Alpine Linux in a chroot: Difference between revisions

Latest revision as of 11:00, 16 June 2025

This page explains how to set up an Alpine Linux chroot environment under a host Linux distro. 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 chroot can also be used to install Alpine Linux from a non-Alpine Linux system or live environment.

Tip: Use alpine-chroot-install script to setup Alpine Linux chroot build environment on any linux host in few seconds.

Prerequisites

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

alpine-chroot-install script

The official alpine-chroot-install script simplifies installation of Alpine Linux build environment on any x86_64 Linux system using chroot. With this script, it takes seconds to prepare a chroot, install fresh Alpine Linux including gcc build environment and execute first command!

The script provides commands to enter-chroot and destroy the chroot. Refer to the documentation page for more information.

Manual set up of chroot

The below variables are used in this page:

${chroot_dir} = Should point to the new root directory(eg./alpine or /var/chroots/alpine)
${mirror} = Should be replaced with one of the available Alpine Linux mirrors.
${arch} = Should be the cpu architecture like x86_64 for current amd64 or x86 for older i386.

Installation

Download the latest apk static package by replacing the variables like ${version} with actual version found on the chosen Download mirror:

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 Linux base installation onto the chroot.

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

Create the required devices

Before you can change root to the new directory i.e ${chroot_dir}, you need to create the required devices

Method 1: 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 2: Creating needed nodes in the manually

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

Entering your chroot

Enter your chroot by running this command as the root user (UID 0):

chroot ${chroot_dir} /bin/ash -l

Using chroot for other purposes

The above chroot method is commonly used to have Alpine Linux installed in a existing system. If you plan to use your chroot for other purposes, then the following steps are needed.

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

Installing bootloader

If you plan to use your chroot to setup a new Alpine Linux system and boot from it, you need a bootloader.

Warning: Bootloaders can be installed only if Alpine Linux chroot was installed to a dedicated partiton mounted at the ${chroot_dir} directory.

If you have a dedicated partition in which the chroot is installed, enter your chroot and follow the steps given in the Syslinux page.

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

@@ Line 1: / Line 1: @@
-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. The guide can also be used to install Alpine Linux from a non-Alpine Linux livecd such as Ubuntu or System rescue CD.
+{{TOC right}}
-This example installation of Alpine Linux in a chroot will work with the lastest release. But it's also possible to make a chroot with '''[[Edge|edge]]''' or older releases of Alpine Linux to test backports.
-== Requirements ==
+This page explains how to set up an Alpine Linux [[Chroot|chroot]] environment under a host Linux distro. 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 chroot can also be used to install Alpine Linux from a non-Alpine Linux system or live environment.
-For the base Alpine Linux you will only need around 6MB of free space; though to build packages you'll need at least 500 MB.
+{{Tip|Use [[#alpine-chroot-install script|alpine-chroot-install script]] to setup Alpine Linux chroot build environment on any linux host in few seconds.}}
 == Prerequisites ==
-The variables below:
-*'''${chroot_dir}''' = Should point to the chroot directory where you
+* Working Linux instalation where to perform all the process
-*'''${mirror}''' = Should be replaced with [http://dl-2.alpinelinux.org/alpine/MIRRORS.txt one of the available Alpine Linux mirrors].
+* 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
+== alpine-chroot-install script ==
+The official [https://github.com/alpinelinux/alpine-chroot-install/ alpine-chroot-install] script simplifies installation of Alpine Linux build environment on any x86_64 Linux system using chroot. With this script, it takes seconds to prepare a chroot, install fresh Alpine Linux including gcc build environment and execute first command!
+The script provides commands to {{ic|enter-chroot}} and {{ic|destroy}} the chroot. Refer to the [https://github.com/alpinelinux/alpine-chroot-install/blob/master/alpine-chroot-install documentation] page for more information.
+== Manual set up of chroot ==
+The below variables are used in this page:
+*'''${chroot_dir}''' = Should point to the new root directory(eg./alpine or /var/chroots/alpine)
+*'''${mirror}''' = Should be replaced with [https://dl-cdn.alpinelinux.org/alpine/MIRRORS.txt one of the available Alpine Linux mirrors].
+*'''${arch}''' =  Should be the cpu architecture like '''x86_64''' for current amd64 or '''x86''' for older i386.
-== Set up APK ==
+=== Installation ===
-Download the latest apk static package:
+Download the latest apk static package by replacing the variables like <tt>${version}</tt> with actual version found on the chosen Download mirror: {{Cmd|curl -LO ${mirror}/latest-stable/main/${arch}/apk-tools-static-${version}.apk}}
-{{Tip|In the command below, replace x86_64 with x86 if running on a 32 bit installation}}
+{{ic|.apk}} packages are just gzipped tarballs, you can unpack them using: {{Cmd|tar -xzf apk-tools-static-*.apk}}
-{{Warning|You will need Kernel version 2.6.22 or later to use apk-tools-static}}
+Install the Alpine Linux base installation onto the chroot. {{Cmd|./sbin/apk.static -X ${mirror}/latest-stable/main -U --allow-untrusted -p ${chroot_dir} --initdb add alpine-base}}
-{{Cmd|wget ${mirror}/v3.0/main/x86_64/apk-tools-static-2.4.4-r0.apk}}
+=== Create the required devices ===
-.apk packages are just gzipped tarballs, unpack using:
+Before you can change root to the new directory i.e ${chroot_dir}, you need to create the required devices
-{{Cmd|mkdir apk-tools-static
-tar -xzf apk-tools-static-2.4.4-r0.apk -C apk-tools-static}}
-== Install the alpine base installation onto the chroot ==
+==== Method 1: Using the host's /dev ====
-{{Cmd|./apk-tools-static/sbin/apk.static -X ${mirror}/v3.0/main -U --allow-untrusted --root ${chroot_dir} --initdb add alpine-base}}
+{{Cmd|mount -o bind /dev ${chroot_dir}/dev}}
-== Set up the chroot ==
+{{Note|Bind mounts can be made read-only which would limit the chroot from writing to the devices}}
-Set up some devices in the chroot
+==== Method 2: Creating needed nodes in the manually ====
-{{Tip|Manually creating devices is not needed if you choose to mount /dev of the hosts in the chroot described later.}}
+{{Warning|Manually creating devices will only provide the ones that have been created}}
 {{Cmd|mknod -m 666 ${chroot_dir}/dev/full c 1 7
@@ Line 41: / Line 55: @@
 mknod -m 666 ${chroot_dir}/dev/tty c 5 0}}
-If you need SCSI disc access:
+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}}
 {{Cmd|mknod -m 666 ${chroot_dir}/dev/sda b 8 0
@@ Line 47: / Line 63: @@
 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/sda4 b 8 4
-mknod -m 666 ${chroot_dir}/dev/sda5 b 8 5
-mknod -m 666 ${chroot_dir}/dev/sda6 b 8 6
 mknod -m 666 ${chroot_dir}/dev/sdb b 8 16
-mknod -m 666 ${chroot_dir}/dev/sda1 b 8 17
+mknod -m 666 ${chroot_dir}/dev/sdb1 b 8 17}}
-mknod -m 666 ${chroot_dir}/dev/sda2 b 8 18
-mknod -m 666 ${chroot_dir}/dev/sda3 b 8 19
+=== Make the process fs and /sys fs available ===
-mknod -m 666 ${chroot_dir}/dev/sda4 b 8 20
-mknod -m 666 ${chroot_dir}/dev/sda5 b 8 21
+{{Cmd|mount -t proc none ${chroot_dir}/proc
-mknod -m 666 ${chroot_dir}/dev/sda6 b 8 22}}
+mount -o bind /sys ${chroot_dir}/sys}}
+=== Set up name resolution ===
 A resolv.conf is needed for name resolution:
-{{Cmd|cp /etc/resolv.conf ${chroot_dir}/etc/
+You can either copy your host's resolv.conf:
-mkdir -p ${chroot_dir}/root}}
+{{Cmd|cp -L /etc/resolv.conf ${chroot_dir}/etc/}}
-If you don't want to copy the resolv.conf from the local machine, you can create a new one using Googles DNS servers:
+or instead you can create a new one (this example uses OpenDNS):
-{{Cmd|echo 'nameserver 8.8.8.8' > ${chroot_dir}/etc/resolv.conf}}
+{{Cmd|echo -e 'nameserver 8.8.8.8\nnameserver 2620:0:ccc::2' > ${chroot_dir}/etc/resolv.conf}}
-Set up APK mirror:
+=== Prepare the APK repositories ===
+Set up APK main repository (replace <tt>${branch}</tt> with the latest stable branch name, e.g. v3.3):
 {{Cmd|mkdir -p ${chroot_dir}/etc/apk
-echo "${mirror}/v3.0/main" > ${chroot_dir}/etc/apk/repositories}}
+echo "${mirror}/${branch}/main" > ${chroot_dir}/etc/apk/repositories}}
+=== Entering your chroot ===
+Enter your chroot by running this command as the root user (UID 0): {{Cmd|chroot ${chroot_dir} /bin/ash -l}}
+== Using chroot for other purposes ==
+The above chroot method is commonly used to have Alpine Linux installed in a existing system. If you plan to use your chroot for other purposes, then the following steps are needed.
+=== Preparing init services ===
+If you plan to use your chroot with a init system or setup a new system on another device you should add these services:
+{{Cmd|rc-update add devfs sysinit
+rc-update add dmesg sysinit
+rc-update add mdev sysinit
+rc-update add hwclock boot
+rc-update add modules boot
+rc-update add sysctl boot
+rc-update add hostname boot
+rc-update add bootmisc boot
+rc-update add syslog boot
+rc-update add mount-ro shutdown
+rc-update add killprocs shutdown
+rc-update add savecache shutdown}}
+=== Installing bootloader ===
-== Entering your chroot ==
+If you plan to use your chroot to setup a new Alpine Linux system and boot from it, you need a bootloader.
-At this point, Alpine has been succesfully installed onto the chroot directory. Before you chroot in you
+{{Warning|Bootloaders can be installed only if Alpine Linux chroot was installed to a dedicated partiton mounted at the <nowiki>${chroot_dir}</nowiki> directory.}} If you have a dedicated partition in which the chroot is installed, [[#Entering your chroot|enter your chroot]] and follow the steps given in the [[Bootloaders#Syslinux|Syslinux]] page.
-will probably want to mount /proc and /sys in the chroot:
-{{Cmd|mount -t proc none ${chroot_dir}/proc
+== Troubleshooting ==
-mount -o bind /sys ${chroot_dir}/sys}}
+=== Hardened kernels or alpine as chroot host ===
-If you don't want to create special device files yourself, mount the hosts device directory onto the chroot:
+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>
-{{Cmd|mount -o bind /dev ${chroot_dir}/dev}}
-You can now chroot:
+<code>kernel.grsecurity.chroot_deny_chmod = 0</code>
-{{Cmd|chroot ${chroot_dir} /bin/sh -l}}
-Alpine Linux has a great meta-package for building Alpine packages from source available called alpine-sdk. To install, run:
+Then reload the sysctl configuration:
-{{Cmd|apk add alpine-sdk}}
-If you are using Alpine as a Native build system you will have to make sure that chroot can run chmod. Add following to /etc/sysctl.conf
+<code>sysctl -p</code>
- kernel.grsecurity.chroot_deny_chmod = 0
+=== chroot: cannot run command ' ... Exec format error ===
-Then run the following command
+This usually indicates that you booted with one architecture (e.g. armf) and are trying to chroot into another (e.g. x86_64). The binaries must be built for the architecture that the host runs!
-{{Cmd|sysctl -p}}
+Note that with '''one exception you can run 32 bit x86 chroot in x86_64, but not viceversa'''!
-== Alpine Linux in a chroot on Fedora ==
+=== WARNING: Ignoring APKINDEX.xxxx.tar.gz ===
-If you want to generate a chroot on a Fedora based system, you can use this [http://git.alpinelinux.org/cgit/fab/scripts/tree/alpine-chroot.sh script].
+Make sure <code>${chroot_dir}/etc/apk/repositories</code> is valid and run: {{Cmd|# apk update}}
-{{Note|Maybe you are able to use this script on other distribution but this is not tested.}}
+== See also ==
-= Troubleshooting =
+*[https://github.com/alpinelinux/alpine-chroot-install/ alpine-chroot-install]
-== WARNING: Ignoring APKINDEX.xxxx.tar.gz ==
+* https://web.archive.org/web/20190808203313/https://isc.sans.edu/forums/diary/Forensic+use+of+mount+bind/22854/
-Make sure ${chroot_dir}/etc/apk/repositories is valid and inside the chroot run:
+* Alpine Linux in a chroot on Fedora : https://git.alpinelinux.org/cgit/user/fab/scripts/tree/alpine-chroot.sh {{dead link}} script
-{{Cmd|apk update}}
+* Alpine Linux aarch64 in a chroot on AWS Linux : https://gist.github.com/emolitor/0567e51c0ce04f4b025fc78d2cf0b4f1 script
-[[Category:Installation]]
+[[Category: Installation]]
+[[category: System Administration]]