NAME

ftpd - file transfer protocol server

SYNOPSIS

in.ftpd [ -dl ] [ -ttimeout ] host.socket

DESCRIPTION

ftpd is the Internet File Transfer Protocol (FTP) server process. The server is invoked by the Internet daemon inetd(1M) each time a connection to the FTP service [see services(4)] is made, with the connection available as descriptor 0 and the host and socket the connection originated from (in hex and decimal respectively) as argument.

Inactive connections are timed out after 90 seconds.

The following options are available:

-ttimeout

     Set  the  inactivity  timeout  period  to  timeout,  in
     seconds.   The FTP server will timeout an inactive ses-
     sion after 15 minutes.

Requests

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 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 RFC 959.

ftpd interprets file names according to the globbing conventions used by sh(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) If the user name appears in the file /etc/ftpusers, ftp access is denied.

3)   ftp access is denied  unless  the  user's  shell  (from
     /etc/passwd)  is listed in the file /etc/shells, or the
     user's shell is one of the following:
     /bin/sh
     /bin/ksh
     /bin/csh
     /usr/bin/sh
     /usr/bin/ksh
     /usr/bin/csh

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.

home_directory

Make the home directory owned by ftp and unwritable by anyone.

home_directory/usr/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.

home_directory/etc

Make this directory owned by the super-user and unwritable by anyone. Copies of the files passwd(4), group(4), and netconfig must be present for the ls command to work properly. These files should be mode 444.

home_directory/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.

home_directory/dev

Make this directory owned by the super-user and unwritable by anyone. Change directories to this directory and do the following:

FTP="`grep ^ftp: /etc/passwd | cut -d: -f6`"
MAJORMINOR="`ls -l /dev/tcp | nawk '{ gsub(/,/, ""); print $5, $6}'`
mknod $FTP/dev/tcp c $MAJORMINOR
chmod 666 $FTP/dev/tcp

SEE ALSO

ftp(1), getsockopt(3N), passwd(4), services(4).

Postel, Jon, and  Joyce  Reynolds,  File  Transfer  Protocol
(FTP),  RFC  959,  Network  Information Center, SRI Interna-
tional, Menlo Park, Calif., October 1985.

NOTES

The anonymous account is inherently dangerous and should be 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.

/etc/ftpusers contains a list of users who cannot access the system; the format of the file is one username per line.