ftpd



FTPD(8)                 OpenBSD System Manager's Manual                FTPD(8)


NAME

     ftpd - Internet File Transfer Protocol server


SYNOPSIS

     ftpd [-46ADdlMnPSUW] [-T maxtimeout] [-t timeout] [-u mask]


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).

     The options are as follows:

     -4      When -D is specified, forces ftpd to use IPv4 addresses only.

     -6      When -D is specified, forces ftpd to use IPv6 addresses only.

     -A      Permit only anonymous FTP connections (unless the -n option is
             specified), accounts listed in /etc/ftpchroot or users in a login
             class with the ``ftp-chroot'' variable set (see below).  Other
             connection attempts are refused.

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

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

     -l      Each successful and failed FTP 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.

     -M      Enables multihomed mode.  Instead of simply using ~ftp for
             anonymous transfers, a directory matching the fully qualified
             name of the IP number the client connected to, and located inside
             ~ftp, is used instead.

     -n      Do not permit anonymous FTP logins.  Normally they are permitted.

     -P      Permit illegal port numbers or addresses for PORT command
             initiated connects.  By default ftpd violates the RFC and thus
             constrains the PORT command to non-reserved ports and requires it
             use the same source address as the connection came from.  This
             prevents the "FTP bounce attack" against services on both the
             local machine and other local machines.

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

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

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

     -U      Each concurrent FTP session is logged to the file /var/run/utmp,
             making them visible to commands such as who(1).  -U and -W are
             mutually exclusive.

     -u mask
             Force the umask to mask, instead of the default specified in
             /etc/login.conf (usually 022).  Also disallows chmod.

     -W      Do not save login records to /var/log/wtmp.  -W and -U are
             mutually exclusive.

     The file /etc/nologin can be used to disable FTP access.  If the file
     exists, ftpd displays it and exits.  Note: this method will disable all
     non-root logins; see login(1) for further details.  If the file
     /etc/ftpwelcome exists, ftpd prints it before issuing the ``ready''
     message.  If the welcome file exists (/etc/motd by default), ftpd prints
     it after a successful login.  If the file .message exists in a directory,
     ftpd prints it when that directory is entered.

     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 (not implemented)
           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
           EPRT       specify data connection port
           EPSV       prepare for server-to-server transfer
           HELP       give help information
           LIST       give list of files in a directory (ls -lgA)
           LPRT       specify data connection port
           LPSV       prepare for server-to-server transfer
           MDTM       show last modification time of file
           MKD        make a directory
           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
           REIN       reinitialize (not implemented)
           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
           SMNT       structure mount (not implemented)
           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; not valid after login
           XCUP       change to parent of current working directory (deprec.)
           XCWD       change working directory (deprecated)
           XMKD       make a directory (deprecated)
           XPWD       print the current working directory (deprecated)
           XRMD       remove a directory (deprecated)

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

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

     The remaining FTP requests specified in Internet RFC 959 are recognized,
     but not implemented.  MDTM and SIZE are specified in RFC 3659.

     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 by using the service and type of ftp, as defined
     in the /etc/login.conf file (see login.conf(5)).  An authentication style
     may be specified by appending with a colon (`:') following the
     authentication style, i.e. ``joe:skey''.  The allowed authentication
     styles for ftpd may be explicitly specified by the ``auth-ftp'' entry in
     /etc/login.conf.

     ftpd authenticates users according to five rules.

           1.   The login name must be in the password database 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 login name must not appear in the file /etc/ftpusers.

           3.   The user must have a standard shell as described by shells(5).

           4.   If the user name appears in the file /etc/ftpchroot, 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).  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.

           5.   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).

     Once a user is authenticated the user must be approved by any approval
     script defined (see login.conf(5)).  If a valid approval script (by
     either :approve=...: or :approve-ftp=...: for the user's class) is
     defined then it is run and must exit with a 0 (success) status.  When
     ftpd is running under the -D flag (and debugging is not turned on) then
     the approval script will be called with at least the following variables
     specified via the -v option (see login.conf(5)) to the approve script:

           Variable    Description
           FTPD_HOST   The server's (virtual) hostname

     For example (the line is broken to fit the page):

           /usr/libexec/auth/approve_ftpd -v FTPD_HOST=ftp.mycompany.com \
                   username class service

     When the user logs in to the anonymous FTP account, 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 (mode 555).

           ~ftp/bin  Make this directory owned by ``root'' and unwritable by
                     anyone (mode 511).  This directory is optional unless you
                     have commands you wish the anonymous FTP user to be able
                     to run (the ls(1) command exists as a built-in).  Any
                     programs in this directory should be mode 111 (executable
                     only).

           ~ftp/etc  Make this directory owned by ``root'' and unwritable by
                     anyone (mode 511).  The files pwd.db (see pwd_mkdb(8))
                     and group(5) must be present for the ls(1) command to be
                     able to produce owner names rather than numbers.  The
                     password field in pwd.db is not used, and should not
                     contain real passwords.  The file motd, if present, will
                     be printed after a successful login.  These files should
                     be mode 444.

           ~ftp/pub  Make this directory mode 555 and owned by ``root''.  This
                     is traditionally where publicly accessible files are
                     stored for download.

     If logging to the /var/log/ftpd file is enabled, information will be
     written in the following format:

           time            The time and date of the download, in ctime(3)
                           format.
           elapsed time    The elapsed time, in seconds.
           remote host     The remote host (or IP number).
           bytes           The number of bytes transferred.
           path            The full path (relative to the FTP chroot space) of
                           the file transferred.
           type            The type of transfer; either `a' for ASCII or `b'
                           for binary.
           unused          Unused field containing a `*', for compatibility.
           unused          Unused field containing an `o', for compatibility.
           user type       The type of user; either `a' for anonymous or `r'
                           for a real user (should always be anonymous).
           name            Either a system login name or the value given for
                           ``email address'' if an anonymous user.
           service name    The network service name (always ftp).
           unused          Unused field containing a `0', for compatibility.
           real name       The system login name if the connection is not
                           anonymous, or a `*' if it is.

     Although fields exist for logging information on real users, this file is
     only used for anonymous downloads.  Unused fields exist only for
     compatibility with other ftpd implementations.


LOGIN.CONF VARIABLES

     The ftpd daemon uses the following FTP-specific parameters:

     auth-ftp    The list of authentication types available to this class.
                 See login.conf(5).

     ftp-chroot  A boolean value.  If set, users in this class will be
                 automatically chrooted to the user's login directory.

     ftp-dir     A path to a directory.  This value overrides the login
                 directory for users in this class.  A leading tilde (`~') in
                 ftp-dir will be expanded to the user's home directory based
                 on the contents of the password database.

     welcome     The path of the file containing the welcome message.  If this
                 variable is not set, /etc/motd is used.


PORT ALLOCATION

     For passive mode data connections, ftpd will listen to a random high TCP
     port.  The interval of ports used are configurable using sysctl(8)
     variables net.inet.ip.porthifirst and net.inet.ip.porthilast.


FILES

     /etc/ftpchroot     list of normal users who should be chrooted
     /etc/ftpusers      list of unwelcome/restricted users
     /etc/ftpwelcome    welcome notice
     /etc/login.conf    authentication styles
     /etc/motd          printed after a successful login
     /etc/nologin       displayed and access refused
     /var/log/ftpd      log file for anonymous downloads
     /var/log/wtmp      login account records
     /var/run/ftpd.pid  process ID if running in daemon mode
     /var/run/utmp      list of users on the system


SEE ALSO

     ftp(1), login(1), skey(1), who(1), chroot(2), ctime(3), group(5),
     login.conf(5), motd(5), services(5), shells(5), ftp-proxy(8), inetd(8),
     pwd_mkdb(8), sysctl(8), syslogd(8)


STANDARDS

     J. Postel and J. Reynolds, FILE TRANSFER PROTOCOL (FTP), RFC 959, October
     1985.

     P. Hethmon, Extensions to FTP, RFC 3659, March 2007.


HISTORY

     The ftpd command appeared in 4.2BSD.

OpenBSD 5.4                   September 27, 2012                   OpenBSD 5.4

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