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Mon Oct 17 19:51:45 2011 UTC (2 years, 10 months ago) by swift
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Changes since 1.13: +13 -7 lines
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Enhancing information on downsides wrt multiple partitions.

This hopefully also clears up some of the confusion that is surrounding
separate /usr partitions. Yes, it now mentions that an initramfs might be
needed in that case.

And no, we do not "recommend" a separate /usr partition, nor do we
"not recommend" it.

1 <?xml version='1.0' encoding='UTF-8'?>
2 <!DOCTYPE sections SYSTEM "/dtd/book.dtd">
3
4 <!-- The content of this document is licensed under the CC-BY-SA license -->
5 <!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
6
7 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-install-arm-disk.xml,v 1.13 2011/09/04 14:34:01 swift Exp $ -->
8
9 <sections>
10
11 <version>8</version>
12 <date>2011-10-17</date>
13
14 <!-- TODO: Add section about MTD and such -->
15
16 <section>
17 <title>Introduction to Block Devices</title>
18
19 <subsection>
20 <include href="hb-install-blockdevices.xml"/>
21 </subsection>
22
23 <subsection>
24 <title>Partitions</title>
25 <body>
26
27 <p>
28 Although it is theoretically possible to use a full disk to house your Linux
29 system, this is almost never done in practice. Instead, full disk block devices
30 are split up in smaller, more manageable block devices. On <keyval id="arch"/>
31 systems, these are called <e>partitions</e>.
32 </p>
33
34 <p>
35 Partitions are divided in three types:
36 <e>primary</e>, <e>extended</e> and <e>logical</e>.
37 </p>
38
39 <p>
40 A <e>primary</e> partition is a partition which has its information stored in
41 the MBR (master boot record). As an MBR is very small (512 bytes) only four
42 primary partitions can be defined (for instance, <path>/dev/sda1</path> to
43 <path>/dev/sda4</path>).
44 </p>
45
46 <p>
47 An <e>extended</e> partition is a special primary partition (meaning the
48 extended partition must be one of the four possible primary partitions) which
49 contains more partitions. Such a partition didn't exist originally, but as
50 four partitions were too few, it was brought to life to extend the formatting
51 scheme without losing backward compatibility.
52 </p>
53
54 <p>
55 A <e>logical</e> partition is a partition inside the extended partition. Their
56 definitions aren't placed inside the MBR, but are declared inside the extended
57 partition.
58 </p>
59
60 </body>
61 </subsection>
62 </section>
63 <section>
64 <title>Designing a Partitioning Scheme</title>
65 <subsection>
66 <title>Default Partitioning Scheme</title>
67 <body>
68
69 <warn>
70 The NetWinder firmware, NeTTrom, can only read ext2 partitions reliably so you
71 must have a separate ext2 boot partition.
72 </warn>
73
74 <p>
75 If you are not interested in drawing up a partitioning scheme for your system,
76 you can use the partitioning scheme we use throughout this book:
77 </p>
78
79 <table>
80 <tr>
81 <th>Partition</th>
82 <th>Filesystem</th>
83 <th>Size</th>
84 <th>Description</th>
85 </tr>
86 <tr>
87 <ti><path>/dev/sda1</path></ti>
88 <ti>ext2</ti>
89 <ti>32M</ti>
90 <ti>Boot partition</ti>
91 </tr>
92 <tr>
93 <ti><path>/dev/sda2</path></ti>
94 <ti>(swap)</ti>
95 <ti>512M</ti>
96 <ti>Swap partition</ti>
97 </tr>
98 <tr>
99 <ti><path>/dev/sda3</path></ti>
100 <ti>ext3</ti>
101 <ti>Rest of the disk</ti>
102 <ti>Root partition</ti>
103 </tr>
104 </table>
105
106 <p>
107 If you are interested in knowing how big a partition should be, or even how
108 many partitions you need, read on. Otherwise continue now with partitioning
109 your disk by reading <uri link="#fdisk">Using fdisk to Partition your
110 Disk</uri>.
111 </p>
112
113 </body>
114 </subsection>
115 <subsection>
116 <title>How Many and How Big?</title>
117 <body>
118
119 <p>
120 The number of partitions is highly dependent on your environment. For instance,
121 if you have lots of users, you will most likely want to have your
122 <path>/home</path> separate as it increases security and makes backups easier.
123 If you are installing Gentoo to perform as a mailserver, your
124 <path>/var</path> should be separate as all mails are stored inside
125 <path>/var</path>. A good choice of filesystem will then maximise your
126 performance. Gameservers will have a separate <path>/opt</path> as most gaming
127 servers are installed there. The reason is similar for <path>/home</path>:
128 security and backups. You will definitely want to keep <path>/usr</path> big:
129 not only will it contain the majority of applications, the Portage tree alone
130 takes around 500 Mbyte excluding the various sources that are stored in it.
131 </p>
132
133 <p>
134 As you can see, it very much depends on what you want to achieve. Separate
135 partitions or volumes have the following advantages:
136 </p>
137
138 <ul>
139 <li>
140 You can choose the best performing filesystem for each partition or volume
141 </li>
142 <li>
143 Your entire system cannot run out of free space if one defunct tool is
144 continuously writing files to a partition or volume
145 </li>
146 <li>
147 If necessary, file system checks are reduced in time, as multiple checks can
148 be done in parallel (although this advantage is more with multiple disks than
149 it is with multiple partitions)
150 </li>
151 <li>
152 Security can be enhanced by mounting some partitions or volumes read-only,
153 nosuid (setuid bits are ignored), noexec (executable bits are ignored) etc.
154 </li>
155 </ul>
156
157 <p>
158 However, multiple partitions have disadvantages as well. If not configured
159 properly, you will have a system with lots of free space on one partition and
160 none on another. Another nuisance is that separate partitions - especially
161 for important mountpoints like <path>/usr</path> or <path>/var</path> - often
162 require the administrator to boot with an initramfs to mount the partition
163 before other boot scripts start. This isn't always the case though, so YMMV.
164 </p>
165
166 <p>
167 There is also a 15-partition limit for SCSI and SATA.
168 </p>
169
170 <p>
171 As an example partitioning, we show you one for a 20GB disk, used as a
172 demonstration laptop (containing webserver, mailserver, gnome, ...):
173 </p>
174
175 <pre caption="Filesystem usage example">
176 $ <i>df -h</i>
177 Filesystem Type Size Used Avail Use% Mounted on
178 /dev/sda5 ext3 509M 132M 351M 28% /
179 /dev/sda2 ext3 5.0G 3.0G 1.8G 63% /home
180 /dev/sda7 ext3 7.9G 6.2G 1.3G 83% /usr
181 /dev/sda8 ext3 1011M 483M 477M 51% /opt
182 /dev/sda9 ext3 2.0G 607M 1.3G 32% /var
183 /dev/sda1 ext2 51M 17M 31M 36% /boot
184 /dev/sda6 swap 516M 12M 504M 2% &lt;not mounted&gt;
185 <comment>(Unpartitioned space for future usage: 2 GB)</comment>
186 </pre>
187
188 <p>
189 <path>/usr</path> is rather full (83% used) here, but once
190 all software is installed, <path>/usr</path> doesn't tend to grow that much.
191 Although allocating a few gigabytes of disk space for <path>/var</path> may
192 seem excessive, remember that Portage uses this partition by default for
193 compiling packages. If you want to keep <path>/var</path> at a more reasonable
194 size, such as 1GB, you will need to alter your <c>PORTAGE_TMPDIR</c> variable
195 in <path>/etc/make.conf</path> to point to the partition with enough free space
196 for compiling extremely large packages such as OpenOffice.
197 </p>
198
199 </body>
200 </subsection>
201 </section>
202 <section id="fdisk">
203 <title>Using fdisk to Partition your Disk</title>
204 <subsection>
205 <body>
206
207 <p>
208 The following parts explain how to create the example partition layout
209 described previously, namely:
210 </p>
211
212 <table>
213 <tr>
214 <th>Partition</th>
215 <th>Description</th>
216 </tr>
217 <tr>
218 <ti><path>/dev/sda1</path></ti>
219 <ti>Boot partition</ti>
220 </tr>
221 <tr>
222 <ti><path>/dev/sda2</path></ti>
223 <ti>Swap partition</ti>
224 </tr>
225 <tr>
226 <ti><path>/dev/sda3</path></ti>
227 <ti>Root partition</ti>
228 </tr>
229 </table>
230
231 <p>
232 Change your partition layout according to your own preference.
233 </p>
234
235 </body>
236 </subsection>
237 <subsection>
238 <title>Viewing the Current Partition Layout</title>
239 <body>
240
241 <p>
242 <c>fdisk</c> is a popular and powerful tool to split your disk into partitions.
243 Fire up <c>fdisk</c> on your disk (in our example, we use
244 <path>/dev/sda</path>):
245 </p>
246
247 <pre caption="Starting fdisk">
248 # <i>fdisk /dev/sda</i>
249 </pre>
250
251 <p>
252 Once in <c>fdisk</c>, you'll be greeted with a prompt that looks like this:
253 </p>
254
255 <pre caption="fdisk prompt">
256 Command (m for help):
257 </pre>
258
259 <p>
260 Type <c>p</c> to display your disk's current partition configuration:
261 </p>
262
263 <pre caption="An example partition configuration">
264 Command (m for help): <i>p</i>
265
266 Disk /dev/sda: 240 heads, 63 sectors, 2184 cylinders
267 Units = cylinders of 15120 * 512 bytes
268
269 Device Boot Start End Blocks Id System
270 /dev/sda1 1 14 105808+ 83 Linux
271 /dev/sda2 15 49 264600 82 Linux swap
272 /dev/sda3 50 70 158760 83 Linux
273 /dev/sda4 71 2184 15981840 5 Extended
274 /dev/sda5 71 209 1050808+ 83 Linux
275 /dev/sda6 210 348 1050808+ 83 Linux
276 /dev/sda7 349 626 2101648+ 83 Linux
277 /dev/sda8 627 904 2101648+ 83 Linux
278 /dev/sda9 905 2184 9676768+ 83 Linux
279
280 Command (m for help):
281 </pre>
282
283 <p>
284 This particular disk is configured to house seven Linux filesystems (each with
285 a corresponding partition listed as "Linux") as well as a swap partition
286 (listed as "Linux swap").
287 </p>
288
289 </body>
290 </subsection>
291 <subsection>
292 <title>Removing all Partitions</title>
293 <body>
294
295 <p>
296 We will first remove all existing partitions from the disk. Type <c>d</c> to
297 delete a partition. For instance, to delete an existing <path>/dev/sda1</path>:
298 </p>
299
300 <pre caption="Deleting a partition">
301 Command (m for help): <i>d</i>
302 Partition number (1-4): <i>1</i>
303 </pre>
304
305 <p>
306 The partition has been scheduled for deletion. It will no longer show up if you
307 type <c>p</c>, but it will not be erased until your changes have been saved. If
308 you made a mistake and want to abort without saving your changes, type <c>q</c>
309 immediately and hit enter and your partition will not be deleted.
310 </p>
311
312 <p>
313 Now, assuming that you do indeed want to wipe out all the partitions on your
314 system, repeatedly type <c>p</c> to print out a partition listing and then type
315 <c>d</c> and the number of the partition to delete it. Eventually, you'll end
316 up with a partition table with nothing in it:
317 </p>
318
319 <pre caption="An empty partition table">
320 Disk /dev/sda: 30.0 GB, 30005821440 bytes
321 240 heads, 63 sectors/track, 3876 cylinders
322 Units = cylinders of 15120 * 512 = 7741440 bytes
323
324 Device Boot Start End Blocks Id System
325
326 Command (m for help):
327 </pre>
328
329 <p>
330 Now that the in-memory partition table is empty, we're ready to create the
331 partitions. We will use a default partitioning scheme as discussed previously.
332 Of course, don't follow these instructions to the letter if you don't want the
333 same partitioning scheme!
334 </p>
335
336 </body>
337 </subsection>
338 <subsection>
339 <title>Creating the Boot Partition</title>
340 <body>
341
342 <p>
343 We first create a small boot partition. Type <c>n</c> to create a new partition,
344 then <c>p</c> to select a primary partition, followed by <c>1</c> to select the
345 first primary partition. When prompted for the first cylinder, hit enter. When
346 prompted for the last cylinder, type <c>+32M</c> to create a partition 32 Mbyte
347 in size:
348 </p>
349
350 <pre caption="Creating the boot partition">
351 Command (m for help): <i>n</i>
352 Command action
353 e extended
354 p primary partition (1-4)
355 <i>p</i>
356 Partition number (1-4): <i>1</i>
357 First cylinder (1-3876, default 1): <comment>(Hit Enter)</comment>
358 Using default value 1
359 Last cylinder or +size or +sizeM or +sizeK (1-3876, default 3876): <i>+32M</i>
360 </pre>
361
362 <p>
363 Now, when you type <c>p</c>, you should see the following partition printout:
364 </p>
365
366 <pre caption="Created boot partition">
367 Command (m for help): <i>p</i>
368
369 Disk /dev/sda: 30.0 GB, 30005821440 bytes
370 240 heads, 63 sectors/track, 3876 cylinders
371 Units = cylinders of 15120 * 512 = 7741440 bytes
372
373 Device Boot Start End Blocks Id System
374 /dev/sda1 1 14 105808+ 83 Linux
375 </pre>
376
377 <p>
378 We need to make this partition bootable. Type <c>a</c> to toggle the bootable
379 flag on a partition and select <c>1</c>. If you press <c>p</c> again, you will
380 notice that an <path>*</path> is placed in the "Boot" column.
381 </p>
382
383 </body>
384 </subsection>
385 <subsection>
386 <title>Creating the Swap Partition</title>
387 <body>
388
389 <p>
390 Let's now create the swap partition. To do this, type <c>n</c> to create a new
391 partition, then <c>p</c> to tell fdisk that you want a primary partition. Then
392 type <c>2</c> to create the second primary partition, <path>/dev/sda2</path> in
393 our case. When prompted for the first cylinder, hit enter. When prompted for
394 the last cylinder, type <c>+512M</c> to create a partition 512MB in size. After
395 you've done this, type <c>t</c> to set the partition type, <c>2</c> to select
396 the partition you just created and then type in <c>82</c> to set the partition
397 type to "Linux Swap". After completing these steps, typing <c>p</c> should
398 display a partition table that looks similar to this:
399 </p>
400
401 <pre caption="Partition listing after creating a swap partition">
402 Command (m for help): <i>p</i>
403
404 Disk /dev/sda: 30.0 GB, 30005821440 bytes
405 240 heads, 63 sectors/track, 3876 cylinders
406 Units = cylinders of 15120 * 512 = 7741440 bytes
407
408 Device Boot Start End Blocks Id System
409 /dev/sda1 * 1 14 105808+ 83 Linux
410 /dev/sda2 15 81 506520 82 Linux swap
411 </pre>
412
413 </body>
414 </subsection>
415 <subsection>
416 <title>Creating the Root Partition</title>
417 <body>
418
419 <p>
420 Finally, let's create the root partition. To do this, type <c>n</c> to create a
421 new partition, then <c>p</c> to tell fdisk that you want a primary partition.
422 Then type <c>3</c> to create the third primary partition, <path>/dev/sda3</path>
423 in our case. When prompted for the first cylinder, hit enter. When prompted for
424 the last cylinder, hit enter to create a partition that takes up the rest of the
425 remaining space on your disk. After completing these steps, typing <c>p</c>
426 should display a partition table that looks similar to this:
427 </p>
428
429 <pre caption="Partition listing after creating the root partition">
430 Command (m for help): <i>p</i>
431
432 Disk /dev/sda: 30.0 GB, 30005821440 bytes
433 240 heads, 63 sectors/track, 3876 cylinders
434 Units = cylinders of 15120 * 512 = 7741440 bytes
435
436 Device Boot Start End Blocks Id System
437 /dev/sda1 * 1 14 105808+ 83 Linux
438 /dev/sda2 15 81 506520 82 Linux swap
439 /dev/sda3 82 3876 28690200 83 Linux
440 </pre>
441
442 </body>
443 </subsection>
444 <subsection>
445 <title>Saving the Partition Layout</title>
446 <body>
447
448 <p>
449 To save the partition layout and exit <c>fdisk</c>, type <c>w</c>.
450 </p>
451
452 <pre caption="Save and exit fdisk">
453 Command (m for help): <i>w</i>
454 </pre>
455
456 <p>
457 Now that your partitions are created, you can continue with <uri
458 link="#filesystems">Creating Filesystems</uri>.
459 </p>
460
461 </body>
462 </subsection>
463 </section>
464 <section id="filesystems">
465 <title>Creating Filesystems</title>
466 <subsection>
467 <title>Introduction</title>
468 <body>
469
470 <p>
471 Now that your partitions are created, it is time to place a filesystem on them.
472 If you don't care about what filesystem to choose and are happy with what we use
473 as default in this handbook, continue with <uri
474 link="#filesystems-apply">Applying a Filesystem to a Partition</uri>.
475 Otherwise read on to learn about the available filesystems...
476 </p>
477
478 </body>
479 </subsection>
480
481 <subsection>
482 <include href="hb-install-filesystems.xml"/>
483 </subsection>
484
485 <subsection id="filesystems-apply">
486 <title>Applying a Filesystem to a Partition</title>
487 <body>
488
489 <p>
490 To create a filesystem on a partition or volume, there are tools available for
491 each possible filesystem:
492 </p>
493
494 <table>
495 <tr>
496 <th>Filesystem</th>
497 <th>Creation Command</th>
498 </tr>
499 <tr>
500 <ti>ext2</ti>
501 <ti><c>mkfs.ext2</c></ti>
502 </tr>
503 <tr>
504 <ti>ext3</ti>
505 <ti><c>mkfs.ext3</c></ti>
506 </tr>
507 <tr>
508 <ti>ext4</ti>
509 <ti><c>mkfs.ext4</c></ti>
510 </tr>
511 <tr>
512 <ti>reiserfs</ti>
513 <ti><c>mkreiserfs</c></ti>
514 </tr>
515 <tr>
516 <ti>xfs</ti>
517 <ti><c>mkfs.xfs</c></ti>
518 </tr>
519 <tr>
520 <ti>jfs</ti>
521 <ti><c>mkfs.jfs</c></ti>
522 </tr>
523 </table>
524
525 <p>
526 For instance, to have the boot partition (<path>/dev/sda1</path> in our
527 example) in ext2 and the root partition (<path>/dev/sda3</path> in our example)
528 in ext3 (as in our example), you would use:
529 </p>
530
531 <pre caption="Applying a filesystem on a partition">
532 # <i>mkfs.ext2 /dev/sda1</i>
533 # <i>mkfs.ext3 /dev/sda3</i>
534 </pre>
535
536 <p>
537 Now create the filesystems on your newly created partitions (or logical
538 volumes).
539 </p>
540
541 </body>
542 </subsection>
543 <subsection>
544 <title>Activating the Swap Partition</title>
545 <body>
546
547 <p>
548 <c>mkswap</c> is the command that is used to initialize swap partitions:
549 </p>
550
551 <pre caption="Creating a Swap signature">
552 # <i>mkswap /dev/sda2</i>
553 </pre>
554
555 <p>
556 To activate the swap partition, use <c>swapon</c>:
557 </p>
558
559 <pre caption="Activating the swap partition">
560 # <i>swapon /dev/sda2</i>
561 </pre>
562
563 <p>
564 Create and activate the swap with the commands mentioned above.
565 </p>
566
567 </body>
568 </subsection>
569 </section>
570 <section>
571 <title>Mounting</title>
572 <body>
573
574 <p>
575 Now that your partitions are initialized and are housing a filesystem, it is
576 time to mount those partitions. Use the <c>mount</c> command. Don't forget to
577 create the necessary mount directories for every partition you created. As an
578 example we mount the root and boot partition:
579 </p>
580
581 <pre caption="Mounting partitions">
582 # <i>mount /dev/sda3 /mnt/gentoo</i>
583 # <i>mkdir /mnt/gentoo/boot</i>
584 # <i>mount /dev/sda1 /mnt/gentoo/boot</i>
585 </pre>
586
587 <note>
588 If you want your <path>/tmp</path> to reside on a separate partition, be sure to
589 change its permissions after mounting: <c>chmod 1777 /mnt/gentoo/tmp</c>. This
590 also holds for <path>/var/tmp</path>.
591 </note>
592
593 <p>
594 We will also have to mount the proc filesystem (a virtual interface with the
595 kernel) on <path>/proc</path>. But first we will need to place our files on the partitions.
596 </p>
597
598 <p>
599 Continue with <uri link="?part=1&amp;chap=5">Installing the Gentoo
600 Installation Files</uri>.
601 </p>
602
603 </body>
604 </section>
605 </sections>

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