Poster of Linux kernelThe best gift for a Linux geek


Section: User Contributed Perl Documentation (1) Updated: 2010-08-25
Local index Up


multistrap - multiple repository bootstraps  


 multistrap [-a ARCH] [-d DIR] -f CONFIG_FILE
 multistrap [--simulate] -f CONFIG_FILE
 multistrap -?|-h|--help|--version



-?|-h|--help|--version - output the help text and exit successfully.

--dry-run - collate all the configuration settings and output a bare summary.

--simulate - same as --dry-run

(The following options can also be set in the configuration file.)

-a|--arch - architecture of the packages to put into the multistrap.

-d|--dir - directory into which the bootstrap will be installed.

-f|--file - configuration file for multistrap [required]

--tidy-up - remove apt cache data, downloaded Packages files and the apt package cache. Same as cleanup=true.

--no-auth - allow the use of unauthenticated repositories. Same as noauth=true

--source-dir DIR - move the contents of var/cache/apt/archives/ from inside the chroot to the specified external directory, then add the Debian source packages for each used binary. Same as retainsources=DIR If the specified directory does not exist, nothing is done. Requires --tidy-up in order to calculate the full list of source packages, including dependencies.  


multistrap provides a debootstrap-like method based on apt and extended to provide support for multiple repositories, using a configuration file to specify the relevant suites, architecture, extra packages and the mirror to use for each bootstrap.

The aim is to create a complete bootstrap / root filesystem with all packages installed and configured, instead of just the base system.

Example configuration:

 # same as --tidy-up option if set to true
 # same as --no-auth option if set to true
 # keyring packages listed in each bootstrap will
 # still be installed.
 # extract all downloaded archives (default is true)
 # whether to add the /suite to be explicit about where apt
 # needs to look for packages. Default is false.
 # aptsources is a list of sections to be used
 # the /etc/apt/sources.list.d/multistrap.sources.list
 # of the target. Order is not important
 # the bootstrap option determines which repository
 # is used to calculate the list of Priority: required packages
 # and which packages go into the rootfs.
 # The order of sections is not important.

This will result in a completely normal debootstrap of Debian lenny from the specified mirror, for armel in '/opt/multistrap/'. (This configuration is retained in the package as /usr/share/multistrap/lenny.conf)

Specify a package to extend the multistrap to include that package and all dependencies of that package.

Specify more repositories for the bootstrap by adding new sections. Section names need to be listed in the bootstrap general option for the packages to be included in the bootstrap.

Specify which repositories will be available to the final system at boot by listing the section names in the aptsources general option, e.g. to exclude some internal sources or when using a local mirror when building the rootfs.

Section names are case-insensitive.

All dependencies are resolved only by apt, using all bootstrap repositories, to use only the most recent and most suitable dependencies. Note that multistrap turns off Install-Recommends so if the multistrap needs a package that is only a Recommended dependency, the recommended package needs to be specified in the packages line explicitly. See "Explicit suite specification" for more information on getting specific packages from specific suites.

'Architecture' and 'directory' can be overridden on the command line. Some other general options also have command line options.  


"aptsources" lists the sections which should be used to create the /etc/apt/sources.list.d/multistrap.list apt sources in the final system. Not all "aptsources" have to appear in the "bootstrap" section if you have some internal or local sources which are not accessible to the installed root filesystem.

"bootstrap" lists the sections which will be used to create the multistrap itself. Only packages listed in "bootstrap" will be downloaded and unpacked by multistrap.

Make sure "bootstrap" lists all sections you need for apt to be able to find all the packages to be unpacked for the multistrap.

(Older versions of multistrap supported the same option under the "debootstrap" name - this spelling is still supported but new configuration files should be "bootstrap" instead.  

General settings:

'arch' can be overridden on the command line using the "--arch" option.

'directory' specifies the top level directory where the bootstrap will be created - it is not packed into a .tgz once complete.

'bootstrap' lists the Sections which will be used to specify the packages which will be downloaded (and optionally unpacked) into the bootstrap.

'aptsources' lists the Sections which will be used to specify the apt sources in the final system, e.g. if you need to use a local repository to generate the rootfs which will not be available to the device at runtime, list that section in "bootstrap" but not in "aptsources".

If you want a package to be in the rootfs, it must be specified in the "bootstrap" list under General.

The order of section names in either list is not important.

As with debootstrap, multistrap will continue after errors, as long as the configuration file can be correctly parsed.

multistrap also implements the machine:variant support originally used in Emdebian Crush, although in a different implementation. Using the cascading configuration support, particular machine:variant combinations can be supported by simple changes on the command line.

Setting "tarballname" to true also packs up the final filesystem into a tarball.

Note that multistrap ignores any unrecognised options in the config file - this allows for backwards-compatible behaviour as well as overloading the multistrap config files to support other tools (like pbuilder). Use the "--simulate" option to see the combined configuration settings.  

Section settings


The section name (in [] brackets) needs to be unique for this configuration file and any configuration files which this file includes. Section names are case insensitive (all comparisons happen after conversion to lower case).

'packages' is the list of packages to be added when this Section is listed in "bootstrap".

'source' is the apt source to use for this Section. (To use a local source on the same machine, ensure you use "copy://" not "file://", so that apt is told to copy the packages into the rootfs instead of assuming it can try to download them later - because that ``later'' will never actually happen.

'keyring' lists the package which contains the key used by the source listed in this Section. If no keyring is specified, the "noauth" option must be set to true. See Secure Apt.

'suite' is the suite to use from this source. Note that this must be the suite, not the codename.

Suites change from time to time: (oldstable, stable, testing, sid) The codename (etch, lenny, squeeze, sid) does not change.  

Secure Apt

To use authenticated apt repositories, multistrap either needs to be able to install an appropriate keyring package from the existing apt sources outside the multistrap environment or have the relevant keys already configured using apt-key on the host system.

If relevant packages exist, specify them in the 'keyring' option for each repository. multistrap will then check that apt has already installed this package so that the repository can be authenticated before any packages are downloaded from it.

Note that all repositories to be used with multistrap must be authenticated or apt will fail. Similarly, secure apt can only be disabled for all repositories (by using the --no-auth command line option or setting the general noauth option in the configuration file), even if only one repository does not have a suitable keyring available. Not all packages need keyring packages, if you configure apt-key appropriately.

The keyring package(s) will also be installed inside the multistrap environment to match the installed apt sources for the multistrap.

All configuration of apt-key needs to be done for the machine running multistrap itself.  


multistrap is stateless - if the directory exists, it will simply proceed as normal and apt will try to pick up where it left off.  

Root Filesystem Configuration

multistrap unpacks the downloaded packages but other stages of system configuration are not attempted. Examples include:


Any device-specific device nodes will also need to be created using MAKEDEV or "" - a helper script that can work around some of the issues with MAKEDEV. requires a device table file along the lines of the one in the mtd-utils source package. See /usr/share/doc/multistrap/examples/device_table.txt

Once multistrap has successfully created the basic file and directory layout, other device-specific scripts are needed before the filesystem can be packaged up and installed onto the target device.

Once installed, the packages themselves need to be configured using the package maintainer scripts and "dpkg --configure -a", unless this is a native multistrap.

For "dpkg" to work, /proc and /sysfs must be mounted (or mountable), /dev/pts is also recommended.

See also:  


To configure the unpacked packages (whether in native or cross mode), certain environment variables are needed:

Debconf needs to be told to accept that user interaction is not desired:


Perl needs to be told to accept that no locales are available inside the chroot and not to complain:


Then, dpkg can configure the packages:

chroot method (PATH = top directory of chroot):

 LC_ALL=C LANGUAGE=C LANG=C chroot /PATH/ dpkg --configure -a

at a login shell:

 # dpkg --configure -a

(As above, dpkg needs /proc and /sysfs mounted first.)  

Native mode - multistrap

multistrap was not intended for native support, it was developed for cross architecture support. In order for multiple repositories to be used, multistrap only unpacks the packages selected by apt.

In native mode, various post-multistrap operations are likely to be needed that debootstrap would do for you:

 1. copy /etc/hosts into the chroot
 2. clean the environment to unset LANGUAGE, LC_ALL and LANG
    to silence nuisance perl warnings that obscure other errors

(An alternative to unset the localisation variables is to add locales to your multistrap configuration file in the 'packages' option.

A native multistrap can be used directly with chroot, so "multistrap" runs "dpkg --configure -a" at the end of the multistrap process.  

Cascading configuration

To support multiple variants of a basic (common) configuration, "multistrap" allows configuration files to include other (more general) configuration files. i.e. the most detailed / specific configuration file is specified on the command line and that file includes another file which is shared by other configurations.

Base file:




Specifying just the armel.conf file will get the rest of the settings from crosschroot.conf so that common changes only need to be made in a single file.

It is strongly recommended that any changes to the configuration files involved in any particular cascade are tested using the "--simulate" option to multistrap which will output a summary of the options that have been set once the cascade is complete. Note that multistrap does not warn you if a configuration file contains an unrecognised option (for future compatibility with backported configurations), so a simple typo can result in an option not being set.  

Machine:variant support

The old packages.conf variables from emsandbox can all be converted into "multistrap" configuration variables. The machine:variant support in "multistrap" concentrates on the scripts, and

Once "multistrap" has unpacked the downloaded packages, the "" can be called, passing the location and architecture of the root filesystem, so that other fine tuning can take place. At this stage, any operations inside the rootfs must not try to execute any binaries within the rootfs. As the final stage of the multistrap process, "" is copied into the root directory of the rootfs.

One advantage of using machine:variant support is that the entire rootfilesystem can be managed by a single call to multistrap - this is useful when building root filesystems in userspace.

To enable machine:variant support, specify the path to the scripts to be called in the variant configuration file (General section):



Restricting package selection

"multistrap" includes Required packages by default, the current list of packages can be seen using:

 grep-available  -FPriority 'required' -sPackage

If the OmitRequired option is set to true, these packages will not be added - whilst useful, this option can easily lead to a useless rootfs. Only the packages specified manually in the configuration files will be used in the calculations - dependencies of those packages will be added but no others.

Packages with Priority: important or standard are never included by "multistrap" unless specifically included in a "packages=" option in a section specified in the "bootstrap" general option.  

Recommends behaviour

The Debian default behaviour after the Lenny release was to consider recommended packages as extra packages to be installed when any one package is selected. Recommended packages are those which the maintainer considers that would be present on "most" installations of that package and allowing Recommends means allowing Recommends of recommended packages and so on.

The multistrap default is to turn recommends OFF.

Set the allowrecommends option to true in the General section to use typical Debian behaviour.  

Explicit suite specification

Sometimes, apt needs to be told to get a particular package from a particular suite, ignoring a more recent version in another suite in the same set of sources.

"multistrap" can operate with and without the explicit suite option, the default is to let apt use the most recent version from the collection of specified bootstrap sources.

Explicit suite specification has no effect on the final installed system - if your aptsources includes a repository which in turn includes a newer version of the package(s) specified explicitly, the next "apt-get upgrade" on the device will bring in the newer version.

Also, when specifying packages to get from a specific suite, apt will also try and ensure that the dependencies for that package are also from the same suite and this can cause apt to be unable to resolve the complete set of dependencies. In this situation, being explicit about one package selection may require being explicit about some (not necessarily all) of the dependencies of that package as well.

When using this support in Lenny, ensure that each section uses the suite (oldstable, stable, testing, sid) and not the codename (etch, lenny, squeeze, sid) in the "suite" configuration item as the version of apt in Lenny and previous cannot use the codename.

To test, on Lenny, try:

 $ sudo apt-get install apt/stable

Compare with

 $ sudo apt-get install apt/lenny


Omitting deb-src listings

Some multistrap environments do not need access to the Debian sources of packages being installed, typically this is required when preparing a build (or cross-build) chroot using multistrap.

To turn off this additional source (and save both download time and apt-cache size), use the omitdebsrc field in each Section.




Foreign architecture bootstraps can operate under "fakeroot" ("multistrap" is designed to do as much as it can within a single call to make this easier) but the configuration stage which normally happens with a native architecture bootstrap requires "chroot" and "chroot" itself will not operate under "fakeroot".

Therefore, if "multistrap" detects that "fakeroot" is in use, native mode configuration is skipped with a reminder warning.

The same problem applies to "apt-get install" and therefore the installation of the keyring package on the host system is also skipped if fakeroot is detected.



General settings:
Section settings
Secure Apt
Root Filesystem Configuration
Native mode - multistrap
Cascading configuration
Machine:variant support
Restricting package selection
Recommends behaviour
Explicit suite specification
Omitting deb-src listings

This document was created by man2html, using the manual pages.
Time: 21:24:08 GMT, April 16, 2011