chroot

CHROOT(2)                  Linux Programmer's Manual                 CHROOT(2)

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  capabil-
       ity 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 en-
       sure 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  descrip-
       tors 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 direc-
       tory.  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.

SEE ALSO
       chroot(1), chdir(2), pivot_root(2), path_resolution(7), switch_root(8)

COLOPHON
       This  page  is  part of release 5.05 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/.

Linux                             2019-03-06                         CHROOT(2)