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1 <?xml version='1.0'?>
2 <?xml-stylesheet href="/xsl/guide.xsl" type="text/xsl"?>
3
4 <!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
5
6 <guide link="/doc/uml.html">
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
10 <abstract>
11 This guide shows Gentoo Linux developers how to set up and use
12 user-mode linux for testing potentially system-breaking changes.
13 </abstract>
14
15 <version>0.05</version>
16 <date>5 Mar 2002</date>
17
18 <chapter>
19 <title>Obtaining User-Mode Linux</title>
20 <section>
21 <body>
22 <p>As the user-mode linux website
23 (<uri>http://user-mode-linux.sourceforge.net</uri>)
24 states, user-mode linux
25 allows a user to "run Linux inside itself". Specifically,
26 user-mode linux provides a virtual machine on which a user can "[r]un buggy
27 software, experiment with new Linux kernels or distributions, and poke around
28 in the internals of Linux, all without risking your main Linux setup." Changes
29 to Gentoo core packages such as <e>sys-apps/baselayout</e> or <e>sys-libs/glibc</e>
30 have the potential to break the system and render it unbootable; with user-mode
31 linux we can test these changes without having to worry about breaking the live
32 system.
33 </p>
34 <p>
35 Installing user-mode linux is essentially identical to a normal kernel
36 install. First install the kernel sources (appropriately patched for
37 user-mode linux), and then configure the user-mode linux kernel in the
38 usual fashion:
39 </p>
40 <pre>
41 # <i>emerge sys-kernel/usermode-sources</i>
42 # <i>cd /usr/src/uml/linux</i>
43 # <i>make menuconfig <comment>ARCH=um</comment></i>
44 # <i>make linux <comment>ARCH=um</comment></i>
45 # <i>cp linux /usr/local/bin/linux</i>
46 </pre>
47 <warn>The <e>ARCH=um</e> fragment is <e>extremely</e> important!</warn>
48 <impo>
49 For the user-mode linux kernel to properly boot a Gentoo system the
50 kernel needs to be configured to <e>not</e> automatically mount
51 <path>/dev</path> (devfs) by default.
52 Also, you will almost certainly
53 want to make sure that you have <e>tmpfs</e> (the "Virtual Memory
54 Filesystem") compiled in, since by default the Gentoo linux bootscripts
55 store their information in a small tmpfs partition.
56 (The binary kernels available
57 from the user-mode website do automatically mount <path>/dev</path>,
58 and they don't have tmpfs compiled in; don't bother with them.)
59 </impo>
60 <p>I highly recommend reading the user-mode linux documentation, but the
61 basic idea is that running the <path>/usr/local/bin/linux</path> program
62 boots the user-mode kernel and tries to bring up the system stored in
63 the file <path>root_fs</path> that should be located in the current working
64 directory.</p>
65 <p>It won't hurt to also install the user-mode linux tools.</p>
66 <pre>
67 # <i>emerge sys-apps/usermode-utilities</i>
68 </pre>
69 <p>These tools facilitate networking (among other things)
70 between the user-mode linux virtual system
71 and the host Linux system.</p>
72 </body>
73 </section>
74 </chapter>
75
76 <chapter>
77 <title>Creating <path>root_fs</path></title>
78
79 <section>
80 <title>Making the Gentoo chroot</title>
81 <body>
82 <p>
83 The <path>root_fs</path> file needed for user-mode linux is
84 a single file that contains an entire Gentoo Linux filesystem.
85 To generate this file you will need to have Loopback device
86 support enabled in the host (non-user-mode) kernel.
87 </p>
88 <p>Generating the <path>root_fs</path> file itself will be
89 our last step. First we will generate a Gentoo filesystem in
90 an ordinary chroot. We need the build tarball available, which
91 could be downloaded separately, extracted from a build cd, or
92 extracted from a build .iso.
93 </p>
94 <pre caption="Mounting a build .iso">
95 # <i>mkdir /mnt/loop</i>
96 # <i>mount -o loop /path/to/build-&lt;TAB&gt;.iso /mnt/loop</i>
97 </pre>
98 <p>
99 Setting up the chroot is essentially identical to an ordinary Gentoo
100 Linux build.
101 </p>
102 <pre>
103 # <i>mkdir /mnt/gentoo</i>
104 # <i>cd /mnt/gentoo</i>
105 # <i>tar xvjpf /path/to/build-&lt;TAB&gt;.tar.bz2</i>
106 </pre>
107 <p>
108 Go ahead and unmount the .iso. You don't need it anymore.
109 </p>
110 <pre>
111 # <i>cp /etc/resolv.conf /mnt/gentoo/etc/</i>
112 # <i>mount -o bind /proc /mnt/gentoo/proc</i>
113 # <i>mkdir -p /mnt/gentoo/usr/portage/distfiles</i>
114 # <i>mkdir -p /mnt/gentoo/usr/portage/packages</i>
115 # <i>mount -o bind /usr/portage/distfiles /mnt/gentoo/usr/portage/distfiles</i>
116 # <i>mount -o bind /usr/portage/packages /mnt/gentoo/usr/portage/packages</i>
117 # <i>chroot /mnt/gentoo /bin/bash</i>
118 # <i>env-update</i>
119 # <i>source /etc/profile</i>
120 </pre>
121 <p>
122 By bind-mounting <path>/usr/portage/distfiles</path> and
123 <path>/usr/portage/packages</path> we avoid having to download
124 or build packages that are already present on the Gentoo host.
125 </p>
126 <p>
127 Bootstrap and build the system in the usual fashion:
128 </p>
129 <pre>
130 # <i>emerge rsync</i>
131 # <i>cd /usr/portage</i>
132 # <i>nano -w /etc/make.conf</i>
133 # <i>nano -w /etc/make.profile/packages</i>
134 # <i>nano -w /usr/portage/profiles/package.mask</i>
135 # <i>scripts/bootstrap.sh &amp;&amp; emerge --usepkg system</i>
136 </pre>
137 <warn>
138 The <path>/etc/make.profile/packages</path> file needs to be
139 edited to remove grub from the default system (just remove the "*"
140 from the beginning of the "*sys-apps/grub" line). The grub ebuild
141 tries to mount the /boot partition, which will fail in our chroot.
142 </warn>
143 <note>
144 Make sure you examine <path>/etc/make.profile/packages</path>
145 and <path>/usr/portage/profiles/package.mask</path> to be sure that
146 any to-be-tested packages that you want to install aren't masked out.
147 As currently written, <path>scripts/bootstrap.sh</path> will compile
148 the bootstrap packages from source. To use already-existing packages,
149 add <c>alias emerge="emerge --usepkg"</c> somewhere near the top of
150 the bootstrap script.
151 </note>
152 <p>
153 Add any additional packages you desire. Feel free to give your virtual
154 Gentoo system a hostname, if you so desire. In <path>/etc/fstab</path>
155 you will want <path>/dev/ROOT</path> to be <path>/dev/ubd/0</path>, with
156 a fs type of either ext2, ext3, or reiserfs. Set <path>/dev/SWAP</path>
157 to be <path>/dev/ubd/1</path>, and comment out <path>/dev/BOOT</path>.
158 </p>
159 <p>
160 Exit the chroot, unmount all of the bind mounts,
161 tar up the new Gentoo distro, and clean up:
162 </p>
163 <pre>
164 # <i>exit</i>
165 # <i>umount /mnt/gentoo/usr/portage/distfiles</i>
166 # <i>umount /mnt/gentoo/usr/portage/packages</i>
167 # <i>umount /mnt/gentoo/proc</i>
168 # <i>du -ks /mnt/gentoo</i>
169 261744 /mnt/gentoo
170 # <i>tar cvjpf ~/gentoo.tbz2 *</i>
171 # <i>cd</i>
172 # <i>rm -rf /mnt/gentoo</i>
173 </pre>
174 </body>
175 </section>
176
177 <section>
178 <title>Making <path>root_fs</path></title>
179 <body>
180 <p>
181 Our Gentoo chroot is nearly 300 MB in size, so
182 <path>root_fs</path> needs to be at least that size.
183 We'll choose 0.5 GB as a reasonable size.
184 </p>
185 <pre>
186 # <i>dd if=/dev/zero of=root_fs seek=500 count=1 bs=1M</i>
187 # <i>mke2fs -F root_fs</i>
188 # <i>mount -o loop root_fs /mnt/loop</i>
189 # <i>tar xvjpf gentoo.tbz2 -C /mnt/loop</i>
190 # <i>umount /mnt/loop</i>
191 </pre>
192 <p>
193 It would also be nice to have a 0.5 GB swap partition.
194 </p>
195 <pre>
196 # <i>dd if=/dev/zero of=swap_fs seek=500 count=1 bs=1M</i>
197 # <i>mkswap -f swap_fs</i>
198 </pre>
199 <p>
200 Now see if it works!
201 </p>
202 <pre>
203 # <i>linux ubd0=root_fs ubd1=swap_fs</i>
204 </pre>
205 <note>
206 User-mode linux uses xterms for the virtual consoles that
207 are run at boot time, so you need to make sure that the
208 terminal from which you run user-mode linux has $DISPLAY
209 properly set (along with proper xhost/xauth permissions).
210 </note>
211 <p>
212 With any luck you should be able to log into your user-mode linux
213 Gentoo system. The only thing keeping this user-mode linux version
214 of Gentoo from being fully functional is networking from the virtual
215 machine to the host. Such networking is supposed to be trivial,
216 but I have yet to get it to work for me. Should you find a workable
217 solution, please let me know!
218 </p>
219 </body>
220 </section>
221 </chapter>
222
223 <chapter>
224 <title>Networking</title>
225
226 <section>
227 <body>
228 <p>
229 Thanks to Martin Schlemmer (Azarah), I now know how
230 to get networking to function from within a user-mode
231 system. The idea is that we set up a private network
232 consisting of the user-mode system and the host system,
233 and then the user-mode system routes all of its packets
234 to the host, which then forwards packets to the net.
235 Make sure that the host kernel has
236 Networking --> IP: Netfilter Configuration --> IP tables support
237 --> Full NAT --> MASQUERADE target support and
238 Network Device Support --> Ethertap network tap
239 compiled as modules; then do the following on the
240 <e>host</e> machine:
241 </p>
242 <pre>
243 # <i>modprobe ethertap</i>
244 # <i>modprobe iptable_nat</i>
245 # <i>iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE</i>
246 # <i>echo 1 > /proc/sys/net/ipv4/ip_forward</i>
247 </pre>
248 <p>
249 The iptables line sets up IP Masquerading between the private
250 network that our user-mode system will be on and the internet
251 (reachable via <c>eth0</c> in our case). The echo line then
252 turns on packet forwarding between the private network and the
253 interface that the default gateway is on (eth0 for us).
254 </p>
255 <p>
256 Now we bring up the user-mode system and see if networking
257 is functional.
258 </p>
259 <pre>
260 # <i>linux ubd0=root_fs ubd1=swap_fs eth0=ethertap,tap0,,192.168.0.254</i>
261 <comment>(login to user-mode system)</comment>
262 # <i>ifconfig eth0 192.168.0.1 up</i>
263 # <i>ping -c 2 192.168.0.254</i>
264 PING 192.168.0.254 (192.168.0.254): 56 octets data
265 64 octets from 192.168.0.254: icmp_seq=0 ttl=255 time=0.8 ms
266 64 octets from 192.168.0.254: icmp_seq=1 ttl=255 time=0.6 ms
267
268 --- 192.168.0.254 ping statistics ---
269 2 packets transmitted, 2 packets received, 0% packet loss
270 round-trip min/avg/max = 0.6/0.7/0.8 ms
271 <i>route add default gw 192.168.0.254</i>
272 <i>netstat -rn</i>
273 Kernel IP routing table
274 Destination Gateway Genmask Flags MSS Window irtt Iface
275 192.168.0.0 0.0.0.0 255.255.255.0 U 40 0 0 eth0
276 0.0.0.0 192.168.0.254 0.0.0.0 UG 40 0 0 eth0
277 <i>scp user@192.168.0.254:/etc/resolv.conf /etc/resolv.conf</i> <comment>(if needed)</comment>
278 <i>ping -c 2 www.gentoo.org</i>
279 PING www.gentoo.org (207.170.82.202): 56 octets data
280 64 octets from 207.170.82.202: icmp_seq=0 ttl=240 time=119.6 ms
281 64 octets from 207.170.82.202: icmp_seq=1 ttl=240 time=92.0 ms
282
283 --- www.gentoo.org ping statistics ---
284 2 packets transmitted, 2 packets received, 0% packet loss
285 round-trip min/avg/max = 92.0/105.8/119.6 ms
286 </pre>
287 <p>
288 On the user-mode system we assign the user-mode eth0 interface
289 the private IP address 192.168.0.1 and bring up the interface. The
290 host has private IP address 192.168.0.254, and we ping it to make sure
291 that our networking is, indeed, up. The route line adds a default
292 gateway, namely our host, we use scp to retrieve a working
293 <path>/etc/resolv.conf</path> (if necessary), and we ping www.gentoo.org
294 to make sure that name resolution (and general access to the internet)
295 is working from our user-mode system. Now the user-mode system can
296 <c>emerge</c> at will!
297 </p>
298 </body>
299 </section>
300 </chapter>
301
302 <chapter>
303 <title>Testing the .iso</title>
304
305 <section>
306 <body>
307 <p>
308 Perhaps the true ideal of Gentoo Linux testing would be
309 to boot the .iso with user-mode linux and do the complete
310 Gentoo install from within the user-mode linux virtual system.
311 </p>
312 <p>
313 Booting the .iso, or actually the initrd from the .iso, is pretty
314 straightforward.
315 </p>
316 <pre>
317 # <i>mount -o loop /path/to/build-&lt;TAB&gt;.iso /mnt/loop</i>
318 # <i>cp /mnt/loop/isolinux/rescue.gz .</i>
319 # <i>linux load_ramdisk=1 prompt_ramdisk=0 ramdisk_size=22000 \</i>
320 &gt; <i>initrd=rescue.gz root=/dev/ram0 ubd0=root_fs ubd1=swap_fs \</i>
321 &gt; <i>ubd2=/dev/cdroms/cdrom0 eth0=ethertap,tap0,,192.168.0.254</i>
322 </pre>
323 <p>Now you can follow the Gentoo install doc essentially verbatim,
324 although you'll need to know that the root filesystem will be
325 <path>/dev/ubd/0</path>, the swap "partition"
326 will be <path>/dev/ubd/1</path>, and the CD rom
327 will be <path>/dev/ubd/2</path>.</p>
328 </body>
329 </section>
330 </chapter>
331
332
333 </guide>

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