Ubuntu Manpage: chroot - change root directory

NAME

       chroot - change root directory

LIBRARY

       Standard C library (libc, -lc)

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 <= 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 '.' can be
outside the tree rooted at '/'. 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 to indicate the
       error.

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.

STANDARDS

       None.

HISTORY

       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).

       The  magic  symbolic  link,  /proc/pid/root,  can  be  used  to  discover a process's root
       directory; see proc(5) for details.

       FreeBSD has a stronger jail() system call.