FTPD

Section: Maintenance Commands (8C)
Updated: April 27, 1985
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NAME

ftpd - DARPA Internet File Transfer Protocol server

SYNOPSIS

/usr/etc/ftpd [ -d ] [ -l ] [ -ttimeout ]

DESCRIPTION

Ftpd is the DARPA Internet File Transfer Prototocol 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.

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 -lg'')
MKD            make a directory
MODE           specify data transfer mode
NLST           give name list of files in directory (``ls'')
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
STOR           store a file
STOU           store a file with a unique name
STRU           specify data transfer structure
TYPE           specify data transfer type
USER           specify user name
XCUP           change to parent of current working directory
XCWD           change working directory
XMKD           make a directory
XPWD           print the current working directory
XRMD           remove a directory

The remaining ftp requests specified in Internet RFC 959 are recognized, but not implemented.

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.

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 commands. 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 work properly. 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.

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.