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Man page of FAKECHROOT
Updated: 17 Nov 2016
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fakechroot - gives a fake chroot environment
fakechroot runs a command in an environment where is additional possibility to
use chroot(8) command without root privileges. This is useful for allowing
users to create own chrooted environment with possibility to install another
packages without need for root privileges.
fakechroot replaces some C library functions (chroot(2), open(2), etc.)
by ones that simulate the effect of being called with root privileges.
These wrapper functions are provided as a shared library libfakechroot.so
which is loaded through the "LD_PRELOAD" mechanism of the dynamic loader.
In fake chroot you can install i.e. Debian bootstrap with debootstrap(8)
command. In such environment you can run i.e. apt-get(8) command to install
another packages. You don't need a special privileges and you can run it on
common user's account.
- -l library|--lib library
Specify an alternative wrapper library. The default is libfakechroot.so
- -d ldso|--elfloader ldso
Specify an alternative dynamic linker. This dynamic linker will be invoked
Use system libraries before chroot's libraries. This might be a workaround if
system dynamic linker cannot load libc.so from fake chroot.
Try this setting if you noticed following errors:
$ fakechroot /usr/sbin/chroot /tmp/sarge /bin/true
/bin/true: relocation error: /srv/sarge/lib/tls/libc.so.6: symbol _dl
_starting_up, version GLIBC_PRIVATE not defined in file ld-linux.so.2
with link time reference
$ fakechroot /usr/sbin/chroot /tmp/centos4 /bin/true
- -e|--environment type
Load additional configuration with environment. This configuration file
is a shell script which is executed before calling command. The
script can set additional environment variables, like i.e.:
"FAKECHROOT_EXCLUDE_PATH", "FAKECHROOT_CMD_SUBST" or "LD_LIBRARY_PATH".
The environment type is guessed based on command name with optional extension
removed (e.g. running gettext.sh loads "gettext" environment file). If
command argument is fakeroot(1) this argument is omitted and next argument
is taken as environment type.
The configuration file name is type.env and is searched at
$HOME/.fakechroot and /etc/fakechroot directories.
The default environment type is default and its configuration file name is
The special environment none means that no environment settings are loaded
- -c|--config-dir directory
Specify a directory which contains additional configuration for fakechroot. The
default directory are "$HOME/.fakechroot" and "/etc/fakechroot".
- -b|--bindir directory
Specify a directory which contains the replacement executables
shipped with fakechroot.
Those are script files with the extension ".fakechroot".
By default they are distributed over the
"bin" and "sbin" directories in fakechroot's install prefix,
but sometimes a fixed location at build time is not feasible.
- [--] command
Any command you want to be run as fakechroot. Use '--' if in the command
you have other options that may confuse fakechroot's option parsing.
An example session with fakechroot:
uid=1000(dexter) gid=1000(dexter) groups=1000(dexter)
$ fakechroot fakeroot debootstrap sid /tmp/sid
I: Retrieving Release
I: Retrieving Release.gpg
I: Checking Release signature
I: Base system installed successfully.
$ fakechroot fakeroot chroot /tmp/sid apt-get install -q hello
Reading package lists...
Building dependency tree...
Reading state information...
The following NEW packages will be installed:
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 57.4 kB of archives.
After this operation, 558 kB of additional disk space will be used.
Get:1 http://ftp.us.debian.org/debian/ sid/main hello amd64 2.8-4 [57.4 kB]
Fetched 57.4 kB in 0s (127 kB/s)
Selecting previously unselected package hello.
(Reading database ... 24594 files and directories currently installed.)
Unpacking hello (from .../archives/hello_2.8-4_amd64.deb) ...
Processing triggers for man-db ...
Processing triggers for install-info ...
Setting up hello (2.8-4) ...
$ fakechroot chroot /tmp/sid hello
fakeroot(1) is a complementary tool which emulates root environment. fakeroot
and fakechroot might wrap the same C library functions, i.e. mknod(2)
function. It is important to start fake environment in proper order. fakeroot
should be started inside fakechroot:
$ fakechroot fakeroot chroot /tmp/sid /bin/mknod /tmp/device c 1 2
fakechroot is a regular, non-setuid program. It does not enhance a user's
fakechroot should not be used as a tool for enhancing system security i.e. by
separating (sandboxing) applications. It is very easy to escape from a fake
fakechroot should not be run with real root privileges. It might decrease the
security of the system because the fakechroot provides own version of core
functions with behavior depended on some environment variables.
The shared library containing the wrapper functions.
The value is true for fake chroot environment.
The version number of the current fakechroot library.
The root directory of fake chroot environment.
If this variable is set then "fakechroot version" string is printed to
standard output and the current process is terminated with status taken from
this variable. It can be a method to check if fakechroot is preloaded
$ case "`FAKECHROOT_DETECT=1 /bin/echo`" in fakechroot*) echo LOADED;; esac
The fakechroot library will dump some debugging info if this variable is set.
The root directory for unix sockets. The default value is the same as
"FAKECHROOT_BASE" and it can be set separately if the "FAKECHROOT_BASE" is
too long and the unix socket path could exceed the limit of 108 bytes.
The list of directories which are excluded from being chrooted. The elements
of list are separated with colon.
The /dev, /proc and /sys directories are excluded by default if this
environment variable is not set.
This list has to contain at most 100 elements.
A path to another dynamic linker (i.e. /lib/ld-linux.so.2 for i386
architecture, /lib64/ld-linux-x86-64.so.2 for x86_64 architecture).
This dynamic linker will be invoked directly. The dynamic linker don't allow
to change "argv" besides the file name of the executable file, so some
application won't work correctly, i.e. busybox(1).
A list of command substitutions. If a program tries to execute one of
the commands given (path relative to the chroot, trailing dot is removed) then
the substitute command runs instead (path to substitute command is not
The substituted command inherits "FAKECHROOT_*" variables but the original
"FAKECHROOT_BASE" variable which is saved as "FAKECHROOT_BASE_ORIG". It
means that substituted command runs outside fakechroot environment. Also
original command name is saved as "FAKECHROOT_CMD_ORIG".
will substitute "/bin/true" for "/usr/bin/mkfifo" and will make possible to
install sysvinit binary package.
Give as many substitute commands as you want, separated by ":"
It is suggested to substitute at least:
to make debootstrap(8) working correctly.
To prevent some looping, the command substitution is done only if
"FAKECHROOT_CMD_ORIG" variable is not set currently.
- LD_LIBRARY_PATH, LD_PRELOAD
Fakechroot is implemented by wrapping system calls. This is accomplished by
setting "LD_PRELOAD=libfakechroot.so". If this library can't be found by
dynamic linker, the /etc/ld.so.conf file or "LD_LIBRARY_PATH" variable
have to be modified.
/lib/ld-linux.so.2 and /lib64/ld-linux-x86-64.so.2 are always loaded
from real environment. This path is hardcoded by linker for all binaries.
You can set the "FAKECHROOT_ELFLOADER" environment variable or use
Every command executed within fakechroot needs to be linked to the same
version of the dynamic linker from real environment. If the libraries in
chroot are not compatible, try to use "--use-system-libs" option.
You can provide symlinks to the outside. The symlink have to be created
before chroot is called. It can be useful for accessing the real /proc
and /dev directory. You can also set the "FAKECHROOT_EXCLUDE_PATH"
$ export FAKECHROOT_EXCLUDE_PATH=/tmp:/proc:/dev:/sys:/var/run:/home
Statically linked binaries doesn't work, especially ldconfig(8), so you have
to wrap this command with dummy version and set the proper
"FAKECHROOT_CMD_SUBST" environment variable.
ldd(1) also doesn't work. You have to use "alias
ldd='LD_TRACE_LOADED_OBJECTS=1'" or to use a wrapper instead. The wrapper is
installed as ldd.fakechroot and can be used with "FAKECHROOT_CMD_SUBST"
The full screen applications hangs up if /dev/tty file is not a real
device. Link /dev/tty file or whole /dev directory to the real one or
remove it from fake chroot environment with "FAKECHROOT_EXCLUDE_PATH"
lckpwdf(3) and ulckpwdf(3) are ignored so passwd(1) command should work
Your real uid should exist in /etc/passwd. Create it with adduser --uid
realuid realuser inside fake chroot environment.
debuild(1) cleans environment. Use --preserve-env option to prevent this
rpmbuild(8) uses own glob(3) implementation which breaks fakechroot so
buildroot directory have to be the same inside and outside fakechroot.
fakeroot(1), debuild(1), debootstrap(8), rinse(8),
If you find the bug or want to implement new features, please report it at
Copyright (c) 2003-2016 Piotr Roszatycki <email@example.com>
Copyright (c) 2007 Mark Eichin <firstname.lastname@example.org>
Copyright (c) 2006, 2007 Alexander Shishkin <email@example.com>
Copyright (c) 2006, 2007 Lionel Tricon <firstname.lastname@example.org>
fakechroot is distributed under the GNU Lesser General Public License (LGPL
2.1 or greater).
- SECURITY ASPECTS
- SEE ALSO
This document was created by
using the manual pages.
Time: 13:33:19 GMT, February 20, 2019