chroot(2) — Linux manual page


chroot(2)                  System Calls Manual                 chroot(2)

NAME         top

       chroot - change root directory

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <unistd.h>

       int chroot(const char *path);

   Feature Test Macro Requirements for glibc (see

           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:

DESCRIPTION         top

       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

       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

           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         top

       On success, zero is returned.  On error, -1 is returned, and
       errno is set to indicate the error.

ERRORS         top

       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 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.

STANDARDS         top


HISTORY         top

       SVr4, 4.4BSD, SUSv2 (marked LEGACY).  This function is not part
       of POSIX.1-2001.

NOTES         top

       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.

SEE ALSO         top

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

Linux man-pages (unreleased)     (date)                        chroot(2)

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