chroot: Run a command with a different root directory
chroot runs a command with a specified root directory.
On many systems, only the super-user can do this.5.
chroot option newroot [command [args]…] chroot option
Ordinarily, file names are looked up starting at the root of the
directory structure, i.e.,
chroot changes the root to
newroot (which must exist), then changes the working
/, and finally runs
command with optional
command is not specified, the default is the value of the
environment variable or
/bin/sh if not set, invoked with the
command must not be a special built-in utility
(see Special built-in utilities).
The program accepts the following options. Also see Common options. Options must precede operands.
Use this option to override the supplementary
groups to be
used by the new process.
The items in the list (names or numeric IDs) must be separated by commas.
--groups=’ to disable the supplementary group look-up
implicit in the
command is run with the same credentials
as the invoking process.
Use this option to run it as a different
user and/or with a
user is specified then the supplementary groups
are set according to the system defined list for that user,
unless overridden with the
Use this option to not change the working directory to
/ after changing
the root directory to
newroot, i.e., inside the chroot.
This option is only permitted when
newroot is the old
and therefore is mostly useful together with the
--userspec options to retain the previous working directory.
The user and group name look-up performed by the
--groups options, is done both outside and inside
the chroot, with successful look-ups inside the chroot taking precedence.
If the specified user or group items are intended to represent a numeric ID,
then a name to ID resolving step is avoided by specifying a leading ‘
See Disambiguating names and IDs.
Here are a few tips to help avoid common problems in using chroot.
To start with a simple example, make
command refer to a statically
linked binary. If you were to use a dynamically linked executable, then
you’d have to arrange to have the shared libraries in the right place under
your new root directory.
For example, if you create a statically linked
and put it in
/tmp/empty, you can run this command as root:
$ chroot /tmp/empty /ls -Rl /
Then you’ll see output like this:
/: total 1023 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
If you want to use a dynamically linked executable, say
then first run ‘
ldd bash’ to see what shared objects it needs.
Then, in addition to copying the actual binary, also copy the listed
files to the required positions under your intended new root directory.
Finally, if the executable requires any other files (e.g., data, state,
device files), copy them into place, too.
chroot is installed only on systems that have the
chroot function, so portable scripts should not rely on its
125 if chroot itself fails 126 if command is found but cannot be invoked 127 if command cannot be found the exit status of command otherwise
some systems (e.g., FreeBSD) can be configured to allow certain regular
users to use the
chroot system call, and hence to run this program.
Also, on Cygwin, anyone can run the
chroot command, because the
underlying function is non-privileged due to lack of support in MS-Windows.
chroot command avoids the
chroot system call
newroot is identical to the old
/ directory for consistency
with systems where this is allowed for non-privileged users.