Ubuntu Manpage: schroot.conf - chroot definition file for schroot

name
description
chroot names
security
example
files
authors
copyright
see also

Provided by: schroot_1.6.10-9ubuntu0.1_amd64

NAME

       schroot.conf - chroot definition file for schroot

DESCRIPTION

schroot.conf is a plain UTF-8 text file, describing the chroots available for use with schroot.

Comments are introduced following a ‘#’ (“hash”) character at the beginning of a line, or following any
other text. All text right of the ‘#’ is treated as a comment.

The configuration format is an INI-style format, split into groups of key-value pairs separated by
section names in square brackets.

General options
A chroot is defined as a group of key-value pairs, which is started by a name in square brackets on a
line by itself. The file may contain multiple groups which therefore define multiple chroots.

A chroot definition is started by the name of the chroot in square brackets. For example,

[sid]

The name is subject to certain naming restrictions. For further details, see the section “Chroot Names”
below.

This is then followed by several key-value pairs, one per line:

type=type
The type of the chroot. Valid types are ‘plain’, ‘directory’, ‘file’, ‘loopback’, ‘block-device’,
‘btrfs-snapshot’, ‘zfs-snapshot’ and ‘lvm-snapshot’. If empty or omitted, the default type is
‘plain’. Note that ‘plain’ chroots do not run setup scripts and mount filesystems; ‘directory’ is
recommended for normal use (see “Plain and directory chroots”, below).

description=description
A short description of the chroot. This may be localised for different languages; see the section
“Localisation” below.

priority=number
Set the priority of a chroot. number is a positive integer indicating whether a distribution is
older than another. For example, “oldstable” and “oldstable-security” might be ‘0’, while
“stable” and “stable-security” are ‘1’, “testing” is ‘2’ and “unstable” is ‘3’. The values are
not important, but the difference between them is. This option is deprecated and no longer used
by schroot, but is still permitted to be used; it will be obsoleted and removed in a future
release.

message-verbosity=verbosity
Set the verbosity of messages printed by schroot when setting up, running commands and cleaning up
the chroot. Valid settings are ‘quiet’ (suppress most messages), ‘normal’ (the default) and
‘verbose’ (show all messages). This setting is overridden by the options --quiet and --verbose.

users=user1,user2,...
A comma-separated list of users which are allowed access to the chroot. If empty or omitted, no
users will be allowed access (unless a group they belong to is also specified in groups).

groups=group1,group2,...
A comma-separated list of groups which are allowed access to the chroot. If empty or omitted, no
groups of users will be allowed access.

root-users=user1,user2,...
A comma-separated list of users which are allowed password-less root access to the chroot. If
empty or omitted, no users will be allowed root access without a password (but if a user or a
group they belong to is in users or groups, respectively, they may gain access with a password).
See the section “Security” below.

root-groups=group1,group2,...
A comma-separated list of groups which are allowed password-less root access to the chroot. If
empty or omitted, no users will be allowed root access without a password (but if a user or a
group they belong to is in users or groups, respectively, they may gain access with a password).
See the section “Security” below.

aliases=alias1,alias2,...
A comma-separated list of aliases (alternate names) for this chroot. For example, a chroot named
“sid” might have an ‘unstable’ alias for convenience. Aliases are subject to the same naming
restrictions as the chroot name itself.

profile=directory

script-config=filename
The behaviour of the chroot setup scripts may be customised on a per-chroot basis by setting a
specific configuration profile. The directory is relative to /etc/schroot. The default is
‘default’. The files in this directory are sourced by the setup scripts, and so their behaviour
may be customised by selecting the appropriate profile. Alternatives are ‘minimal’ (minimal
configuration), ‘desktop’ (for running desktop applications in the chroot, making more
functionality from the host system available in the chroot) and ‘sbuild’ (for using the chroot for
Debian package building). Other packages may provide additional profiles. The default values of
the keys setup.config, setup.copyfiles, setup.fstab and setup.nssdatabases are set based upon the
profile setting.

Note that the profile key replaces the older script-config key. The script-config key is exactly
the same as profile, but has “/config” appended to it. The default filename is ‘default/config’.
Either of these keys may be used. If both are present, then script-config will take precedence
(profile will be unset). script-config is deprecated and will be removed in a future release.
Note that profile is equivalent to script-config if the file sourced by script-config only
contains the standard variables provided by schroot; if any additional variables or shell script
fragments have been added, please also set setup.config, which will continue to allow this file to
be sourced. It is recommended to replace the use of the sourced file with additional keys in
schroot.conf where possible, but it will continue to be possible to source an additional
configuration file using setup.config.

Desktop users should note that the fstab file desktop/fstab will need editing if you use gdm3;
please see the comments in this file for further instructions. The preserve-environment key
should also be set to ‘true’ so that the environment is preserved inside the chroot.

If none of the configuration profiles provided above meet your needs, then they may be edited to
further customise them, and/or copied and used as a template for entirely new profiles.

Note that the different profiles have different security implications; see the section “Security”
below for further details.

setup.config=filename
This key specifies a file which the setup scripts will source when they are run. This defaults to
the same value as set by script-config. The file is a Bourne shell script, and in consequence may
contain any valid shell code, in addition to simple variable assignments. This will, for example,
allow behaviour to be customised according to the specific chroot type or name. Note that the
script will be sourced once for each and every script invocation, and must be idempotent.

All the default settings in this file are now settable using configuration keys in schroot.conf,
as detailed below. Existing configurations should be modified to use these keys in place of this
file. See schroot-script-config(5) for further details. This type of setup script configuration
file is no longer provided as part of the standard profiles, but will continue to be sourced if
present and this key is set.

setup.copyfiles=filename
A file containing a list of files to copy into the chroot (one file per line). The file will have
the same absolute location inside the chroot.

setup.fstab=filename
The filesystem table file to be used to mount filesystems within the chroot. The format of this
file is the same as for /etc/fstab, documented in fstab(5). The only difference is that the
mountpoint path fs_dir is relative to the chroot, rather than the root. Also note that
mountpoints are canonicalised on the host, which will ensure that absolute symlinks point inside
the chroot, but complex paths containing multiple symlinks may be resolved incorrectly; it is
inadvisable to use nested symlinks as mountpoints.

setup.nssdatabases=filename
A file listing the system databases to copy into the chroot. The default databases are ‘passwd’,
‘shadow’, ‘group’ and ‘gshadow’. Other potential databases which could be added include
‘services’, ‘protocols’, ‘networks’, and ‘hosts’. The databases are copied using getent(1) so all
database sources listed in /etc/nsswitch.conf will be used for each database.

setup.services=service1,service2,...
A comma-separated list of services to run in the chroot. These will be started when the session
is started, and stopped when the session is ended.

command-prefix=command,option1,option2,...
A comma-separated list of a command and the options for the command. This command and its options
will be prefixed to all commands run inside the chroot. This is useful for adding commands such
as nice, ionice or eatmydata for all commands run inside the chroot. nice and ionice will affect
CPU and I/O scheduling. eatmydata ingores filesystem fsync operations, and is useful for
throwaway snapshot chroots where you don't care about dataloss, but do care about high speed.

personality=persona
Set the personality (process execution domain) to use. This option is useful when using a 32-bit
chroot on 64-bit system, for example. Valid options on Linux are ‘bsd’, ‘hpux’, ‘irix32’,
‘irix64’, ‘irixn32’, ‘iscr4’, ‘linux’, ‘linux32’, ‘linux_32bit’, ‘osf4’, ‘osr5’, ‘riscos’,
‘scorvr3’, ‘solaris’, ‘sunos’, ‘svr4’, ‘uw7’, ‘wysev386’, and ‘xenix’. The default value is
‘linux’. There is also the special option ‘undefined’ (personality not set). For a 32-bit chroot
on a 64-bit system, ‘linux32’ is the option required. The only valid option for non-Linux systems
is ‘undefined’. The default value for non-Linux systems is ‘undefined’.

preserve-environment=true|false
By default, the environment will not be preserved inside the chroot, instead a minimal environment
will be used. Set to true to always preserve the environment. This is useful for example when
running X applications inside the chroot, which need the environment to function correctly. The
environment may also be preserved using the --preserve-environment option.

shell=shell
When running a login shell a number of potential shells will be considered, in this order: the
command in the SHELL environment variable (if --preserve-environment is used, or
preserve-environment is enabled), the user's shell in the ‘passwd’ database, /bin/bash and finally
/bin/sh. This setting overrides this list, and will use the shell specified. It may be
overridden using the --shell option.

environment-filter=regex
The environment to be set in the chroot will be filtered in order to remove environment variables
which may pose a security risk. Any environment variable matching the specified POSIX extended
regular expression will be removed prior to executing any command in the chroot.

Plain and directory chroots
Chroots of type ‘plain’ or ‘directory’ are directories accessible in the filesystem. The two types are
equivalent except for the fact that directory chroots run setup scripts, whereas plain chroots do not.
In consequence, filesystems such as /proc are not mounted in plain chroots; it is the responsibility of
the system administrator to configure such chroots by hand, whereas directory chroots are automatically
configured. Additionally, directory chroots implement the filesystem union chroot options (see
“Filesystem Union chroot options”, below).

These chroot types have an additional (mandatory) configuration option:

directory=directory
The directory containing the chroot environment. This is where the root will be changed to when
executing a login shell or a command. The directory must exist and have read and execute
permissions to allow users access to it. Note that on Linux systems it will be bind-mounted
elsewhere for use as a chroot; the directory for ‘plain’ chroots is mounted with the --rbind
option to mount(8), while for ‘directory’ chroots --bind is used instead so that sub-mounts are
not preserved (they should be set in the fstab file just like in /etc/fstab on the host).

File chroots
Chroots of type ‘file’ are files on the current filesystem containing an archive of the chroot files.
They implement the source chroot options (see “Source chroot options”, below). Note that a corresponding
source chroot (of type ‘file’) will be created for each chroot of this type; this is for convenient
access to the source archive, e.g. for the purpose of updating. These additional options are also
implemented:

file=filename
The file containing the archived chroot environment (mandatory). This must be a tar (tape
archive), optionally compressed with gzip, bzip2, xz, lzop or lz4. The file extensions used to
determine the type are .tar, .tar.gz, .tar.bz2, .tar.xz, .tar.lzop, .tar.lz4, .tgz, .tbz, .txz,
.tzo and .tlz4. This file must be owned by the root user, and not be writable by other. Note
that zip archives are no longer supported; zip was not able to archive named pipes and device
nodes, so was not suitable for archiving chroots.

location=path
This is the path to the chroot inside the archive. For example, if the archive contains a chroot
in /squeeze, you would specify “/squeeze” here. If the chroot is the only thing in the archive,
i.e. / is the root filesystem for the chroot, this option should be left blank, or omitted
entirely.

Loopback chroots
Chroots of type ‘loopback’ are a filesystem available as a file on disk, accessed via a loopback mount.
The file will be loopback mounted and unmounted on demand. Loopback chroots implement the mountable
chroot and filesystem union chroot options (see “Mountable chroot options” and “Filesystem Union chroot
options”, below), plus an additional option:

file=filename
This is the filename of the file containing the filesystem, including the absolute path. For
example “/srv/chroot/sid”.

Block device chroots
Chroots of type ‘block-device’ are a filesystem available on an unmounted block device. The device will
be mounted and unmounted on demand. Block device chroots implement the mountable chroot and filesystem
union chroot options (see “Mountable chroot options” and “Filesystem Union chroot options”, below), plus
an additional option:

device=device
This is the device name of the block device, including the absolute path. For example,
“/dev/sda5”.

Btrfs snapshot chroots
Chroots of type ‘btrfs-snapshot’ are a Btrfs snapshot created from an existing Btrfs subvolume on a
mounted Btrfs filesystem. A snapshot will be created from this source subvolume on demand at the start
of a session, and then the snapshot will be mounted. At the end of the session, the snapshot will be
unmounted and deleted. This chroot type implements the source chroot options (see “Source chroot
options”, below). Note that a corresponding source chroot (of type ‘directory’) will be created for each
chroot of this type; this is for convenient access to the source volume. These additional options are
also implemented:

btrfs-source-subvolume=directory
The directory containing the source subvolume.

btrfs-snapshot-directory=directory
The directory in which to store the snapshots of the above source subvolume.

ZFS snapshot chroots
Chroots of type ‘zfs-snapshot’ are a ZFS clone created from an existing ZFS dataset. A snapshot and
clone will be created from this source subvolume on demand at the start of a session, and then the clone
will be mounted. At the end of the session, the clone will be unmounted and the clone and snapshot will
be deleted. This chroot type implements the source chroot options (see “Source chroot options”, below).
Note that a corresponding source chroot (of type ‘directory’) will be created for each chroot of this
type; this is for convenient access to the source volume. These additional options are also implemented:

zfs-dataset=dataset_name
Name of the ZFS source dataset to use.

zfs-snapshot-options=snapshot_options
Snapshot options. These are additional options to pass to zfs snapshot.

LVM snapshot chroots
Chroots of type ‘lvm-snapshot’ are a filesystem available on an LVM logical volume (LV). A snapshot LV
will be created from this LV on demand, and then the snapshot will be mounted. At the end of the
session, the snapshot LV will be unmounted and removed.

LVM snapshot chroots implement the source chroot options (see “Source chroot options”, below), and all
the options for ‘block-device’. Note that a corresponding source chroot (of type ‘block-device’) will be
created for each chroot of this type; this is for convenient access to the source device. This additional
option is also implemented:

lvm-snapshot-options=snapshot_options
Snapshot options. These are additional options to pass to lvcreate(8). For example, “-L 2g” to
create a snapshot 2 GiB in size. Note: the LV name (-n), the snapshot option (-s) and the
original LV path may not be specfied here; they are set automatically by schroot.

Custom chroots
Chroots of type ‘custom’ are a special type of chroot, used for implementing new types of chroot not
supported by any of the above chroot types. This may be useful for implementing and testing a new chroot
type without needing to write any C++ code. However, you will need to write your own setup script to do
the setup work, since by itself this chroot type does very little. You will also need to add custom keys
to your chroot definition for use in the setup script; unlike the configuration for the above chroot
types, no validation of the options will take place unless you do it yourself in your custom setup
script. These additional options are also implemented:

custom-session-cloneable=true|false
Set whether or not sessions may be cloned using this chroot (enabled by default).

custom-session-purgeable=true|false
Set whether or not sessions may be cloned using this chroot (disabled by default).

custom-source-cloneable=true|false
Set whether or not source chroots may be cloned using this chroot (disabled by default).

Source chroot options
The ‘btrfs-snapshot’, ‘file’ and ‘lvm-snapshot’ chroot types implement source chroots. Additionally,
chroot types with union support enabled implement source chroots (see “Filesystem Union chroot options”,
below). These are chroots which automatically create a copy of themselves before use, and are usually
session managed. These chroots additionally provide an extra chroot in the source: namespace, to allow
convenient access to the original (non-snapshotted) data, and to aid in chroot maintenance. I.e. for a
chroot named wheezy (chroot:wheezy), a corresponding source:wheezy chroot will be created. For
compatibility with older versions of schroot which did not support namespaces, a chroot with a -source
suffix appended to the chroot name will be created in addition (i.e. wheezy-source using the above
example). Note that these compatibility names will be removed in schroot 1.5.0, so the use of the
source: namespace is preferred over the use of the -source suffix form. See schroot(1) for further
details.

These chroots provide the following additional options:

source-clone=true|false
Set whether the source chroot should be automatically cloned (created) for this chroot. The
default is true to automatically clone, but if desired may be disabled by setting to false. If
disabled, the source chroot will be inaccessible.

source-users=user1,user2,...
A comma-separated list of users which are allowed access to the source chroot. If empty or
omitted, no users will be allowed access. This will become the users option in the source chroot.

source-groups=group1,group2,...
A comma-separated list of groups which are allowed access to the source chroot. If empty or
omitted, no users will be allowed access. This will become the groups option in the source
chroot.

source-root-users=user1,user2,...
A comma-separated list of users which are allowed password-less root access to the source chroot.
If empty or omitted, no users will be allowed root access without a password (but if a user is in
users, they may gain access with a password). This will become the root-users option in the
source chroot. See the section “Security” below.

source-root-groups=group1,group2,...
A comma-separated list of groups which are allowed password-less root access to the source chroot.
If empty or omitted, no users will be allowed root access without a password (but if a user's
group is in groups, they may gain access with a password). This will become the root-groups
option in the source chroot. See the section “Security” below.

Mountable chroot options
The ‘block-device’, ‘loopback’ and ‘lvm-snapshot’ chroot types implement device mounting. These are
chroots which require the mounting of a device in order to access the chroot. These chroots provide the
following additional options:

mount-options=options
Mount options for the block device. These are additional options to pass to mount(8). For
example, “-o atime,sync,user_xattr”.

location=path
This is the path to the chroot inside the filesystem on the device. For example, if the
filesystem contains a chroot in /chroot/sid, you would specify “/chroot/sid” here. If the chroot
is the only thing on the filesystem, i.e. / is the root filesystem for the chroot, this option
should be left blank, or omitted entirely.

Filesystem Union chroot options
The ‘block-device’, ‘directory’ and ‘loopback’ chroot types allow for the creation of a session using
filesystem unions to overlay the original filesystem with a separate writable directory. The original
filesystem is read-only, with any modifications made to the filesystem made in the overlying writable
directory, leaving the original filesystem unchanged. A union permits multiple sessions to access and
make changes to a single chroot simultaneously, while keeping the changes private to each session. To
enable this feature, set union-type to any supported value. If enabled, the chroot will also be a source
chroot, which will provide additional options (see “Source chroot options”, above). All entries are
optional.

union-type=type
Set the union filesystem type. Currently supported filesystems are ‘aufs’, ‘overlayfs’, ‘overlay’
(as of Linux 4.0+) and ‘unionfs’. The default is ‘none’, which disables this feature.

union-mount-options=options
Union filesystem mount options (branch configuration), used for mounting the union filesystem
specified with union-type. This replaces the complete “-o” string for mount and allows for the
creation of complex filesystem unions. Note that ‘aufs’, ‘overlayfs’ and ‘unionfs’ each have
different supported mount options. Note: One can use the variables
“${CHROOT_UNION_OVERLAY_DIRECTORY}” and “${CHROOT_UNION_UNDERLAY_DIRECTORY}” to refer to the
writable overlay session directory and read-only underlying directory which are to form the union.
See schroot-setup(5) for a complete variable list.

union-overlay-directory=directory
Specify the directory where the writeable overlay session directories will be created. The
default is ‘/var/lib/schroot/union/overlay’.

union-underlay-directory=directory
Specify the directory where the read-only underlying directories will be created. The default is
‘/var/lib/schroot/union/underlay’.

Customisation
In addition to the configuration keys listed above, it is possible to add custom keys. These keys will
be used to add additional environment variables to the setup script environment when setup scripts are
run. The only restriction is that the key name consists only of alphanumeric characters and hyphens,
begins with an alphabet character and contains at least one period. That is to say, that it matches the
extended regular expression “^([a-z][a-z0-9]*\.)+[a-z][a-z0-9-]*$”.

For example:
debian.apt-update=true
debian.distribution=unstable

would set the following environment:
DEBIAN_APT_UPDATE=true
DEBIAN_DISTRIBUTION=unstable

Note that it is an error to use different key names which would set the same environment variable by
mixing periods and hyphens.

Custom configuration keys may also be modified at runtime using the --option option. However, for
security, only selected keys may be modified. These keys are specified using the following options:

user-modifiable-keys=key1,key2,..
Set the keys which users may modify using --option.

root-modifiable-keys=key1,key2,.. Set the keys which the
root user may modify using --option. Note that the root user may use the keys specified in
user-modifiable-keys in addition to those specified here.

Localisation
Some keys may be localised in multiple languages. This is achieved by adding the locale name in square
brackets after the key name. For example:
description[en_GB]=British English translation

This will localise the description key for the en_GB locale.
description[fr]=French translation

This will localise the description key for all French locales.

CHROOT NAMES

       A  number  of  characters  or  words  are  not  permitted in a chroot name, session name or configuration
       filename.  The name must begin with a lowercase or an  uppercase  letter,  or  a  digit.   The  remaining
       characters may additionally be dash (‘-’), period (‘.’), or underscore (‘_’).

       The rationale for these restrictions is as follows:

       Generic
              Unfortunately,  not  all the places that deal with chroot names can handle non-printable and other
              characters properly, and it's hard to update all of them.  This is mostly about the various  shell
              scripts where it's also unwise to assume authors always create safe code.

       ‘dpkg-old’
       ‘dpkg-dist’
       ‘dpkg-new’
       ‘dpkg-tmp’
              These  names may not appear at the end of a name.  These are saved copies of conffiles used by the
              dpkg package manager, and will be ignored.

SECURITY

Untrusted users
Note that giving untrusted users root access to chroots is a serious security risk! Although the
untrusted user will only have root access to files inside the chroot, in practice there are many obvious
ways of breaking out of the chroot and of disrupting services on the host system. As always, this boils
down to trust.

Do not give chroot root access to users you would not trust with root access to the host system.

Profiles
Depending upon which profile you have configured with the script-config option, different filesystems
will be mounted inside the chroot, and different files will be copied into the chroot from the host.
Some profiles will mount the host's /dev, while others will not. Some profiles also bind mount
additional parts of the host filesystem in order to allow use of certain features, including user's home
directories and specific parts of /var. Check the profile's fstab file to be certain of what will be
mounted, and the other profile files to see which files and system databases will be copied into the
chroot. Choose a different profile or edit the files to further restrict what is made available inside
the chroot.

There is a tradeoff between security (keeping the chroot as minimal as possible) and usability (which
sometimes requires access to parts of the host filesystem). The different profiles make different
tradeoffs, and it is important that you assess which meets the security/usability tradeoff you require.

EXAMPLE

       # Sample configuration

       [sid]
       type=plain
       description=Debian unstable
       description[fr_FR]=Debian instable
       directory=/srv/chroot/sid
       priority=3
       users=jim
       groups=sbuild
       root-users=rleigh
       aliases=unstable,default

       [etch]
       type=block-device
       description=Debian testing (32-bit)
       priority=2
       groups=users
       #groups=sbuild-security
       aliases=testing
       device=/dev/hda_vg/etch_chroot
       mount-options=-o atime
       personality=linux32

       [sid-file]
       type=file
       description=Debian sid file-based chroot
       priority=3
       groups=sbuild
       file=/srv/chroots/sid.tar.gz

       [sid-snapshot]
       type=lvm-snapshot
       description=Debian unstable LVM snapshot
       priority=3
       groups=sbuild
       users=rleigh
       source-root-users=rleigh
       source-root-groups=admin
       device=/dev/hda_vg/sid_chroot
       mount-options=-o atime,sync,user_xattr
       lvm-snapshot-options=--size 2G

FILES

Chroot definitions
/etc/schroot/schroot.conf
The system-wide chroot definition file. This file must be owned by the root user, and not be
writable by other.

/etc/schroot/chroot.d
Additional chroot definitions may be placed in files under this directory. They are treated in
exactly that same manner as /etc/schroot/schroot.conf. Each file may contain one or more chroot
definitions.

Setup script configuration
The directory /etc/schroot/default contains the default settings used by setup scripts.

config Main configuration file read by setup scripts. The format of this file is described in
schroot-script-config(5). This is the default value for the script-config key. Note that this
was formerly named /etc/schroot/script-defaults. The following files are referenced by default:

copyfiles
A list of files to copy into the chroot from the host system. Note that this was formerly named
/etc/schroot/copyfiles-defaults.

fstab A file in the format decribed in fstab(5), used to mount filesystems inside the chroot. The mount
location is relative to the root of the chroot. Note that this was formerly named
/etc/schroot/mount-defaults.

nssdatabases
System databases (as described in /etc/nsswitch.conf on GNU/Linux systems) to copy into the chroot
from the host. Note that this was formerly named /etc/schroot/nssdatabases-defaults.

AUTHORS

       Roger Leigh.

COPYRIGHT

       Copyright © 2005-2012  Roger Leigh <rleigh@debian.org>

       schroot  is  free  software:  you can redistribute it and/or modify it under the terms of the GNU General
       Public License as published by the Free Software Foundation, either version 3 of the License, or (at your
       option) any later version.