NAME

ftpd − DARPA Internet File Transfer Protocol server

SYNOPSIS

/usr/etc/in.ftpd host.socket

DESCRIPTION

Ftpd is the DARPA Internet File Transfer Prototocol server process.  The server is invoked by the Internet daemon inetd(8C) each time a connection to the ftp service (see services(5)) 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 60 seconds. 

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

Request Description
ACCTspecify account (ignored)
ALLOallocate storage (vacuously)
APPEappend to a file
CWDchange working directory
DELEdelete a file
HELPgive help information
LISTgive list files in a directory (“ls -lg”)
MODEspecify data transfer mode
NLSTgive name list of files in directory (“ls”)
NOOPdo nothing
PASSspecify password
PORTspecify data connection port
QUITterminate session
RETRretrieve a file
RNFRspecify rename-from file name
RNTOspecify rename-to file name
STORstore a file
STRUspecify data transfer structure
TYPEspecify data transfer type
USERspecify user name
XCUPchange to parent of current working directory
XCWDchange working directory
XMKDmake a directory
XPWDprint the current working directory
XRMDremove a directory

The remaining ftp requests specified in Internet RFC 765 are recognized, but not implemented. 

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 /usr/etc/ftpusers.

3)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.

~ftpMake the home directory owned by “ftp” and unwritable by anyone. 

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

~ftp/etcMake 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.

SEE ALSO

ftp(1C), ftpusers(5)

BUGS

There is no support for aborting commands. 

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. 

Sun Release 3.2  —  Last change: 23 October 1984