TFTPD(8)

NAME
tftpd - Internet Trivial File Transfer Protocol server

SYNOPSIS
/usr/libexec/tftpd [-cCln] [-s directory] [-u user] [directory ...]

DESCRIPTION
The tftpd utility is a server which supports the Internet Trivial File Transfer Protocol (RFC 1350). The TFTP server operates at the port indicated in the ‘tftp’ service description; see services(5). The server is normally started by inetd(8).

The use of tftp(1) does not require an account or password on the remote system. Due to the lack of authentication information, tftpd will allow only publicly readable files to be accessed. Files containing the string ``/../'' or starting with ``../'' are not allowed. Files may be written only if they already exist and are publicly writable. Note that this extends the concept of “public” to include all users on all hosts that can be reached through the network; this may not be appropriate on all systems, and its implications should be considered before enabling tftp service. The server should have the user ID with the lowest possible privilege.

Access to files may be restricted by invoking tftpd with a list of directories by including up to 20 pathnames as server program arguments in /etc/inetd.conf. In this case access is restricted to files whose names are prefixed by one of the given directories. The given directories are also treated as a search path for relative filename requests.

The -s option provides additional security by changing tftpd's root directory, thereby prohibiting accesses outside of the specified directory. Because chroot(2) requires super-user privileges, tftpd must be run as root. However, after performing the chroot(), tftpd will set its user id to that of the specified user, or “nobody” if no -u option is specified.

The options are:

-c  Changes the default root directory of a connecting host via chroot based on the connecting IP address. This prevents multiple clients from writing to the same file at the same time. If the directory does not exist, the client connection is refused. The -s option is required for -c and the specified directory is used as a base.

-C  Operates the same as -c except it falls back to -s's directory if a directory does not exist for the client's IP.

-l  Log all requests using syslog(3) with the facility of LOG_FTP. Note: Logging of LOG_FTP messages must also be enabled in the syslog configuration file, syslog.conf(5).

-n  Suppress negative acknowledgement of requests for nonexistent relative filenames.

-s directory
    Cause tftpd to change its root directory to directory. After changing roots but before accepting commands, tftpd will switch credentials to an unprivileged user.

-u user
    Switch credentials to user (default “nobody”) when the -s option is used. The user must be specified by name, not a numeric UID.

SEE ALSO
tftp(1), chroot(2), inetd(8), syslogd(8) K. R. Sollins, The TFTP Protocol (Revision 2), July 1992, RFC 1350, STD 33.

HISTORY
The tftpd utility appeared in 4.2BSD; the -s option was introduced in FreeBSD 2.2, the -u option was introduced in FreeBSD 4.2, and the -c option was introduced in FreeBSD 4.3.

BUGS
Files larger than 33488896 octets (65535 blocks) cannot be transferred without client and server supporting blocksize negotiation (RFC 1783).

Many tftp clients will not transfer files over 16744448 octets (32767 blocks).