NAME

chroot — change root directory

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <unistd.h>

int
chroot(const char *dirname);

int
fchroot(int fd);

DESCRIPTION

dirname is the address of the pathname of a directory, terminated by an ASCII NUL. chroot() causes dirname to become the root directory, that is, the starting point for path searches of pathnames beginning with ‘/’.

In order for a directory to become the root directory a process must have execute (search) access for that directory.

If the current working directory is not at or under the new root directory, it is silently set to the new root directory. It should be noted that, on most other systems, chroot() has no effect on the process's current directory.

This call is restricted to the super-user.

The fchroot() function performs the same operation on an open directory file known by the file descriptor fd.

RETURN VALUES

Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate an error.

ERRORS

chroot() will fail and the root directory will be unchanged if:

[ENOTDIR]

A component of the path name is not a directory.

[ENAMETOOLONG]

A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} characters.

[ENOENT]

The named directory does not exist.

[EACCES]

Search permission is denied for any component of the path name.

[ELOOP]

Too many symbolic links were encountered in translating the pathname.

[EFAULT]

dirname points outside the process's allocated address space.

[EIO]

An I/O error occurred while reading from or writing to the file system.

[EPERM]

The effective user ID of the calling process is not the super-user.

fchroot() will fail and the root directory will be unchanged if:

[EACCES]

Search permission is denied for the directory referenced by the file descriptor.

[EBADF]

The argument fd is not a valid file descriptor.

[EIO]

An I/O error occurred while reading from or writing to the file system.

[ENOTDIR]

The argument fd does not reference a directory.

[EPERM]

The effective user ID of the calling process is not the super-user.

SEE ALSO

chdir(2)

STANDARDS

The chroot() function conforms to X/Open System Interfaces and Headers Issue 5 (“XSH5”), with the restriction that the calling process' working directory must be at or under the new root directory. Otherwise, the working directory is silently set to the new root directory; this is an extension to the standard.

chroot() was declared a legacy interface, and subsequently removed in IEEE Std 1003.1-2001 (“POSIX.1”).

HISTORY

The chroot() function call appeared in 4.2BSD. Working directory handling was changed in NetBSD 1.4 to prevent one way a process could use a second chroot() call to a different directory to "escape" from the restricted subtree. The fchroot() function appeared in NetBSD 1.4.