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| 1 | | -This document describes one way to create the initrd directory hierarchy |
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| 2 | | -in order to allow an initrd to be built into your kernel. The trick |
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| 3 | | -here is to steal the initrd file used on your Linux laptop, Ubuntu in |
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| 4 | | -this case. There are probably much better ways of doing this. |
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| 1 | +The rcutorture scripting tools automatically create an initrd containing |
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| 2 | +a single statically linked binary named "init" that loops over a |
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| 3 | +very long sleep() call. In both cases, this creation is done by |
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| 4 | +tools/testing/selftests/rcutorture/bin/mkinitrd.sh. |
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| 5 | 5 | |
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| 6 | | -That said, here are the commands: |
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| 6 | +However, if you don't like the notion of statically linked bare-bones |
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| 7 | +userspace environments, you might wish to press an existing initrd |
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| 8 | +into service: |
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| 7 | 9 | |
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| 8 | 10 | ------------------------------------------------------------------------ |
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| 9 | 11 | cd tools/testing/selftests/rcutorture |
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| .. | .. |
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| 11 | 13 | mkdir initrd |
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| 12 | 14 | cd initrd |
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| 13 | 15 | cpio -id < /tmp/initrd.img.zcat |
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| 14 | | ------------------------------------------------------------------------- |
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| 15 | | - |
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| 16 | | -Another way to create an initramfs image is using "dracut"[1], which is |
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| 17 | | -available on many distros, however the initramfs dracut generates is a cpio |
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| 18 | | -archive with another cpio archive in it, so an extra step is needed to create |
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| 19 | | -the initrd directory hierarchy. |
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| 20 | | - |
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| 21 | | -Here are the commands to create a initrd directory for rcutorture using |
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| 22 | | -dracut: |
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| 23 | | - |
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| 24 | | ------------------------------------------------------------------------- |
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| 25 | | -dracut --no-hostonly --no-hostonly-cmdline --module "base bash shutdown" /tmp/initramfs.img |
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| 26 | | -cd tools/testing/selftests/rcutorture |
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| 27 | | -mkdir initrd |
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| 28 | | -cd initrd |
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| 29 | | -/usr/lib/dracut/skipcpio /tmp/initramfs.img | zcat | cpio -id < /tmp/initramfs.img |
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| 30 | | ------------------------------------------------------------------------- |
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| 31 | | - |
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| 32 | | -Interestingly enough, if you are running rcutorture, you don't really |
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| 33 | | -need userspace in many cases. Running without userspace has the |
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| 34 | | -advantage of allowing you to test your kernel independently of the |
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| 35 | | -distro in place, the root-filesystem layout, and so on. To make this |
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| 36 | | -happen, put the following script in the initrd's tree's "/init" file, |
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| 37 | | -with 0755 mode. |
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| 38 | | - |
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| 39 | | ------------------------------------------------------------------------- |
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| 40 | | -#!/bin/sh |
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| 41 | | - |
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| 42 | | -[ -d /dev ] || mkdir -m 0755 /dev |
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| 43 | | -[ -d /root ] || mkdir -m 0700 /root |
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| 44 | | -[ -d /sys ] || mkdir /sys |
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| 45 | | -[ -d /proc ] || mkdir /proc |
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| 46 | | -[ -d /tmp ] || mkdir /tmp |
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| 47 | | -mkdir -p /var/lock |
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| 48 | | -mount -t sysfs -o nodev,noexec,nosuid sysfs /sys |
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| 49 | | -mount -t proc -o nodev,noexec,nosuid proc /proc |
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| 50 | | -# Some things don't work properly without /etc/mtab. |
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| 51 | | -ln -sf /proc/mounts /etc/mtab |
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| 52 | | - |
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| 53 | | -# Note that this only becomes /dev on the real filesystem if udev's scripts |
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| 54 | | -# are used; which they will be, but it's worth pointing out |
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| 55 | | -if ! mount -t devtmpfs -o mode=0755 udev /dev; then |
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| 56 | | - echo "W: devtmpfs not available, falling back to tmpfs for /dev" |
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| 57 | | - mount -t tmpfs -o mode=0755 udev /dev |
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| 58 | | - [ -e /dev/console ] || mknod --mode=600 /dev/console c 5 1 |
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| 59 | | - [ -e /dev/kmsg ] || mknod --mode=644 /dev/kmsg c 1 11 |
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| 60 | | - [ -e /dev/null ] || mknod --mode=666 /dev/null c 1 3 |
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| 61 | | -fi |
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| 62 | | - |
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| 63 | | -mkdir /dev/pts |
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| 64 | | -mount -t devpts -o noexec,nosuid,gid=5,mode=0620 devpts /dev/pts || true |
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| 65 | | -mount -t tmpfs -o "nosuid,size=20%,mode=0755" tmpfs /run |
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| 66 | | -mkdir /run/initramfs |
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| 67 | | -# compatibility symlink for the pre-oneiric locations |
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| 68 | | -ln -s /run/initramfs /dev/.initramfs |
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| 69 | | - |
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| 70 | | -# Export relevant variables |
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| 71 | | -export ROOT= |
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| 72 | | -export ROOTDELAY= |
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| 73 | | -export ROOTFLAGS= |
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| 74 | | -export ROOTFSTYPE= |
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| 75 | | -export IP= |
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| 76 | | -export BOOT= |
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| 77 | | -export BOOTIF= |
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| 78 | | -export UBIMTD= |
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| 79 | | -export break= |
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| 80 | | -export init=/sbin/init |
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| 81 | | -export quiet=n |
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| 82 | | -export readonly=y |
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| 83 | | -export rootmnt=/root |
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| 84 | | -export debug= |
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| 85 | | -export panic= |
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| 86 | | -export blacklist= |
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| 87 | | -export resume= |
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| 88 | | -export resume_offset= |
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| 89 | | -export recovery= |
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| 90 | | - |
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| 91 | | -for i in /sys/devices/system/cpu/cpu*/online |
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| 92 | | -do |
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| 93 | | - case $i in |
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| 94 | | - '/sys/devices/system/cpu/cpu0/online') |
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| 95 | | - ;; |
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| 96 | | - '/sys/devices/system/cpu/cpu*/online') |
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| 97 | | - ;; |
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| 98 | | - *) |
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| 99 | | - echo 1 > $i |
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| 100 | | - ;; |
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| 101 | | - esac |
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| 102 | | -done |
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| 103 | | - |
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| 104 | | -while : |
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| 105 | | -do |
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| 106 | | - sleep 10 |
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| 107 | | -done |
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| 108 | | ------------------------------------------------------------------------- |
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| 109 | | - |
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| 110 | | -References: |
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| 111 | | -[1]: https://dracut.wiki.kernel.org/index.php/Main_Page |
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| 112 | | -[2]: http://blog.elastocloud.org/2015/06/rapid-linux-kernel-devtest-with-qemu.html |
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| 113 | | -[3]: https://www.centos.org/forums/viewtopic.php?t=51621 |
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| 16 | +# Manually verify that initrd contains needed binaries and libraries. |
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