FTPD(8)

NAME
ftpd - Internet File Transfer Protocol server

SYNOPSIS
ftpd [-4] [-6] [-d] [-l [-l]] [-A] [-D] [-R] [-S] [-U] [-T maxtimeout] [-t timeout] [-a address] [-p file]

DESCRIPTION
Ftpd is the Internet File Transfer Protocol server process. The server uses the TCP protocol and listens at the port specified in the “ftp” service specification; see services(5).

Available options:

-d  Debugging information is written to the syslog using LOG_FTP.

-l  Each successful and failed ftp(1) session is logged using syslog with a facility of LOG_FTP. If this option is specified twice, the retrieve (get), store (put), append, delete, make directory, remove directory and rename operations and their filename arguments are also logged. Note: LOG_FTP messages are not displayed by syslogd(8) by default, and may have to be enabled in syslogd(8)'s configuration file.

-D  With this option set, ftpd will detach and become a daemon, accepting connections on the FTP port and forking children processes to handle them. This is lower overhead than starting ftpd from inetd(8) and is thus useful on busy servers to reduce load.

-R  With this option set, ftpd will revert to historical behavior with regard to security checks on user operations and restrictions on PORT requests. Currently, ftpd will only honor PORT commands directed to unprivileged ports on the remote user's host (which violates the FTP protocol specification but closes some security holes).

-S  With this option set, ftpd logs all anonymous transfers to the file /var/log/ftpd when this file exists.

-U  In previous versions of ftpd, when a passive mode client requested a data connection to the server, the server would use data ports in the range 1024..4999. Now, by default, the server will use data ports in the range 49152..65535. Specifying this option will revert to the old behavior.

-T  A client may also request a different timeout period; the maximum period allowed may be set to timeout seconds with the -T option. The default limit is 2 hours.

-t  The inactivity timeout period is set to timeout seconds (the default is 15 minutes).

-a  When -D is specified, accept connections only on the specified address.

-p  When -D is specified, write the daemon's process ID to file.

-6  When -D is specified, accept connections via AF_INET6 socket.

-4  When -D is specified, accept IPv4 connections. When -6 is also specified, accept IPv4 connection via AF_INET6 socket. When -6 is not specified, accept IPv4 connection via AF_INET socket.

-A  Allow only anonymous ftp access.

The file /var/run/nologin can be used to disable ftp access. If the file exists, ftpd displays it and exits. If the file /etc/ftpwelcome exists, ftpd prints it before issuing the “ready” message. If the file /etc/ftpmotd exists, ftpd prints it after a successful login. Note the motd file used is the one relative to the login environment. This means the one in ~ftp/etc in the anonymous user's case.

The ftp server currently supports the following ftp requests. The case of the requests is ignored.
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 -lgA”)
MKD | make a directory
MDTM | show last modification time of file
MODE | specify data transfer mode
NLST | give name list of files in directory
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
REST | restart incomplete transfer
RETR | retrieve a file
RMD | remove a directory
RNFR | specify rename-from file name
RNTO | specify rename-to file name
SITE | non-standard commands (see next section)
SIZE | return size of file
STAT | return status of server
STOR | store a file
STOU | store a file with a unique name
STRU | specify data transfer structure
SYST | show operating system type of server system
TYPE | specify data transfer type
USER | specify user name
XCUP | change to parent of current working directory (deprecated)
XCWD | change working directory (deprecated)
XMKD | make a directory (deprecated)
XPWD | print the current working directory (deprecated)
XRMD | remove a directory (deprecated)
LPSV | prepare for server-to-server transfer, multiprotocol
LPRT | specify data connection port, multiprotocol
EPSV | prepare for server-to-server transfer, multiprotocol
EPRT | specify data connection port, multiprotocol

The following non-standard or UNIX specific commands are supported by the SITE request.

Request | Description
UMASK | change umask, e.g. ``SITE UMASK 002''
IDLE | set idle-timer, e.g. ``SITE IDLE 60''
CHMOD | change mode of a file, e.g. ``SITE CHMOD 755 filename''
HELP | give help information

The remaining ftp requests specified in Internet RFC 959 are recognized, but not implemented. MDTM and SIZE are not specified in RFC 959, but will appear in the next updated FTP RFC.

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 Internet RFC 959. If a STAT command is received during a data transfer, preceded by a Telnet IP and Synch, transfer status will be returned.

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 five rules.

1.  The login name must be in the password data base and not have a null password. In this case a password must be provided by the client before any file operations may be performed. If the user has an S/Key key, the response from a successful USER command will include an S/Key challenge. The client may choose to respond with a PASS command giving either a standard password or an S/Key one-time password. The server will automatically determine which type of password it has been given and attempt to authenticate accordingly. See key(1) for more information on S/Key authentication. S/Key is a Trademark of Bellcore.

2.  The login name must not appear in the file /etc/ftpusers.

3.  The login name must not be a member of a group specified in the file /etc/ftpusers. Entries in this file interpreted as group names are prefixed by an "at" ‘@’ sign.

4.  The user must have a standard shell returned by getusershell(3).

5.  If the user name appears in the file /etc/ftpchroot, or the user is a member of a group with a group entry in this file, i.e. one prefixed with ‘@’, the session's root will be changed to the user's login directory by chroot(2) as for an “anonymous” or “ftp” account (see next item). This facility may also be triggered by enabling the boolean "ftp-chroot" capability in login.conf(5). However, the user must still supply a password. This feature is intended as a compromise between a fully anonymous account and a fully privileged account. The account should also be set up as for an anonymous account.

6.  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 an email address for the user should be used as the password). When the -S option is set, all transfers are logged as well.

In the last case, ftpd takes special measures to restrict the client's access privileges. The server performs a chroot(2) 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, following these rules:

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

~ftp/etc
    Make this directory owned by “root” and unwritable by anyone (mode 555). The files pwd.db (see passwd(5)) and group(5) must be present for the ls command to be able to produce owner names rather than numbers. The password field in passwd is not used, and should not contain real passwords. The file ftpmotd, if present, will be printed after a successful login. These files should be mode 444.

~ftp/pub
    Make this directory mode 777 and owned by “ftp”. Guests can then place files which are to be accessible via the anonymous account in this directory.

If the system has multiple IP addresses, ftpd supports the idea of virtual hosts, which provides the ability to define multiple anonymous ftp areas, each one allocated to a different internet address. The file /etc/ftphosts contains information pertaining to each of the virtual hosts. Each host is defined on its own line which contains a number of fields separated by whitespace:

hostname
    Contains the hostname or IP address of the virtual host.

user
    Contains a user record in the system password file. As with normal anonymous ftp, this user's access uid, gid and group memberships determine file access to the anonymous ftp area. The anonymous ftp area (to which any user is chrooted on login) is determined by the home directory defined for the account. User id and group for any ftp account may be the same as for the standard ftp user.

statfile
    File to which all file transfers are logged, which defaults to /var/log/ftpd.

welcome
    This file is the welcome message displayed before the server ready prompt. It defaults to /etc/ftpwelcome.

motd
    This file is displayed after the user logs in. It defaults to /etc/ftpmotd.

Lines beginning with a '#' are ignored and can be used to include comments.

Defining a virtual host for the primary IP address or hostname changes the default for ftp logins to that address. The 'user', 'statfile', 'welcome' and 'motd' fields may be left blank, or a single hypen '-' used to indicate that the default value is to be used.

As with any anonymous login configuration, due care must be given to setup and maintenance to guard against security related problems.

ftpd has internal support for handling remote requests to list files, and will not execute /bin/ls in either a chrooted or non-chrooted environment. The ~/bin/ls executable need not be placed into the chrooted tree, nor need the ~/bin directory exist.

FILES
/etc/ftpusers
    List of unwelcome/restricted users.
/etc/ftpchroot
    List of normal users who should be chroot'd.
/etc/ftphosts
    Virtual hosting configuration file.
/etc/ftpwelcome
    Welcome notice.
/etc/ftpmotd
    Welcome notice after login.
/var/run/nologin
    Displayed and access refused.
/var/log/ftpd
    Log file for anonymous transfers.

SEE ALSO
ftp(1), key(1), getusershell(3), login.conf(5), inetd(8), syslogd(8)

BUGS
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.

HISTORY
The ftpd command appeared in 4.2BSD. IPv6 support was added in WIDE Hydrangea IPv6 stack kit.