xref: /freebsd/libexec/ftpd/ftpd.8 (revision 74bf4e164ba5851606a27d4feff27717452583e5)
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32.\"     @(#)ftpd.8	8.2 (Berkeley) 4/19/94
33.\" $FreeBSD$
34.\"
35.Dd January 27, 2000
36.Dt FTPD 8
37.Os
38.Sh NAME
39.Nm ftpd
40.Nd Internet File Transfer Protocol server
41.Sh SYNOPSIS
42.Nm
43.Op Fl 46ADdEhMmOoRrSUvW
44.Op Fl l Op Fl l
45.Op Fl a Ar address
46.Op Fl P Ar port
47.Op Fl p Ar file
48.Op Fl T Ar maxtimeout
49.Op Fl t Ar timeout
50.Op Fl u Ar umask
51.Sh DESCRIPTION
52The
53.Nm
54utility is the
55Internet File Transfer Protocol
56server process.
57The server uses the
58.Tn TCP
59protocol
60and listens at the port specified with the
61.Fl P
62option or in the
63.Dq ftp
64service specification; see
65.Xr services 5 .
66.Pp
67Available options:
68.Bl -tag -width indent
69.It Fl 4
70When
71.Fl D
72is specified, accept connections via
73.Dv AF_INET
74socket.
75.It Fl 6
76When
77.Fl D
78is specified, accept connections via
79.Dv AF_INET6
80socket.
81.It Fl A
82Allow only anonymous ftp access.
83.It Fl a
84When
85.Fl D
86is specified, accept connections only on the specified
87.Ar address .
88.It Fl D
89With this option set,
90.Nm
91will detach and become a daemon, accepting connections on the FTP port and
92forking children processes to handle them.
93This is lower overhead than starting
94.Nm
95from
96.Xr inetd 8
97and is thus useful on busy servers to reduce load.
98.It Fl d
99Debugging information is written to the syslog using
100.Dv LOG_FTP .
101.It Fl E
102Disable the EPSV command.
103This is useful for servers behind older firewalls.
104.It Fl h
105Disable printing host-specific information, such as the
106server software version or hostname, in server messages.
107.It Fl l
108Each successful and failed
109.Xr ftp 1
110session is logged using syslog with a facility of
111.Dv LOG_FTP .
112If this option is specified twice, the retrieve (get), store (put), append,
113delete, make directory, remove directory and rename operations and
114their filename arguments are also logged.
115By default,
116.Xr syslogd 8
117logs these to
118.Pa /var/log/xferlog .
119.It Fl M
120Prevent anonymous users from creating directories.
121.It Fl m
122Permit anonymous users to overwrite or modify
123existing files if allowed by file system permissions.
124By default, anonymous users cannot modify existing files;
125in particular, files to upload will be created under a unique name.
126.It Fl O
127Put server in write-only mode for anonymous users only.
128RETR is disabled for anonymous users, preventing anonymous downloads.
129This has no effect if
130.Fl o
131is also specified.
132.It Fl o
133Put server in write-only mode.
134RETR is disabled, preventing downloads.
135.It Fl P
136When
137.Fl D
138is specified, accept connections at
139.Ar port ,
140specified as a numeric value or service name, instead of at the default
141.Dq ftp
142port.
143.It Fl p
144When
145.Fl D
146is specified, write the daemon's process ID to
147.Ar file .
148.It Fl R
149With this option set,
150.Nm
151will revert to historical behavior with regard to security checks on
152user operations and restrictions on PORT requests.
153Currently,
154.Nm
155will only honor PORT commands directed to unprivileged ports on the
156remote user's host (which violates the FTP protocol specification but
157closes some security holes).
158.It Fl r
159Put server in read-only mode.
160All commands which may modify the local file system are disabled.
161.It Fl S
162With this option set,
163.Nm
164logs all anonymous file downloads to the file
165.Pa /var/log/ftpd
166when this file exists.
167.It Fl T
168A client may also request a different timeout period;
169the maximum period allowed may be set to
170.Ar timeout
171seconds with the
172.Fl T
173option.
174The default limit is 2 hours.
175.It Fl t
176The inactivity timeout period is set to
177.Ar timeout
178seconds (the default is 15 minutes).
179.It Fl U
180This option instructs ftpd to use data ports in the range of
181.Dv IP_PORTRANGE_DEFAULT
182instead of in the range of
183.Dv IP_PORTRANGE_HIGH .
184Such a change may be useful for some specific firewall configurations;
185see
186.Xr ip 4
187for more information.
188.Pp
189Note that option is a virtual no-op in
190.Fx 5.0
191and above; both port
192ranges are indentical by default.
193.It Fl u
194The default file creation mode mask is set to
195.Ar umask ,
196which is expected to be an octal numeric value.
197Refer to
198.Xr umask 2
199for details.
200This option may be overridden by
201.Xr login.conf 5 .
202.It Fl v
203A synonym for
204.Fl d .
205.It Fl W
206Do not log FTP sessions to
207.Pa /var/log/wtmp .
208.El
209.Pp
210The file
211.Pa /var/run/nologin
212can be used to disable ftp access.
213If the file exists,
214.Nm
215displays it and exits.
216If the file
217.Pa /etc/ftpwelcome
218exists,
219.Nm
220prints it before issuing the
221.Dq ready
222message.
223If the file
224.Pa /etc/ftpmotd
225exists,
226.Nm
227prints it after a successful login.
228Note the motd file used is the one
229relative to the login environment.
230This means the one in
231.Pa ~ftp/etc
232in the anonymous user's case.
233.Pp
234The ftp server currently supports the following ftp requests.
235The case of the requests is ignored.
236Requests marked [RW] are
237disabled if
238.Fl r
239is specified.
240.Bl -column "Request" -offset indent
241.It Sy Request Ta Sy "Description"
242.It ABOR Ta "abort previous command"
243.It ACCT Ta "specify account (ignored)"
244.It ALLO Ta "allocate storage (vacuously)"
245.It APPE Ta "append to a file [RW]"
246.It CDUP Ta "change to parent of current working directory"
247.It CWD Ta "change working directory"
248.It DELE Ta "delete a file [RW]"
249.It EPRT Ta "specify data connection port, multiprotocol"
250.It EPSV Ta "prepare for server-to-server transfer, multiprotocol"
251.It HELP Ta "give help information"
252.It LIST Ta "give list files in a directory" Pq Dq Li "ls -lgA"
253.It LPRT Ta "specify data connection port, multiprotocol"
254.It LPSV Ta "prepare for server-to-server transfer, multiprotocol"
255.It MDTM Ta "show last modification time of file"
256.It MKD Ta "make a directory [RW]"
257.It MODE Ta "specify data transfer" Em mode
258.It NLST Ta "give name list of files in directory"
259.It NOOP Ta "do nothing"
260.It PASS Ta "specify password"
261.It PASV Ta "prepare for server-to-server transfer"
262.It PORT Ta "specify data connection port"
263.It PWD Ta "print the current working directory"
264.It QUIT Ta "terminate session"
265.It REST Ta "restart incomplete transfer"
266.It RETR Ta "retrieve a file"
267.It RMD Ta "remove a directory [RW]"
268.It RNFR Ta "specify rename-from file name [RW]"
269.It RNTO Ta "specify rename-to file name [RW]"
270.It SITE Ta "non-standard commands (see next section)"
271.It SIZE Ta "return size of file"
272.It STAT Ta "return status of server"
273.It STOR Ta "store a file [RW]"
274.It STOU Ta "store a file with a unique name [RW]"
275.It STRU Ta "specify data transfer" Em structure
276.It SYST Ta "show operating system type of server system"
277.It TYPE Ta "specify data transfer" Em type
278.It USER Ta "specify user name"
279.It XCUP Ta "change to parent of current working directory (deprecated)"
280.It XCWD Ta "change working directory (deprecated)"
281.It XMKD Ta "make a directory (deprecated) [RW]"
282.It XPWD Ta "print the current working directory (deprecated)"
283.It XRMD Ta "remove a directory (deprecated) [RW]"
284.El
285.Pp
286The following non-standard or
287.Ux
288specific commands are supported
289by the
290SITE request.
291.Pp
292.Bl -column Request -offset indent
293.It Sy Request Ta Sy Description
294.It UMASK Ta change umask, e.g. ``SITE UMASK 002''
295.It IDLE Ta set idle-timer, e.g. ``SITE IDLE 60''
296.It CHMOD Ta "change mode of a file [RW], e.g. ``SITE CHMOD 755 filename''"
297.It MD5 Ta "report the files MD5 checksum, e.g. ``SITE MD5 filename''"
298.It HELP Ta give help information
299.El
300.Pp
301Note: SITE requests are disabled in case of anonymous logins.
302.Pp
303The remaining ftp requests specified in Internet RFC 959
304are
305recognized, but not implemented.
306MDTM and SIZE are not specified in RFC 959, but will appear in the
307next updated FTP RFC.
308To avoid possible denial-of-service attacks, SIZE requests against
309files larger than 10240 bytes will be denied if the current transfer
310type is ASCII.
311.Pp
312The ftp server will abort an active file transfer only when the
313ABOR
314command is preceded by a Telnet "Interrupt Process" (IP)
315signal and a Telnet "Synch" signal in the command Telnet stream,
316as described in Internet RFC 959.
317If a
318STAT
319command is received during a data transfer, preceded by a Telnet IP
320and Synch, transfer status will be returned.
321.Pp
322The
323.Nm
324utility interprets file names according to the
325.Dq globbing
326conventions used by
327.Xr csh 1 .
328This allows users to utilize the metacharacters
329.Dq Li \&*?[]{}~ .
330.Pp
331The
332.Nm
333utility authenticates users according to six rules.
334.Pp
335.Bl -enum -offset indent
336.It
337The login name must be in the password data base
338and not have a null password.
339In this case a password must be provided by the client before any
340file operations may be performed.
341If the user has an S/Key key, the response from a successful USER
342command will include an S/Key challenge.
343The client may choose to respond with a PASS command giving either
344a standard password or an S/Key one-time password.
345The server will automatically determine which type of
346password it has been given and attempt to authenticate accordingly.
347See
348.Xr key 1
349for more information on S/Key authentication.
350S/Key is a Trademark of Bellcore.
351.It
352The login name must not appear in the file
353.Pa /etc/ftpusers .
354.It
355The login name must not be a member of a group specified in the file
356.Pa /etc/ftpusers .
357Entries in this file interpreted as group names are prefixed by an "at"
358.Ql \&@
359sign.
360.It
361The user must have a standard shell returned by
362.Xr getusershell 3 .
363.It
364If the user name appears in the file
365.Pa /etc/ftpchroot ,
366or the user is a member of a group with a group entry in this file,
367i.e., one prefixed with
368.Ql \&@ ,
369the session's root will be changed to the directory specified
370in this file or to the user's login directory by
371.Xr chroot 2
372as for an
373.Dq anonymous
374or
375.Dq ftp
376account (see next item).
377See
378.Xr ftpchroot 5
379for a detailed description of the format of this file.
380This facility may also be triggered by enabling the boolean "ftp-chroot"
381capability in
382.Xr login.conf 5 .
383However, the user must still supply a password.
384This feature is intended as a compromise between a fully anonymous
385account and a fully privileged account.
386The account should also be set up as for an anonymous account.
387.It
388If the user name is
389.Dq anonymous
390or
391.Dq ftp ,
392an
393anonymous ftp account must be present in the password
394file (user
395.Dq ftp ) .
396In this case the user is allowed
397to log in by specifying any password (by convention an email address for
398the user should be used as the password).
399When the
400.Fl S
401option is set, all transfers are logged as well.
402.El
403.Pp
404In the last case,
405.Nm
406takes special measures to restrict the client's access privileges.
407The server performs a
408.Xr chroot 2
409to the home directory of the
410.Dq ftp
411user.
412As a special case if the
413.Dq ftp
414user's home directory pathname contains the
415.Pa /./
416separator,
417.Nm
418uses its left-hand side as the name of the directory to do
419.Xr chroot 2
420to, and its right-hand side to change the current directory to afterwards.
421A typical example for this case would be
422.Pa /usr/local/ftp/./pub .
423In order that system security is not breached, it is recommended
424that the
425.Dq ftp
426subtree be constructed with care, following these rules:
427.Bl -tag -width "~ftp/pub" -offset indent
428.It Pa ~ftp
429Make the home directory owned by
430.Dq root
431and unwritable by anyone.
432.It Pa ~ftp/etc
433Make this directory owned by
434.Dq root
435and unwritable by anyone (mode 555).
436The files pwd.db (see
437.Xr passwd 5 )
438and
439.Xr group 5
440must be present for the
441.Xr ls 1
442command to be able to produce owner names rather than numbers.
443The password field in
444.Xr passwd 5
445is not used, and should not contain real passwords.
446The file
447.Pa ftpmotd ,
448if present, will be printed after a successful login.
449These files should be mode 444.
450.It Pa ~ftp/pub
451This directory and the subdirectories beneath it should be owned
452by the users and groups responsible for placing files in them,
453and be writable only by them (mode 755 or 775).
454They should
455.Em not
456be owned or writable by
457.Dq ftp
458or its group, otherwise guest users
459can fill the drive with unwanted files.
460.El
461.Pp
462If the system has multiple IP addresses,
463.Nm
464supports the idea of virtual hosts, which provides the ability to
465define multiple anonymous ftp areas, each one allocated to a different
466internet address.
467The file
468.Pa /etc/ftphosts
469contains information pertaining to each of the virtual hosts.
470Each host is defined on its own line which contains a number of
471fields separated by whitespace:
472.Bl -tag -offset indent -width hostname
473.It hostname
474Contains the hostname or IP address of the virtual host.
475.It user
476Contains a user record in the system password file.
477As with normal anonymous ftp, this user's access uid, gid and group
478memberships determine file access to the anonymous ftp area.
479The anonymous ftp area (to which any user is chrooted on login)
480is determined by the home directory defined for the account.
481User id and group for any ftp account may be the same as for the
482standard ftp user.
483.It statfile
484File to which all file transfers are logged, which
485defaults to
486.Pa /var/log/ftpd .
487.It welcome
488This file is the welcome message displayed before the server ready
489prompt.
490It defaults to
491.Pa /etc/ftpwelcome .
492.It motd
493This file is displayed after the user logs in.
494It defaults to
495.Pa /etc/ftpmotd .
496.El
497.Pp
498Lines beginning with a '#' are ignored and can be used to include
499comments.
500.Pp
501Defining a virtual host for the primary IP address or hostname
502changes the default for ftp logins to that address.
503The 'user', 'statfile', 'welcome' and 'motd' fields may be left
504blank, or a single hyphen '-' used to indicate that the default
505value is to be used.
506.Pp
507As with any anonymous login configuration, due care must be given
508to setup and maintenance to guard against security related problems.
509.Pp
510The
511.Nm
512utility has internal support for handling remote requests to list
513files, and will not execute
514.Pa /bin/ls
515in either a chrooted or non-chrooted environment.
516The
517.Pa ~/bin/ls
518executable need not be placed into the chrooted tree, nor need the
519.Pa ~/bin
520directory exist.
521.Sh FILES
522.Bl -tag -width ".Pa /var/log/xferlog" -compact
523.It Pa /etc/ftpusers
524List of unwelcome/restricted users.
525.It Pa /etc/ftpchroot
526List of normal users who should be chroot'd.
527.It Pa /etc/ftphosts
528Virtual hosting configuration file.
529.It Pa /etc/ftpwelcome
530Welcome notice.
531.It Pa /etc/ftpmotd
532Welcome notice after login.
533.It Pa /var/run/nologin
534Displayed and access refused.
535.It Pa /var/log/ftpd
536Log file for anonymous transfers.
537.It Pa /var/log/xferlog
538Default place for session logs.
539.El
540.Sh SEE ALSO
541.Xr ftp 1 ,
542.Xr key 1 ,
543.Xr umask 2 ,
544.Xr getusershell 3 ,
545.Xr ftpchroot 5 ,
546.Xr login.conf 5 ,
547.Xr inetd 8 ,
548.Xr syslogd 8
549.Sh BUGS
550The server must run as the super-user
551to create sockets with privileged port numbers.
552It maintains
553an effective user id of the logged in user, reverting to
554the super-user only when binding addresses to sockets.
555The
556possible security holes have been extensively
557scrutinized, but are possibly incomplete.
558.Sh HISTORY
559The
560.Nm
561utility appeared in
562.Bx 4.2 .
563IPv6 support was added in WIDE Hydrangea IPv6 stack kit.
564