chroot - change root directory
int chroot(const char *path);
Feature Test Macro Requirements for glibc (see feature_test_macros
- 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
() changes the root directory of the calling process to that
specified in path
. This directory will be used for pathnames beginning
. The root directory is inherited by all children of the calling
Only a privileged process (Linux: one with the CAP_SYS_CHROOT
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
A slightly trickier variation also works under some circumstances if
(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.
On success, zero is returned. On error, -1 is returned, and errno
Depending on the filesystem, other errors can be returned. The more general
errors are listed below:
- Search permission is denied on a component of the path prefix. (See also
- path points outside your accessible address space.
- An I/O error occurred.
- Too many symbolic links were encountered in resolving path.
- path is too long.
- The file does not exist.
- Insufficient kernel memory was available.
- A component of path is not a directory.
- The caller has insufficient privilege.
SVr4, 4.4BSD, SUSv2 (marked LEGACY). This function is not part of POSIX.1-2001.
A child process created via fork
(2) inherits its parent's root directory.
The root directory is left unchanged by execve
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.