FTPD(8)

NAME
ftpd - DARPA Internet File Transfer Protocol server

SYNOPSIS
/usr/sbin/ftpd [ -d ] [ -l ] [ -ttimeout ] [ -Tmaxtimeout ]

DESCRIPTION
Ftpd is the DARPA Internet File Transfer Protocol server process. The server uses the TCP protocol and listens at the port specified in the ``ftp'' service specification; see services(5).

If the -d option is specified, debugging information is written to the syslog.

If the -l option is specified, each ftp session is logged in the syslog.

The ftp server will timeout an inactive session after 15 minutes. If the -t option is specified, the inactivity timeout period will be set to timeout seconds. A client may also request a different timeout period; the maximum period allowed may be set to timeout seconds with the -T option. The default limit is 2 hours.

The ftp server currently supports the following ftp requests; case is not distinguished.

Request	Description
ABOR	abort previous command
ACCT	specify account (ignored)
ALLO	allocate storage (vacuously)
APPE	append to a file
CDUP	change to parent of current working directory
CWD	change working directory
DELE	delete a file
HELP	give help information
LIST	give list files in a directory (``ls -lgA'')
MKD	make a directory
MDTM	show last modification time of file
MODE	specify data transfer mode
NLST	give name list of files in directory
NOOP	do nothing
PASS	specify password
PASV	prepare for server-to-server transfer
PORT	specify data connection port
PWD	print the current working directory
QUIT	terminate session
RETR	retrieve a file
RMD	remove a directory
RNFR	specify rename-from file name
RNTO	specify rename-to file name
SITE	non-standard commands (see next section)
SIZE	return size of file
STAT	return status of server
STOR	store a file
STOU	store a file with a unique name
STRU	specify data transfer structure
SYST	show operating system type of server system
TYPE	specify data transfer type
USER	specify user name
XCUP	change to parent of current working directory (deprecated)
XCWD	change working directory (deprecated)
XMKD	make a directory (deprecated)
XPWD	print the current working directory (deprecated)
XRMD	remove a directory (deprecated)

The following non-standard or UNIX specific commands are supported by the SITE request.

Request	Description
UMASK	change umask. E.g. SITE UMASK 002
IDLE	set idle-timer. E.g. SITE IDLE 60
CHMOD	change mode of a file. E.g. SITE CHMOD 755 filename
HELP	give help information. E.g. SITE HELP

The remaining ftp requests specified in Internet RFC 959 are recognized, but not implemented. MDTM and SIZE are not specified in RFC 959, but will appear in the next updated FTP RFC.

The ftp server will abort an active file transfer only when the ABOR command is preceded by a Telnet "Interrupt Process" (IP) signal and a Telnet "Synch" signal in the command Telnet stream, as described in Internet RFC 959. If a STAT command is received during a data transfer, preceded by a Telnet IP and Synch, transfer status will be returned.

Ftpd interprets file names according to the ``globbing'' conventions used by csh(1). This allows users to utilize the metacharacters ``*?[]{}~''.

Ftpd authenticates users according to three rules.

1)  The user name must be in the password data base, /etc/passwd, and not have a null password. In this case a password must be provided by the client before any file operations may be performed.

2)  The user name must not appear in the file /etc/ftpusers.

3)  The user must have a standard shell returned by getusershell(3).

4)  If the user name is ``anonymous'' or ``ftp'', an anonymous ftp account must be present in the password file (user ``ftp''). In this case the user is allowed to log in by specifying any password (by convention this is given as the client host's name).

In the last case, ftpd takes special measures to restrict the client's access privileges. The server performs a chroot(2) command to the home directory of the ``ftp'' user. In order that system security is not breached, it is recommended that the ``ftp'' subtree be constructed with care; the following rules are recommended.

~ftp)
    Make the home directory owned by ``ftp'' and unwritable by anyone.

~ftp/bin)
    Make this directory owned by the super-user and unwritable by anyone. The program ls(1) must be present to support the list command. This program should have mode 111.

~ftp/etc)
    Make this directory owned by the super-user and unwritable by anyone. The files passwd(5) and group(5) must be present for the ls command to be able to produce owner names rather than numbers. The password field in passwd is not used, and should not contain real encrypted passwords. These files should be mode 444.

~ftp/pub)
    Make this directory mode 777 and owned by ``ftp''. Users should then place files which are to be accessible via the anonymous account in this directory.

SEE ALSO
ftp(1C), getusershell(3), syslogd(8)

BUGS
The anonymous account is inherently dangerous and should avoided when possible.

The server must run as the super-user to create sockets with privileged port numbers. It maintains an effective user id of the logged in user, reverting to the super-user only when binding addresses to sockets. The possible security holes have been extensively scrutinized, but are possibly incomplete.