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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.
231 </p>
232 </body>
233 </section>
234 </chapter>
235
236 <chapter>
237 <title>Networking</title>
238
239 <section>
240 <body>
241 <p>
242 Thanks to Martin Schlemmer (Azarah), I now know how
243 to get networking to function from within a user-mode
244 system. The idea is that we set up a private network
245 consisting of the user-mode system and the host system,
246 and then the user-mode system routes all of its packets
247 to the host, which then forwards packets to the net.
248 Make sure that the host kernel has
249 Networking --> IP: Netfilter Configuration --> IP tables support
250 --> Full NAT --> MASQUERADE target support and
251 Network Device Support --> Ethertap network tap
252 compiled as modules; then do the following on the
253 <e>host</e> machine:
254 </p>
255 <pre>
256 # <i>modprobe ethertap</i>
257 # <i>modprobe iptable_nat</i>
258 # <i>iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE</i>
259 # <i>echo 1 > /proc/sys/net/ipv4/ip_forward</i>
260 </pre>
261 <p>
262 The iptables line sets up IP Masquerading between the private
263 network that our user-mode system will be on and the internet
264 (reachable via <c>eth0</c> in our case). The echo line then
265 turns on packet forwarding between the private network and the
266 interface that the default gateway is on (eth0 for us).
267 </p>
268 <p>
269 Now we bring up the user-mode system and see if networking
270 is functional.
271 </p>
272 <pre>
273 # <i>linux ubd0=root_fs ubd1=swap_fs eth0=ethertap,tap0,,192.168.0.254</i>
274 <comment>(login to user-mode system)</comment>
275 # <i>ifconfig eth0 192.168.0.1 up</i>
276 # <i>ping -c 2 192.168.0.254</i>
277 PING 192.168.0.254 (192.168.0.254): 56 octets data
278 64 octets from 192.168.0.254: icmp_seq=0 ttl=255 time=0.8 ms
279 64 octets from 192.168.0.254: icmp_seq=1 ttl=255 time=0.6 ms
280
281 --- 192.168.0.254 ping statistics ---
282 2 packets transmitted, 2 packets received, 0% packet loss
283 round-trip min/avg/max = 0.6/0.7/0.8 ms
284 <i>route add default gw 192.168.0.254</i>
285 <i>netstat -rn</i>
286 Kernel IP routing table
287 Destination Gateway Genmask Flags MSS Window irtt Iface
288 192.168.0.0 0.0.0.0 255.255.255.0 U 40 0 0 eth0
289 0.0.0.0 192.168.0.254 0.0.0.0 UG 40 0 0 eth0
290 <i>scp user@192.168.0.254:/etc/resolv.conf /etc/resolv.conf</i> <comment>(if needed)</comment>
291 <i>ping -c 2 www.gentoo.org</i>
292 PING www.gentoo.org (207.170.82.202): 56 octets data
293 64 octets from 207.170.82.202: icmp_seq=0 ttl=240 time=119.6 ms
294 64 octets from 207.170.82.202: icmp_seq=1 ttl=240 time=92.0 ms
295
296 --- www.gentoo.org ping statistics ---
297 2 packets transmitted, 2 packets received, 0% packet loss
298 round-trip min/avg/max = 92.0/105.8/119.6 ms
299 </pre>
300 <p>
301 On the user-mode system we assign the user-mode eth0 interface
302 the private IP address 192.168.0.1 and bring up the interface. The
303 host has private IP address 192.168.0.254, and we ping it to make sure
304 that our networking is, indeed, up. The route line adds a default
305 gateway, namely our host, we use scp to retrieve a working
306 <path>/etc/resolv.conf</path> (if necessary), and we ping www.gentoo.org
307 to make sure that name resolution (and general access to the internet)
308 is working from our user-mode system. Now the user-mode system can
309 <c>emerge</c> at will!
310 </p>
311 </body>
312 </section>
313 </chapter>
314
315 <chapter>
316 <title>Testing the .iso</title>
317
318 <section>
319 <body>
320 <p>
321 Perhaps the true ideal of Gentoo Linux testing would be
322 to boot the .iso with user-mode linux and do the complete
323 Gentoo install from within the user-mode linux virtual system.
324 </p>
325 <p>
326 Booting the .iso, or actually the initrd from the .iso, is pretty
327 straightforward.
328 </p>
329 <pre>
330 # <i>mount -o loop /path/to/build-&lt;TAB&gt;.iso /mnt/loop</i>
331 # <i>cp /mnt/loop/isolinux/rescue.gz .</i>
332 # <i>linux load_ramdisk=1 prompt_ramdisk=0 ramdisk_size=22000 \</i>
333 &gt; <i>initrd=rescue.gz root=/dev/ram0 ubd0=root_fs ubd1=swap_fs \</i>
334 &gt; <i>ubd2=/dev/cdroms/cdrom0 eth0=ethertap,tap0,,192.168.0.254</i>
335 </pre>
336 <p>Now you can follow the Gentoo install doc essentially verbatim,
337 although you'll need to know that the root filesystem will be
338 <path>/dev/ubd/0</path>, the swap "partition"
339 will be <path>/dev/ubd/1</path>, and the CD rom
340 will be <path>/dev/ubd/2</path>.</p>
341 </body>
342 </section>
343 </chapter>
344
345
346 </guide>

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