chroot(2) - Linux manual page (original) (raw)

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 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 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)](../man2/open.2.html).  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)](../man2/chdir.2.html) 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)](../man2/chdir.2.html) 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 top

   On success, zero is returned.  On error, -1 is returned, and _[errno](../man3/errno.3.html)_
   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)](../man7/path%5Fresolution.7.html).)

   **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 top

   None.

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)](../man2/fork.2.html) inherits its parent's root
   directory.  The root directory is left unchanged by [execve(2)](../man2/execve.2.html).

   The magic symbolic link, _/proc/_pid_/root_, can be used to discover a
   process's root directory; see [proc(5)](../man5/proc.5.html) for details.

   FreeBSD has a stronger **jail**() system call.

SEE ALSO top

   [chroot(1)](../man1/chroot.1.html), [chdir(2)](../man2/chdir.2.html), [pivot_root(2)](../man2/pivot%5Froot.2.html), [path_resolution(7)](../man7/path%5Fresolution.7.html),
   [switch_root(8)](../man8/switch%5Froot.8.html)

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   man-pages@man7.org

Linux man-pages 6.10 2024-07-23 chroot(2)

Pages that refer to this page:capsh(1), chroot(1), dpkg(1), nsenter(1), systemd-detect-virt(1), chdir(2), clone(2), getrandom(2), mount(2), openat2(2), pivot_root(2), syscalls(2), unshare(2), cap_launch(3), getcwd(3), syslog(3), system(3), core(5), proc(5), proc_pid_mountinfo(5), proc_pid_root(5), systemd.exec(5), capabilities(7), path_resolution(7), pthreads(7), lloadd(8), slapd(8), switch_root(8)