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


     chroot - change root directory


     #include <unistd.h>
     int chroot(const char *path);
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
         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


     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
     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
     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  descrip-
     tors may allow access to files outside the chroot tree.


     On  success,  zero is returned.  On error, -1 is returned, and errno is
     set appropriately.


     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.
            path is too long.
     ENOENT The file does not exist.
     ENOMEM Insufficient kernel memory was available.
            A component of path is not a directory.
     EPERM  The caller has insufficient privilege.


     SVr4, 4.4BSD, SUSv2 (marked LEGACY).  This  function  is  not  part  of


     A  child  process created via fork(2) inherits its parent's root direc-
     tory.  The root directory is left unchanged by execve(2).
     FreeBSD has a stronger jail() system call.


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


     This page is part of release 4.16 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

Linux 2017-09-15 CHROOT(2)

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