CHROOT
Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
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NAME
chroot - change root directory
SYNOPSIS
#include <unistd.h>
int chroot(const char *path);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
chroot():
-
- Since glibc 2.2.2:
-
_XOPEN_SOURCE && ! (_POSIX_C_SOURCE >= 200112L)
|| /* Since glibc 2.20: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
-
-
Before glibc 2.2.2: none
DESCRIPTION
chroot()
changes the root directory of the calling process to that specified in
path.
This directory will be used for pathnames beginning with
/.
The root directory is inherited by all children of the calling process.
Only a privileged process (Linux: one with the
CAP_SYS_CHROOT
capability in its user namespace) may call
chroot().
This call changes an ingredient in the pathname resolution process
and does nothing else.
In particular, it is not intended to be used
for any kind of security purpose, neither to fully sandbox a process nor
to restrict filesystem system calls.
In the past,
chroot()
has been used by daemons to restrict themselves prior to passing paths
supplied by untrusted users to system calls such as
open(2).
However, if a folder is moved out of the chroot directory, an attacker
can exploit that to get out of the chroot directory as well.
The easiest way to do that is to
chdir(2)
to the to-be-moved directory, wait for it to be moved out, then open a
path like ../../../etc/passwd.
A slightly
trickier variation also works under some circumstances if
chdir(2)
is not permitted.
If a daemon allows a "chroot directory" to be specified,
that usually means that if you want to prevent remote users from accessing
files outside the chroot directory, you must ensure that folders are never
moved out of it.
This call does not change the current working directory,
so that after the call aq.aq can
be outside the tree rooted at aq/aq.
In particular, the superuser can escape from a "chroot jail"
by doing:
mkdir foo; chroot foo; cd ..
This call does not close open file descriptors, and such file
descriptors may allow access to files outside the chroot tree.
RETURN VALUE
On success, zero is returned.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
Depending on the filesystem, other errors can be returned.
The more general errors are listed below:
- EACCES
-
Search permission is denied on a component of the path prefix.
(See also
path_resolution(7).)
- EFAULT
-
path
points outside your accessible address space.
- EIO
-
An I/O error occurred.
- ELOOP
-
Too many symbolic links were encountered in resolving
path.
- ENAMETOOLONG
-
path
is too long.
- ENOENT
-
The file does not exist.
- ENOMEM
-
Insufficient kernel memory was available.
- ENOTDIR
-
A component of
path
is not a directory.
- EPERM
-
The caller has insufficient privilege.
CONFORMING TO
SVr4, 4.4BSD, SUSv2 (marked LEGACY).
This function is not part of POSIX.1-2001.
NOTES
A child process created via
fork(2)
inherits its parent's root directory.
The root directory is left unchanged by
execve(2).
FreeBSD has a stronger
jail()
system call.
SEE ALSO
chroot(1),
chdir(2),
pivot_root(2),
path_resolution(7),
switch_root(8)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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