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NetBSD 6.1.5 - man page for ftpd (netbsd section 8)

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

NAME
     ftpd -- Internet File Transfer Protocol server

SYNOPSIS
     ftpd [-46DdHlnQqrsUuWwX] [-a anondir] [-C user[@host]] [-c confdir] [-e emailaddr]
	  [-h hostname] [-L xferlogfile] [-P dataport] [-V version]

DESCRIPTION
     ftpd is the Internet File Transfer Protocol server process.  The server uses the TCP proto-
     col and listens at the port specified in the ``ftp'' service specification; see services(5).

     Available options:

     -4      When -D is specified, bind to IPv4 addresses only.

     -6      When -D is specified, bind to IPv6 addresses only.

     -a anondir
	     Define anondir as the directory to chroot(2) into for anonymous logins.  Default is
	     the home directory for the ftp user.  This can also be specified with the
	     ftpd.conf(5) chroot directive.

     -C user[@host]
	     Check whether user (as if connecting from host, if provided) would be granted access
	     under the restrictions given in ftpusers(5), and exit without attempting a connec-
	     tion.  ftpd exits with an exit code of 0 if access would be granted, or 1 otherwise.
	     This can be useful for testing configurations.

     -c confdir
	     Change the root directory of the configuration files from ``/etc'' to confdir.  This
	     changes the directory for the following files: /etc/ftpchroot, /etc/ftpusers,
	     /etc/ftpwelcome, /etc/motd, and the file specified by the ftpd.conf(5) limit direc-
	     tive.

     -D      Run as daemon.  ftpd will listen on the default FTP port for incoming connections
	     and fork a child for each connection.  This is lower overhead than starting ftpd
	     from inetd(8) and thus might be useful on busy servers to reduce load.

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

     -e emailaddr
	     Use emailaddr for the ``%E'' escape sequence (see Display file escape sequences)

     -H      Equivalent to ``-h `hostname`''.

     -h hostname
	     Explicitly set the hostname to advertise as to hostname.  The default is the host-
	     name associated with the IP address that ftpd is listening on.  This ability (with
	     or without -h), in conjunction with -c confdir, is useful when configuring 'virtual'
	     FTP servers, each listening on separate addresses as separate names.  Refer to
	     inetd.conf(5) for more information on starting services to listen on specific IP
	     addresses.

     -L xferlogfile
	     Log wu-ftpd style 'xferlog' entries to xferlogfile.

     -l      Each successful and failed FTP session is logged using syslog with a facility of
	     LOG_FTP.  If this option is specified more than once, the retrieve (get), store
	     (put), append, delete, make directory, remove directory and rename operations and
	     their file name arguments are also logged.

     -n      Don't attempt translation of IP addresses to hostnames.

     -P dataport
	     Use dataport as the data port, overriding the default of using the port one less
	     that the port ftpd is listening on.

     -Q      Disable the use of pid files for keeping track of the number of logged-in users per
	     class.  This may reduce the load on heavily loaded FTP servers.

     -q      Enable the use of pid files for keeping track of the number of logged-in users per
	     class.  This is the default.

     -r      Permanently drop root privileges once the user is logged in.  The use of this option
	     may result in the server using a port other than the (listening-port - 1) for PORT
	     style commands, which is contrary to the RFC 959 specification, but in practice very
	     few clients rely upon this behaviour.  See SECURITY CONSIDERATIONS below for more
	     details.

     -s      Require a secure authentication mechanism like Kerberos or S/Key to be used.

     -U      Don't log each concurrent FTP session to /var/run/utmp.  This is the default.

     -u      Log each concurrent FTP session to /var/run/utmp, making them visible to commands
	     such as who(1).

     -V version
	     Use version as the version to advertise in the login banner and in the output of
	     STAT and SYST instead of the default version information.	If version is empty or
	     '-' then don't display any version information.

     -W      Don't log each FTP session to /var/log/wtmp.

     -w      Log each FTP session to /var/log/wtmp, making them visible to commands such as
	     last(1).  This is the default.

     -X      Log wu-ftpd style 'xferlog' entries to the syslog, prefixed with ``xferlog: '',
	     using a facility of LOG_FTP.  These syslog entries can be converted to a wu-ftpd
	     style xferlog file suitable for input into a third-party log analysis tool with a
	     command similar to:
		   sed -ne 's/^.*xferlog: //p' /var/log/xferlog > wuxferlog

     The file /etc/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/motd exists (under the chroot directory if applicable),
     ftpd prints it after a successful login.  This may be changed with the ftpd.conf(5) direc-
     tive motd.

     The ftpd 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
	   EPSV       prepare for server-to-server transfer
	   EPRT       specify data connection port
	   FEAT       list extra features that are not defined in RFC 959
	   HELP       give help information
	   LIST       give list files in a directory (``ls -lA'')
	   LPSV       prepare for server-to-server transfer
	   LPRT       specify data connection port
	   MLSD       list contents of directory in a machine-processable form
	   MLST       show a pathname in a machine-processable form
	   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
	   OPTS       define persistent options for a given command
	   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)

     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''
	   RATEGET    set maximum get rate throttle in bytes/second, e.g. ``SITE RATEGET 5k''
	   RATEPUT    set maximum put rate throttle in bytes/second, e.g. ``SITE RATEPUT 5k''
	   UMASK      change umask, e.g. ``SITE UMASK 002''

     The following FTP requests (as specified in RFC 959 and RFC 2228) are recognized, but are
     not implemented: ACCT, ADAT, AUTH, CCC, CONF, ENC, MIC, PBSZ, PROT, REIN, and SMNT.

     The ftpd 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 use the metacharacters ``*?[]{}~''.

   User authentication
     ftpd authenticates users according to five rules.

	   1.	The login name must be in the password data base, passwd(5), 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 skey(1) for more
		information on S/Key authentication.  S/Key is a Trademark of Bellcore.

	   2.	The login name must be allowed based on the information in ftpusers(5).

	   3.	The user must have a standard shell returned by getusershell(3).  If the user's
		shell field in the password database is empty, the shell is assumed to be
		/bin/sh.  As per shells(5), the user's shell must be listed with full path in
		/etc/shells.

	   4.	If directed by the file ftpchroot(5) the session's root directory will be changed
		by chroot(2) to the directory specified in the ftpd.conf(5) chroot directive (if
		set), or to the home directory of the user.  This facility may also be triggered
		by enabling the boolean ftp-chroot 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.

	   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).

		The server performs a chroot(2) to the directory specified in the ftpd.conf(5)
		chroot directive (if set), the -a anondir directory (if set), or to the home
		directory of the ``ftp'' user.

		The server then performs a chdir(2) to the directory specified in the
		ftpd.conf(5) homedir directive (if set), otherwise to /.

		If other restrictions are required (such as disabling of certain commands and the
		setting of a specific umask), then appropriate entries in ftpd.conf(5) are
		required.

		If the first character of the password supplied by an anonymous user is ``-'',
		then the verbose messages displayed at login and upon a CWD command are sup-
		pressed.

   Display file escape sequences
     When ftpd displays various files back to the client (such as /etc/ftpwelcome and /etc/motd),
     various escape strings are replaced with information pertinent to the current connection.

     The supported escape strings are:
	   Escape  Description
	   %c	   Class name.
	   %C	   Current working directory.
	   %E	   Email address given with -e.
	   %L	   Local hostname.
	   %M	   Maximum number of users for this class.  Displays ``unlimited'' if there's no
		   limit.
	   %N	   Current number of users for this class.
	   %R	   Remote hostname.
	   %s	   If the result of the most recent ``%M'' or ``%N'' was not ``1'', print an
		   ``s''.
	   %S	   If the result of the most recent ``%M'' or ``%N'' was not ``1'', print an
		   ``S''.
	   %T	   Current time.
	   %U	   User name.
	   %%	   A ``%'' character.

   Setting up a restricted ftp subtree
     In order that system security is not breached, it is recommended that the subtrees for the
     ``ftp'' and ``chroot'' accounts be constructed with care, following these rules (replace
     ``ftp'' in the following directory names with the appropriate account name for 'chroot'
     users):

	   ~ftp 	  Make the home directory owned by ``root'' and unwritable by anyone.

	   ~ftp/bin	  Make this directory owned by ``root'' and unwritable by anyone (mode
			  555).  Generally any conversion commands should be installed here (mode
			  111).

	   ~ftp/etc	  Make this directory owned by ``root'' and unwritable by anyone (mode
			  555).  The files pwd.db (see passwd(5)) and group (see group(5)) must
			  be present for the LIST command to be able to display owner and group
			  names instead of numbers.  The password field in passwd(5) 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	  This directory and the subdirectories beneath it should be owned by the
			  users and groups responsible for placing files in them, and be writable
			  only by them (mode 755 or 775).  They should not be owned or writable
			  by ftp or its group.

	   ~ftp/incoming  This directory is where anonymous users place files they upload.  The
			  owners should be the user ``ftp'' and an appropriate group.  Members of
			  this group will be the only users with access to these files after they
			  have been uploaded; these should be people who know how to deal with
			  them appropriately.  If you wish anonymous FTP users to be able to see
			  the names of the files in this directory the permissions should be 770,
			  otherwise they should be 370.

			  The following ftpd.conf(5) directives should be used:
				modify guest off
				umask  guest 0707
				upload guest on

			  This will result in anonymous users being able to upload files to this
			  directory, but they will not be able to download them, delete them, or
			  overwrite them, due to the umask and disabling of the commands men-
			  tioned above.

	   ~ftp/tmp	  This directory is used to create temporary files which contain the
			  error messages generated by a conversion or LIST command.  The owner
			  should be the user ``ftp''.  The permissions should be 300.

			  If you don't enable conversion commands, or don't want anonymous users
			  uploading files here (see ~ftp/incoming above), then don't create this
			  directory.  However, error messages from conversion or LIST commands
			  won't be returned to the user.  (This is the traditional behaviour.)
			  Note that the ftpd.conf(5) directive upload can be used to prevent
			  users uploading here.

     To set up "ftp-only" accounts that provide only FTP, but no valid shell login, you can
     copy/link /sbin/nologin to /sbin/ftplogin, and enter /sbin/ftplogin to /etc/shells to allow
     logging-in via FTP into the accounts, which must have /sbin/ftplogin as login shell.

FILES
     /etc/ftpchroot   List of normal users whose root directory should be changed via chroot(2).
     /etc/ftpd.conf   Configure file conversions and other settings.
     /etc/ftpusers    List of unwelcome/restricted users.
     /etc/ftpwelcome  Welcome notice before login.
     /etc/motd	      Welcome notice after login.
     /etc/nologin     If it exists, displayed and access is refused.
     /var/run/ftpd.pids-CLASS
		      State file of logged-in processes for the ftpd class 'CLASS'.
     /var/run/utmp    List of logged-in users on the system.
     /var/log/wtmp    Login history database.

SEE ALSO
     ftp(1), skey(1), who(1), getusershell(3), ftpchroot(5), ftpd.conf(5), ftpusers(5),
     login.conf(5), syslogd(8)

STANDARDS
     ftpd recognizes all commands in RFC 959, follows the guidelines in RFC 1123, recognizes all
     commands in RFC 2228 (although they are not supported yet), and supports the extensions from
     RFC 2389, RFC 2428, and RFC 3659.

HISTORY
     The ftpd command appeared in 4.2BSD.

     Various features such as the ftpd.conf(5) functionality, RFC 2389, and RFC 3659 support was
     implemented in NetBSD 1.3 and later releases by Luke Mewburn.

BUGS
     The server must run as the super-user to create sockets with privileged port numbers (i.e,
     those less than IPPORT_RESERVED, which is 1024).  If ftpd is listening on a privileged port
     it maintains an effective user id of the logged in user, reverting to the super-user only
     when binding addresses to privileged sockets.  The -r option can be used to override this
     behaviour and force privileges to be permanently revoked; see SECURITY CONSIDERATIONS below
     for more details.

     ftpd may have trouble handling connections from scoped IPv6 addresses, or IPv4 mapped
     addresses (IPv4 connection on AF_INET6 socket).  For the latter case, running two daemons,
     one for IPv4 and one for IPv6, will avoid the problem.

SECURITY CONSIDERATIONS
     RFC 959 provides no restrictions on the PORT command, and this can lead to security prob-
     lems, as ftpd can be fooled into connecting to any service on any host.  With the
     ``checkportcmd'' feature of the ftpd.conf(5), PORT commands with different host addresses,
     or TCP ports lower than IPPORT_RESERVED will be rejected.	This also prevents 'third-party
     proxy ftp' from working.  Use of this option is strongly recommended, and enabled by
     default.

     By default ftpd uses a port that is one less than the port it is listening on to communicate
     back to the client for the EPRT, LPRT, and PORT commands, unless overridden with -P
     dataport.	As the default port for ftpd (21) is a privileged port below IPPORT_RESERVED,
     ftpd retains the ability to switch back to root privileges to bind these ports.  In order to
     increase security by reducing the potential for a bug in ftpd providing a remote root com-
     promise, ftpd will permanently drop root privileges if one of the following is true:

	   1.	ftpd is running on a port greater than IPPORT_RESERVED and the user has logged in
		as a 'guest' or 'chroot' user.

	   2.	ftpd was invoked with -r.

     Don't create ~ftp/tmp if you don't want anonymous users to upload files there.  That direc-
     tory is only necessary if you want to display the error messages of conversion commands to
     the user.	Note that if uploads are disabled with the ftpd.conf(5) directive upload, then
     this directory cannot be abused by the user in this way, so it should be safe to create.

     To avoid possible denial-of-service attacks, SIZE requests against files larger than 10240
     bytes will be denied if the current transfer TYPE is 'A' (ASCII).

BSD					   May 1, 2009					      BSD


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