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.\"     @(#)ftpd.8	8.2 (Berkeley) 4/19/94
.\" $FreeBSD: src/libexec/ftpd/ftpd.8,v 1.67 2004/05/16 22:11:40 ru Exp $
.\"
.Dd Nov 1, 2004
.Dt FTPD 8
.Os
.Sh NAME
.Nm ftpd
.Nd Internet File Transfer Protocol server
.Sh SYNOPSIS
.Nm
.Op Fl 46ADdEhMmOoRrUuvW
.Op Fl L Ar logparam Op Fl L Ar logparam
.Op Fl l Op Fl l
.Op Fl a Ar addrparam Op Fl a Ar addrparam
.Op Fl P Ar port
.Op Fl p Ar file
.Op Fl S Ar logtype
.Op Fl T Ar maxtimeout
.Op Fl t Ar timeout
.Op Fl u Ar umask
.Op Fl X Ar logtype
.Op Fl z Ar secparam Op Fl z Ar secparam Op ...
.Sh DESCRIPTION
The
.Nm
utility is the
Internet File Transfer Protocol
server process.  The server uses the
.Tn TCP
protocol
and listens at the port specified with the
.Fl P
option or in the
.Dq ftp
service specification; see
.Xr services 5 .
.Pp
Available options:
.Bl -tag -width indent
.It Fl 4
When
.Fl D
is specified, accept connections via
.Dv AF_INET
socket.
.It Fl 6
When
.Fl D
is specified, accept connections via
.Dv AF_INET6
socket.
.It Fl A
Allow only anonymous ftp access.
.It Fl a
Configure network addresses. This option may be specified several times to set
different address parameters. The possible values of
.Ar addrparam
are:
.Bl -tag -width indent
.Pp
.It Cm bind=\fIaddress\fR
When
.Fl D
is specified, accept connections only on the specified \fIaddress\fR. The value
of the \fIaddress\fR parameter may be a numeric host address string (a
dotted-decimal IPv4 address or an IPv6 hex address) or a symbolic host name.
.It Cm pasvip=\fIaddress\fR
Override the IP address that will be advertised to IPv4 clients in response to
the PASV and LPSV commands. The \fIaddress\fR parameter describes an IPv4
family address.
.Pp
When
.Fl D
is not specified, the value of the \fIaddress\fR string may be a numeric
IPv4 family address in the dotted-decimal notation or a symbolic host name,
which will be resolved after the connection of the client. If
.Fl D
is specified, only the numeric host address string is supported.
.El
.It Fl D
With this option set,
.Nm
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
.Nm
from
.Xr inetd 8
and is thus useful on busy servers to reduce load.
.It Fl d
Debugging information is written to the syslog using
.Dv LOG_FTP .
.It Fl E
Disable the EPSV and EPRT commands.
This is useful for servers behind older firewalls.
.It Fl h
Disable printing host-specific information, such as the
server software version or hostname, in server messages.
.It Fl L
Set the logging parameters. This option may be specified many times to enable
different logging features. The possible values of
.Ar logparam
are:
.Bl -tag -width anon-abs
.It Cm anon-abs
Pathnames of the transferred files in the
.Cm anon
.Xr xferlog 5
format (used for anonymous file downloads) will be interpreted as pathnames in
the real file system.
.It Cm wu-abs
If the FTP session has been chrooted, pathnames of the transferred files in the
original and extended wu-ftpd
.Xr xferlog 5
formats will be interpreted as pathnames in the real file system.
.El
.Pp
In case of the chrooted FTP session the only way to obtain a pathname in the
real file system is to concatenate the known pathname of the chroot point and a
pathname of a file in the current chrooted environment. Therefore the
.Cm anon-abs
and
.Cm wu-abs
parameters should be used with the caution that 
.Nm
unable to determine renames of the chroot point in the real file system if they
occur after the change of the session root.
.It Fl l
Each successful and failed
.Xr ftp 1
session is logged using syslog with a facility of
.Dv LOG_FTP .
The authentication events in some cases are logged with a facility of
.Dv LOG_AUTH
or
.Dv LOG_AUTHPRIV .
.Pp
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.
.Pp
The format, in which the information about the retrieve (get), store (put) and
append operations will be logged, may be changed to the wu-ftpd style
.Xr xferlog 5
one with help of the
.Fl X
option.
.It Fl M
Prevent anonymous users from creating directories.
.It Fl m
Permit anonymous users to overwrite or modify
existing files if allowed by file system permissions.
By default, anonymous users cannot modify existing files;
in particular, files to upload will be created under a unique name.
.It Fl O
Put server in write-only mode for anonymous users only.
RETR is disabled for anonymous users, preventing anonymous downloads.
This has no effect if
.Fl o
is also specified.
.It Fl o
Put server in write-only mode.
RETR is disabled, preventing downloads.
.It Fl P
When
.Fl D
is specified, accept connections at
.Ar port ,
specified as a numeric value or service name, instead of at the default
.Dq ftp
port.
.It Fl p
When
.Fl D
is specified, write the daemon's process ID to
.Ar file .
.It Fl R
With this option set,
.Nm
will revert to historical behavior with regard to security checks on
user operations and restrictions on PORT requests.
Currently,
.Nm
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).
.It Fl r
Put server in read-only mode.
All commands which may modify the local file system are disabled.
.It Fl S
With this option set,
.Nm
logs all file transfers to the file
.Pa /var/log/ftpd
when this file exists. This file name may be overridden in the virtual hosting
configuration file. The possible values of
.Ar logtype
are:
.Bl -tag -width wu-orig
.It Cm anon
Server logs only anonymous file downloads in its own
.Xr xferlog 5
format.
.It Cm wu-orig
Log all file transfers in the original wu-ftpd
.Xr xferlog 5
format.
.It Cm wu-ext
Log all file transfers in the extended wu-ftpd style
.Xr xferlog 5
format. In this case the information about restarted downloads and about
appends will also be available.
.El
.It Fl T
A client may also request a different timeout period;
the maximum period allowed may be set to
.Ar timeout
seconds with the
.Fl T
option.
The default limit is 2 hours.
.It Fl t
The inactivity timeout period is set to
.Ar timeout
seconds (the default is 15 minutes).
.It Fl U
This option instructs ftpd to use data ports in the default port range
instead of in the high port range.
Such a change may be useful for some specific firewall configurations.
.Pp
Please note that the conception of various port ranges, whose are used to
selecting a local port number, may not be implemented in some operating
systems. Also both port ranges may be identical by default. See the
.Cm NOTES
section for more information about the implementation of this feature.
.It Fl u
The default file creation mode mask is set to
.Ar umask ,
which is expected to be an octal numeric value.
Refer to
.Xr umask 2
for details. See also the
.Cm NOTES
section for the information about the implementation of this feature in ports
of this
.Nm .
.It Fl v
A synonym for
.Fl d .
.It Fl W
Do not log FTP sessions to
.Pa /var/log/wtmp .
.It Fl X
Log all file transfers to the syslog in the wu-ftpd style
.Xr xferlog 5
format. File transfers will be logged regardless of the logging state which is
set by the
.Fl l
option, but if the
.Fl l
option is specified twice, the information about the retrieve (get), store
(put) and append operations will be logged in this format.
.Pp
The possible values of
.Ar logtype
are:
.Bl -tag -width wu-orig
.It Cm wu-orig
Log all file transfers in the original wu-ftpd format.
.It Cm wu-ext
Log all file transfers in the extended wu-ftpd style format. In this case the
information about restarted downloads and about appends will also be available.
.El
.It Fl z
Configure the TLS/SSL security mechanism. This option may be specified many
times to set different security parameters. The possible values of
.Ar secparam
are:
.Bl -tag -width indent
.Pp
Security policy options
.It Cm secure
Don't fall back into the non-secure mode if the TLS/SSL handshake fails.
.It Cm nosecure
Disable the TLS/SSL encryption at all and allow only non-secure clients.
.It Protocol negotiation options
.It Cm tls
Use only the RFC2228-compliant FTP-TLS negotiation mode; don't try to negotiate
something different.
.It Cm ssl
Use only the FTP-SSL compatibility mode (for early implementations of the
FTP-SSL upgrade); don't try to negotiate something different.
.El
.Pp
By default both FTP-TLS and FTP-SSL security extensions and the non-secure
standard mode are allowed.
.Pp
Options inside both groups above are mutually exclusive, but a protocol
negotiation option may be used after a security policy option to specify
the security extension to be used (in this case it overrides the
.Cm nosecure
option and turns on the TLS/SSL encryption with the selected negotiation mode).
.Pp
User policy options
.Bl -tag -width indent
.It Cm refnu
Require the TLS/SSL encryption for non-anonymous users.
.It Cm defau
Disable the TLS/SSL encryption for anonymous users.
.El
.Pp
X.509 certificate options
.Pp
Basic options
.Bl -tag -width indent
.It Cm verify=\fIlevel\fR
Set the X.509 certificate verification level. Possible values are:
.br
\fI0\fR (default) - the server will not send the client certificate request to
the client, so the client will not send the certificate.
.br
\fI1\fR - the server sends the client certificate request to the client.
The certificate returned (if any) is checked. If the verification process
fails, the TLS/SSL handshake is immediately terminated.
.br
\fI2\fR - the server sends the client certificate request to the client.
If the client did not return the certificate or if the verification process
fails, the TLS/SSL handshake is immediately terminated.
.It Cm cert=\fIcertfile\fR
The certificate to use. This certificate will be passed to the client. If it is
not specified, it will be default to \fIftpd.pem\fR.
.It Cm key=\fIkeyfile\fR
The private key that matches the certificate specified by the
.Cm cert
option. If this is not specified (but
.Cm cert
is), the 
.Cm cert=\fIcertfile\fR
will be searched for the private key. Both files are assumed to be in
PEM format. Default is \fIftpd.pem\fR.
.El
.Pp
If the client certificate is presented for the control connection,
.Nm
expects that the certificate presented for the data connection must match with
it.
.Pp
Alternate verify locations
.Bl -tag -width indent
.It Cm CAfile=\fIcafile\fR
The file that contains the trusted CA certificate in PEM format. The file can
contain several CA certificates.
.It Cm CApath=\fIcapath\fR
The directory that contains trusted CA certificates in PEM format. Each file
contains one CA certificate. The files are looked up by the CA subject name
hash value, which must hence be available. If more than one CA certificate with
the same name hash value exist, the extension must be different
(e.g. 9d66eef0.0, 9d66eef0.1 etc). The search is performed in the ordering of
the extension number.
.It Cm CRLfile=\fIcrlfile\fR
The file that contains the Certificate Revocation List (CRL) in PEM format. The
file can contain several CRLs.
.It Cm CRLpath=\fIcrlpath\fR
The directory that contains CRLs in PEM format. Each file contains one CRL. The
files are looked up by the issuer name hash value, which must hence be
available. If more than one CRL with the same name hash value exist, the
extension must be different (e.g. 9d66eef0.r0, 9d66eef0.r1 etc). The search is
performed in the ordering of the extension number.
.El
.Pp
If none of both
.Cm CAfile
and
.Cm CApath 
(or
.Cm CRLfile
and
.Cm CRLpath )
are specified, both \fIcafile\fR and \fIcapath\fR (or \fIcrlfile\fR and
\fIcrlpath\fR) will be set to default values, otherwise each of \fIcafile\fR
and \fIcapath\fR (\fIcrlfile\fR and \fIcrlpath\fR) will be set to the specified
value or blank if not specified. The default values are \fIcert.pem\fR and
\fIcrl.pem\fR files for \fIcafile\fR and \fIcrlfile\fR, respectively, and
\fIcerts/\fR subdirectory in OpenSSL directory is the default value for both
\fIcapath\fR and \fIcrlpath\fR.
.Pp
When looking up CA certificates, they will be searched in \fIcafile\fR, then
those in \fIcapath\fR. Certificate matching is done based on the subject name,
the key identifier (if present), and the serial number as taken from the
certificate to be verified. If the first certificate which matching the
parameters is found, the verification process will be performed.
.Pp
CRLs are looked up in the similar order: they will be searched in
\fIcrlfile\fR, then those in \fIcrlpath\fR. CRL matching is done based on the
issuer name. If the first CRL for this issuer is found, the verification
process will be performed.
.Pp
X.509 certificate-based user authentication
.Bl -tag -width indent
.It Cm auth=\fIauthmode\fR
Enable support for the X.509 certificate-based user authentication. Possible
values of the authentication mode are:
.br
\fI0\fR (default) - only the standard (typically password-based) authentication
is allowed.
.br
\fI1\fR - the certificate-based authentication is sufficient; the fallback to
the standard authentication is allowed in case of failure.
.br
\fI2\fR - only the certificate-based authentication is allowed.
.br
\fI3\fR - both certificate-based and standard authentications are required.
.El
.Pp
The support for the user authentication that is based upon the authentication
information obtained from X.509 certificates is possible only for
TLS/SSL-enabled FTP clients; standard FTP clients will always be authenticated
through the standard authentication procedure. This type of authentication
implies that the server must obtain the certificate from the client, and hence
the certificate verification level (described above) must have the non-zero
value.
.Pp
The client must still issue the login name. If the X.509 authentication was
successful and the fallback to the standard authentication is not required, the
user will be successfully authenticated without asking for the password.
.Pp
If the certificate-based authentication was used and the standard
authentication was not, PAM modules (see
.Xr pam 8 )
from the authentication management group will not be used. PAM modules from the
account management group will always be used for all authentication modes. The
.Xr login.conf 5
(see also the
.Cm NOTES
section) functionality is also will be used for all modes.
.Pp
Relations between client certificates and system login names are guided by the
.Pa /etc/x509.auth
file. Each relation is defined by its own line that contains a number of fields
separated by colons:
.Bl -tag -offset indent -width userlist
.It service
The name of the service associated with this entry. The
.Nm
utility uses the
.Dq ftpd
service name.
.It action
Specifies the action, which will be executed if the client information matches
with corresponding fields of the configuration line. This field may be
presented by one of the following keywords:
.br
.Dq allow
- the certificate is allowed to use the requested login name; the
authentication procedure succeeds.
.br
.Dq deny
- the certificate is denied to use requested login name; the authentication
procedure fails.
.It userlist
Contains a comma-separated list of login names those will be compared with the
login name issued by the client.
.Pp
If the login name begins with the `/' symbol, it designates a field of the
X.509 client certificate that includes the User ID of the end user. This
designation may be specified in two forms:
.br
``/ObjType'' - the field "ObjType" will be extracted and used as the login
name.
.br
``//ObjType[/domain.name]'' - the field "ObjType" will be treated as an
Internet email address. In this case the part of the email address before `@'
symbol will be used as the login name; if ``domain.name'' is specified, the
part after `@' symbol will be verified against it (the ``domain.name'' part is
not case-sensitive).
.Pp
If the login name is presented by the `*' symbol, it matches with any login
name issued by the client.
.It certificate
Describes the X.509 client certificate that is authorized to use the userlist.
If this field isn't starts with a directive, it contains the one line
distinguished name (the certificate's subject name). The directives are:
.br
``-r'' - the rest part is interpreted as a regular expression (see
.Xr regex 3 )
that describes the distinguished name and can match multiple certificates, each
of which is authorized to use the userlist.
.br
``-f'' - the rest part is interpreted as a file name that contains the X.509
certificate or a set of certificates in PEM format, each of which is authorized
to use the userlist. For security reasons this file will be used for the
authentication only if it is a regular file and is not a symbolic link. If the
file name begins with the tilde character (`~'), then this symbol will be
substituted by the login directory that is associated with the login name
issued by the client.
.br
``-p'' - this directive allows the usage of an external program to check the
certificate. The rest part of the field is interpreted as the full file name of
the program. The external authentication program must accept the login name and
the certificate from stdin and return the results of the authentication (a
reply code and the login name associated with the certificate) to stdout.
.El
.Pp
Lines beginning with the `#' symbol are ignored and can be used to include
comments. The components of fields are case-sensitive (the exception is noted
above); spaces are not ignored and are treated as parts of respective
components. All fields are mandatory, lines with unrecognized tokens (keywords,
directives, etc.) in one or more fields are ignored.
.Pp
Fields of each line and userlists are proceeded from left to right. The file
itself is proceeded line-by-line from top to bottom until the first match
for the given service in the 'userlist' and 'certificate' fields with
corresponding values those are provided by the client.
.Pp
If the match is found, the 'action' field of the configuration line will be
analized and the authentication procedure succeeds or fails depending to its
value. If no match is found, the certificate-based user authentication fails.
.Pp
Other TLS/SSL specific options
.Bl -tag -width indent
.It Cm cipher=\fIcipherlist\fR
The cipher preference list. The \fIcipherlist\fR consists of one or more cipher
strings separated by colons. The actual cipher string can take several different
forms. It can consists of a single cipher suite. It can represent a list of
cipher suites containing a certain algorithm, or cipher suites of a certain
type.
.Pp
Lists of cipher suites can be combined in a single cipher string using the
\fI+\fR character. It is used as the logical \fIand\fR operation.
.Pp
Each cipher string can be optionally preceded by the characters \fI!\fR,
\fI-\fR or \fI+\fR. If \fI!\fR is used then the ciphers are permanently deleted
from the list. If \fI-\fR is used then the ciphers are deleted from the list,
but some of all of them can be added again by later options. If \fI+\fR is used
then the ciphers are moved to the end of the list. Additionally the cipher
string \fI@STRENGTH\fR can be used at any point to sort the current cipher list
in order of an encryption algorithm key length.
.Pp
The following is the short list of permitted cipher strings and their meanings,
see the accompanying documentation for more information.
.br
\fIDEFAULT\fR - The default cipher list (determined at a compilation time).
.br
\fIALL\fR - All cipher suites except the ciphers those offering no encryption.
.br
\fIHIGH\fR - "High" encryption cipher suites (those with key lengths larger
than 128 bits).
.br
\fIMEDIUM\fR - "Medium" encryption cipher suites (those using 128 bit
encryption).
.br
\fILOW\fR - "Low" encryption cipher suites (those using 64 or 56 bit encryption
algorithms but excluding export cipher suites).
.br
\fIEXP\fR, \fIEXPORT\fR - Export encryption algorithms (including 40 and 56
bits algorithms).
.br
\fITLSv1\fR, \fISSLv3\fR, \fISSLv2\fR - TLS v1.0, SSL v3.0 or SSL v2.0 cipher
suites respectively.
.It Cm logfile=\fIlogfile\fR
The file where the TLS/SSL debugging information will be logged.
.It Cm debug
Turn on the TLS/SSL debugging code (it requires the
.Cm logfile
option).
.Pp
.El
Compatibility options
.Bl -tag -width indent
.It Cm apbu
Allow switching of the protection state of data connections before the
completed user login. By default this operation is disabled until the user will
be successfully logged in, and it is allowed at any time after that.
.It Cm uorc
Use "334" reply code in the FTP-SSL compatibility mode instead of "234". It may
be useful as a workaround for some early client implementations of the FTP-SSL
upgrade.
.El
.El
.Pp
The file
.Pa /var/run/nologin
(in FreeBSD) or 
.Pa /etc/nologin
(in Linux, see also
.Xr pam 8 )
can be used to disable ftp access.
If the file exists,
.Nm
displays it and exits.
If the file
.Pa /etc/ftpwelcome
exists,
.Nm
prints it before issuing the
.Dq ready
message.
If the file
.Pa /etc/ftpmotd
exists,
.Nm
prints it after a successful login.  Note the motd file used is the one
relative to the login environment.  This means the one in
.Pa ~ftp/etc
in the anonymous user's case.
.Pp
The ftp server currently supports the following ftp requests.
The case of the requests is ignored.  Requests marked [RW] are
disabled if
.Fl r
is specified.
.Bl -column "Request" -offset indent
.It Sy Request Ta Sy "Description"
.It ABOR Ta "abort previous command"
.It ACCT Ta "specify account (ignored)"
.It ALLO Ta "allocate storage (vacuously)"
.It APPE Ta "append to a file [RW]"
.It AUTH Ta "specify authentication/security mechanism"
.It CDUP Ta "change to parent of current working directory"
.It CWD Ta "change working directory"
.It DELE Ta "delete a file [RW]"
.It EPRT Ta "specify data connection port, multiprotocol"
.It EPSV Ta "prepare for server-to-server transfer, multiprotocol"
.It FEAT Ta "return list of supported extensions"
.It HELP Ta "give help information"
.It LIST Ta "give list files in a directory" Pq Dq Li "ls -lgA"
.It LPRT Ta "specify data connection port, multiprotocol"
.It LPSV Ta "prepare for server-to-server transfer, multiprotocol"
.It MDTM Ta "show last modification time of file"
.It MKD Ta "make a directory [RW]"
.It MODE Ta "specify data transfer" Em mode
.It NLST Ta "give name list of files in directory"
.It NOOP Ta "do nothing"
.It OPTS Ta "specify the behavior of FTP commands"
.It PASS Ta "specify password"
.It PASV Ta "prepare for server-to-server transfer"
.It PBSZ Ta "specify protection buffer size"
.It PORT Ta "specify data connection port"
.It PROT Ta "specify data connection protection level"
.It PWD Ta "print the current working directory"
.It QUIT Ta "terminate session"
.It REST Ta "restart incomplete transfer"
.It RETR Ta "retrieve a file"
.It RMD Ta "remove a directory [RW]"
.It RNFR Ta "specify rename-from file name [RW]"
.It RNTO Ta "specify rename-to file name [RW]"
.It SITE Ta "non-standard commands (see next section)"
.It SIZE Ta "return size of file"
.It STAT Ta "return status of server"
.It STOR Ta "store a file [RW]"
.It STOU Ta "store a file with a unique name [RW]"
.It STRU Ta "specify data transfer" Em structure
.It SYST Ta "show operating system type of server system"
.It TYPE Ta "specify data transfer" Em type
.It USER Ta "specify user name"
.It XCUP Ta "change to parent of current working directory (deprecated)"
.It XCWD Ta "change working directory (deprecated)"
.It XMKD Ta "make a directory (deprecated) [RW]"
.It XPWD Ta "print the current working directory (deprecated)"
.It XRMD Ta "remove a directory (deprecated) [RW]"
.El
.Pp
The following non-standard or
.Ux
specific commands are supported
by the
SITE request.
.Pp
.Bl -column Request -offset indent
.It Sy Request Ta Sy Description
.It UMASK Ta change umask, e.g. ``SITE UMASK 002''
.It IDLE Ta set idle-timer, e.g. ``SITE IDLE 60''
.It CHMOD Ta "change mode of a file [RW], e.g. ``SITE CHMOD 755 filename''"
.It MD5 Ta "report the files MD5 checksum, e.g. ``SITE MD5 filename''"
.It HELP Ta give help information
.El
.Pp
Note: SITE requests are disabled in case of anonymous logins.
.Pp
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.
To avoid possible denial-of-service attacks, SIZE requests against
files larger than 10240 bytes will be denied if the current transfer
type is ASCII.
.Pp
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.
.Pp
The
.Nm
utility interprets file names according to the
.Dq globbing
conventions used by
.Xr csh 1 .
This allows users to utilize the metacharacters
.Dq Li \&*?[]{}~ .
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The
.Nm
utility authenticates users according to six rules.
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.Bl -enum -offset indent
.It
The login name must be in the user database and not have a null password
(the exception is possible if PAM modules from the authentication management
group are used to set up a template user account; see below).
If a client is connected via TLS/SSL and the X.509 certificate-based
authentication is sufficient, it will be used instead of the password-based
one. Otherwise the standard authentication will be used.
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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
.Xr key 1
for more information on S/Key authentication.
S/Key is a Trademark of Bellcore.
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See also the
.Cm NOTES
section for the information about built-in implementation of S/Key in ports of
this
.Nm .
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If
.Xr pam 8
is used for the authentication, PAM modules from the authentication management
group may set up some user account as the template. This user account will be
used in all routines for whose the user account (the user record) in the system
user database is mentioned, so an FTP user will have access privileges of
this system user account.
.It
The login name must not appear in the file
.Pa /etc/ftpusers ,
otherwise the login attempt will be refused without asking for a password.
.It
The user account name must not be a member of a group specified in the file
.Pa /etc/ftpusers ,
otherwise the login attempt will be refused without asking for a password.
Entries in this file interpreted as group names are prefixed by an "at"
.Ql \&@
sign.
.It
The user account must have a standard shell returned by
.Xr getusershell 3 .
.It
If the user account name appears in the file
.Pa /etc/ftpchroot ,
or the user account is a member of a group with a group entry in this file,
i.e. one prefixed with
.Ql \&@ ,
the session's root will be changed to the directory specified
in this file or to the user's login directory by
.Xr chroot 2
as for an
.Dq anonymous
or
.Dq ftp
account (see next item).
See
.Xr ftpchroot 5
for a detailed description of the format of this file.
This facility may also be triggered by enabling the boolean "ftp-chroot"
capability in
.Xr login.conf 5
(see also the
.Cm NOTES
section).
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.
.It
If the user name is
.Dq anonymous
or
.Dq ftp ,
an
anonymous ftp account must be present in the user
database (user
.Dq 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
.Fl S
option is set, all transfers are logged as well.
.El
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In the last case,
.Nm
takes special measures to restrict the client's access privileges.
The server performs a
.Xr chroot 2
to the home directory of the
.Dq ftp
user.
As a special case if the
.Dq ftp
user's home directory pathname contains the
.Pa /./
separator,
.Nm
uses its left-hand side as the name of the directory to do
.Xr chroot 2
to, and its right-hand side to change the current directory to afterwards.
A typical example for this case would be
.Pa /usr/local/ftp/./pub .
In order that system security is not breached, it is recommended
that the
.Dq ftp
subtree be constructed with care, following these rules:
.Bl -tag -width "~ftp/pub" -offset indent
.It Pa ~ftp
Make the home directory owned by
.Dq root
and unwritable by anyone.
.It Pa ~ftp/etc
Make this directory owned by
.Dq root
and unwritable by anyone (mode 555).
The files pwd.db (see
.Xr passwd 5 )
and
.Xr group 5
must be present for the
.Xr ls 1
command to be able to produce owner names rather than numbers.
The password field in
.Xr passwd 5
is not used, and should not contain real passwords.
The file
.Pa ftpmotd ,
if present, will be printed after a successful login.
These files should be mode 444.
.It Pa ~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
.Em not
be owned or writable by
.Dq ftp
or its group, otherwise guest users
can fill the drive with unwanted files.
.El
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If the system has multiple IP addresses,
.Nm
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
.Pa /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:
.Bl -tag -offset indent -width hostname
.It hostname
Contains the hostname or IP address of the virtual host.
.It user[:anondir]
Contains a user record in the system user database.
As with normal anonymous ftp, this user's access uid, gid and group
memberships determine file access to the anonymous ftp area.
If anondir is specified, it determines the anonymous ftp area (to which any
user is chrooted on login), otherwise the anonymous ftp area is determined by
the home directory defined for the account, or by the directory specified in
the
.Xr ftpchroot 5
file.
.It statfile
File to which all file transfers are logged, which
defaults to
.Pa /var/log/ftpd .
.It welcome
This file is the welcome message displayed before the server ready
prompt.
It defaults to
.Pa /etc/ftpwelcome .
.It motd
This file is displayed after the user logs in.
It defaults to
.Pa /etc/ftpmotd .
.El
.Pp
Lines beginning with a '#' are ignored and can be used to include
comments.
.Pp
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 hyphen '-' used to indicate that the default
value is to be used.
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As with any anonymous login configuration, due care must be given
to setup and maintenance to guard against security related problems.
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The
.Nm
utility has internal support for handling remote requests to list
files, and will not execute
.Pa /bin/ls
in either a chrooted or non-chrooted environment.  The
.Pa ~/bin/ls
executable need not be placed into the chrooted tree, nor need the
.Pa ~/bin
directory exist.
.Sh FILES
.Bl -tag -width ".Pa /var/log/xferlog" -compact
.It Pa /etc/ftpusers
List of unwelcome/restricted users.
.It Pa /etc/ftpchroot
List of normal users who should be chroot'd.
.It Pa /etc/ftphosts
Virtual hosting configuration file.
.It Pa /etc/ftpwelcome
Welcome notice.
.It Pa /etc/ftpmotd
Welcome notice after login.
.It Pa /etc/x509.auth
Configuration file for relations between client certificates and system login
names.
.It Pa /var/run/nologin or /etc/nologin
Displayed and access refused.
.It Pa /var/log/ftpd
Log file for all file transfers.
.El
.Sh SEE ALSO
.Xr ftp 1 ,
.Xr ftps 1 ,
.Xr key 1 ,
.Xr openssl 1 ,
.Xr umask 2 ,
.Xr getusershell 3 ,
.Xr regex 3 ,
.Xr ftpchroot 5 ,
.Xr login.conf 5 ,
.Xr xferlog 5 ,
.Xr inetd 8 ,
.Xr pam 8 ,
.Xr syslogd 8
.Sh NOTES
The default value of the umask defined in
.Nm
is 022 (write access for the owner only). In FreeBSD the value of the umask
specified through the
.Fl u
command-line option (and the default value too) may be overridden by the
.Xr login.conf 5 .
.Pp
The
.Fl U
command-line option instructs ftpd to use data ports in the range of
.Dv IP_PORTRANGE_DEFAULT
instead of in the range of
.Dv IP_PORTRANGE_HIGH .
This option is virtual no-op in FreeBSD 5.0 and above (both port ranges are
indentical by default). The conception of various port ranges is not
implemented in Linux, so in this operating system the
.Fl U
option has no effect. See
.Xr ip 4
in FreeBSD or
.Xr ip 7
in Linux for more information about available port ranges.
.Pp
The support for the
.Xr login.conf 5
is available only in BSD systems. The general part of the capabilities of the
.Xr login.conf 5
may be implemented with help of 
.Xr pam 8 .
The capabilities, those are distinctive to the
.Nm , 
are also implemented with help of its own functionality.
.Pp
Currently the support for S/Key is not available in both FreeBSD and Linux
ports.
.Sh 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.
.Sh HISTORY
The
.Nm
utility appeared in
.Bx 4.2 .
IPv6 support was added in WIDE Hydrangea IPv6 stack kit.
.Pp
Modifications for TLS/SSL support, RFC2228 features and Linux port were made
by Nick Leuta <skynick@mail.sc.ru>