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1 <?xml version='1.0' encoding="UTF-8"?>
2 <?xml-stylesheet href="/xsl/guide.xsl" type="text/xsl"?>
3
4 <!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
5
6 <guide link="/doc/en/uml.xml">
7 <title>Gentoo Linux Developer's guide to system testing with User-Mode Linux</title>
8 <author title="Editor"><mail link="g2boojum@gentoo.org">Grant Goodyear</mail></author>
9 <author title="Editor"><mail link="zhen@gentoo.org">John Davis</mail></author>
10
11 <abstract>
12 This guide shows Gentoo Linux developers how to set up and use
13 user-mode linux for testing potentially system-breaking changes.
14 </abstract>
15
16 <version>0.07</version>
17 <date>21 March 2003</date>
18
19 <chapter>
20 <title>Obtaining User-Mode Linux</title>
21 <section>
22 <body>
23 <p>As the user-mode linux website
24 (<uri>http://user-mode-linux.sourceforge.net</uri>)
25 states, user-mode linux
26 allows a user to "run Linux inside itself". Specifically,
27 user-mode linux provides a virtual machine on which a user can "[r]un buggy
28 software, experiment with new Linux kernels or distributions, and poke around
29 in the internals of Linux, all without risking your main Linux setup." Changes
30 to Gentoo core packages such as <e>sys-apps/baselayout</e> or <e>sys-libs/glibc</e>
31 have the potential to break the system and render it unbootable; with user-mode
32 linux we can test these changes without having to worry about breaking the live
33 system.
34 </p>
35 <p>
36 Installing user-mode linux is essentially identical to a normal kernel
37 install. First install the kernel sources (appropriately patched for
38 user-mode linux), and then configure the user-mode linux kernel in the
39 usual fashion:
40 </p>
41 <pre>
42 # <i>emerge sys-kernel/usermode-sources</i>
43 # <i>cd /usr/src/uml/linux</i>
44 # <i>make menuconfig <comment>ARCH=um</comment></i>
45 # <i>make linux <comment>ARCH=um</comment></i>
46 # <i>cp linux /usr/local/bin/linux</i>
47 </pre>
48 <warn>The <e>ARCH=um</e> fragment is <e>extremely</e> important!</warn>
49 <impo>
50 For the user-mode linux kernel to properly boot a Gentoo system the
51 kernel needs to be configured to <e>not</e> automatically mount
52 <path>/dev</path> (devfs) by default.
53 Also, you will almost certainly
54 want to make sure that you have <e>tmpfs</e> (the "Virtual Memory
55 Filesystem") compiled in, since by default the Gentoo linux bootscripts
56 store their information in a small tmpfs partition.
57 (The binary kernels available
58 from the user-mode website do automatically mount <path>/dev</path>,
59 and they don't have tmpfs compiled in; don't bother with them.)
60 </impo>
61 <p>I highly recommend reading the user-mode linux documentation, but the
62 basic idea is that running the <path>/usr/local/bin/linux</path> program
63 boots the user-mode kernel and tries to bring up the system stored in
64 the file <path>root_fs</path> that should be located in the current working
65 directory.</p>
66 <p>It won't hurt to also install the user-mode linux tools.</p>
67 <pre>
68 # <i>emerge sys-apps/usermode-utilities</i>
69 </pre>
70 <p>These tools facilitate networking (among other things)
71 between the user-mode linux virtual system
72 and the host Linux system.</p>
73 </body>
74 </section>
75 </chapter>
76
77 <chapter>
78 <title>Creating <path>root_fs</path></title>
79
80 <section>
81 <title>Making the Gentoo chroot</title>
82 <body>
83 <p>
84 The <path>root_fs</path> file needed for user-mode linux is
85 a single file that contains an entire Gentoo Linux filesystem.
86 To generate this file you will need to have Loopback device
87 support enabled in the host (non-user-mode) kernel.
88 </p>
89 <p>Generating the <path>root_fs</path> file itself will be
90 our last step. First we will generate a Gentoo filesystem in
91 an ordinary chroot. We need the stage tarball available, which
92 could be downloaded separately, extracted from a liveCD, or
93 extracted from a liveCD .iso.
94 </p>
95 <pre caption="Mounting a liveCD .iso">
96 # <i>mkdir /mnt/loop</i>
97 # <i>mount -o loop /path/to/build-&lt;TAB&gt;.iso /mnt/loop</i>
98 </pre>
99 <p>
100 Setting up the chroot is essentially identical to an ordinary Gentoo
101 Linux build.
102 </p>
103 <pre>
104 # <i>mkdir /mnt/gentoo</i>
105 # <i>cd /mnt/gentoo</i>
106 # <i>tar xvjpf /path/to/build-&lt;TAB&gt;.tar.bz2</i>
107 </pre>
108 <p>
109 Go ahead and unmount the .iso. You don't need it anymore.
110 </p>
111 <pre>
112 # <i>cp /etc/resolv.conf /mnt/gentoo/etc/</i>
113 # <i>mount -o bind /proc /mnt/gentoo/proc</i>
114 # <i>mkdir -p /mnt/gentoo/usr/portage/distfiles</i>
115 # <i>mkdir -p /mnt/gentoo/usr/portage/packages</i>
116 # <i>mount -o bind /usr/portage/distfiles /mnt/gentoo/usr/portage/distfiles</i>
117 # <i>mount -o bind /usr/portage/packages /mnt/gentoo/usr/portage/packages</i>
118 # <i>chroot /mnt/gentoo /bin/bash</i>
119 <!--per bug 16134, added emerge sync to supress warning, etc-->
120 # <i>emerge sync</i>
121 # <i>env-update</i>
122 # <i>source /etc/profile</i>
123 </pre>
124 <p>
125 By bind-mounting <path>/usr/portage/distfiles</path> and
126 <path>/usr/portage/packages</path> we avoid having to download
127 or build packages that are already present on the Gentoo host.
128 </p>
129 <p>
130 Bootstrap and build the system in the usual fashion:
131 </p>
132 <pre>
133 <!--removed the emerge sync below because it is done above-->
134 # <i>cd /usr/portage</i>
135 # <i>nano -w /etc/make.conf</i>
136 # <i>nano -w /etc/make.profile/packages</i>
137 # <i>nano -w /usr/portage/profiles/package.mask</i>
138 # <i>scripts/bootstrap.sh &amp;&amp; emerge --usepkg system</i>
139 </pre>
140 <warn>
141 <!--Changed grub to virtual/bootloader-->
142 The <path>/etc/make.profile/packages</path> file needs to be
143 edited to remove the virtual/bootloader ebuild from the default system (just remove the "*"
144 from the beginning of the "*virtual/bootloader" line). The virtual/bootloader ebuild
145 tries to mount the /boot partition, which will fail in our chroot.
146 </warn>
147 <note>
148 Make sure you examine <path>/etc/make.profile/packages</path>
149 and <path>/usr/portage/profiles/package.mask</path> to be sure that
150 any to-be-tested packages that you want to install aren't masked out.
151 As currently written, <path>scripts/bootstrap.sh</path> will compile
152 the bootstrap packages from source. To use already-existing packages,
153 add <c>alias emerge="emerge --usepkg"</c> somewhere near the top of
154 the bootstrap script.
155 </note>
156 <p>
157 Add any additional packages you desire. Feel free to give your virtual
158 Gentoo system a hostname, if you so desire. In <path>/etc/fstab</path>
159 you will want <path>/dev/ROOT</path> to be <path>/dev/ubd/0</path>, with
160 a fs type of either ext2, ext3, or reiserfs. Set <path>/dev/SWAP</path>
161 to be <path>/dev/ubd/1</path>, and comment out <path>/dev/BOOT</path>.
162 </p>
163 <p>
164 Exit the chroot, unmount all of the bind mounts,
165 tar up the new Gentoo distro, and clean up:
166 </p>
167 <pre>
168 # <i>exit</i>
169 # <i>umount /mnt/gentoo/usr/portage/distfiles</i>
170 # <i>umount /mnt/gentoo/usr/portage/packages</i>
171 # <i>umount /mnt/gentoo/proc</i>
172 # <i>du -ks /mnt/gentoo</i>
173 <!-- wtf is this? 261744 /mnt/gentoo-->
174 <!-- added dir change to be more explicit-->
175 # <i>cd /mnt/gentoo</i>
176 # <i>tar cvjpf ~/gentoo.tbz2 *</i>
177 # <i>cd</i>
178 # <i>rm -rf /mnt/gentoo</i>
179 </pre>
180
181 <p> At this point, remember to set your root password. </p>
182
183 <pre caption="Setting root password">
184 # <c>passwd</c>
185 </pre>
186
187 <p>You might also want to consider reviewing the final steps of the
188 <uri link="http://www.gentoo.org/doc/en/gentoo-x86-install.xml">Gentoo Linux x86 Installation Guide</uri>. </p>
189 </body>
190 </section>
191
192 <section>
193 <title>Making <path>root_fs</path></title>
194 <body>
195 <p>
196 Our Gentoo chroot is nearly 300 MB in size, so
197 <path>root_fs</path> needs to be at least that size.
198 We'll choose 0.5 GB as a reasonable size.
199 </p>
200 <pre>
201 # <i>dd if=/dev/zero of=root_fs seek=500 count=1 bs=1M</i>
202 # <i>mke2fs -F root_fs</i>
203 # <i>mount -o loop root_fs /mnt/loop</i>
204 # <i>tar xvjpf gentoo.tbz2 -C /mnt/loop</i>
205 # <i>umount /mnt/loop</i>
206 </pre>
207 <p>
208 It would also be nice to have a 0.5 GB swap partition.
209 </p>
210 <pre>
211 # <i>dd if=/dev/zero of=swap_fs seek=500 count=1 bs=1M</i>
212 # <i>mkswap -f swap_fs</i>
213 </pre>
214 <p>
215 Now see if it works!
216 </p>
217 <pre>
218 # <i>linux ubd0=root_fs ubd1=swap_fs</i>
219 </pre>
220 <note>
221 User-mode linux uses xterms for the virtual consoles that
222 are run at boot time, so you need to make sure that the
223 terminal from which you run user-mode linux has $DISPLAY
224 properly set (along with proper xhost/xauth permissions).
225 </note>
226 <p>
227 With any luck you should be able to log into your user-mode linux
228 Gentoo system. The only thing keeping this user-mode linux version
229 of Gentoo from being fully functional is networking from the virtual
230 machine to the host. Such networking is supposed to be trivial,
231 but I have yet to get it to work for me. Should you find a workable
232 solution, please let me know!
233 </p>
234 </body>
235 </section>
236 </chapter>
237
238 <chapter>
239 <title>Networking</title>
240
241 <section>
242 <body>
243 <p>
244 Thanks to Martin Schlemmer (Azarah), I now know how
245 to get networking to function from within a user-mode
246 system. The idea is that we set up a private network
247 consisting of the user-mode system and the host system,
248 and then the user-mode system routes all of its packets
249 to the host, which then forwards packets to the net.
250 Make sure that the host kernel has
251 Networking --> IP: Netfilter Configuration --> IP tables support
252 --> Full NAT --> MASQUERADE target support and
253 Network Device Support --> Ethertap network tap
254 compiled as modules; then do the following on the
255 <e>host</e> machine:
256 </p>
257 <pre>
258 # <i>modprobe ethertap</i>
259 # <i>modprobe iptable_nat</i>
260 # <i>iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE</i>
261 # <i>echo 1 > /proc/sys/net/ipv4/ip_forward</i>
262 </pre>
263 <p>
264 The iptables line sets up IP Masquerading between the private
265 network that our user-mode system will be on and the internet
266 (reachable via <c>eth0</c> in our case). The echo line then
267 turns on packet forwarding between the private network and the
268 interface that the default gateway is on (eth0 for us).
269 </p>
270 <p>
271 Now we bring up the user-mode system and see if networking
272 is functional.
273 </p>
274 <pre>
275 # <i>linux ubd0=root_fs ubd1=swap_fs eth0=ethertap,tap0,,192.168.0.254</i>
276 <comment>(login to user-mode system)</comment>
277 # <i>ifconfig eth0 192.168.0.1 up</i>
278 # <i>ping -c 2 192.168.0.254</i>
279 PING 192.168.0.254 (192.168.0.254): 56 octets data
280 64 octets from 192.168.0.254: icmp_seq=0 ttl=255 time=0.8 ms
281 64 octets from 192.168.0.254: icmp_seq=1 ttl=255 time=0.6 ms
282
283 --- 192.168.0.254 ping statistics ---
284 2 packets transmitted, 2 packets received, 0% packet loss
285 round-trip min/avg/max = 0.6/0.7/0.8 ms
286 <i>route add default gw 192.168.0.254</i>
287 <i>netstat -rn</i>
288 Kernel IP routing table
289 Destination Gateway Genmask Flags MSS Window irtt Iface
290 192.168.0.0 0.0.0.0 255.255.255.0 U 40 0 0 eth0
291 0.0.0.0 192.168.0.254 0.0.0.0 UG 40 0 0 eth0
292 <i>scp user@192.168.0.254:/etc/resolv.conf /etc/resolv.conf</i> <comment>(if needed)</comment>
293 <i>ping -c 2 www.gentoo.org</i>
294 PING www.gentoo.org (207.170.82.202): 56 octets data
295 64 octets from 207.170.82.202: icmp_seq=0 ttl=240 time=119.6 ms
296 64 octets from 207.170.82.202: icmp_seq=1 ttl=240 time=92.0 ms
297
298 --- www.gentoo.org ping statistics ---
299 2 packets transmitted, 2 packets received, 0% packet loss
300 round-trip min/avg/max = 92.0/105.8/119.6 ms
301 </pre>
302 <p>
303 On the user-mode system we assign the user-mode eth0 interface
304 the private IP address 192.168.0.1 and bring up the interface. The
305 host has private IP address 192.168.0.254, and we ping it to make sure
306 that our networking is, indeed, up. The route line adds a default
307 gateway, namely our host, we use scp to retrieve a working
308 <path>/etc/resolv.conf</path> (if necessary), and we ping www.gentoo.org
309 to make sure that name resolution (and general access to the internet)
310 is working from our user-mode system. Now the user-mode system can
311 <c>emerge</c> at will!
312 </p>
313 </body>
314 </section>
315 </chapter>
316
317 <chapter>
318 <title>Testing the .iso</title>
319
320 <section>
321 <body>
322 <p>
323 Perhaps the true ideal of Gentoo Linux testing would be
324 to boot the .iso with user-mode linux and do the complete
325 Gentoo install from within the user-mode linux virtual system.
326 </p>
327 <p>
328 Booting the .iso, or actually the initrd from the .iso, is pretty
329 straightforward.
330 </p>
331 <pre>
332 # <i>mount -o loop /path/to/build-&lt;TAB&gt;.iso /mnt/loop</i>
333 # <i>cp /mnt/loop/isolinux/rescue.gz .</i>
334 # <i>linux load_ramdisk=1 prompt_ramdisk=0 ramdisk_size=22000 \</i>
335 &gt; <i>initrd=rescue.gz root=/dev/ram0 ubd0=root_fs ubd1=swap_fs \</i>
336 &gt; <i>ubd2=/dev/cdroms/cdrom0 eth0=ethertap,tap0,,192.168.0.254</i>
337 </pre>
338 <p>Now you can follow the Gentoo install doc essentially verbatim,
339 although you'll need to know that the root filesystem will be
340 <path>/dev/ubd/0</path>, the swap "partition"
341 will be <path>/dev/ubd/1</path>, and the CD rom
342 will be <path>/dev/ubd/2</path>.</p>
343 </body>
344 </section>
345 </chapter>
346
347
348 </guide>

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