 | * The set-user style:: Set user-specific variables (like @code{su}) |
165 | * The login style:: Clear the environment (like @code{login}) |
166 | |
167 | How Become handles groups |
168 | |
169 | * Primary group selection:: Setting the new primary group |
170 | * Subsidiary groups:: Setting subsidiary group memberships |
171 | |
172 | Considerations for X authority |
173 | |
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174 | * The user-group method:: A fairly secure way of handling X authority |
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175 | * Using xauth:: A less secure method, which might be easier |
176 | |
177 | Become administration |
178 | |
179 | * Configuration files:: Overview of Become's configuration files |
180 | * Standalone or networked:: The two main types of Become installations |
181 | * The configuration file:: How to define who's allowed to do what |
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182 | * Networked configuration:: Considerations for networked installations |
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183 | |
184 | The configuration file |
185 | |
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186 | * Requests and rules:: How the configuration file works |
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187 | * Basic syntax:: Quick overview of Become's syntax |
188 | * Classes:: Defining classes of things |
189 | * Predefined classes:: Become predefines some (maybe) useful classes |
190 | * Allow statements:: Allow users to become other users |
191 | * Other statements:: Some other useful statements |
192 | * Example configuration file:: An example, showing a few features. |
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193 | * Checking and querying:: Checking and querying configuration files |
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194 | * Complete grammar:: Complete grammar for Become config files |
195 | |
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196 | Checking and querying the configuration file |
197 | |
198 | * Verifying config files:: Checking a configuration file is correct |
199 | * Querying config files:: Asking questions about privileges |
200 | * Output formats:: Different ways of formatting output |
201 | * Restricting output:: Being selective about what gets output |
202 | * bcquery reference:: Complete command line reference |
203 | |
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204 | Networked configuration |
205 | |
206 | * Choosing servers:: Which servers Become tries to talk to |
207 | * Setting up keys:: How to generate keys for Become |
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208 | * Issuing a new key:: How to issue new keys without disruption |
209 | |
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210 | Invoking Become |
211 | |
212 | * Becoming another user:: Options for becoming another user |
213 | * Starting Become daemons:: Options for starting Become daemons |
214 | * Debugging options:: Options to use when Become goes wrong |
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215 | |
216 | @end detailmenu |
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217 | @end menu |
218 | |
219 | @c -------------------------------------------------------------------------- |
220 | @node Copying, Introduction, Top, Top |
221 | @unnumbered The GNU General Public License |
222 | |
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223 | @include gpl.texi |
224 | |
225 | |
226 | @c -------------------------------------------------------------------------- |
227 | @node Introduction, Becoming someone else, Copying, Top |
228 | @unnumbered Introduction |
229 | |
230 | |
231 | It's often useful to be able to share accounts between a number of |
232 | users. For example, a group maintaining an externally visible service |
233 | need to be able to start and kill the server process. Giving such a |
234 | shared account a password is a fairly bad plan: such passwords tend not |
235 | to get changed very often, and they have a habit of spreading beyond the |
236 | group of legitimate users. |
237 | |
238 | The Become program presented here offers a solution to the problems of |
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239 | shared accounts. It allows the system administrator to define which |
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240 | users are allowed access to which accounts, on which hosts, and to |
241 | execute which commands. Such shared accounts can then, in general, have |
242 | their passwords removed. |
243 | |
244 | This coincidentally has another advantage: when `becoming' to a shared |
245 | account, a user can retain her@footnote{Or his. I'll choose one or the |
246 | other fairly randomly throughout this manual.} own environment, which |
247 | she's carefully crafted and honed over the years, rather then being |
248 | presented with some lowest-common-denominator setup which probably |
249 | doesn't even use the right shell. |
250 | |
251 | The configuration file for Become can either be distributed to all the |
252 | various hosts in a network or a few carefully set up and secure servers |
253 | (@pxref{Standalone or networked}). |
254 | |
255 | |
256 | @c -------------------------------------------------------------------------- |
257 | @node Becoming someone else, Administering Become, Introduction, Top |
258 | @chapter Becoming someone else |
259 | |
260 | |
261 | The simplest way to become someone else is to say |
262 | |
263 | @example |
264 | become @var{user} |
265 | @end example |
266 | |
267 | @noindent |
268 | Become will check to see whether you're allowed to become @var{user}. If you |
269 | are, it starts a shell process with the user-id set to @var{user}. Any |
270 | commands you type are executed with the privileges of @var{user}. |
271 | |
272 | The full invocation is slightly more complicated: |
273 | |
274 | @example |
275 | become [@var{option}@dots{}] [@var{env-var}@dots{}] @var{user} [@var{command} [@var{arg}@dots{}]] |
276 | @end example |
277 | |
278 | Actually, the @var{option}s, @var{env-var}s and @var{user} can be in any |
279 | order -- the important point is that all of them appear before the |
280 | @var{command}, if there is one. |
281 | |
282 | @menu |
283 | * Terminology:: Some important terms defined |
284 | * Environment:: Login styles and environment variables |
285 | * Group permissions:: How Become handles group permissions |
286 | * X authority:: Problems with X authority files |
287 | * Running commands:: Running commands other than a shell |
288 | @end menu |
289 | |
290 | |
291 | |
292 | @node Terminology, Environment, Becoming someone else, Becoming someone else |
293 | @section Terminology |
294 | |
295 | The following terms get used quite a bit in the following text: |
296 | |
297 | @table @asis |
298 | @item request |
299 | An invocation of Become, asking permission to become another user. |
300 | |
301 | @item old user |
302 | The (real) user id of the process which invoked Become; usually, this will be |
303 | your normal user id. |
304 | |
305 | @item target user |
306 | The user whom you want to become, named in a request. |
307 | @end table |
308 | |
309 | |
310 | |
311 | @node Environment, Group permissions, Terminology, Becoming someone else |
312 | @section How Become sets up the environment |
313 | |
314 | There are thorny problems with handling the user's environment. It seems |
315 | that (the author's initial assessment notwithstanding) there is no single |
316 | best way of handling environment variables. As a result, Become can do just |
317 | about everything you might want it to. This gets slightly complicated. |
318 | Don't worry: it's not as hard as all that. |
319 | |
320 | @menu |
321 | * New environment variables:: Become adds some useful environment variables |
322 | * Login styles:: Choose how Become sets the environment |
323 | * Tweaking the environment:: Altering individual environment variables |
324 | * Removed variables:: Some environment variables aren't passed on |
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325 | @end menu |
326 | |
327 | |
328 | @node New environment variables, Login styles, Environment, Environment |
329 | @subsection Environment variables created by Become |
330 | |
331 | To help you (and, more importantly, your startup scripts) keep track of who |
332 | you are, and who you were originally, Become adds some variables to the |
333 | environment of any processes it starts. |
334 | |
335 | @table @code |
336 | @item BECOME_USER |
337 | The name of the target user (i.e., the user you are now). It might be useful |
338 | to test this value in shell startup scripts, for example. |
339 | |
340 | @item BECOME_HOME |
341 | The home directory of the target user. It can be handy to read startup and |
342 | other configuration files from here. |
343 | |
344 | @item BECOME_OLD_USER |
345 | The name of the user who invoked Become. |
346 | |
347 | @item BECOME_OLD_HOME |
348 | The home directory of the `old' user. |
349 | |
350 | @item BECOME_ORIGINAL_USER |
351 | This is intended to be the name you logged in with. If it's unset, Become |
352 | sets it to be the same as @code{BECOME_OLD_USER}; otherwise it leaves it |
353 | unchanged. |
354 | |
355 | @item BECOME_ORIGINAL_HOME |
356 | This is intended to be the home directory you logged in with. If it's unset, |
357 | Become sets it to be the same as @code{BECOME_OLD_HOME}; otherwise, it leaves |
358 | it unchanged. |
359 | @end table |
360 | |
361 | Don't even think about relying on these variables as a form of |
362 | authentication. It won't work. They're provided only to help organise |
363 | startup scripts. |
364 | |
365 | |
366 | |
367 | @node Login styles, Tweaking the environment, New environment variables, Environment |
368 | @subsection Login styles |
369 | |
370 | Originally, Become always tried to preserve your environment. There's a |
371 | rational explanation for this approach, which is given in the description of |
372 | the `preserve' style below. Unfortunately, not everyone liked this |
373 | approach. As a result, there's now a collection of different login styles. |
374 | |
375 | Login styles are selected by giving command line arguments: |
376 | |
377 | @table @code |
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378 | @item -e |
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379 | @itemx --preserve |
380 | The original style: try to preserve the existing user's environment as much |
381 | as possible. |
382 | |
383 | @item -s |
384 | @itemx --set-user |
385 | Set some user-specific variables, like @code{USER} and @code{HOME} to reflect |
386 | the target user rather than the old user. All other variables are preserved. |
387 | |
388 | @item -l |
389 | @itemx --login |
390 | Attempts to make the `become' process as much like a real login as possible. |
391 | All variables not explicitly preserved are deleted, and a new environment is |
392 | built, reflecting the target user. |
393 | @end table |
394 | |
395 | The various styles, and the reasons behind them, are described below. |
396 | |
397 | @menu |
398 | * The preserve style:: Preserve the current environment |
399 | * The set-user style:: Set user-specific variables (like @code{su}) |
400 | * The login style:: Clear the environment (like @code{login}) |
401 | @end menu |
402 | |
403 | |
404 | @node The preserve style, The set-user style, Login styles, Login styles |
405 | @subsubsection The `preserve' login style |
406 | |
407 | You've spent many hours (days? weeks, even?) customising and honing your |
408 | startup files, learning how to use your shell, and tweaking your favourite |
409 | text editor until it's just the way you like it. So there can be few things |
410 | more annoying than logging into a shared account to find out that the shell's |
411 | wrong, your editor startup files are ignored, and nothing works quite the way |
412 | you'd like it to. Typically you can't change this without annoying the other |
413 | users: the result is a horrible compromise which dissatisfies everyone |
414 | equally. |
415 | |
416 | The `preserve' style lets you take your standard environment with you when |
417 | you become someone else. It tries hard not to modify any environment |
418 | variables. |
419 | |
420 | Become starts your standard shell. If you have an environment variable |
421 | @code{SHELL} defined, than this is executed. Otherwise, the shell specified |
422 | in your entry in the password file is used. (You must have permission to |
423 | execute whatever shell is chosen as the target user, or you'll just be given |
424 | an error message.) |
425 | |
426 | Most programs look at environment variables in preference to looking up |
427 | entries in the password database; e.g., they tend to use @code{USER} or |
428 | @code{LOGNAME} for the user name, and @code{HOME} for your home directory. |
429 | As a result, most programs will continue to find their configuration files in |
430 | your home directory. Also, systems like RCS will use your real name, rather |
431 | than the name of the user that you have become. |
432 | |
433 | To make best use of this login style, you may need to adjust your login |
434 | scripts to notice when @code{BECOME_USER} is someone else, and read in |
435 | appropriate definitions. For example, a `bash' user might say something like |
436 | this in her @file{.bashrc}: |
437 | |
438 | @example |
439 | if [ -n "$BECOME_HOME" ]; then . $BECOME_HOME/.bashrc |
440 | @end example |
441 | |
442 | @noindent |
443 | Similarly, a C shell user (either `tcsh' or `csh') might say something like |
444 | |
445 | @example |
446 | if ($?BECOME_HOME) source $@{BECOME_HOME@}/.cshrc |
447 | @end example |
448 | |
449 | (Note that plain Bourne shell users have a slight problem, because the Bourne |
450 | shell only reads configuration things on a login, not when a normal |
451 | interactive shell is started.) |
452 | |
453 | |
454 | @node The set-user style, The login style, The preserve style, Login styles |
455 | @subsubsection The `set-user' login style |
456 | |
457 | The author sees the main use of Become as allowing a user to acquire the |
458 | privileges associated with a shared account without all the problems which |
459 | shared accounts usually cause. To the author's way of thinking, one of the |
460 | main problems is that your environment gets replaced by something alien and |
461 | wrong. People disagree with me over this point, and for this reason the |
462 | `set-user' style exists. |
463 | |
464 | The objective of `set-user' style is to behave similarly to the standard |
465 | @code{su} command. Unless they've been preserved explicitly (@pxref{Tweaking |
466 | the environment}), `set-user' mode sets the following environment variables: |
467 | |
468 | @table @code |
469 | @item USER |
470 | @itemx LOGNAME |
471 | The name of the target user. |
472 | |
473 | @item HOME |
474 | The home directory of the target user. |
475 | |
476 | @item SHELL |
477 | The target user's default shell |
478 | @end table |
479 | |
480 | The result of this is that the shell will read the target user's |
481 | configuration files and present you with the environment set up there. |
482 | |
483 | I can't think of this style as being anything other than a migration aid |
484 | while users are getting used to the freedom offered by the `preserve' style. |
485 | |
486 | |
487 | @node The login style, , The set-user style, Login styles |
488 | @subsubsection The `login' login style |
489 | |
490 | The `login' style causes Become to attempt to emulate a full login. Become |
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491 | will empty the environment of almost variables which aren't explicitly |
492 | preserved (@pxref{Tweaking the environment}). However, the following |
493 | variables are retained: |
494 | |
495 | @itemize @bullet |
496 | @item |
497 | TERM |
498 | @item |
499 | DISPLAY |
500 | @item |
501 | TZ |
502 | @end itemize |
503 | |
504 | @noindent |
505 | It will set the following variables: |
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506 | |
507 | @table @code |
508 | @item USER |
509 | @itemx LOGNAME |
510 | The name of the target user. |
511 | |
512 | @item HOME |
513 | The home directory of the target user. |
514 | |
515 | @item SHELL |
516 | The target user's default shell |
517 | |
518 | @item MAIL |
519 | An educated guess at where the target user's mailbox is. |
520 | @end table |
521 | |
522 | By default, it runs the target user's shell, informing it that this is a |
523 | login by setting the first character of @code{argv[0]} to @samp{-}. |
524 | |
525 | Become makes no entries in the @file{utmp} and @file{wtmp} files. |
526 | |
527 | |
528 | |
529 | @node Tweaking the environment, Removed variables, Login styles, Environment |
530 | @subsection Tweaking individual environment variables |
531 | |
532 | Become's login styles provide a sort of course-grained control over the |
533 | environment. Sometimes the control isn't fine enough. Become lets you tweak |
534 | individual variables: you can set, delete, or preserve named variables from |
535 | modification. |
536 | |
537 | There are three different things you can do with environment variables: |
538 | |
539 | @itemize @bullet |
540 | @item |
541 | Set a variable called @var{var} to a value @var{value}, by saying |
542 | |
543 | @example |
544 | @var{var}=@var{value} |
545 | @end example |
546 | |
547 | @noindent |
548 | The variable is preserved from automatic deletion by the login-style rules. |
549 | |
550 | @item |
551 | Delete a variable called @var{var} from the environment, by saying |
552 | |
553 | @example |
554 | @var{var}- |
555 | @end example |
556 | |
557 | @item |
558 | Preserve a variable @var{var} from being deleted or modified by Become's |
559 | login-style rules, but not change its value, by saying |
560 | |
561 | @example |
562 | @var{var}! |
563 | @end example |
564 | @end itemize |
565 | |
566 | Just to try and make this slightly more sensible, here's an example. Suppose |
567 | I want my @code{XAUTHORITY} variable to be set when I become user `fred': |
568 | |
569 | @example |
570 | become XAUTHORITY=$HOME/.Xauthority fred |
571 | @end example |
572 | |
573 | @noindent |
574 | should do the job nicely. Similarly, if I want to log in as `bob', but don't |
575 | want my @code{EDITOR} variable to change: |
576 | |
577 | @example |
578 | become --login EDITOR! bob |
579 | @end example |
580 | |
581 | @noindent |
582 | (Of course, in this example, I'm at the mercy of Bob's shell init files as to |
583 | whether his choice of editor overrides mine.) |
584 | |
585 | |
586 | |
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587 | @node Removed variables, , Tweaking the environment, Environment |
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588 | @subsection Variables removed from the environment |
589 | |
590 | Some variables are removed from the environment which Become passes to a |
591 | program for security reasons: |
592 | |
593 | @table @code |
594 | @item LD_* |
595 | @itemx SHLIB_PATH |
596 | @itemx LIBPATH |
597 | @itemx _RLD_* |
598 | These variables are used on various systems as a search path for shared |
599 | libraries. Clearly, by manipulating these search paths, an attacker could |
600 | replace a standard shared library with one of his own. |
601 | |
602 | @item IFS |
603 | The shell input field separator. Modifying this variable radically alters |
604 | the way shells parse their inputs. (In particular, consider the case where |
605 | @code{IFS} contains @samp{/}.) |
606 | |
607 | @item ENV |
608 | @itemx BASH_ENV |
609 | Used by some shells: it contains the name of a file to read on every shell |
610 | invocation. |
611 | |
612 | @item KRB_CONF |
613 | @ignore |
614 | I'm not really sure what's going on here, so I'll just have to bluff my way |
615 | through. I think that the following is more-or-less accurate, having browsed |
616 | a small amount of Kerberos-related documentation. |
617 | @end ignore |
618 | Contains the name of a Kerberos configuration file. By manipulating this |
619 | variable, an attacker could persuade a program to believe the wrong |
620 | authentication server. |
621 | @end table |
622 | |
623 | Also note that the @code{PATH} variable is modified: any items which aren't |
624 | absolute pathnames are removed from the path. This check may become stricter |
625 | in future, although getting the balance between security and convenience is |
626 | particularly hard here. |
627 | |
628 | |
629 | |
7a53967a |
630 | @node Group permissions, X authority, Environment, Becoming someone else |
631 | @section How Become handles groups |
632 | |
633 | As well as handling changes of user id, Become also changes group ids. |
634 | The exact changes Become makes are under user control. |
635 | |
636 | @menu |
637 | * Primary group selection:: Setting the new primary group |
638 | * Subsidiary groups:: Setting subsidiary group memberships |
639 | @end menu |
640 | |
641 | |
642 | @node Primary group selection, Subsidiary groups, Group permissions, Group permissions |
643 | @subsection Choosing a new primary group |
644 | |
645 | By default, the primary group is chosen according to the login style |
646 | (@pxref{Login styles}): the `preserve' style retains the current primary |
647 | group, while `set-user' and `login' styles choose the target's primary group. |
648 | |
649 | You can override Become's default choice using the @code{--group} (@code{-g} |
650 | for short) option: |
651 | |
652 | @example |
653 | become --group=@var{group} @dots{} |
654 | @end example |
655 | |
656 | The chosen @var{group} may be either a group name or a numeric gid. The |
657 | group must be one of the following: |
658 | |
659 | @itemize @bullet |
660 | @item |
661 | Your current primary group. |
662 | @item |
663 | One of your current subsidiary groups. |
664 | @item |
665 | The target user's primary group. |
666 | @item |
667 | One of the target user's subsidiary groups. |
668 | @end itemize |
669 | |
670 | Become will raise an error if this isn't the case. |
671 | |
672 | |
673 | @node Subsidiary groups, , Primary group selection, Group permissions |
674 | @subsection Handling subsidiary group memberships |
675 | |
676 | Subsidiary group memberships are a powerful tool for managing permissions |
677 | under Unix. Traditionally, they tend to be tied to particular users. Become |
678 | tries to be sightly more intelligent about group memberships. |
679 | |
680 | Become has a concept of @dfn{group style}, analogous to login style |
681 | (@pxref{Login styles}). The styles are selected by giving command line |
682 | arguments: |
683 | |
684 | @table @code |
685 | @item -k |
686 | @itemx --keep-groups |
687 | Retain the existing group memberships; don't add any new groups. |
688 | |
689 | @item -m |
690 | @itemx --merge-groups |
691 | Merge group memberships of the target user with the exiting memberships. |
692 | |
693 | @item -r |
694 | @itemx --replace-groups |
695 | Replace the existing group memberships with the target user's memberships. |
696 | @end table |
697 | |
698 | Again, the defaults are dependent on the chosen login style. Both `preserve' |
699 | and `set-user' merge group memberships; the `login' style replaces the set of |
700 | groups. |
701 | |
702 | Note that you can do perverse things like replace all the subsidiary groups |
703 | but retain your primary group (using the @code{--group} option; |
704 | @pxref{Primary group selection}) if you like: Become won't try to stop you. |
705 | |
706 | |
707 | |
708 | @node X authority, Running commands, Group permissions, Becoming someone else |
709 | @section Considerations for X authority |
710 | |
711 | Other users can't read your @file{.Xauthority} file, if you have one. This |
712 | is as it should be: anyone who can read it can connect to your X server and |
713 | read or generate events. However, once you've become another user, you can't |
714 | open any X windows; this can be annoying if your favourite editor is X-based. |
715 | |
716 | There are two basic approaches. Either you can send the shared account a |
717 | copy of your display's magic cookie, or you can retain permission to read the |
718 | cookie file. |
719 | |
10bc033f |
720 | Be aware that allowing a shared account to connect to your X display is a |
721 | security risk. |
722 | |
7a53967a |
723 | @menu |
10bc033f |
724 | * The user-group method:: A fairly secure way of handling X authority |
7a53967a |
725 | * Using xauth:: A less secure method, which might be easier |
726 | @end menu |
727 | |
728 | |
729 | @node The user-group method, Using xauth, X authority, X authority |
730 | @subsection The user-group method for handling X authority |
731 | |
10bc033f |
732 | This method is secure only if your site uses the `user-group' system. In |
733 | this system, each user is allocated a group containing only that user. |
734 | Usually this is made the user's default primary group, although that's not |
735 | necessary here. |
7a53967a |
736 | |
737 | When you start a new X session, ensure that your cookie file is owned by you |
738 | and your private group. Change the file's permissions so that it's group |
739 | readable. Finally, ensure that your private group is retained when you |
740 | become someone else (@pxref{Group permissions}), and that the |
741 | @code{XAUTHORITY} variable is set correctly. |
742 | |
10bc033f |
743 | Note that Unix's security mechanisms aren't designed to prevent processes |
744 | owned by the same user from interfering with each other. This method does |
745 | not provide complete security. |
746 | |
7a53967a |
747 | The following Bourne shell code in a @file{.xinitrc} should do most of the |
748 | work: |
749 | |
750 | @example |
751 | XAUTHORITY="$HOME/.Xauthority" |
752 | export XAUTHORITY |
753 | chgrp mygroup $XAUTHORITY |
754 | chmod 640 $XAUTHORITY |
755 | @end example |
756 | |
757 | @noindent |
758 | In a C shell, this becomes |
759 | |
760 | @example |
761 | setenv XAUTHORITY $@{HOME@}/.Xauthority |
762 | chgrp mygroup $XAUTHORITY |
763 | chmod 640 $XAUTHORITY |
764 | @end example |
765 | |
766 | The @code{XAUTHORITY} file is preserved by both the `preserve' and `set-user' |
767 | login styles, so this isn't a problem. You can now become other users, and |
768 | your X permissions will follow you around correctly. |
769 | |
770 | It's probably worth noting that the @code{xauth} program annoyingly resets |
771 | the permissions on the cookie file every time it writes to it. This will be |
772 | particularly irritating if you use @code{ssh}'s X forwarding capabilities, |
773 | because every @code{ssh} connection will reset the permissions. You can deal |
774 | with this problem by putting a line |
775 | |
776 | @example |
777 | chmod 640 $@{XAUTHORITY-$HOME/.Xauthority@} 2>/dev/null |
778 | @end example |
779 | |
780 | @noindent |
781 | in your @file{.bashrc} or @file{.profile} (for Bourne-like shell users) or |
782 | |
783 | @example |
784 | if ($?XAUTHORITY) then |
785 | chmod 640 $XAUTHORITY >&/dev/null |
786 | else |
787 | chmod 640 $@{HOME@}/.Xauthority >&/dev/null |
788 | endif |
789 | @end example |
790 | |
791 | @noindent |
792 | in @file{.cshrc} for C shell users. |
793 | |
794 | |
7a53967a |
795 | @node Using xauth, , The user-group method, X authority |
10bc033f |
796 | @subsection The @code{xauth} method for handling X authority |
7a53967a |
797 | |
798 | This method sends your X cookie to the shared account. It's therefore |
799 | intrinsically dangerous: you must be able to trust the other users of the |
800 | shared account not to take undue advantage of this situation. |
801 | |
802 | The following (Bourne) shell snippet illustrates how you might send an |
803 | authorisation cookie to the shared account, to allow it to connect to your |
804 | display: |
805 | |
806 | @example |
807 | if test -n "$BECOME_HOME"; then |
808 | XAUTHORITY="$BECOME_HOME/.Xauthority"; export XAUTHORITY |
809 | elif test -n "$DISPLAY" && test -z "done_xauth_cookie"; then |
810 | case "$DISPLAY" in |
811 | :0.0) display=`hostname`:0.0 ;; |
812 | *) display="$DISPLAY" ;; |
813 | esac |
814 | xauth extract - $display | \ |
815 | become someone -c 'xauth -f $BECOME_HOME/.Xauthority merge -' |
816 | done_xauth_cookie=yes; export done_xauth_cookie |
817 | fi |
818 | @end example |
819 | |
820 | The equivalent C shell code is |
821 | |
822 | @example |
823 | if ($?BECOME_HOME) then |
824 | setenv XAUTHORITY "$@{BECOME_HOME@}/.Xauthority |
825 | else if ($?DISPLAY && ! $?done_xauth_cookie) then |
826 | if ($DISPLAY == :0.0) then |
827 | set display="`hostname`:0.0" |
828 | else |
829 | set display="$DISPLAY" |
830 | endif |
831 | xauth extract - $display | \ |
832 | become someone -c 'xauth -f $BECOME_HOME/.Xauthority merge -' |
833 | endif |
834 | @end example |
835 | |
836 | It works as follows: |
837 | |
838 | @itemize @bullet |
839 | @item |
840 | If the variable @code{BECOME_HOME} is set, then we're probably really someone |
841 | else, so point to the shared account's authority file. |
842 | |
843 | @item |
844 | Otherwise, check to see whether we have a display, and the authorisation has |
845 | not already been sent. If this is so, resolve a local display name into a |
846 | remote one (just in case) and then send it to the shared account. |
847 | @end itemize |
848 | |
849 | |
850 | |
851 | @node Running commands, , X authority, Becoming someone else |
852 | @section Executing specific commands |
853 | |
854 | As well as starting shells, Become can run single commands. This can be |
855 | useful in two ways: |
856 | |
857 | @itemize @bullet |
858 | @item |
859 | It enables Become to be used in scripts. |
860 | |
861 | @item |
862 | It allows access to shared accounts to be controlled on the basis of the |
863 | command to be run. |
864 | @end itemize |
865 | |
866 | To run a command as another user, say: |
867 | |
868 | @example |
869 | become @var{user} @var{command} [@var{argument}@dots{}] |
870 | @end example |
871 | |
872 | If the request is granted, Become runs @var{command}, passing it any |
873 | arguments following the command name. Become doesn't run a shell, so there's |
874 | no extra escaping which needs to be done. |
875 | |
876 | If you really want to run a shell command as another user, you can use the |
877 | @code{-c} option: |
878 | |
879 | @example |
880 | become @var{user} -c @var{shell-command} |
881 | @end example |
882 | |
883 | This is exactly equivalent to |
884 | |
885 | @example |
886 | become @var{user} /bin/sh -c @var{shell-command} |
887 | @end example |
888 | |
889 | in every way. In particular, you must have permission to run @file{/bin/sh} |
890 | as @var{user} for it to work: Become doesn't attempt to interpret the shell |
891 | command in any way. Also note that Become always uses the Bourne shell, |
892 | regardless of your current shell preference, or @var{user}'s default shell. |
893 | (This is done to provide a stable programming interface which works |
894 | irrespective of changes to the shared account's configuration.) |
895 | |
896 | |
897 | @c -------------------------------------------------------------------------- |
898 | @node Administering Become, Invoking Become, Becoming someone else, Top |
899 | @chapter Become administration |
900 | |
901 | |
902 | This chapter will explain how Become is administrated and maintained. |
903 | |
904 | @menu |
905 | * Configuration files:: Overview of Become's configuration files |
906 | * Standalone or networked:: The two main types of Become installations |
907 | * The configuration file:: How to define who's allowed to do what |
908 | * Networked configuration:: Considerations for networked installations |
909 | @end menu |
910 | |
911 | |
912 | |
913 | @node Configuration files, Standalone or networked, Administering Become, Administering Become |
914 | @section Configuration files |
915 | |
916 | Become keeps its configuration and administrative files in a directory |
917 | usually named @file{/etc/become}, although this can be changed with the |
918 | @code{--with-etcdir} option to the configuration script when you build |
919 | Become. |
920 | |
921 | Not all of the files are needed on all machines. |
922 | |
923 | @table @file |
924 | @item become.conf |
925 | The main configuration file, containing a description of which users are |
926 | allowed to become which other users, where, and what they're allowed to run |
927 | when they get there. Only needed on servers or standalone machines. |
928 | |
929 | @item become.server |
930 | A list of servers to contact. Only needed on client machines. |
931 | |
932 | @item become.key |
f60a3434 |
933 | The signing key to use when sending requests to servers. Needed on servers, |
934 | but not on standalone machines. |
935 | |
936 | @item become.pubkey |
937 | The verification keys to use when checking server responses. Needed on |
938 | clients, but not on standalone machines. |
7a53967a |
939 | |
940 | @item become.pid |
941 | The process id of the server. Created automatically by Become's server when |
942 | in starts up. |
7a53967a |
943 | @end table |
944 | |
945 | |
946 | @node Standalone or networked, The configuration file, Configuration files, Administering Become |
947 | @section Installation types |
948 | |
949 | |
950 | Become can be installed in two different ways, depending on how you want to |
951 | administer it: |
952 | |
953 | @itemize @bullet |
954 | @item |
955 | In a @dfn{standalone} installation, each Become request is dealt with |
956 | locally: the program reads the configuration file, and decides whether it |
957 | should grant or deny permission. |
958 | |
959 | Standalone installations don't depend on servers being available, or even on |
10bc033f |
960 | the existence of a network. They're useful for small sites, or sites with a |
7a53967a |
961 | small number of users. The disadvantages are that reading the configuration |
962 | file takes a while, so the program doesn't feel as responsive as it should, |
963 | and ensuring that all the hosts' configuration files are synchronised becomes |
964 | difficult when you have lots of machines. |
965 | |
966 | @item |
967 | In a @dfn{network} installation, any Become requests are sent on to a |
968 | collection of servers. The servers analyse the request and send a reply back |
969 | which either authorises or forbids access. |
970 | |
971 | A networked installation clearly depends on the servers' reliability. The |
972 | client reacts only to the first reply it receives, so as long as there is one |
973 | server running, everything should continue as normal. |
974 | |
975 | A networked installation is useful when you have a large number of client |
976 | machines, particularly ones which may not be awake all the time. The full |
977 | configuration file only needs to be installed on a small number of servers; |
978 | the clients require only a list of server machines to contact, and an |
979 | encryption key to use. |
980 | @end itemize |
981 | |
982 | |
983 | |
984 | @node The configuration file, Networked configuration, Standalone or networked, Administering Become |
985 | @section The configuration file |
986 | |
987 | The main configuration file, usually called @file{/etc/become/become.conf}, |
988 | contains all the rules which Become uses to decide whether to grant or deny |
989 | requests. It may also contain additional information for the benefit of |
990 | Become daemons, if you're using a networked installation. |
991 | |
992 | @menu |
10bc033f |
993 | * Requests and rules:: How the configuration file works |
7a53967a |
994 | * Basic syntax:: Quick overview of Become's syntax |
995 | * Classes:: Defining classes of things |
996 | * Predefined classes:: Become predefines some (maybe) useful classes |
997 | * Allow statements:: Allow users to become other users |
998 | * Other statements:: Some other useful statements |
999 | * Example configuration file:: An example, showing a few features. |
10bc033f |
1000 | * Checking and querying:: Checking and querying configuration files |
7a53967a |
1001 | * Complete grammar:: Complete grammar for Become config files |
1002 | @end menu |
1003 | |
1004 | |
10bc033f |
1005 | @node Requests and rules, Basic syntax, The configuration file, The configuration file |
1006 | @subsection Requests and rules |
1007 | |
1008 | Become looks at four pieces of information when it's analysing a request: |
1009 | |
1010 | @itemize @bullet |
1011 | @item |
1012 | the user's current identity; |
1013 | @item |
1014 | the identity the user wishes to assume; |
1015 | @item |
1016 | the host which generated the request; and |
1017 | @item |
1018 | the command the user wishes to run. |
1019 | @end itemize |
1020 | |
1021 | Each of these pieces of information is looked at when Become decides whether |
1022 | to honour a request. |
1023 | |
1024 | The configuration file's main purpose is to describe the conditions under |
1025 | which Become should honour a request. These conditions are described by a |
1026 | number of @emph{rules}. A rule consists of two lists of users (called `from' |
1027 | and `to'), a list of hosts, and a list of commands. A rule matches a request |
1028 | if: |
1029 | |
1030 | @itemize @bullet |
1031 | @item |
1032 | the user's current identity is in the rule's `from' list; |
1033 | @item |
1034 | the target user's identity is in the rule's `to' list; |
1035 | @item |
1036 | the host is in the rule's host list; and |
1037 | @item |
1038 | the command to be run is in the rule's command list. |
1039 | @end itemize |
1040 | |
1041 | A request is honoured if there is a rule which matches the request. |
1042 | |
1043 | |
1044 | @node Basic syntax, Classes, Requests and rules, The configuration file |
7a53967a |
1045 | @subsection Basic configuration file syntax |
1046 | |
1047 | The configuration file consists of a sequence of statements, each terminated |
1048 | by a semicolon. |
1049 | |
1050 | Comments begin with a @samp{#} character, and continue to the end of the |
1051 | line. This is the only time newlines behave specially: newlines behave just |
1052 | like any other whitespace characters within statements. |
1053 | |
1054 | Strings are enclosed in double-quote characters (@samp{"}). Within a string, |
1055 | a backslash causes the following character to be treated literally, whatever |
1056 | it may be (including quotes, backslashes and newlines). |
1057 | |
1058 | Names begin with an alphabetic character or an underscore, and consist of |
1059 | letters, digits and underscores. |
1060 | |
7a53967a |
1061 | |
1062 | @node Classes, Predefined classes, Basic syntax, The configuration file |
1063 | @subsection Classes |
1064 | |
1065 | A @dfn{class} in Become is a set of users, hosts or commands. You can define |
1066 | and name your own classes using statements of the form: |
1067 | |
1068 | @example |
1069 | user @var{name} = @var{class-expr} ; |
1070 | command @var{name} = @var{class-expr} ; |
1071 | host @var{name} = @var{class-expr} ; |
1072 | @end example |
1073 | |
1074 | A @var{class-expr} is an expression defining a class. You can build a |
1075 | complex class out of simple classes using the operators (in ascending |
1076 | precedence order) @samp{,}, @samp{-}, @samp{|} and @samp{&}, which represent |
1077 | the set options `union', `subtraction', `union' (again!), and `intersection'. |
1078 | Subexpressions can be parenthesised to override the default precedence. |
1079 | Once a class name has been defined, as shown above, it can be used in |
1080 | subsequent class expressions. |
1081 | |
1082 | A single user may be designated by either a user name (in quotes) or an |
1083 | integer uid. Commands and hosts may be designated by quoted strings which |
1084 | may contain wildcards. Host strings are matched against both numeric (dotted |
1085 | quad) IP addresses and the reverse-resolved hostname. Command strings are |
1086 | matched against the absolute pathname of the command the user wants to |
1087 | execute. |
1088 | |
1089 | |
1090 | |
1091 | @node Predefined classes, Allow statements, Classes, The configuration file |
1092 | @subsection Predefined classes |
1093 | |
1094 | In an attempt to make life a bit easier, Become creates a collection of |
1095 | predefined classes. |
1096 | |
1097 | The standard classes @code{all} and @code{none} match anything and nothing |
1098 | respectively. The @code{all} class is useful in some contexts: it gives you |
1099 | a way of saying `everything except@dots{}', for example: |
1100 | |
1101 | @example |
1102 | user MUNDANES = all - SYSHACKS; |
1103 | @end example |
1104 | |
1105 | @noindent |
10bc033f |
1106 | The @code{none} class is provided because it's needed internally anyway and |
1107 | someone might come up with a use for it. |
7a53967a |
1108 | |
1109 | Become also defines some other classes: |
1110 | |
1111 | @itemize @bullet |
1112 | @item |
1113 | For each username @var{user}, Become adds a class called @samp{@var{user}} |
1114 | which matches just that user. |
1115 | |
1116 | @item |
1117 | For each group name @var{group}, Become creates a class called |
1118 | @samp{@var{group}} which matches any user who is a member of that group. |
1119 | |
1120 | @item For each netgroup @var{netgroup}, Become creates two classes: |
1121 | @samp{u_@var{netgroup}} which matches any user listed in the netgroup, and |
1122 | @samp{h_@var{netgroup}} which matches any host listed in the netgroup. |
1123 | @end itemize |
1124 | |
1125 | If a name is used for both a user @emph{and} a group, then corresponding |
1126 | class ends up containing the user together with all of the group members. |
1127 | For this reason, it's probably better to use the predefined classes for |
1128 | groups rather than individual users -- use quoted user names for individual |
1129 | users. |
1130 | |
1131 | Note that users and groups are read using the standard @code{get*ent} calls |
1132 | @emph{and} directly from the NIS server (if there is one). The idea here is |
1133 | that a Become server can be run on a machine which allows restricted logins. |
1134 | It still needs to know about all the users known to the outside world. |
1135 | |
1136 | Netgroups are read only from the NIS servers. In particular, although GNU |
10bc033f |
1137 | systems allow netgroup databases to be stored in local files, Become won't |
7a53967a |
1138 | read them because there's no defined interface for enumerating netgroups. |
1139 | |
1140 | |
1141 | @node Allow statements, Other statements, Predefined classes, The configuration file |
1142 | @subsection Allow statements |
1143 | |
10bc033f |
1144 | The @code{allow} statement defines the rules Become uses when deciding |
1145 | whether to grant a request; see @ref{Requests and rules}. |
7a53967a |
1146 | |
1147 | @example |
1148 | allow [[@var{host-class}]] [@var{user-class}] -> [@var{user-class}] [ : @var{command-class}] |
1149 | @end example |
1150 | |
1151 | (The @var{host-class} is optional, but must be enclosed in square brackets if |
1152 | present.) |
1153 | |
1154 | The four classes in an allow statement are called, respectively, the `host', |
1155 | the `to-user', the `from-user' and the `command'. Any of the four classes |
1156 | may be omitted, and an omitted class defaults to `all'. |
1157 | |
1158 | When a request is received, Become checks the fields in the request against |
1159 | the classes in each allow statement of the configuration file. If a |
1160 | statement matches, the request is granted; if there are no full matches, |
1161 | the request is denied. |
1162 | |
1163 | |
1164 | @node Other statements, Example configuration file, Allow statements, The configuration file |
1165 | @subsection Other statements |
1166 | |
1167 | Two other statement types are defined. They only have an effect on Become in |
1168 | daemon mode: |
1169 | |
1170 | @example |
1171 | port @var{port} ; |
1172 | keyfile @var{key-file} ; |
1173 | @end example |
1174 | |
1175 | @noindent |
1176 | The @code{port} statement specifies the port to which the server should |
1177 | listen; the @var{port} may be be an integer or a quoted service name. The |
1178 | @code{keyfile} statement instructs Become to use the key from the file named |
1179 | @var{key-file}, which must be a quoted string. |
1180 | |
1181 | |
10bc033f |
1182 | @node Example configuration file, Checking and querying, Other statements, The configuration file |
7a53967a |
1183 | @subsection An example configuration file |
1184 | |
1185 | @example |
1186 | # |
1187 | # become.conf |
1188 | # |
1189 | # Example configuration file |
1190 | # |
1191 | |
1192 | allow wheel -> "root"; |
1193 | |
1194 | user NEWS = "fred", "jim"; |
1195 | allow NEWS -> "news"; |
1196 | |
1197 | user HTTP = "jim", "bob"; |
10bc033f |
1198 | allow ["www.somewhere.com"] |
1199 | HTTP -> "httpd" : "/bin/kill", "/etc/init.d/httpd"; |
1200 | @end example |
1201 | |
1202 | |
1203 | @node Checking and querying, Complete grammar, Example configuration file, The configuration file |
1204 | @subsection Checking and querying the configuration file |
1205 | |
1206 | At a reasonably sized site, Become configuration files can get rather large, |
1207 | and becomes tricky to work out exactly who's allowed to do what and where. |
1208 | |
1209 | The @code{bcquery} tool provided allows Become configuration files to be |
1210 | verified and queried. It can be used to ensure that a file is syntactically |
1211 | correct before it is deployed, or to enquire about privileges granted. |
1212 | |
1213 | @menu |
1214 | * Verifying config files:: Checking a configuration file is correct |
1215 | * Querying config files:: Asking questions about privileges |
1216 | * Output formats:: Different ways of formatting output |
1217 | * Restricting output:: Being selective about what gets output |
1218 | * bcquery reference:: Complete command line reference |
1219 | @end menu |
1220 | |
1221 | @node Verifying config files, Querying config files, Checking and querying, Checking and querying |
1222 | @subsubsection Verifying configuration files |
1223 | |
1224 | A common use of @code{bcquery} is to ensure that a configuration file is |
1225 | actually valid. The command |
1226 | |
1227 | @example |
1228 | bcquery [-file @var{file}] -check |
7a53967a |
1229 | @end example |
1230 | |
10bc033f |
1231 | @noindent |
1232 | verifies that a configuration file conforms to Become's expectations. If |
1233 | there are any errors in @var{file}, they are reported, and @code{bcquery} |
1234 | will return a nonzero exit code. |
1235 | |
1236 | If no @var{file} is specified, @code{bcquery} will read the configuration |
1237 | file which Become itself reads by default, usually |
1238 | @code{/etc/become/become.conf}. |
1239 | |
1240 | |
1241 | @node Querying config files, Output formats, Verifying config files, Checking and querying |
1242 | @subsubsection Querying configuration files |
7a53967a |
1243 | |
10bc033f |
1244 | The @code{bcquery} program will list all rules which match a selected request |
1245 | pattern. For example, you can display all rules which allow a particular |
1246 | user to change identity, or all rules which allow people to assume root |
1247 | privileges on a particular host. |
1248 | |
1249 | @example |
1250 | bcquery [-file @var{file}] @var{query} |
1251 | @end example |
1252 | |
1253 | The following simple queries are supported: |
1254 | |
1255 | @table @asis |
1256 | @item @code{-from} @var{user} |
1257 | Matches any rule containing @var{user} in its `from' list. |
1258 | @item @code{-to} @var{user} |
1259 | Matches any rule containing @var{user} in its `to' list. |
1260 | @item @code{-host} @var{host} |
1261 | Matches any rule containing @var{host} in its host list. |
1262 | @item @code{-command} @var{cmd} |
1263 | Matches any rule containing @var{cmd} in its `command' list. |
1264 | @end table |
1265 | |
1266 | @noindent |
1267 | Simple queries can be combined using the following operators: |
1268 | |
1269 | @table @asis |
1270 | @item @var{query-a} @code{-or} @var{query-b} |
1271 | Matches a rule matched by either @var{query-a} or @var{query-b}. |
1272 | @item @var{query-a} @code{-and} @var{query-b} |
1273 | Matches a rule matched by both @var{query-a} and @var{query-b}. |
1274 | @item @code{-not} @var{query} |
1275 | Matches a rule which is not matched by @var{query}. |
1276 | @item @code{(} @var{query} @code{)} |
1277 | Matches a rule matched by @var{query} (overrides default precedence). |
1278 | @end table |
1279 | |
1280 | The @code{-and}, @code{-or} and @code{-not} operators may be written |
1281 | @code{&}, @code{|} and @code{!} respectively, if you prefer, and the |
1282 | @code{-and} operator is optional. These characters (and the parentheses |
1283 | @code{(} and @code{)}) may need to be quoted to prevent interpretation by the |
1284 | shell. |
1285 | |
1286 | Some examples may explain what's going on: |
1287 | |
1288 | @table @samp |
1289 | @item bcquery -from hacker |
1290 | Displays all rules applying to user `hacker'. |
1291 | @item bcquery -host somehost -to root |
1292 | Displays rules allowing people to become root on @code{somehost}. |
1293 | @end table |
1294 | |
1295 | |
1296 | @node Output formats, Restricting output, Querying config files, Checking and querying |
1297 | @subsubsection Output formats |
1298 | |
1299 | The @code{bcquery} program has two distinct output formats: `rows' and |
1300 | `columns'. |
1301 | |
1302 | The `columns' format is probably the simpler to understand, and certainly the |
1303 | easier to read. Each matching record is displayed with the lists of users, |
1304 | hosts and commands in columns. A query on the example configuration file |
1305 | (@pxref{Example configuration file}) is shown below: |
1306 | |
1307 | @example |
1308 | FROM TO HOST COMMAND |
1309 | |
1310 | frankie root ALL ALL |
1311 | selina |
1312 | |
1313 | fred news ALL ALL |
1314 | jim |
1315 | |
1316 | jim httpd www.somewhere.com /bin/kill |
1317 | bob /etc/init.d/httpd |
1318 | @end example |
1319 | |
1320 | @noindent |
1321 | The `columns' format can only show simple lists. A more complex class |
1322 | definition will show up as @samp{<complex>} in a `columns' format listing. |
1323 | |
1324 | The `rows' format is capable of displaying classes in their full generality, |
1325 | but is harder to parse and read. It displays each list in the form of an |
1326 | expression, in more or less the same syntax as a class definition |
1327 | (@pxref{Classes}). |
1328 | |
1329 | The default behaviour is to use `columns' format where possible, or `rows' |
1330 | format if some of the lists are too complex to be represented in columns. |
1331 | You can select a format explicitly using the @code{-columns} or @code{-rows} |
1332 | options, which is useful if you're trying to parse the output of |
1333 | @code{bcquery} with a script. |
1334 | |
1335 | |
1336 | @node Restricting output, bcquery reference, Output formats, Checking and querying |
1337 | @subsubsection Restricting output |
1338 | |
1339 | It's also possible to suppress bits of information about each matched rule. |
1340 | For example, you can show only the `from' list, or just the `to' and `host' |
1341 | lists. This is done with the @code{-output} option. |
1342 | |
1343 | Each list is given a letter; the `from' list is called @samp{f}, the `to' |
1344 | list @samp{t}, the host list @samp{h} and the command list @samp{c}. You can |
1345 | select which lists are displayed by giving the corresponding letters (the |
1346 | order isn't important). You can also turn individual lists on or off by |
1347 | preceding the characters with @samp{+} or @samp{-} characters. If you start |
1348 | with a @samp{+} or @samp{-}, then the last-set selection (or the initial |
1349 | default of all-lists-enabled) is modified. |
1350 | |
1351 | For example, @samp{-output ftc} shows only the `from', `to' and `command' |
1352 | lists. This could be written @samp{-output -h} too, to turn the hosts list |
1353 | off. |
1354 | |
1355 | This option is mainly useful with the `columns' output format (@pxref{Output |
1356 | formats}) to save scripts having to select columns out themselves. |
1357 | |
1358 | |
1359 | @node bcquery reference, , Restricting output, Checking and querying |
1360 | @subsubsection @code{bcquery} options summary |
1361 | |
1362 | @example |
1363 | bcquery [@var{option}@dots{}] [@var{query}] |
1364 | @end example |
1365 | |
1366 | The @var{option}s available are: |
1367 | |
1368 | @table @asis |
1369 | @item @code{-help} |
1370 | Displays a summary of the available options, and exits. |
1371 | |
1372 | @item @code{-file} @var{file} |
1373 | Read @var{file}, rather than the compiled-in default (usually |
1374 | @file{/etc/become/become.conf}). |
1375 | |
1376 | @item @code{-dump} |
1377 | Don't read a configuration file. Instead, display the query tree parsed from |
1378 | the command line. This is a debugging feature. |
1379 | |
1380 | @item @code{-check} |
1381 | Don't attempt to output any rules. Instead, just check the configuration |
1382 | file for validity. |
1383 | |
1384 | @item @code{-output} @var{spec} |
1385 | Selects which columns are to be displayed for each matching rule. |
1386 | For full details, see @ref{Restricting output}. |
1387 | |
1388 | @item @code{-columns} |
1389 | @itemx @code{-rows} |
1390 | Forces `columns' or `rows' output format. @xref{Output formats}. |
1391 | |
1392 | @item @code{-nohead} |
1393 | Suppress the header line at the top of the output in `columns' mode. Makes |
1394 | the output more amenable to automatic processing (but harder to read). |
1395 | |
1396 | @item @code{-from} @var{user} |
1397 | @itemx @code{-to} @var{user} |
1398 | @itemx @code{-host} @var{hostname} |
1399 | @itemx @code{-command} @var{cmd} |
1400 | Simple queries for selecting rules. @xref{Querying config files}. |
1401 | |
1402 | @item @code{-and} |
1403 | @itemx @code{-or} |
1404 | @itemx @code{-not} |
1405 | Operators for combining queries into something useful. @xref{Querying config |
1406 | files}. |
1407 | @end table |
1408 | |
1409 | |
1410 | @node Complete grammar, , Checking and querying, The configuration file |
7a53967a |
1411 | @subsection Complete grammar for configuration files |
1412 | |
1413 | @format |
1414 | @var{file} ::= @var{file} @var{statement} |
1415 | |
1416 | @var{statement} ::= @var{class-def} |
1417 | | @var{allow-spec} |
1418 | | @var{port-spec} |
1419 | | @var{key-spec} |
1420 | |
1421 | @var{class-def} ::= @samp{user} @var{name} = @var{class-expr} @samp{;} |
1422 | | @samp{command} @var{name} = @var{class-expr} @samp{;} |
1423 | | @samp{host} @var{name} = @var{class-expr} @samp{;} |
1424 | |
1425 | @var{allow-spec} ::= @samp{allow} @var{opt-host-spec} @var{opt-user-spec} |
1426 | @samp{->} @var{opt-user-spec} @var{opt-command-spec} @samp{;} |
1427 | |
1428 | @var{opt-host-spec} ::= @samp{[} @var{class-expr} @samp{]} |
1429 | | @var{empty} |
1430 | |
1431 | @var{opt-user-spec} ::= @var{class-expr} |
1432 | | @var{empty} |
1433 | |
1434 | @var{opt-command-spec} ::= @samp{:} @var{class-expr} |
1435 | | @var{empty} |
1436 | |
1437 | @var{port-spec} ::= @samp{port} @var{integer} @samp{;} |
1438 | | @samp{port} @var{string} @samp{;} |
1439 | |
1440 | @var{key-spec} ::= @samp{keyfile} @var{string} @samp{;} |
1441 | |
1442 | @var{class-expr} ::= @var{class-diff-expr} |
1443 | | @var{class-expr} @samp{,} @var{class-diff-expr} |
1444 | |
1445 | @var{class-diff-expr} ::= @var{class-isect-expr} |
1446 | | @var{class-diff-expr} @samp{-} @var{class-union-expr} |
1447 | |
1448 | @var{class-union-expr} ::= @var{class-isect-expr} |
1449 | | @var{class-union-expr} @samp{|} @var{class-isect-expr} |
1450 | |
1451 | @var{class-isect-expr} ::= @var{class-primary} |
1452 | | @var{class-isect-expr} @samp{&} @var{class-primary} |
1453 | |
1454 | @var{class-primary} ::= @samp{(} @var{class-expr} @samp{)} |
1455 | | @var{string} |
1456 | | @var{integer} |
1457 | |
1458 | @var{integer} ::= one or more digits (@samp{0}--@samp{9}) |
1459 | |
1460 | @var{name} ::= an alphabetic character or underscore, followed by zero or |
1461 | more alphanumeric characters or underscores |
1462 | |
1463 | @var{string} ::= @samp{"} @var{string-chars} @samp{"} |
1464 | |
1465 | @var{string-chars} ::= @var{string-chars} @var{string-char} |
1466 | | @var{empty} |
1467 | |
1468 | @var{string-char} ::= a @samp{\} followed by any character |
1469 | | any character other than @samp{"}, @samp{\} or newline |
1470 | |
1471 | @var{empty} ::= |
1472 | @end format |
1473 | |
1474 | |
10bc033f |
1475 | |
7a53967a |
1476 | @node Networked configuration, , The configuration file, Administering Become |
1477 | @section Networked configuration |
1478 | |
1479 | If you're planning to use Become in a standalone way, you can skip this |
1480 | section. |
1481 | |
1482 | @menu |
1483 | * Choosing servers:: Which servers Become tries to talk to |
1484 | * Setting up keys:: How to generate keys for Become |
7a53967a |
1485 | * Issuing a new key:: How to issue new keys without disruption |
1486 | @end menu |
1487 | |
1488 | |
1489 | @node Choosing servers, Setting up keys, Networked configuration, Networked configuration |
1490 | @subsection Choosing servers |
1491 | |
1492 | Become notices that it's meant to send requests to a server if it finds a |
1493 | @file{become.server} file. This file contains entries of the form |
1494 | |
1495 | @example |
1496 | @var{host} [: @var{port}] |
1497 | @end example |
1498 | |
1499 | If the @var{port} is omitted, Become chooses a port by looking at the |
1500 | services database for a service which matches the name by which Become was |
1501 | invoked: normally this will be @samp{become}. |
1502 | |
1503 | Become sends a request to all of the servers and believes the first valid |
1504 | reply it receives. Since servers ignore requests they believe to be invalid, |
1505 | this enables you to change Become's key without disrupting service |
1506 | (@pxref{Issuing a new key}). |
1507 | |
1508 | If you're using NIS, you should try to ensure that Become servers runs only |
1509 | on NIS servers; the NIS master is probably a good choice. |
1510 | |
1511 | Become isn't particularly processor-intensive, and doesn't seem to require |
1512 | very much memory. |
1513 | |
1514 | |
f60a3434 |
1515 | @node Setting up keys, Issuing a new key, Choosing servers, Networked configuration |
7a53967a |
1516 | @subsection Setting up keys |
1517 | |
1518 | Communication between Become clients and the server is encrypted to ensure |
1519 | that it's not feasible to gain unauthorised privilege by subverting the |
f60a3434 |
1520 | network. Become uses the DSA algorithm to ensure authenticity of replies. |
7a53967a |
1521 | |
1522 | Each client machine, and the server, must have a copy of the same key. The |
1523 | key is usually stored in @file{/etc/become/become.key}. Become's keys are |
1524 | 128 bits long. |
1525 | |
f60a3434 |
1526 | The key file can be generated using Catacomb's @code{key} program. The |
1527 | commands |
7a53967a |
1528 | |
1529 | @example |
8fc4c5cd |
1530 | key -k /etc/become/become.key add -adsa -e"now + 1 year" become-dsa |
f60a3434 |
1531 | key -k /etc/become/become.key extract -f -secret /etc/become/become.pubkey |
7a53967a |
1532 | @end example |
1533 | |
1534 | @noindent |
f60a3434 |
1535 | will generate a suitable DSA key, and extract the public part. You should |
1536 | install the public key on all of your client computers, writable only by |
1537 | root. The private key should be only on the server, and readable or writable |
1538 | only by root. |
7a53967a |
1539 | |
f60a3434 |
1540 | If you have multiple servers, they can all have different private keys. |
1541 | You'll need to put all of the public keys in the |
1542 | @file{/etc/become/become.pubkey} file. |
7a53967a |
1543 | |
7a53967a |
1544 | |
f60a3434 |
1545 | @node Issuing a new key, , Setting up keys, Networked configuration |
7a53967a |
1546 | @subsection Issuing a new key |
1547 | |
1548 | When you're sending out a new key, you run a risk of disrupting service. The |
1549 | server reads a new key; the clients still have the old one. |
1550 | |
f60a3434 |
1551 | We used to recommend running two servers. Now, however, you can generate the |
1552 | new key, install the new public key on the clients in addition to the old |
1553 | one, and then install the new private key on the server. The clients try all |
1554 | valid public keys when attempting to authenticate a response, so this |
1555 | approach will work. |
7a53967a |
1556 | |
1557 | |
1558 | @c -------------------------------------------------------------------------- |
1559 | @node Invoking Become, , Administering Become, Top |
1560 | @chapter Invoking Become |
1561 | |
1562 | |
1563 | This chapter provides an exhaustive description of Become's command line |
1564 | options, organised in a reference-manual sort of way. |
1565 | |
1566 | @menu |
1567 | * Becoming another user:: Options for becoming another user |
1568 | * Starting Become daemons:: Options for starting Become daemons |
1569 | * Debugging options:: Options to use when Become goes wrong |
1570 | @end menu |
1571 | |
1572 | |
1573 | |
1574 | @node Becoming another user, Starting Become daemons, Invoking Become, Invoking Become |
1575 | @section Becoming another user |
1576 | |
1577 | @subsection Synopsis |
1578 | |
1579 | @example |
1580 | become [@var{option}@dots{}] [@var{env-var}@dots{}] @var{user} [@var{command} [@var{argument}@dots{}]] |
1581 | @end example |
1582 | |
1583 | Actually, you can put the @var{option}s, @var{env-var}s and @var{user} in any |
1584 | order you like; the important thing is that all of them appear before the |
1585 | command, if any. |
1586 | |
1587 | |
1588 | @subsection Usage |
1589 | |
1590 | The @var{option}s appropriate for this mode are as follows: |
1591 | |
1592 | @table @code |
1593 | @item -h |
1594 | @itemx --help |
1595 | Display a (fairly verbose) help message describing the various command line |
1596 | options and exits successfully. |
1597 | |
1598 | @item -u |
1599 | @itemx --usage |
1600 | Display a terse summary of the command line options and exits successfully. |
1601 | |
1602 | @item -v |
1603 | @itemx |
1604 | Display's Become's version number and exits successfully. |
1605 | |
1606 | @item -e |
1607 | @item --preserve-environment |
1608 | Selects the `preserve' login style (@pxref{The preserve style}). All |
1609 | environment variables are preserved. The default command is the current |
1610 | user's own shell. The default primary group becomes the current primary |
1611 | group; the default group style is set to `merge'. |
1612 | |
1613 | @item -s |
1614 | @itemx --su |
1615 | @itemx --set-user |
1616 | Selects the `set-user' login style (@pxref{The set-user style}). Most |
1617 | environment variables are preserved, but @code{USER}, @code{LOGNAME}, |
1618 | @code{HOME} and other user-specific variables are altered to reflect the |
1619 | target user's configuration. The default command is the target user's shell. |
1620 | The default primary group becomes the target user's primary group; the |
1621 | default group style is set to `merge'. |
1622 | |
1623 | @item -l |
1624 | @itemx --login |
1625 | Selects the `login' login style (@pxref{The login style}). The environment |
1626 | is cleared and rebuilt, in a similar way to the behaviour of @code{login}. |
1627 | The default command is the target user's shell. The default primary group |
1628 | becomes the target user's primary group; the default group style is set to |
1629 | `replace'. |
1630 | |
1631 | @item -g @var{group} |
1632 | @itemx --group=@var{group} |
1633 | Selects @var{group} as the primary group; it may be either a group name or a |
1634 | numeric group id. Note that @var{group} must be the primary group or |
1635 | a subsidiary group of either the current user or the target user. |
1636 | |
1637 | @item -k |
1638 | @itemx --keep-groups |
1639 | Selects the `keep' group style (@pxref{Subsidiary groups}). The current set |
1640 | of subsidiary group memberships are passed on unchanged. |
1641 | |
1642 | @item -m |
1643 | @itemx --merge-groups |
1644 | Selects the `merge' group style (@pxref{Subsidiary groups}). The current set |
1645 | of subsidiary group memberships are merged with the subsidiary groups of the |
1646 | target user. |
1647 | |
1648 | @item -r |
1649 | @itemx --replace-groups |
1650 | Selects the `replace' group style (@pxref{Subsidiary groups}). The target |
1651 | user's subsidiary group memberships are passed on; the current subsidiary |
1652 | groups are discarded. |
1653 | |
1654 | @item -c @var{shell-cmd} |
1655 | @itemx --command=@var{shell-cmd} |
1656 | Sets the @var{command} and @var{argument}s to invoke |
1657 | @code{/bin/sh -c @var{shell-cmd}}; i.e., to execute a Bourne shell command |
1658 | instead of just @code{exec}ing a program. Note that permissions are checked |
1659 | for executing the Bourne shell @code{/bin/sh}; the contents of the |
1660 | @var{shell-cmd} are not inspected. |
1661 | @end table |
1662 | |
1663 | The @var{env-var} arguments fine-tune the environment passed to the command. |
1664 | Each @var{env-var} setting must be one of the following: |
1665 | |
1666 | @table @code |
1667 | @item @var{var}=@var{value} |
1668 | Assign the variable named @var{var} the value @var{value}. Protect the |
1669 | variable @var{var} from modifications by the login style. |
1670 | |
1671 | @item @var{var}! |
1672 | Protect the variable @var{var} from modifications by the login style, but |
1673 | don't change its value. |
1674 | |
1675 | @item @var{var}- |
1676 | Remove the variable @var{var} from the environment; do not pass it on. |
1677 | @end table |
1678 | |
1679 | The @var{user} specifies the user as whom the @var{command} should be |
1680 | executed (i.e., the @dfn{target user}). It may be a user name or a numeric |
1681 | user id. |
1682 | |
1683 | The @var{command} specifies a command to execute. If @var{command} does not |
1684 | contain a path, it is looked for using the current @code{PATH} environment |
1685 | variable. The resulting pathname is canonified if necessary, to produce an |
1686 | absolute pathname. Note that symbolic links are @emph{not} resolved -- this |
1687 | prevents an attack whereby a user could invoke a program, passing it an |
1688 | unusual @code{argv[0]} which might cause unusual behaviour. |
1689 | |
1690 | The @var{command} name is used both as the command to execute and passed to |
1691 | the command as @code{argv[0]}. It is not possible to specify an alternative |
10bc033f |
1692 | value to be passed as @code{argv[0]}. Subsequent arguments, if supplied, are |
7a53967a |
1693 | passed as @code{argv[1]} upwards. |
1694 | |
1695 | If no @var{command} is given, a shell is invoked; the particulars of the |
1696 | shell are determined by the login style (see above). |
1697 | |
1698 | The @var{command} is executed as follows: |
1699 | |
1700 | @itemize @bullet |
1701 | @item |
1702 | The subsidiary groups are chosen as determined by the group style. |
1703 | @item |
1704 | The real and effective gids are set. |
1705 | @item |
1706 | The real and effective uids are set. |
1707 | @item |
1708 | The @var{command} is called using the standard @code{execve} system call. |
1709 | @end itemize |
1710 | |
1711 | |
1712 | |
1713 | @node Starting Become daemons, Debugging options, Becoming another user, Invoking Become |
1714 | @section Starting Become daemons |
1715 | |
1716 | @subsection Synopsis |
1717 | |
1718 | @example |
1719 | become --daemon [@var{option}@dots{}] |
1720 | @end example |
1721 | |
1722 | |
1723 | @subsection Usage |
1724 | |
1725 | The following options are appropriate to this mode: |
1726 | |
1727 | @table @code |
1728 | @item -h |
1729 | @itemx --help |
1730 | Display a (fairly verbose) help message describing the various command line |
1731 | options and exits successfully. |
1732 | |
1733 | @item -u |
1734 | @itemx --usage |
1735 | Display a terse summary of the command line options and exits successfully. |
1736 | |
1737 | @item -v |
1738 | @itemx |
1739 | Display's Become's version number and exits successfully. |
1740 | |
1741 | @item -d |
1742 | @itemx --daemon |
1743 | Start a Become server, instead of processing a request. Become will read its |
1744 | command line options, read in the configuration file (and verify that it's |
1745 | correct) and then fork into the background to wait for incoming requests. |
1746 | Become relinquishes all setuid privileges (by setting all uids to the real |
1747 | uid) when it enters daemon mode. It is therefore only really useful to run a |
1748 | daemon as the superuser. |
1749 | |
1750 | @item -p @var{port} |
1751 | @itemx --port=@var{port} |
1752 | Listen for requests on @var{port}. This option is overridden by the |
1753 | @code{port} option in the configuration file. |
1754 | |
1755 | @item -f @var{file} |
1756 | @itemx --config-file=@var{file} |
10bc033f |
1757 | Read configuration from @var{file}, instead of the default (set at |
1758 | compile time, usually @file{/etc/become/become.conf}). |
7a53967a |
1759 | @end table |
1760 | |
1761 | The syntax of the configuration file is described in @ref{The configuration |
1762 | file}. |
1763 | |
1764 | |
1765 | @node Debugging options, , Starting Become daemons, Invoking Become |
1766 | @section Debugging options |
1767 | |
1768 | Some options are only useful when trying to find out why Become is |
1769 | misbehaving. Of course, this never happens, so here are the options which |
1770 | you won't need to use: |
1771 | |
1772 | @table @code |
1773 | @item -T[@var{file}] |
1774 | @itemx --trace[=@var{file}] |
1775 | Write trace information to @var{file} (or to standard output, if no |
1776 | @var{file} is specified). You must be able to create the file and open it |
1777 | for writing. |
1778 | |
1779 | @item -L[@var{feature}...] |
1780 | @itemx --trace-level[=@var{feature}] |
1781 | Selects which features Become ought to trace. Each feature is allocated a |
1782 | letter; simply string together the letters for the features you want to |
1783 | debug. The letters @samp{D} and @samp{A} stand respectively for `default' |
1784 | and `all' features; you can subtract from them by saying, for example, |
1785 | @samp{A-xyz} to select all features except @samp{x}, @samp{y} and @samp{z}. |
1786 | The exact list of features supported at any one time can be listed by giving |
1787 | the @code{--trace-level} option without an argument. |
1788 | |
1789 | @item -I @var{user} |
1790 | @itemx --impersonate=@var{user} |
1791 | Pretend to be @var{user} instead of yourself when the request is checked. |
1792 | This option can only be used if it wasn't disabled at compile-time and if |
1793 | Become is not running setuid. Even so, Become will only inform you of the |
1794 | outcome; it will not execute any commands. |
1795 | @end table |
1796 | |
1797 | |
1798 | |
1799 | @c -------------------------------------------------------------------------- |
1800 | |
1801 | @c --- No index yet --- |
1802 | @c |
1803 | @c @node Concept index, , Invoking Become, Top |
1804 | @c @unnumbered Concept index |
1805 | @c @printindex cp |
1806 | @c |
10bc033f |
1807 | @contents |
7a53967a |
1808 | |
1809 | @bye |
1810 | |
1811 | @c ----- That's all, folks -------------------------------------------------- |