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.\"     @(#)chroot.2	8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: January 3 2021 $
.Dt CHROOT 2
.Os
.Sh NAME
.Nm chroot
.Nd change root directory
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn chroot "const char *dirname"
.Sh DESCRIPTION
.Fa dirname
is the address of the pathname of a directory, terminated by an 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.
.Sh RETURN VALUES
.Rv -std
.Sh EXAMPLES
The following example changes the root directory to
.Va newroot ,
sets the current directory to the new root, and drops some
setuid privileges.
There may be other privileges which need to be dropped as well.
.Bd -literal -offset indent
#include <err.h>
#include <unistd.h>

if (chroot(newroot) != 0 || chdir("/") != 0)
	err(1, "%s", newroot);
setresuid(getuid(), getuid(), 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 pathname is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Dv NAME_MAX
characters, or an entire pathname (including the terminating NUL)
exceeded
.Dv PATH_MAX
bytes.
.It Bq Er ENOENT
The named directory does not exist.
.It Bq Er EACCES
Search permission is denied for any component of the pathname.
.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
.Sh SEE ALSO
.Xr chdir 2
.Sh HISTORY
The
.Fn chroot
system call first appeared in
.At v7 .
.Sh CAVEATS
There are ways for a root process to escape from the chroot jail.
Changes to the directory hierarchy made from outside the chroot jail
may allow a restricted process to escape, even if it is unprivileged.
Passing directory file descriptors via
.Xr recvmsg 2
from outside the chroot jail may also allow a process to escape.