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 an argument. 

Inactive connections are timed out after 90 seconds. 

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

OPTIONS

−ttimeout Set the inactivity timeout period to timeout , in seconds.  The FTP server will timeout an inactive session after 15 minutes. 

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 International, 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. 

SunOS 5.1  —  Last change: 5 Jul 1990