.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992 .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .\" Modified by Michael Haardt .\" Modified 1993-07-21 by Rik Faith .\" Modified 1994-08-21 by Michael Chastain .\" Modified 1996-06-13 by aeb .\" Modified 1996-11-06 by Eric S. Raymond .\" Modified 1997-08-21 by Joseph S. Myers .\" Modified 2004-06-23 by Michael Kerrisk .\" .TH CHROOT 2 2020-12-21 "Linux" "Linux Programmer's Manual" .SH NAME chroot \- change root directory .SH SYNOPSIS .B #include .PP .BI "int chroot(const char *" path ); .PP .RS -4 Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .RE .PP .BR chroot (): .ad l .RS 4 .PD 0 .TP 4 Since glibc 2.2.2: .nf _XOPEN_SOURCE && ! (_POSIX_C_SOURCE\ >=\ 200112L) || /* Since glibc 2.20: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE .fi .TP 4 Before glibc 2.2.2: none .PD .RE .ad b .SH DESCRIPTION .BR chroot () changes the root directory of the calling process to that specified in .IR path . This directory will be used for pathnames beginning with \fI/\fP. The root directory is inherited by all children of the calling process. .PP Only a privileged process (Linux: one with the .B CAP_SYS_CHROOT capability in its user namespace) may call .BR chroot (). .PP 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, .BR chroot () has been used by daemons to restrict themselves prior to passing paths supplied by untrusted users to system calls such as .BR 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 .BR chdir (2) to the to-be-moved directory, wait for it to be moved out, then open a path like ../../../etc/passwd. .PP .\" This is how the "slightly trickier variation" works: .\" https://github.com/QubesOS/qubes-secpack/blob/master/QSBs/qsb-014-2015.txt#L142 A slightly trickier variation also works under some circumstances if .BR 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. .PP This call does not change the current working directory, so that after the call \(aq\fI.\fP\(aq can be outside the tree rooted at \(aq\fI/\fP\(aq. In particular, the superuser can escape from a "chroot jail" by doing: .PP .in +4n .EX mkdir foo; chroot foo; cd .. .EE .in .PP This call does not close open file descriptors, and such file descriptors may allow access to files outside the chroot tree. .SH RETURN VALUE On success, zero is returned. On error, \-1 is returned, and .I errno is set appropriately. .SH ERRORS Depending on the filesystem, other errors can be returned. The more general errors are listed below: .TP .B EACCES Search permission is denied on a component of the path prefix. (See also .BR path_resolution (7).) .\" Also search permission is required on the final component, .\" maybe just to guarantee that it is a directory? .TP .B EFAULT .I path points outside your accessible address space. .TP .B EIO An I/O error occurred. .TP .B ELOOP Too many symbolic links were encountered in resolving .IR path . .TP .B ENAMETOOLONG .I path is too long. .TP .B ENOENT The file does not exist. .TP .B ENOMEM Insufficient kernel memory was available. .TP .B ENOTDIR A component of .I path is not a directory. .TP .B EPERM The caller has insufficient privilege. .SH CONFORMING TO SVr4, 4.4BSD, SUSv2 (marked LEGACY). This function is not part of POSIX.1-2001. .\" SVr4 documents additional EINTR, ENOLINK and EMULTIHOP error conditions. .\" X/OPEN does not document EIO, ENOMEM or EFAULT error conditions. .SH NOTES A child process created via .BR fork (2) inherits its parent's root directory. The root directory is left unchanged by .BR execve (2). .PP The magic symbolic link, .IR /proc/[pid]/root , can be used to discover a process's root directory; see .BR proc (5) for details. .PP FreeBSD has a stronger .BR jail () system call. .SH SEE ALSO .BR chroot (1), .BR chdir (2), .BR pivot_root (2), .BR path_resolution (7), .BR switch_root (8) .SH COLOPHON This page is part of release 5.10 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.