Alpine Linux in a chroot: Difference between revisions

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= Setting up a 'edge' build environment in a chroot =
{{TOC right}}


This document explains how to set up an Alpine build environment in a chroot under a "normal" Linux distro, such as Arch, Debian, Fedora, Gentoo,  or Ubuntu. Once inside the chroot environment, you can build, debug and run alpine packages.
Inside the chroot environment, you can build, debug, and run Alpine packages or develop things. It's the most known way to do so without replacing your system or using a Virtual Machine.
This document explains how to set up an Alpine build environment in a chroot under a host Linux distro, that can also be used to install Alpine Linux from a non-Alpine Linux system or live environment.


== Introduction  ==
{{Tip|You can use the [https://github.com/alpinelinux/alpine-chroot-install/ alpine-chroot-install] script to do all these steps for you.}}


You will need a few Gigabytes to have enough pace for kernel compiling and storing all the binary packages and iso image.
== Requirements ==


== Create a build environment  ==
* Working Linux instalation where to perform all the process
* Linux kernel 2.6.22, with <code>curl</code> and <code>chroot</code> binary installed
* target media with at least 100M, 900MB for more complete solution as minimum
* internet connection


We are setting up our Build Environment in chroot.<br>
== Prerequisites ==


'''Note:''' The variables below:  
The variables below:  


*'''${build_dir}''' = You can name it whatever you like.
*'''${chroot_dir}''' = Should point to the new root directory
*'''${mirror}''' = Should be replaced with one of the available alpine-mirrors:
*'''${mirror}''' = Should be replaced with [https://dl-cdn.alpinelinux.org/alpine/MIRRORS.txt one of the available Alpine Linux mirrors].
*'''${arch}''' =  Should be the cpu architecture like x86 (i386) or amd64(x86_64)..


Choose a mirror from the [http://dl-2.alpinelinux.org/alpine/MIRRORS.txt mirror list].
== Set up APK ==


<br> Let's start by getting the latest apk static package:  
Download the latest apk static package (replace <tt>${version}</tt> with actual version):


{{Tip|In the command below, replace x86_64 with x86 if running on a 32bit installation}}
{{Cmd|curl -LO ${mirror}/latest-stable/main/${arch}/apk-tools-static-${version}.apk}}


{{Cmd|wget http://dl-3.alpinelinux.org/alpine/v2.2/main/x86_64/apk-tools-static-2.1.0-r1.apk}}
.apk packages are just gzipped tarballs, you can unpack them using:
{{Cmd|tar -xzf apk-tools-static-*.apk}}


Unpack the tarball
== Install the alpine base installation onto the chroot ==
{{Cmd|tar -xzf apk-tools-static-2.1.0-r1.apk}}


We are setting up a basic chroot:
{{Cmd|./sbin/apk.static -X ${mirror}/latest-stable/main -U --allow-untrusted -p ${chroot_dir} --initdb add alpine-base}}


{{Cmd|mkdir ${build_dir}
== Seting up the chroot ==
sudo ./sbin/apk.static -X ${mirror}/v2.2/main -U --allow-untrusted --root ${build_dir} --initdb add alpine-base alpine-sdk
mkdir -p ./${build_dir}/proc
sudo mount --bind /proc ./${build_dir}/proc}}


Lets setup our needed devices:
Before you change root to the new directory, you need to create the required devices


{{Cmd|sudo mknod -m 666 ./${build_dir}/dev/full c 1 7
===== Method 1.a Simple way: Using the host's /dev =====
sudo mknod -m 666 ./${build_dir}/dev/ptmx c 5 2
sudo mknod -m 644 ./${build_dir}/dev/random c 1 8
sudo mknod -m 644 ./${build_dir}/dev/urandom c 1 9
sudo mknod -m 666 ./${build_dir}/dev/zero c 1 5
sudo mknod -m 666 ./${build_dir}/dev/tty c 5 0}}
seems as /dev/null is wrong


{{Cmd|sudo rm -f ./${build_dir}/dev/null && sudo mknod -m 666 ./${build_dir}/dev/null c 1 3}}
{{Cmd|mount -o bind /dev ${chroot_dir}/dev}}


We need a resolv.conf is needed for the DNS servers and the /root directory:
{{Note|Bind mounts can be made read-only which would limit the chroot from writing to the devices}}


{{Cmd|sudo cp /etc/resolv.conf ./${build_dir}/etc/
===== Method 1.b Manual way: Creating needed nodes =====
mkdir -p ./${build_dir}/root}}


If you don't want to copy the resolv.conf from the local machine, create this file with your DNS server entry.
{{Warning|Manually creating devices will only provide the ones that have been created}}
{{Cmd|echo 'nameserver 8.8.8.8' >/etc/resolv.conf}}


We are setting up apk mirrors:
{{Cmd|mknod -m 666 ${chroot_dir}/dev/full c 1 7
mknod -m 666 ${chroot_dir}/dev/ptmx c 5 2
mknod -m 644 ${chroot_dir}/dev/random c 1 8
mknod -m 644 ${chroot_dir}/dev/urandom c 1 9
mknod -m 666 ${chroot_dir}/dev/zero c 1 5
mknod -m 666 ${chroot_dir}/dev/tty c 5 0}}


{{Cmd|sudo mkdir -p ./${build_dir}/etc/apk
If you need SCSI disc access you can create the device nodes like this:
echo "${mirror}/v2.2/packages/main" > ./${build_dir}/etc/apk/repositories}}


At this point you should be able to enter your chroot:
{{Note|Every device can have 15 sub-nodes, you should always increment by 16 for every new device}}


{{Cmd|sudo chroot ./${build_dir} /bin/sh -l}}
{{Cmd|mknod -m 666 ${chroot_dir}/dev/sda b 8 0
mknod -m 666 ${chroot_dir}/dev/sda1 b 8 1
mknod -m 666 ${chroot_dir}/dev/sda2 b 8 2
mknod -m 666 ${chroot_dir}/dev/sda3 b 8 3
mknod -m 666 ${chroot_dir}/dev/sdb b 8 16
mknod -m 666 ${chroot_dir}/dev/sdb1 b 8 17}}


If you are using Alpine as a Native build system you will have to make sure that chroot can run chmod. Add following to /etc/sysctl.conf
==== Make the process fs and /sys fs available ====


kernel.grsecurity.chroot_deny_chmod = 0
{{Cmd|mount -t proc none ${chroot_dir}/proc
mount -o bind /sys ${chroot_dir}/sys}}


Then run the following command
==== Set up name resolution ====


{{Cmd|sysctl -p}}
A resolv.conf is needed for name resolution:


Now you can move on to [[Creating_an_Alpine_package|creating packages for Alpine.]]
You can either copy your host's resolv.conf:
{{Cmd|cp -L /etc/resolv.conf ${chroot_dir}/etc/}}


== Alpine Linux in a chroot on Fedora ==
or instead you can create a new one (this example uses OpenDNS):
{{Cmd|echo -e 'nameserver 8.8.8.8\nnameserver 2620:0:ccc::2' > ${chroot_dir}/etc/resolv.conf}}


If you want to generate a chroot on a Fedora based system, you can use this [http://files.affolter-engineering.ch/alpinelinux/chroot/alpine-chroot.sh script].
==== Prepare the APK repositories ====


{{Note|Maybe you are able to use this script on other distribution but this is not tested.}}
Set up APK main repository (replace <tt>${branch}</tt> with the latest stable branch name, e.g. v3.3):
 
{{Cmd|mkdir -p ${chroot_dir}/etc/apk
echo "${mirror}/${branch}/main" > ${chroot_dir}/etc/apk/repositories}}
 
{{Warning|The chroot methods are commonly used to have Alpine installed in a existing system. Because of this, the steps for preparing a bootloader are not included.}}
 
==== Entering your chroot ====
 
You then can enter your chroot by running this command as the root user (UID 0).
 
{{Cmd|chroot ${chroot_dir} /bin/ash -l}}
 
==== Preparing init services ====
 
If you plan to use your chroot with a init system or setup a new system on another device you should add these services:
 
{{Cmd|rc-update add devfs sysinit
rc-update add dmesg sysinit
rc-update add mdev sysinit
 
rc-update add hwclock boot
rc-update add modules boot
rc-update add sysctl boot
rc-update add hostname boot
rc-update add bootmisc boot
rc-update add syslog boot
 
rc-update add mount-ro shutdown
rc-update add killprocs shutdown
rc-update add savecache shutdown}}
 
<!-- TODO: Create a page dedicated to installing GRUB and Syslinux and reference them here
==== Adding a bootloader ====
 
[[GRUB]]
 
{{Warning|Run this only if Alpine was installed to a dedicated partiton mounted at the <nowiki>${chroot_dir}</nowiki> directory.}}
 
{{Cmd|<nowiki>apk add syslinux
dd if=/usr/share/syslinux/mbr.bin of=/dev/sda</nowiki>}}
 
{{Warning|Make sure that the device you give the <code>dd</code> utility is the one you want to install the bootloader to. This process cannot be reverted!}}
-->
= Troubleshooting =
 
== Hardened kernels or alpine as chroot host ==
 
If you are using Alpine as a native build system you will have to make sure that you can run <code>chmod</code> from a chroot. Add the following to <code>/etc/sysctl.conf</code>
 
<code>kernel.grsecurity.chroot_deny_chmod = 0</code>
 
Then reload the sysctl configuration
 
<code>sysctl -p</code>
 
== chroot: cannot run command ' ... Exec format error ==
 
This usually indicates that you booted with one architecture (e.g. armf) and are trying to chroot into another (e.g. x86_64). The binaries must be built for the architecture that the host runs!
 
Note that with '''one exception you can run 32 bit x86 chroot in x86_64, but not viceversa'''!
 
== WARNING: Ignoring APKINDEX.xxxx.tar.gz ==
 
Make sure <code>${chroot_dir}/etc/apk/repositories</code> is valid and run:
 
<code>apk update</code>
 
= External links =
 
* You can also use script [https://github.com/alpinelinux/alpine-chroot-install/ alpine-chroot-install]
* https://web.archive.org/web/20190808203313/https://isc.sans.edu/forums/diary/Forensic+use+of+mount+bind/22854/
* Alpine Linux in a chroot on Fedora : https://git.alpinelinux.org/cgit/user/fab/scripts/tree/alpine-chroot.sh {{dead link}} script
* Alpine Linux aarch64 in a chroot on AWS Linux : https://gist.github.com/emolitor/0567e51c0ce04f4b025fc78d2cf0b4f1 script
 
[[Category: Installation]]
[[category: System Administration]]

Latest revision as of 19:33, 30 August 2023

Inside the chroot environment, you can build, debug, and run Alpine packages or develop things. It's the most known way to do so without replacing your system or using a Virtual Machine. This document explains how to set up an Alpine build environment in a chroot under a host Linux distro, that can also be used to install Alpine Linux from a non-Alpine Linux system or live environment.

Tip: You can use the alpine-chroot-install script to do all these steps for you.

Requirements

  • Working Linux instalation where to perform all the process
  • Linux kernel 2.6.22, with curl and chroot binary installed
  • target media with at least 100M, 900MB for more complete solution as minimum
  • internet connection

Prerequisites

The variables below:

  • ${chroot_dir} = Should point to the new root directory
  • ${mirror} = Should be replaced with one of the available Alpine Linux mirrors.
  • ${arch} = Should be the cpu architecture like x86 (i386) or amd64(x86_64)..

Set up APK

Download the latest apk static package (replace ${version} with actual version):

curl -LO ${mirror}/latest-stable/main/${arch}/apk-tools-static-${version}.apk

.apk packages are just gzipped tarballs, you can unpack them using:

tar -xzf apk-tools-static-*.apk

Install the alpine base installation onto the chroot

./sbin/apk.static -X ${mirror}/latest-stable/main -U --allow-untrusted -p ${chroot_dir} --initdb add alpine-base

Seting up the chroot

Before you change root to the new directory, you need to create the required devices

Method 1.a Simple way: Using the host's /dev

mount -o bind /dev ${chroot_dir}/dev

Note: Bind mounts can be made read-only which would limit the chroot from writing to the devices
Method 1.b Manual way: Creating needed nodes
Warning: Manually creating devices will only provide the ones that have been created


mknod -m 666 ${chroot_dir}/dev/full c 1 7 mknod -m 666 ${chroot_dir}/dev/ptmx c 5 2 mknod -m 644 ${chroot_dir}/dev/random c 1 8 mknod -m 644 ${chroot_dir}/dev/urandom c 1 9 mknod -m 666 ${chroot_dir}/dev/zero c 1 5 mknod -m 666 ${chroot_dir}/dev/tty c 5 0

If you need SCSI disc access you can create the device nodes like this:

Note: Every device can have 15 sub-nodes, you should always increment by 16 for every new device

mknod -m 666 ${chroot_dir}/dev/sda b 8 0 mknod -m 666 ${chroot_dir}/dev/sda1 b 8 1 mknod -m 666 ${chroot_dir}/dev/sda2 b 8 2 mknod -m 666 ${chroot_dir}/dev/sda3 b 8 3 mknod -m 666 ${chroot_dir}/dev/sdb b 8 16 mknod -m 666 ${chroot_dir}/dev/sdb1 b 8 17

Make the process fs and /sys fs available

mount -t proc none ${chroot_dir}/proc mount -o bind /sys ${chroot_dir}/sys

Set up name resolution

A resolv.conf is needed for name resolution:

You can either copy your host's resolv.conf:

cp -L /etc/resolv.conf ${chroot_dir}/etc/

or instead you can create a new one (this example uses OpenDNS):

echo -e 'nameserver 8.8.8.8\nnameserver 2620:0:ccc::2' > ${chroot_dir}/etc/resolv.conf

Prepare the APK repositories

Set up APK main repository (replace ${branch} with the latest stable branch name, e.g. v3.3):

mkdir -p ${chroot_dir}/etc/apk echo "${mirror}/${branch}/main" > ${chroot_dir}/etc/apk/repositories

Warning: The chroot methods are commonly used to have Alpine installed in a existing system. Because of this, the steps for preparing a bootloader are not included.


Entering your chroot

You then can enter your chroot by running this command as the root user (UID 0).

chroot ${chroot_dir} /bin/ash -l

Preparing init services

If you plan to use your chroot with a init system or setup a new system on another device you should add these services:

rc-update add devfs sysinit rc-update add dmesg sysinit rc-update add mdev sysinit rc-update add hwclock boot rc-update add modules boot rc-update add sysctl boot rc-update add hostname boot rc-update add bootmisc boot rc-update add syslog boot rc-update add mount-ro shutdown rc-update add killprocs shutdown rc-update add savecache shutdown

Troubleshooting

Hardened kernels or alpine as chroot host

If you are using Alpine as a native build system you will have to make sure that you can run chmod from a chroot. Add the following to /etc/sysctl.conf

kernel.grsecurity.chroot_deny_chmod = 0

Then reload the sysctl configuration

sysctl -p

chroot: cannot run command ' ... Exec format error

This usually indicates that you booted with one architecture (e.g. armf) and are trying to chroot into another (e.g. x86_64). The binaries must be built for the architecture that the host runs!

Note that with one exception you can run 32 bit x86 chroot in x86_64, but not viceversa!

WARNING: Ignoring APKINDEX.xxxx.tar.gz

Make sure ${chroot_dir}/etc/apk/repositories is valid and run:

apk update

External links

Retrieved from "https://wiki.alpinelinux.org/w/index.php?title=Alpine_Linux_in_a_chroot&oldid=24849"