ftpd(8c)
NAME
ftpd − DARPA Internet File Transfer Protocol server
SYNTAX
/etc/ftpd [ −d ] [ −l ] [ −ttimeout ]
DESCRIPTION
The ftpd server is the DARPA Internet File Transfer Protocol server process. The server uses the TCP protocol and is invoked by inetd(8c) when it receives a connection on the port specified in the “ftp” service specification. For further information, see services(5).
If the −d option is specified, certain debugging messages printed by ftpd will be enabled.
If the −l option is specified, each ftp session is logged on the standard output. This allows a line of the form “/etc/ftpd -l > /tmp/ftplog” to be used to conveniently maintain a log of ftp sessions.
The ftp server will timeout an inactive session after 60 seconds. 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
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.
The ftpd server interprets file names according to the “globbing” conventions used by csh(1). This allows users to utilize the metacharacters “*?[]{}~”.
The ftpd server 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)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() and group() 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.
RESTRICTIONS
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.