knowledge/technology/linux/archiso.md

obj	arch-wiki	repo	rev
application	https://wiki.archlinux.org/title/Archiso	https://gitlab.archlinux.org/archlinux/archiso	2024-12-17

archiso

Archiso is a highly-customizable tool for building Arch Linux live CD/USB ISO images. The official images are built with archiso and include the following packages. It can be used as the basis for rescue systems, linux installers or other systems. This wiki article explains how to install archiso, and how to configure it to control aspects of the resulting ISO image such as included packages and files. Technical requirements and build steps can be found in the official project documentation. Archiso is implemented with a number of bash scripts. The core component of archiso is the mkarchiso command. Its options are documented in mkarchiso -h and not covered here.

Prepare a custom profile

Archiso comes with two profiles, releng and baseline.

• releng is used to create the official monthly installation ISO. It can be used as a starting point for creating a customized ISO image.
• baseline is a minimal configuration, that includes only the bare minimum packages required to boot the live environment from the medium.

If you wish to adapt or customize one of archiso's shipped profiles, copy it from /usr/share/archiso/configs/profile-name/ to a writable directory with a name of your choice. For example:

cp -r /usr/share/archiso/configs/releng/ archlive

Profile structure

An archiso profile contains configuration that defines the resulting ISO image. The profile structure is documented in /usr/share/doc/archiso/README.profile.rst.

An archiso profile consists of several configuration files and a directory for files to be added to the resulting image.

   profile/
   ├── airootfs/
   ├── efiboot/
   ├── syslinux/
   ├── grub/
   ├── bootstrap_packages.arch
   ├── packages.arch
   ├── pacman.conf
   └── profiledef.sh

The required files and directories are explained in the following sections.

profiledef.sh

This file describes several attributes of the resulting image and is a place for customization to the general behavior of the image.

The image file is constructed from some of the variables in profiledef.sh: <iso_name>-<iso_version>-<arch>.iso
(e.g. archlinux-202010-x86_64.iso).

• iso_name: The first part of the name of the resulting image (defaults to mkarchiso)

• iso_label: The ISO's volume label (defaults to MKARCHISO)

• iso_publisher: A free-form string that states the publisher of the resulting image (defaults to mkarchiso)

• iso_application: A free-form string that states the application (i.e. its use-case) of the resulting image (defaults
  to mkarchiso iso)

• iso_version: A string that states the version of the resulting image (defaults to "")

• install_dir: A string (maximum eight characters long, which must consist of [a-z0-9]) that states the
  directory on the resulting image into which all files will be installed (defaults to mkarchiso)

• buildmodes: An optional list of strings, that state the build modes that the profile uses. Only the following are
  understood:

  • bootstrap: Build a compressed file containing a minimal system to bootstrap from
  • iso: Build a bootable ISO image (implicit default, if no buildmodes are set)
  • netboot: Build artifacts required for netboot using iPXE

• bootmodes: A list of strings, that state the supported boot modes of the resulting image. Only the following are
  understood:

  • bios.syslinux.mbr: Syslinux for x86 BIOS booting from a disk
  • bios.syslinux.eltorito: Syslinux for x86 BIOS booting from an optical disc
  • uefi-ia32.grub.esp: GRUB for IA32 UEFI booting from a disk
  • uefi-ia32.grub.eltorito: GRUB for IA32 UEFI booting from an optical disc
  • uefi-x64.grub.esp: GRUB for x64 UEFI booting from a disk
  • uefi-x64.grub.eltorito: GRUB for x64 UEFI booting from an optical disc
  • uefi-ia32.systemd-boot.esp: systemd-boot for IA32 UEFI booting from a disk
  • uefi-ia32.systemd-boot.eltorito: systemd-boot for IA32UEFI booting from an optical disc
  • uefi-x64.systemd-boot.esp: systemd-boot for x64 UEFI booting from a disk
  • uefi-x64.systemd-boot.eltorito: systemd-boot for x64 UEFI booting from an optical disc
    Note that BIOS El Torito boot mode must always be listed before UEFI El Torito boot mode.

• arch: The architecture (e.g. x86_64) to build the image for. This is also used to resolve the name of the packages
  file (e.g. packages.x86_64)

• pacman_conf: The pacman.conf to use to install packages to the work directory when creating the image (defaults to
  the host's /etc/pacman.conf)

• airootfs_image_type: The image type to create. The following options are understood (defaults to squashfs):

  • squashfs: Create a squashfs image directly from the airootfs work directory
  • ext4+squashfs: Create an ext4 partition, copy the airootfs work directory to it and create a squashfs image from it
  • erofs: Create an EROFS image for the airootfs work directory

• airootfs_image_tool_options: An array of options to pass to the tool to create the airootfs image. mksquashfs and
  mkfs.erofs are supported. See mksquashfs --help or mkfs.erofs --help for all possible options

• bootstrap_tarball_compression: An array containing the compression program and arguments passed to it for
  compressing the bootstrap tarball (defaults to cat). For example: bootstrap_tarball_compression=(zstd -c -T0 --long -19).

• file_permissions: An associative array that lists files and/or directories who need specific ownership or
  permissions. The array's keys contain the path and the value is a colon separated list of owner UID, owner GID and
  access mode. E.g. file_permissions=(["/etc/shadow"]="0:0:400"). When directories are listed with a trailing backslash (/) all files and directories contained within the listed directory will have the same owner UID, owner GID, and access mode applied recursively.

bootstrap_packages.arch

All packages to be installed into the environment of a bootstrap image have to be listed in an architecture specific file (e.g. bootstrap_packages.x86_64), which resides top-level in the profile.

Packages have to be listed one per line. Lines starting with a # and blank lines are ignored.

This file is required when generating bootstrap images using the bootstrap build mode.

packages.arch

All packages to be installed into the environment of an ISO image have to be listed in an architecture specific file (e.g. packages.x86_64), which resides top-level in the profile.

Packages have to be listed one per line. Lines starting with a # and blank lines are ignored.

This file is required when generating ISO images using the iso or netboot build modes.

pacman.conf

A configuration for pacman is required per profile.

Some configuration options will not be used or will be modified:

• CacheDir: the profile's option is only used if it is not the default (i.e. /var/cache/pacman/pkg) and if it is
  not the same as the system's option. In all other cases the system's pacman cache is used.
• HookDir: it is always set to the /etc/pacman.d/hooks directory in the work directory's airootfs to allow
  modification via the profile and ensure interoparability with hosts using dracut
• RootDir: it is always removed, as setting it explicitely otherwise refers to the host's root filesystem (see
  man 8 pacman for further information on the -r option used by pacstrap)
• LogFile: it is always removed, as setting it explicitely otherwise refers to the host's pacman log file (see
  man 8 pacman for further information on the -r option used by pacstrap)
• DBPath: it is always removed, as setting it explicitely otherwise refers to the host's pacman database (see
  man 8 pacman for further information on the -r option used by pacstrap)

airootfs

This optional directory may contain files and directories that will be copied to the work directory of the resulting image's root filesystem.
The files are copied before packages are being installed to work directory location.
Ownership and permissions of files and directories from the profile's airootfs directory are not preserved. The mode will be 644 for files and 755 for directories, all of them will be owned by root. To set custom ownership and/or permissions, use file_permissions in profiledef.sh.

With this overlay structure it is possible to e.g. create users and set passwords for them, by providing airootfs/etc/passwd, airootfs/etc/shadow, airootfs/etc/gshadow (see man 5 passwd, man 5 shadow and man 5 gshadow respectively).
If user home directories exist in the profile's airootfs, their ownership and (and top-level) permissions will be altered according to the provided information in the password file.

Boot loader configuration

A profile may contain configuration for several boot loaders. These reside in specific top-level directories, which are explained in the following subsections.

The following custom template identifiers are understood and will be replaced according to the assignments of the respective variables in profiledef.sh:

• %ARCHISO_LABEL%: Set this using the iso_label variable in profiledef.sh.
• %INSTALL_DIR%: Set this using the install_dir variable in profiledef.sh.
• %ARCH%: Set this using the arch variable in profiledef.sh.

Additionally there are also custom template identifiers have harcoded values set by mkarchiso that cannot be overridden:

• %ARCHISO_UUID%: the ISO 9660 modification date in UTC, i.e. its "UUID",
• %ARCHISO_SEARCH_FILENAME%: file path on ISO 9660 that can be used by GRUB to find the ISO volume
  (for GRUB .cfg files only).

efiboot

This directory is mandatory when the uefi-x64.systemd-boot.esp or uefi-x64.systemd-boot.eltorito bootmodes are selected in profiledef.sh. It contains configuration for systemd-boot.

Note: The directory is a top-level representation of the systemd-boot configuration directories and files found in the root of an EFI system partition.

The custom template identifiers are only understood in the boot loader entry .conf files (i.e. not in loader.conf).

syslinux

This directory is mandatory when the bios.syslinux.mbr or the bios.syslinux.eltorito bootmodes are selected in profiledef.sh.
It contains configuration files for syslinux or isolinux , or pxelinux used in the resulting image.

The custom template identifiers are understood in all .cfg files in this directory.

grub

This directory is mandatory when any of the following bootmodes is used in profiledef.sh:

• uefi-ia32.grub.esp or
• uefi-ia32.grub.eltorito or
• uefi-x64.grub.esp or
• uefi-x64.grub.eltorito

It contains configuration files for GRUB used in the resulting image.

Customization

Selecting packages

Edit packages.x86_64 to select which packages are to be installed on the live system image, listing packages line by line.

Custom local repository

To add packages not located in standard Arch repositories (e.g. packages from the AUR or customized with the ABS), set up a custom local repository and add your custom packages to it. Then add your repository to pacman.conf as follows:

[customrepo]
SigLevel = Optional TrustAll
Server = file:///path/to/customrepo

Note

: The ordering within pacman.conf matters. To give top priority to your custom repository, place it above the other repository entries.
This pacman.conf is only used for building the image. It will not be used in the live environment.
Ensure that the repository is located in a directory accessible by the chrooted mkarchiso process, such as /tmp, to ensure the repository is read correctly during the image building process.

Packages from multilib

To install packages from the multilib repository, simply uncomment that repository in pacman.conf.

Adding files to image

The airootfs directory is used as the starting point for the root directory (/) of the live system on the image. All its contents will be copied over to the working directory before packages are installed.

Place any custom files and/or directories in the desired location under airootfs/. For example, if you have a set of iptables scripts on your current system you want to be used on your live image, copy them over as such:

cp -r /etc/iptables archlive/airootfs/etc

Similarly, some care is required for special configuration files that reside somewhere down the hierarchy. Missing parts of the directory structure can be simply created with mkdir.
Tip: To add a file to the install user's home directory, place it in archlive/airootfs/root/. To add a file to all other users home directories, place it in archlive/airootfs/etc/skel/.

Note

: Custom files that conflict with those provided by packages will be overwritten unless a package specifies them as backup files.

By default, permissions will be 644 for files and 755 for directories. All of them will be owned by the root user. To set different permissions or ownership for specific files and/or folders, use the file_permissions associative array in profiledef.sh.

Adding repositories to the image

To add a repository that can be used in the live environment, create a suitably modified pacman.conf and place it in archlive/airootfs/etc/.

If the repository also uses a key, place the key in archlive/airootfs/usr/share/pacman/keyrings/. The key file name must end with .gpg. Additionally, the key must be trusted. This can be accomplished by creating a GnuPG exported trust file in the same directory. The file name must end with -trusted. The first field is the key fingerprint, and the second is the trust. You can reference /usr/share/pacman/keyrings/archlinux-trusted for an example.

archzfs example

The files in this example are:

airootfs
├── etc
│   ├── pacman.conf
│   └── pacman.d
│       └── archzfs_mirrorlist
└── usr
    └── share
        └── pacman
            └── keyrings
                ├── archzfs.gpg
                └── archzfs-trusted

airootfs/etc/pacman.conf:

[archzfs]
Include = /etc/pacman.d/archzfs_mirrorlist

airootfs/etc/pacman.d/archzfs_mirrorlist:

Server = https://archzfs.com/$repo/$arch
Server = https://mirror.sum7.eu/archlinux/archzfs/$repo/$arch
Server = https://mirror.biocrafting.net/archlinux/archzfs/$repo/$arch
Server = https://mirror.in.themindsmaze.com/archzfs/$repo/$arch
Server = https://zxcvfdsa.com/archzfs/$repo/$arch

airootfs/usr/share/pacman/keyrings/archzfs-trusted:

DDF7DB817396A49B2A2723F7403BD972F75D9D76:4:

archzfs.gpg itself can be obtained directly from the repository site at https://archzfs.com/archzfs.gpg.

Kernel

Although both archiso's included profiles only have linux, ISOs can be made to include other or even multiple kernels.

First, edit packages.x86_64 to include kernel package names that you want. When mkarchiso runs, it will include all work_dir/airootfs/boot/vmlinuz-* and work_dir/boot/initramfs-*.img files in the ISO (and additionally in the FAT image used for UEFI booting).

mkinitcpio presets by default will build fallback initramfs images. For an ISO, the main initramfs image would not typically include the autodetect hook, thus making an additional fallback image unnecessary. To prevent the creation of an fallback initramfs image, so that it does not take up space or slow down the build process, place a custom preset in archlive/airootfs/etc/mkinitcpio.d/pkgbase.preset. For example, for linux-lts:

archlive/airootfs/etc/mkinitcpio.d/linux-lts.preset:

PRESETS=('archiso')

ALL_kver='/boot/vmlinuz-linux-lts'
ALL_config='/etc/mkinitcpio.conf'

archiso_image="/boot/initramfs-linux-lts.img"

Finally create boot loader configuration to allow booting the kernel(s).

Boot loader

Archiso supports syslinux for BIOS booting and GRUB or systemd-boot for UEFI booting. Refer to the articles of the boot loaders for information on their configuration syntax.

mkarchiso expects that GRUB configuration is in the grub directory, systemd-boot configuration is in the efiboot directory and syslinux configuration in the syslinux directory.

UEFI Secure Boot

If you want to make your archiso bootable on a UEFI Secure Boot enabled environment, you must use a signed boot loader.

systemd units

To enable systemd services/sockets/timers for the live environment, you need to manually create the symbolic links just as systemctl enable does it.

For example, to enable gpm.service, which contains WantedBy=multi-user.target, run:

mkdir -p archlive/airootfs/etc/systemd/system/multi-user.target.wants
ln -s /usr/lib/systemd/system/gpm.service archlive/airootfs/etc/systemd/system/multi-user.target.wants/

The required symlinks can be found out by reading the systemd unit, or if you have the service installed, by enabling it and observing the systemctl output.

Login manager

Starting X at boot is done by enabling your login manager's systemd service. If you do not know which .service to enable, you can easily find out in case you are using the same program on the system you build your ISO on. Just use:

ls -l /etc/systemd/system/display-manager.service

Now create the same symlink in archlive/airootfs/etc/systemd/system/.

Changing automatic login

The configuration for getty's automatic login is located under airootfs/etc/systemd/system/getty@tty1.service.d/autologin.conf.

You can modify this file to change the auto login user:

[Service]
ExecStart=
ExecStart=-/sbin/agetty --autologin username --noclear %I 38400 linux

Or remove autologin.conf altogether to disable auto login.

If you are using the serial console, create airootfs/etc/systemd/system/serial-getty@ttyS0.service.d/autologin.conf with the following content instead:

[Service]
ExecStart=
ExecStart=-/sbin/agetty -o '-p -- \\u' --noclear --autologin root --keep-baud 115200,57600,38400,9600 - $TERM

Users and passwords

To create a user which will be available in the live environment, you must manually edit archlive/airootfs/etc/passwd, archlive/airootfs/etc/shadow, archlive/airootfs/etc/group and archlive/airootfs/etc/gshadow.

Note

: If these files exist, they must contain the root user and group.

For example, to add a user archie. Add them to archlive/airootfs/etc/passwd following the passwd syntax:

root:x:0:0:root:/root:/usr/bin/zsh
archie:x:1000:1000::/home/archie:/usr/bin/zsh

Note

: The passwd file must end with a newline.

Add the user to archlive/airootfs/etc/shadow following the syntax of shadow. If you want to define a password for the user, generate a password hash with openssl passwd -6 and add it to the file. For example:

root::14871::::::
archie:$6$randomsalt$cij4/pJREFQV/NgAgh9YyBIoCRRNq2jp5l8lbnE5aLggJnzIRmNVlogAg8N6hEEecLwXHtMQIl2NX2HlDqhCU1:14871::::::

Otherwise, you may keep the password field empty, meaning that the user can log in with no password.

Add the user's group and the groups which they will part of to archlive/airootfs/etc/group according to group syntax. For example:

root:x:0:root
adm:x:4:archie
wheel:x:10:archie
uucp:x:14:archie
archie:x:1000:

Create the appropriate archlive/airootfs/etc/gshadow according to gshadow:

root:!*::root
archie:!*::

Make sure /etc/shadow and /etc/gshadow have the correct permissions:

archlive/profiledef.sh:

file_permissions=(
  ...
  ["/etc/shadow"]="0:0:0400"
  ["/etc/gshadow"]="0:0:0400"
)

After package installation, mkarchiso will create all specified home directories for users listed in archlive/airootfs/etc/passwd and copy work_directory/x86_64/airootfs/etc/skel/* to them. The copied files will have proper user and group ownership.

Changing the distribution name used in the ISO

Start by copying the file /etc/os-release into the etc/ folder in the rootfs. Then, edit the file accordingly. You can also change the name inside of GRUB and syslinux.

Adjusting the size of the root file system

When installing packages in the live environment, for example on hardware requiring DKMS modules, the default size of the root file system might not allow the download and installation of such packages due to its size.

To adjust the size on the fly:

mount -o remount,size=SIZE /run/archiso/cowspace

To adjust the size at the bootloader stage (as a kernel cmdline by pressing e or Tab) use the boot option:

cow_spacesize=SIZE

To adjust the size while building an image add the boot option to:

• efiboot/loader/entries/*.cfg
• grub/*.cfg
• syslinux/*.cfg

Build the ISO

Build an ISO which you can then burn to CD or USB by running:

mkarchiso -v -w /path/to/work_dir -o /path/to/out_dir /path/to/profile/

Replace /path/to/profile/ with the path to your custom profile, or with /usr/share/archiso/configs/releng/ if you are building an unmodified profile.

When run, the script will download and install the packages you specified to work_directory/x86_64/airootfs, create the kernel and init images, apply your customizations and finally build the ISO into the output directory.

Tip: If memory allows, it is preferred to place the working directory on tmpfs.

mkdir ./work
mount -t tmpfs -o size=1G tmpfs ./work
mkarchiso -v -w ./work -o /path/to/out_dir /path/to/profile/
umount -r ./work

Removal of work directory

Warning

: If mkarchiso is interrupted, run findmnt to make sure there are no mount binds before deleting it - otherwise, you may lose data (e.g. an external device mounted at /run/media/user/label gets bound within work/x86_64/airootfs/run/media/user/label during the build process).

The temporary files are copied into work directory. After successfully building the ISO , the work directory and its contents can be deleted. E.g.:

rm -rf /path/to/work_dir