Alpine Linux in a chroot: Difference between revisions

Revision as of 07:09, 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: Using alpine-chroot-install script is recommended as it takes seconds to prepare a chroot and install fresh Alpine Linux including gcc build environment.

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

The below variables are used in this page, replace them by actual values:

${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..

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. 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

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

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

If you plan to use your chroot to setup a new Alpine Linux system and boot from it enter your chroot and follow the steps given in the Syslinux bootloader 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: @@
 {{TOC right}}
-Inside the [[Chroot|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.
+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.
-{{Tip|You can use the [https://github.com/alpinelinux/alpine-chroot-install/ alpine-chroot-install] script to do all these steps for you.}}
+{{Tip| Using [[#alpine-chroot-install script|alpine-chroot-install]] script is recommended as it takes seconds to prepare a chroot and install fresh Alpine Linux including gcc build environment.}}
-== Requirements ==
+== Prerequisites ==
 * Working Linux instalation where to perform all the process
@@ Line 12: / Line 12: @@
 * internet connection
-== Prerequisites ==
+The below variables are used in this page, replace them by actual values:
+*'''${chroot_dir}''' = Should point to the new root directory(eg./alpine or /var/chroots/alpine)
+*'''${mirror}''' = Should be replaced with [https://dl-cdn.alpinelinux.org/alpine/MIRRORS.txt one of the available Alpine Linux mirrors].
+*'''${arch}''' =  Should be the cpu architecture like '''x86_64''' for current amd64 or '''x86''' for older i386..
-The variables below:
+== alpine-chroot-install script ==
-*'''${chroot_dir}''' = Should point to the new root directory
+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. It takes seconds to prepare a chroot, install fresh Alpine Linux including gcc build environment and execute first command!
-*'''${mirror}''' = Should be replaced with [https://dl-cdn.alpinelinux.org/alpine/MIRRORS.txt one of the available Alpine Linux mirrors].
-*'''${arch}''' =  Should be the cpu architecture like x86 (i386) or amd64(x86_64)..
-== Set up APK ==
+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.
-Download the latest apk static package (replace <tt>${version}</tt> with actual version):
+== Manual set up of Chroot ==
-{{Cmd|curl -LO ${mirror}/latest-stable/main/${arch}/apk-tools-static-${version}.apk}}
+=== Installation ===
-.apk packages are just gzipped tarballs, you can unpack them using:
+Download the latest apk static package by replacing the variables like <tt>${version}</tt> with actual version found on the chosen Download mirror: {{Cmd|curl -LO ${mirror}/latest-stable/main/${arch}/apk-tools-static-${version}.apk}}
-{{Cmd|tar -xzf apk-tools-static-*.apk}}
-== Install the alpine base installation onto the chroot ==
+.apk packages are just gzipped tarballs, you can unpack them using: {{Cmd|tar -xzf apk-tools-static-*.apk}}
-{{Cmd|./sbin/apk.static -X ${mirror}/latest-stable/main -U --allow-untrusted -p ${chroot_dir} --initdb add alpine-base}}
+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}}
-== Seting up the chroot ==
+=== Create the required devices ===
-Before you change root to the new directory, you need to 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.a Simple way: Using the host's /dev =====
+==== Method 1: Using the host's /dev ====
 {{Cmd|mount -o bind /dev ${chroot_dir}/dev}}
@@ Line 43: / Line 44: @@
 {{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 =====
+==== Method 2: Creating needed nodes in the manually ====
 {{Warning|Manually creating devices will only provide the ones that have been created}}
@@ Line 65: / Line 66: @@
 mknod -m 666 ${chroot_dir}/dev/sdb1 b 8 17}}
-==== Make the process fs and /sys fs available ====
+=== Make the process fs and /sys fs available ===
 {{Cmd|mount -t proc none ${chroot_dir}/proc
 mount -o bind /sys ${chroot_dir}/sys}}
-==== Set up name resolution ====
+=== Set up name resolution ===
 A resolv.conf is needed for name resolution:
@@ Line 80: / Line 81: @@
 {{Cmd|echo -e 'nameserver 8.8.8.8\nnameserver 2620:0:ccc::2' > ${chroot_dir}/etc/resolv.conf}}
-==== Prepare the APK repositories ====
+=== Prepare the APK repositories ===
 Set up APK main repository (replace <tt>${branch}</tt> with the latest stable branch name, e.g. v3.3):
@@ Line 87: / Line 88: @@
 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 ===
+Enter your chroot by running this command as the root user (UID 0): {{Cmd|chroot ${chroot_dir} /bin/ash -l}}
-==== Entering your chroot ====
+== using chroot for other purposes ==
-You then can enter your chroot by running this command as the root user (UID 0): {{Cmd|chroot ${chroot_dir} /bin/ash -l}}
+The above chroot method is commonly used to have Alpine Linux installed in a existing system. If you plan to use your chroot for other purposes, then the following steps are needed.
-==== Preparing init services ====
+=== Preparing init services ===
 If you plan to use your chroot with a init system or setup a new system on another device you should add these services:
 {{Cmd|rc-update add devfs sysinit
 rc-update add dmesg sysinit
@@ Line 112: / Line 114: @@
 rc-update add savecache shutdown}}
-<!-- TODO: Create a page dedicated to installing GRUB and Syslinux and reference them here
+=== Installing bootloader ===
-==== Adding a bootloader ====
-[[GRUB]]
-{{Warning|Run this only if Alpine was installed to a dedicated partiton mounted at the <nowiki>${chroot_dir}</nowiki> directory.}}
+{{Warning|Bootloaders can be installed only if Alpine Linux chroot was installed to a dedicated partiton mounted at the <nowiki>${chroot_dir}</nowiki> directory.}}
-{{Cmd|<nowiki>apk add syslinux
+If you plan to use your chroot to setup a new Alpine Linux system and boot from it [[#Entering your chroot|enter your chroot]] and follow the steps given in the [[Bootloaders#Syslinux|Syslinux]] bootloader page.
-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 ==