ftpd(1M) (TCP/IP) ftpd(1M)
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:
-d Debugging information is written to the system log.
-l Each ftp session is logged in the system log.
-ttimeout
Set the inactivity timeout period to timeout, in seconds. The
FTP server will timeout an inactive session 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)
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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.
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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.
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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 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.
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