chroot(2) System Calls Manual chroot(2)
NAME
chroot - change root directory
LIBRARY
Standard C library (libc, -lc)
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 <= 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 to indicate the error.
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.
STANDARDS
None.
HISTORY
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)
Linux man-pages 6.7 2023-10-31 chroot(2)
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