CHROOT(2)                 FreeBSD System Calls Manual                CHROOT(2)

NAME

     chroot, fchroot - change root directory

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>

     int
     chroot(const char *dirname);

     int
     fchroot(int fd);

DESCRIPTION

     The dirname argument is the address of the pathname of a directory,
     terminated by an ASCII NUL.  The chroot() system call 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, unless the
     `security.bsd.unprivileged_chroot' sysctl variable is set to 1 and the
     process has enabled the PROC_NO_NEW_PRIVS_CTL procctl(2).

     Depending on the setting of the `kern.chroot_allow_open_directories'
     sysctl variable, open file descriptors 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 the chroot() system call.

     Any other value for `kern.chroot_allow_open_directories' will bypass the
     check for open directories, mimicking the historic insecure behavior of
     chroot() still present on other systems.

     The fchroot() system call is identical to chroot() except it takes a file
     descriptor instead of path.

RETURN VALUES

     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS

     The chroot() and fchroot() system calls will fail and the root directory
     will be unchanged if:

     [EPERM]            The effective user ID is not the super-user and the
                        `security.bsd.unprivileged_chroot' sysctl is 0.

     [EPERM]            The effective user ID is not the super-user and the
                        process has not enabled the PROC_NO_NEW_PRIVS_CTL
                        procctl(2).

     [EPERM]            One or more file descriptors are open directories and
                        the `kern.chroot_allow_open_directories' sysctl is not
                        set to permit this.

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

     [EINTEGRITY]       Corrupted data was detected while reading from the
                        file system.

     The chroot() system call 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 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]           The dirname argument points outside the process's
                        allocated address space.

     The fchroot() system call 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.

     [ENOTDIR]          The file descriptor does not reference a directory.

SEE ALSO

     chdir(2), jail(2)

HISTORY

     The chroot() system call appeared in Version 7 AT&T UNIX.  It was marked
     as "legacy" in Version 2 of the Single UNIX Specification ("SUSv2"), and
     was removed in subsequent standards.  The fchroot() system call first
     appeared in FreeBSD 15.0.

BUGS

     If the process is able to change its working directory to the target
     directory, but another access control check fails (such as a check for
     open directories, or a MAC check), it is possible that this system call
     may return an error, with the working directory of the process left
     changed.

SECURITY CONSIDERATIONS

     The system has many hardcoded paths to files which it may load after the
     process starts.  It is generally recommended to drop privileges
     immediately after a successful chroot call, and restrict write access to
     a limited subtree of the chroot root.  For instance, setup the sandbox so
     that the sandboxed user will have no write access to any well-known
     system directories.

     For complete isolation from the rest of the system, use jail(2) instead.

FreeBSD 15.1-STABLE-HBSD        April 27, 2026                       CHROOT(2)