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   <h1>Setting up gem5 full system</h1>
   <time>Jan 13, 2017 • Jason Lowe-Power</time>
   <hr>
   <p>This is partially a followup to <a href="http://www.lowepower.com/jason/creating-disk-images-for-gem5.html">Creating disk images for
 gem5</a>
 and partially how to setup x86 full system for gem5. In this post, I’ll
 discuss how to create a disk image from scratch and start using it with
 gem5.</p>

 <p>It is important for computer architecture research to use the most
 up-to-date software on the systems we are simulating. Too much computer
 architecture research reports results using kernels from 5+ years ago or
 ancient system software Hopefully, this post will help others be able to
 keep up with the ever-changing system software. This way, researchers
 can use up-to-date versions of Linux and easily update their kernels.</p>

 <p>This post takes a different approach than <a href="http://www.lowepower.com/jason/creating-disk-images-for-gem5.html">Creating disk images for
 gem5</a>.
 Instead of using the gem5 tools, this post uses qemu to create, edit,
 and set up the disk for gem5 usage.</p>

 <p>This post assumes that you have installed qemu on your system. In
 Ubuntu, this can be done with</p>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>sudo apt-get install qemu-kvm libvirt-bin ubuntu-vm-builder bridge-utils
 </code></pre></div></div>

 <p>I also assume you have downloaded and built gem5. All of the full system
 examples use the simple full system scripts that are covered in
 <a href="http://learning.gem5.org/book/part3/index.html">Learning gem5</a>.</p>

 <h2 id="step-1-create-an-empty-disk">Step 1: Create an empty disk</h2>

 <p>Using the qemu disk tools, create a blank raw disk image. In this case,
 I chose to create a disk named “ubuntu-test.img” that is 8GB.</p>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>qemu-img create ubuntu-test.img 8G
 </code></pre></div></div>

 <h2 id="step-2-install-ubuntu-with-qemu">Step 2: Install ubuntu with qemu</h2>

 <p>Now that we have a blank disk, we are going to use qemu to install
 Ubuntu on the disk. I would encourage you to use the server version of
 Ubuntu since gem5 does not have great support for displays. Thus, the
 desktop environment isn’t very useful.</p>

 <p>First, you need to download the installation CD image from the <a href="https://www.ubuntu.com/download/server">Ubuntu
 website</a>.</p>

 <p>Next, use qemu to boot off of the CD image, and set the disk in the
 system to be the blank disk you created above. Ubuntu needs at least 1GB
 of memory to install correctly, so be sure to configure qemu to use at
 least 1GB memory.</p>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>qemu-system-x86_64 -hda ../gem5-fs-testing/ubuntu-test.img -cdrom ubuntu-16.04.1-server-amd64.iso -m 1024 -enable-kvm -boot d
 </code></pre></div></div>

 <p>With this, you can simply follow the on-screen directions to install
 Ubuntu to the disk image. The only gotcha in the installation is that
 gem5’s IDE drivers don’t seem to play nicely with logical paritions.
 Thus, during the Ubuntu install, be sure to manually partition the disk
 and remove any logical partitions. You don’t need any swap space on the
 disk anyway, unless you’re doing something specifically with swap space.</p>

 <h2 id="step-3-boot-up-and-install-needed-software">Step 3: Boot up and install needed software</h2>

 <p>Once you have installed Ubuntu on the disk, quit qemu and remove the
 <code class="highlighter-rouge">-boot d</code> option so that you are not booting off of the CD anymore. Now,
 you can again boot off of the main disk image you have installed Ubuntu
 on.</p>

 <p>Since we’re using qemu, you should have a network connection (although
 <a href="http://wiki.qemu.org/Documentation/Networking#User_Networking_.28SLIRP.29">ping won’t
 work</a>).
 When booting in qemu, you can just use <code class="highlighter-rouge">sudo apt-get install</code> and
 install any software you need on your disk.</p>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>qemu-system-x86_64 -hda ../gem5-fs-testing/ubuntu-test.img -cdrom ubuntu-16.04.1-server-amd64.iso -m 1024 -enable-kvm
 </code></pre></div></div>

 <h2 id="step-4-build-a-kernel">Step 4: Build a kernel</h2>

 <p>Next, you need to build a Linux kernel. Unfortunately, the
 out-of-the-box Ubuntu kernel doesn’t play well with gem5. See the
 error below_.</p>

 <p>First, you need to download latest kernel from
 <a href="https://www.kernel.org/">kernel.org</a>. Then, to build the kernel, you
 are going to want to start with a known-good config file.
 The config file that I’m used for kernel version 4.8.13 can be
 downloaded <a href="{filename}files/config">here</a>. Then, you need to move the
 good config to <code class="highlighter-rouge">.config</code> and the run <code class="highlighter-rouge">make oldconfig</code> which starts the
 kernel configuration process with an existing config file.</p>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>mv &lt;good config&gt; .config
 make oldconfig
 </code></pre></div></div>

 <p>At this point you can select any extra drivers you want to build into
 the kernel. Note: You cannot use any kernel modules unless you are
 planning on copying the modules onto the guest disk at the correct
 location. All drivers must be built into the kernel binary.</p>

 <p>It may be possible to use modules by compiling the binary on the guest
 disk via qemu, but I have not tested this.</p>

 <p>Finally, you need to build the kernel.</p>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>make -j5
 </code></pre></div></div>

 <h2 id="step-5-update-init-script">Step 5: Update init script</h2>

 <p>By default, gem5 expects a modified init script which loads a script off
 of the host to execute in the guest. To use this feature, you need to
 follow the steps below.</p>

 <p>Alternatively, you can install the precompiled binaries for x86 found on
 my website: From qemu, you can run the following, which completes the
 above steps for you.</p>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>wget http://cs.wisc.edu/~powerjg/files/gem5-guest-tools-x86.tgz
 tar xzvf gem5-guest-tools-x86.tgz
 cd gem5-guest-tools/
 sudo ./install
 </code></pre></div></div>

 <p>Now, you can use the <code class="highlighter-rouge">system.readfile</code> parameter in your Python config
 scripts. This file will automatically be loaded (by the <code class="highlighter-rouge">gem5init</code>
 script) and executed.</p>

 <h3 id="manually-installing-the-gem5-init-script">Manually installing the gem5 init script</h3>

 <p>First, build the m5 binary on the host.</p>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>cd util/m5
 make -f Makefile.x86
 </code></pre></div></div>

 <p>Then, copy this binary to the guest and put it in <code class="highlighter-rouge">/sbin</code>. Also, create
 a link from <code class="highlighter-rouge">/sbin/gem5</code>.</p>

 <p>Then, to get the init script to execute when gem5 boots, create file
 /lib/systemd/system/gem5.service with the following:</p>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>[Unit]
 Description=gem5 init script
 Documentation=http://gem5.org
 After=getty.target

 [Service]
 Type=idle
 ExecStart=/sbin/gem5init
 StandardOutput=tty
 StandardInput=tty-force
 StandardError=tty

 [Install]
 WantedBy=default.target
 </code></pre></div></div>

 <p>Enable the gem5 service and disable the ttyS0 service.</p>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>systemctl enable gem5.service
 </code></pre></div></div>

 <p>Finally, create the init script that is executed by the service. In
 <code class="highlighter-rouge">/sbin/gem5init</code>:</p>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c">#!/bin/bash -</span>

 <span class="nv">CPU</span><span class="o">=</span><span class="sb">`</span><span class="nb">cat</span> /proc/cpuinfo | <span class="nb">grep </span>vendor_id | head <span class="nt">-n</span> 1 | cut <span class="nt">-d</span> <span class="s1">' '</span> <span class="nt">-f2-</span><span class="sb">`</span>
 <span class="nb">echo</span> <span class="s2">"Got CPU type: </span><span class="nv">$CPU</span><span class="s2">"</span>

 <span class="k">if</span> <span class="o">[</span> <span class="s2">"</span><span class="nv">$CPU</span><span class="s2">"</span> <span class="o">!=</span> <span class="s2">"M5 Simulator"</span> <span class="o">]</span><span class="p">;</span>
 <span class="k">then
     </span><span class="nb">echo</span> <span class="s2">"Not in gem5. Not loading script"</span>
     <span class="nb">exit </span>0
 <span class="k">fi</span>

 <span class="c"># Try to read in the script from the host system</span>
 /sbin/m5 readfile <span class="o">&gt;</span> /tmp/script
 chmod 755 /tmp/script
 <span class="k">if</span> <span class="o">[</span> <span class="nt">-s</span> /tmp/script <span class="o">]</span>
 <span class="k">then</span>
     <span class="c"># If there is a script, execute the script and then exit the simulation</span>
     su root <span class="nt">-c</span> <span class="s1">'/tmp/script'</span> <span class="c"># gives script full privileges as root user in multi-user mode</span>
     sync
     sleep 10
     /sbin/m5 <span class="nb">exit
 </span><span class="k">fi
 </span><span class="nb">echo</span> <span class="s2">"No script found"</span>
 </code></pre></div></div>

 <h2 id="problems-and-some-solutions">Problems and (some) solutions</h2>

 <h3 id="failed-to-early-mount-api-filesystems">Failed to early mount API filesystems</h3>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>Write protecting the kernel read-only data: 8192k
 Freeing unused kernel memory: 1956K (ffff880001417000 - ffff880001600000)
 Freeing unused kernel memory: 456K (ffff88000178e000 - ffff880001800000)
 [!!!!!!] Failed to early mount API filesystems, freezing.
 </code></pre></div></div>

 <p>Solutions tried: Enable cgroups in the kernel. I think. Nope! I think
 this is the same as the problem below mount-problem_.</p>

 <h3 id="cant-mount-dev">Can’t mount /dev</h3>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>Failed to mount devtmpfs at /dev: No such device
 Freezing execution.
 </code></pre></div></div>

 <p>Something like the above (this was taken from arch linux boot). The
 problem is that that the right devfs is not compiled into the kernel.
 You need to make sure that devtmpfs is enabled.</p>

 <h3 id="panic-kvm-unexpected-exit-exit_reason-8">panic: KVM: Unexpected exit (exit_reason: 8)</h3>

 <p>Exit reason 8 is “shutdown”. See
 <a href="http://lxr.free-electrons.com/source/include/uapi/linux/kvm.h#L188">http://lxr.free-electrons.com/source/include/uapi/linux/kvm.h#L188</a>.
 This seems to happen when there is a triple fault:
 <a href="http://lxr.free-electrons.com/source/arch/x86/kvm/x86.c#L6498">http://lxr.free-electrons.com/source/arch/x86/kvm/x86.c#L6498</a></p>

 <p>I get this error every time I try to boot the unmodified Ubuntu kernel.
 I don’t know how to solve this problem. Instead of trying to solve the
 problem, I used a different config file for “oldconfig” when I compiled
 the kernel from scratch.</p>

 <h3 id="slow-boot">Slow boot</h3>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>[ TIME ] Timed out waiting for device dev-di...\x2da115\x2de3f263d7b53a.device.
 [DEPEND] Dependency failed for /dev/disk/by-...382-f41d-4c99-a115-e3f263d7b53a.
 [DEPEND] Dependency failed for Swap.
 </code></pre></div></div>

 <p>This may happen if you have changed the disk without updating the fstab
 on the disk. To fix it, you can boot the disk in qemu and update fstab
 with the correct UUID.</p>

 <p>I ran into this when I was resizing the disk.</p>

 <h3 id="disk-is-too-small-for-what-you-want-to-do">Disk is too small for what you want to do</h3>

 <p>Resizing an iso is pretty easy. You can use the same method you would if
 you wanted to resize a partition on a regular hard drive.</p>

 <p>First, you need to resize the iso with qemu-image:</p>

 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>qemu-img resize ubuntu-test.img +8G
 </code></pre></div></div>

 <p>Now, you have a disk that has 8 GB of free space at the end of the disk.
 You need to resize the partitions to use this free space. To do this, I
 suggest using gparted just like you would for a real hard drive.</p>

 <p>You can download a gparted ISO from <a href="http://gparted.org/livecd.php">http://gparted.org/livecd.php</a>.
 Once you download the ISO, you can boot it with qemu the same way as we
 booted the installation CD. Then, once its booted you can select the
 disk you want to modify and follow the howto
 (<a href="http://gparted.org/display-doc.php%3Fname%3Dhelp-manual">http://gparted.org/display-doc.php%3Fname%3Dhelp-manual</a>).</p>

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	<h1>Setting up gem5 full system</h1>
	<time>Jan 13, 2017 • Jason Lowe-Power</time>
	<hr>
	<p>This is partially a followup to <a href="http://www.lowepower.com/jason/creating-disk-images-for-gem5.html">Creating disk images for
	gem5</a>
	and partially how to setup x86 full system for gem5. In this post, I’ll
	discuss how to create a disk image from scratch and start using it with
	gem5.</p>

	<p>It is important for computer architecture research to use the most
	up-to-date software on the systems we are simulating. Too much computer
	architecture research reports results using kernels from 5+ years ago or
	ancient system software Hopefully, this post will help others be able to
	keep up with the ever-changing system software. This way, researchers
	can use up-to-date versions of Linux and easily update their kernels.</p>

	<p>This post takes a different approach than <a href="http://www.lowepower.com/jason/creating-disk-images-for-gem5.html">Creating disk images for
	gem5</a>.
	Instead of using the gem5 tools, this post uses qemu to create, edit,
	and set up the disk for gem5 usage.</p>

	<p>This post assumes that you have installed qemu on your system. In
	Ubuntu, this can be done with</p>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>sudo apt-get install qemu-kvm libvirt-bin ubuntu-vm-builder bridge-utils
	</code></pre></div></div>

	<p>I also assume you have downloaded and built gem5. All of the full system
	examples use the simple full system scripts that are covered in
	<a href="http://learning.gem5.org/book/part3/index.html">Learning gem5</a>.</p>

	<h2 id="step-1-create-an-empty-disk">Step 1: Create an empty disk</h2>

	<p>Using the qemu disk tools, create a blank raw disk image. In this case,
	I chose to create a disk named “ubuntu-test.img” that is 8GB.</p>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>qemu-img create ubuntu-test.img 8G
	</code></pre></div></div>

	<h2 id="step-2-install-ubuntu-with-qemu">Step 2: Install ubuntu with qemu</h2>

	<p>Now that we have a blank disk, we are going to use qemu to install
	Ubuntu on the disk. I would encourage you to use the server version of
	Ubuntu since gem5 does not have great support for displays. Thus, the
	desktop environment isn’t very useful.</p>

	<p>First, you need to download the installation CD image from the <a href="https://www.ubuntu.com/download/server">Ubuntu
	website</a>.</p>

	<p>Next, use qemu to boot off of the CD image, and set the disk in the
	system to be the blank disk you created above. Ubuntu needs at least 1GB
	of memory to install correctly, so be sure to configure qemu to use at
	least 1GB memory.</p>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>qemu-system-x86_64 -hda ../gem5-fs-testing/ubuntu-test.img -cdrom ubuntu-16.04.1-server-amd64.iso -m 1024 -enable-kvm -boot d
	</code></pre></div></div>

	<p>With this, you can simply follow the on-screen directions to install
	Ubuntu to the disk image. The only gotcha in the installation is that
	gem5’s IDE drivers don’t seem to play nicely with logical paritions.
	Thus, during the Ubuntu install, be sure to manually partition the disk
	and remove any logical partitions. You don’t need any swap space on the
	disk anyway, unless you’re doing something specifically with swap space.</p>

	<h2 id="step-3-boot-up-and-install-needed-software">Step 3: Boot up and install needed software</h2>

	<p>Once you have installed Ubuntu on the disk, quit qemu and remove the
	<code class="highlighter-rouge">-boot d</code> option so that you are not booting off of the CD anymore. Now,
	you can again boot off of the main disk image you have installed Ubuntu
	on.</p>

	<p>Since we’re using qemu, you should have a network connection (although
	<a href="http://wiki.qemu.org/Documentation/Networking#User_Networking_.28SLIRP.29">ping won’t
	work</a>).
	When booting in qemu, you can just use <code class="highlighter-rouge">sudo apt-get install</code> and
	install any software you need on your disk.</p>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>qemu-system-x86_64 -hda ../gem5-fs-testing/ubuntu-test.img -cdrom ubuntu-16.04.1-server-amd64.iso -m 1024 -enable-kvm
	</code></pre></div></div>

	<h2 id="step-4-build-a-kernel">Step 4: Build a kernel</h2>

	<p>Next, you need to build a Linux kernel. Unfortunately, the
	out-of-the-box Ubuntu kernel doesn’t play well with gem5. See the
	error below_.</p>

	<p>First, you need to download latest kernel from
	<a href="https://www.kernel.org/">kernel.org</a>. Then, to build the kernel, you
	are going to want to start with a known-good config file.
	The config file that I’m used for kernel version 4.8.13 can be
	downloaded <a href="{filename}files/config">here</a>. Then, you need to move the
	good config to <code class="highlighter-rouge">.config</code> and the run <code class="highlighter-rouge">make oldconfig</code> which starts the
	kernel configuration process with an existing config file.</p>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>mv <good config> .config
	make oldconfig
	</code></pre></div></div>

	<p>At this point you can select any extra drivers you want to build into
	the kernel. Note: You cannot use any kernel modules unless you are
	planning on copying the modules onto the guest disk at the correct
	location. All drivers must be built into the kernel binary.</p>

	<p>It may be possible to use modules by compiling the binary on the guest
	disk via qemu, but I have not tested this.</p>

	<p>Finally, you need to build the kernel.</p>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>make -j5
	</code></pre></div></div>

	<h2 id="step-5-update-init-script">Step 5: Update init script</h2>

	<p>By default, gem5 expects a modified init script which loads a script off
	of the host to execute in the guest. To use this feature, you need to
	follow the steps below.</p>

	<p>Alternatively, you can install the precompiled binaries for x86 found on
	my website: From qemu, you can run the following, which completes the
	above steps for you.</p>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>wget http://cs.wisc.edu/~powerjg/files/gem5-guest-tools-x86.tgz
	tar xzvf gem5-guest-tools-x86.tgz
	cd gem5-guest-tools/
	sudo ./install
	</code></pre></div></div>

	<p>Now, you can use the <code class="highlighter-rouge">system.readfile</code> parameter in your Python config
	scripts. This file will automatically be loaded (by the <code class="highlighter-rouge">gem5init</code>
	script) and executed.</p>

	<h3 id="manually-installing-the-gem5-init-script">Manually installing the gem5 init script</h3>

	<p>First, build the m5 binary on the host.</p>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>cd util/m5
	make -f Makefile.x86
	</code></pre></div></div>

	<p>Then, copy this binary to the guest and put it in <code class="highlighter-rouge">/sbin</code>. Also, create
	a link from <code class="highlighter-rouge">/sbin/gem5</code>.</p>

	<p>Then, to get the init script to execute when gem5 boots, create file
	/lib/systemd/system/gem5.service with the following:</p>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>[Unit]
	Description=gem5 init script
	Documentation=http://gem5.org
	After=getty.target

	[Service]
	Type=idle
	ExecStart=/sbin/gem5init
	StandardOutput=tty
	StandardInput=tty-force
	StandardError=tty

	[Install]
	WantedBy=default.target
	</code></pre></div></div>

	<p>Enable the gem5 service and disable the ttyS0 service.</p>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>systemctl enable gem5.service
	</code></pre></div></div>

	<p>Finally, create the init script that is executed by the service. In
	<code class="highlighter-rouge">/sbin/gem5init</code>:</p>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c">#!/bin/bash -</span>

	<span class="nv">CPU</span><span class="o">=</span><span class="sb">`</span><span class="nb">cat</span> /proc/cpuinfo \| <span class="nb">grep </span>vendor_id \| head <span class="nt">-n</span> 1 \| cut <span class="nt">-d</span> <span class="s1">' '</span> <span class="nt">-f2-</span><span class="sb">`</span>
	<span class="nb">echo</span> <span class="s2">"Got CPU type: </span><span class="nv">$CPU</span><span class="s2">"</span>

	<span class="k">if</span> <span class="o">[</span> <span class="s2">"</span><span class="nv">$CPU</span><span class="s2">"</span> <span class="o">!=</span> <span class="s2">"M5 Simulator"</span> <span class="o">]</span><span class="p">;</span>
	<span class="k">then
	</span><span class="nb">echo</span> <span class="s2">"Not in gem5. Not loading script"</span>
	<span class="nb">exit </span>0
	<span class="k">fi</span>

	<span class="c"># Try to read in the script from the host system</span>
	/sbin/m5 readfile <span class="o">></span> /tmp/script
	chmod 755 /tmp/script
	<span class="k">if</span> <span class="o">[</span> <span class="nt">-s</span> /tmp/script <span class="o">]</span>
	<span class="k">then</span>
	<span class="c"># If there is a script, execute the script and then exit the simulation</span>
	su root <span class="nt">-c</span> <span class="s1">'/tmp/script'</span> <span class="c"># gives script full privileges as root user in multi-user mode</span>
	sync
	sleep 10
	/sbin/m5 <span class="nb">exit
	</span><span class="k">fi
	</span><span class="nb">echo</span> <span class="s2">"No script found"</span>
	</code></pre></div></div>

	<h2 id="problems-and-some-solutions">Problems and (some) solutions</h2>

	<h3 id="failed-to-early-mount-api-filesystems">Failed to early mount API filesystems</h3>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>Write protecting the kernel read-only data: 8192k
	Freeing unused kernel memory: 1956K (ffff880001417000 - ffff880001600000)
	Freeing unused kernel memory: 456K (ffff88000178e000 - ffff880001800000)
	[!!!!!!] Failed to early mount API filesystems, freezing.
	</code></pre></div></div>

	<p>Solutions tried: Enable cgroups in the kernel. I think. Nope! I think
	this is the same as the problem below mount-problem_.</p>

	<h3 id="cant-mount-dev">Can’t mount /dev</h3>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>Failed to mount devtmpfs at /dev: No such device
	Freezing execution.
	</code></pre></div></div>

	<p>Something like the above (this was taken from arch linux boot). The
	problem is that that the right devfs is not compiled into the kernel.
	You need to make sure that devtmpfs is enabled.</p>

	<h3 id="panic-kvm-unexpected-exit-exit_reason-8">panic: KVM: Unexpected exit (exit_reason: 8)</h3>

	<p>Exit reason 8 is “shutdown”. See
	<a href="http://lxr.free-electrons.com/source/include/uapi/linux/kvm.h#L188">http://lxr.free-electrons.com/source/include/uapi/linux/kvm.h#L188</a>.
	This seems to happen when there is a triple fault:
	<a href="http://lxr.free-electrons.com/source/arch/x86/kvm/x86.c#L6498">http://lxr.free-electrons.com/source/arch/x86/kvm/x86.c#L6498</a></p>

	<p>I get this error every time I try to boot the unmodified Ubuntu kernel.
	I don’t know how to solve this problem. Instead of trying to solve the
	problem, I used a different config file for “oldconfig” when I compiled
	the kernel from scratch.</p>

	<h3 id="slow-boot">Slow boot</h3>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>[ TIME ] Timed out waiting for device dev-di...\x2da115\x2de3f263d7b53a.device.
	[DEPEND] Dependency failed for /dev/disk/by-...382-f41d-4c99-a115-e3f263d7b53a.
	[DEPEND] Dependency failed for Swap.
	</code></pre></div></div>

	<p>This may happen if you have changed the disk without updating the fstab
	on the disk. To fix it, you can boot the disk in qemu and update fstab
	with the correct UUID.</p>

	<p>I ran into this when I was resizing the disk.</p>

	<h3 id="disk-is-too-small-for-what-you-want-to-do">Disk is too small for what you want to do</h3>

	<p>Resizing an iso is pretty easy. You can use the same method you would if
	you wanted to resize a partition on a regular hard drive.</p>

	<p>First, you need to resize the iso with qemu-image:</p>

	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>qemu-img resize ubuntu-test.img +8G
	</code></pre></div></div>

	<p>Now, you have a disk that has 8 GB of free space at the end of the disk.
	You need to resize the partitions to use this free space. To do this, I
	suggest using gparted just like you would for a real hard drive.</p>

	<p>You can download a gparted ISO from <a href="http://gparted.org/livecd.php">http://gparted.org/livecd.php</a>.
	Once you download the ISO, you can boot it with qemu the same way as we
	booted the installation CD. Then, once its booted you can select the
	disk you want to modify and follow the howto
	(<a href="http://gparted.org/display-doc.php%3Fname%3Dhelp-manual">http://gparted.org/display-doc.php%3Fname%3Dhelp-manual</a>).</p>

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