.\"	$MirOS: src/lib/libc/sys/chroot.2,v 1.3 2005/09/22 20:17:49 tg Exp $
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.\"     @(#)chroot.2	8.1 (Berkeley) 6/4/93
.\"
.Dd March 10, 2004
.Dt CHROOT 2
.Os
.Sh NAME
.Nm chroot
.Nd change root directory
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn chroot "const char *dirname"
.Ft int
.Fn fchroot "int fd"
.Sh DESCRIPTION
.Fa dirname
is the address of the pathname of a directory, terminated by an
.Tn ASCII
NUL.
.Fn chroot
causes
.Fa dirname
to become the root directory, that is, the starting point for path
searches of pathnames beginning with
.Ql / .
.Pp
In order for a directory to become the root directory
a process must have execute (search) access for that directory.
.Pp
If the program is not currently running with an altered root directory,
it should be noted that
.Fn chroot
has no effect on the process's current directory.
.Pp
If the program is already running with an altered root directory, the
process's current directory is changed to the same new root directory.
This prevents the current directory from being further up the directory
tree than the altered root directory.
.Pp
This call is restricted to the superuser.
.Pp
The
.Fn fchroot
function performs the same operation on an open directory file
known by the file descriptor
.Fa fd .
.Sh RETURN VALUES
Upon successful completion, a value of 0 is returned.
Otherwise, a value of \-1 is returned and
.Va errno
is set to indicate an error.
.Sh EXAMPLES
The following example changes the root directory to
.Va newroot ,
sets the current directory to the new root, and drops any
setuid privileges.
.Bd -literal -offset indent
#include <err.h>
#include <unistd.h>

if (chroot(newroot) != 0 || chdir("/") != 0)
	err(1, "%s", newroot);
seteuid(getuid());
setuid(getuid());
.Ed
.Sh ERRORS
.Fn chroot
will fail and the root directory will be unchanged if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path name is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Dv {NAME_MAX}
characters, or an entire path name exceeded
.Dv {PATH_MAX}
characters.
.It Bq Er ENOENT
The named directory does not exist.
.It Bq Er EACCES
Search permission is denied for any component of the path name.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EFAULT
.Fa dirname
points outside the process's allocated address space.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.It Bq Er EPERM
The caller is not the superuser.
.El
.Pp
.Fn fchroot
will fail and the root directory will be unchanged if:

.Bl -tag -width Er
.It Bq Er EACCES
Search permission is denied for the directory referenced
by the file descriptor.
.It Bq Er EBADF
The argument
.Fa fd
is not a valid file descriptor.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.It Bq Er ENOTDIR
The argument
.Fa fd
does not reference a directory.
.It Bq Er EPERM
The effective user ID of the calling process is not the super-user.
.El
.Sh SEE ALSO
.Xr chdir 2
.Sh STANDARDS
The
.Fn chroot
function conforms to
.St -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.
.Pp
.Fn chroot
was declared a legacy interface, and subsequently removed in
.St -p1003.1-2001 .
.Sh HISTORY
The
.Fn chroot
function call appeared in
.Bx 4.2 .
The
.Fn fchroot
function appeared in
.Nx 1.4
and was ported to
.Mx 8 .
.Sh CAVEATS
There are ways for a root process to escape from the chroot jail.