dchroot - Online in the Cloud

PROGRAM:

NAME

dchroot - enter a chroot environment

SYNOPSIS

dchroot [-h|--help | -V|--version | -l|--list | -i|--info | --config | --location]
[--directory=directory] [-d|--preserve-environment] [-q|--quiet | -v|--verbose] [-c
chroot|--chroot=chroot | --all] [COMMAND [ ARG1 [ ARG2 [ ARGn]]]]

DESCRIPTION

dchroot allows the user to run a command or a login shell in a chroot environment. If no
command is specified, a login shell will be started in the user's home directory inside
the chroot.

The command is one or more arguments which will be run in the user's default shell using
its -c option. As a result, shell code may be embedded in this argument. If multiple
command options are used, they are concatenated together, separated by spaces. Users
should be aware of the shell quoting issues this presents, and should use schroot if
necessary, which does not have any quoting issues.

The directory the command or login shell is run in depends upon the context. See
--directory option below for a complete description.

This version of dchroot is a compatibility wrapper around the schroot(1) program. It is
provided for backward compatibility with the dchroot command-line options, but schroot is
recommended for future use. See the section “Incompatibilities” below for known
incompatibilities with older versions of dchroot.

If no chroot is specified, the chroot name or alias ‘default’ will be used as a fallback.

OPTIONS

dchroot accepts the following options:

Basic options
-h, --help
Show help summary.

-a, --all
Select all chroots.

-c, --chroot=chroot
Specify a chroot to use. This option may be used multiple times to specify more
than one chroot, in which case its effect is similar to --all.

-l, --list
List all available chroots.

-i, --info
Print detailed information about the specified chroots. Note that earlier versions
of dchroot did not include this option.

-p, --path
Print location (path) of the specified chroots.

--config
Print configuration of the specified chroots. This is useful for testing that the
configuration in use is the same as the configuration file. Any comments in the
original file will be missing. Note that earlier versions of dchroot did not
include this option.

--directory=directory
Change to directory inside the chroot before running the command or login shell.
If directory is not available, dchroot will exit with an error status.

The default behaviour is as follows (all directory paths are inside the chroot).
Unless the --preserve-environment option is used to preserve the environment, the
login shell or command will run in the user's home directory, or / if the home
directory is not available. When the --preserve-environment option is used, it
will attempt to use the current working directory, again falling back to / if it is
not accessible. If none of the directories are available, dchroot will exit with
an error status.

-d, --preserve-environment
Preserve the user's environment inside the chroot environment. The default is to
use a clean environment; this option copies the entire user environment and sets it
in the session.

-q, --quiet
Print only essential messages.

-v, --verbose
Print all messages. Note that earlier versions of dchroot did not include this
option.

-V, --version
Print version information.

Note that earlier versions of dchroot did not provide long options.

INCOMPATIBILITIES

Debian dchroot prior to version 0.99.0
· Log messages are worded and formatted differently.

· su(1) is no longer used to run commands in the chroot; this is done by dchroot
internally. This change may cause subtle differences. If you find an
incompatibility, please report it so it may be corrected.

· dchroot provides a restricted subset of the functionality implemented by schroot,
but is still schroot underneath. Thus dchroot is still subject to schroot security
checking, including PAM authentication and authorisation, and session management,
for example, and hence may behave slightly differently to older dchroot versions in
some circumstances.

Debian dchroot prior to version 1.5.1
· This version of dchroot uses schroot.conf to store the configuration for available
chroots, rather than the dchroot.conf file used historically. dchroot supported
automatic migration of dchroot.conf to the schroot.conf keyfile format with its
--config option from versions 0.2.2 to 1.5.0; support for the old format is now no
longer available.

DSA dchroot
Machines run by the Debian System Administrators for the Debian Project have a dchroot-dsa
package which provides an alternate dchroot implementation.

· All the above incompatibilities apply.

· This version of dchroot has incompatible command-line options, and while some of
those options are supported or have equivalent options by a different name, the -c
option is not required to specify a chroot, and this version of dchroot cannot
implement this behaviour in a backward-compatible manner (because if -c is omitted,
the default chroot is used). DSA dchroot uses the first non-option as the chroot
to use, only allowing one chroot to be used at once.

DIRECTORY FALLBACKS

dchroot will select an appropriate directory to use within the chroot based upon whether
the --directory or --preserve-environment options are used. When explicitly specifying a
directory, only one directory will be used for safety and consistency, while for a login
shell or command several possibilities may be tried. Note that due to multiple fallbacks
being considered for commands, it is dangerous to run commands using dchroot; use schroot
instead. The following subsections list the fallback sequence for each case. CWD is the
current working directory, DIR is the directory specified with --directory.

Login shell or command
┌────────────────────┬──────────────────────────────────────────┐
│Transition │ │
│(Host → Chroot) │ Comment │
├────────────────────┼──────────────────────────────────────────┤
│CWD → passwd pw_dir │ Normal behaviour (if --directory and │
│ │ --preserve-environment are not used) │
│CWD → / │ If passwd pw_dir is nonexistent │
│FAIL │ If / is nonexistent │
└────────────────────┴──────────────────────────────────────────┘
--preserve-environment used
┌────────────────┬──────────────────────────────────────────┐
│Transition │ │
│(Host → Chroot) │ Comment │
├────────────────┼──────────────────────────────────────────┤
│CWD → CWD │ Normal behaviour (if │
│ │ --preserve-environment used) │
│CWD → / │ If CWD is nonexistent │
│FAIL │ If / is nonexistent │
└────────────────┴──────────────────────────────────────────┘
--directory used
┌────────────────┬──────────────────────────────────────────┐
│Transition │ │
│(Host → Chroot) │ Comment │
├────────────────┼──────────────────────────────────────────┤
│CWD → DIR │ Normal behaviour │
│FAIL │ If DIR is nonexistent │
└────────────────┴──────────────────────────────────────────┘
No fallbacks should exist under any circumstances.

Debugging
Note that --debug=notice will show the internal fallback list computed for the session.

EXAMPLES

$ dchroot -l↵
Available chroots: sarge [default], sid

$ dchroot -p sid↵
/srv/chroot/sid

$ dchroot -q -c sid -- uname -smr↵
Linux 2.6.16.17 ppc
$ dchroot -q -c sid -- "uname -smr"↵
Linux 2.6.16.17 ppc

$ dchroot -q -c sid "ls -1 / | tac | head -n 4"↵
var
usr
tmp
sys

$ dchroot -c sid↵
I: [sid chroot] Running login shell: “/bin/bash”
$

Use -- to allow options beginning with ‘-’ or ‘--’ in the command to run in the chroot.
This prevents them being interpreted as options for dchroot itself. Note that the top
line was echoed to standard error, and the remaining lines to standard output. This is
intentional, so that program output from commands run in the chroot may be piped and
redirected as required; the data will be the same as if the command was run directly on
the host system.

TROUBLESHOOTING

If something is not working, and it's not clear from the error messages what is wrong, try
using the --debug=level option to turn on debugging messages. This gives a great deal
more information. Valid debug levels are ‘none’, and ‘notice’, ‘info’, ‘warning’ and
‘critical’ in order of increasing severity. The lower the severity level, the more
output.

If you are still having trouble, the developers may be contacted on the mailing list:
Debian buildd-tools Developers
<[email protected]>

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