NAME
chroot,
chroot_kernel —
change root directory
LIBRARY
library “libc”
SYNOPSIS
#include
<unistd.h>
int
chroot(const
char *dirname);
int
chroot_kernel(const
char *dirname);
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.
It should be noted that
chroot() has
no effect on the process's current directory.
This call is restricted to the super-user.
Depending on the setting of the
kern.chroot_allow_open_directories sysctl variable,
open filedescriptors which reference directories will make the
chroot()
fail as follows:
If
kern.chroot_allow_open_directories is set to zero,
chroot()
will always fail with EPERM if there are any
directories open.
If
kern.chroot_allow_open_directories is set to one (the
default),
chroot()
will fail with EPERM if there are any directories
open and the process is already subject to a
chroot() call.
Any other value for kern.chroot_allow_open_directories will bypass the check for open directories
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate an error.
The
chroot_kernel()
system call adjusts the kernel's internal namecache and root vnode
references to dirname. If used in conjunction with
chroot() during early boot, it allows for changing
the root mount to any mount point available at that time.
ERRORS
Chroot() will fail and the root directory
will be unchanged if:
- [
ENOTDIR] - A component of the path name is not a directory.
- [
EPERM] - The effective user ID is not the super-user, or one or more filedescriptors are open directories.
- [
ENAMETOOLONG] - A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 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.
SEE ALSO
HISTORY
The chroot() function call appeared in
4.2BSD.