CHROOT(2) BSD System Calls Manual CHROOT(2)
chroot -- change root directory
chroot(const char *dirname);
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 program is not currently running with an altered root directory,
it should be noted that chroot() has no effect on the process's current
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.
This call is restricted to the superuser.
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable errno is set to indicate the
The following example changes the root directory to 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.
if (chroot(newroot) != 0 || chdir("/") != 0)
err(1, "%s", newroot);
setresuid(getuid(), getuid(), getuid());
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 charac-
ters, or an entire pathname (including the terminating
NUL) exceeded PATH_MAX bytes.
[ENOENT] The named directory does not exist.
[EACCES] Search permission is denied for any component of the
[ELOOP] Too many symbolic links were encountered in translat-
ing the pathname.
[EFAULT] dirname points outside the process's allocated address
[EIO] An I/O error occurred while reading from or writing to
the file system.
[EPERM] The caller is not the superuser.
The chroot() system call first appeared in Version 7 AT&T UNIX.
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. Pass-
ing directory file descriptors via recvmsg(2) from outside the chroot
jail may also allow a process to escape.
BSD March 28, 2017 BSD