NetBSD/libexec/ftpd/ftpd.8

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.\"     @(#)ftpd.8	8.2 (Berkeley) 4/19/94
.\"
.Dd September 7, 1998
.Dt FTPD 8
.Os NetBSD
.Sh NAME
.Nm ftpd ,
.Nm ftpd.conf
.Nd
Internet File Transfer Protocol server
.Sh SYNOPSIS
.Nm
.Op Fl dls
.Op Fl a Ar anondir
.Op Fl c Ar confdir
.Op Fl C Ar user
.Sh DESCRIPTION
.Nm
is the Internet File Transfer Protocol server process.
The server uses the
.Tn TCP
protocol and listens at the port specified in the
.Dq ftp
service specification; see
.Xr services 5 .
.Pp
Available options:
.Bl -tag -width Ds
.It Fl a
Define the directory to
.Xr chroot 2
into for anonymous logins.
Default is the home directory for the ftp user.
.It Fl c
Change the root directory of the configuration files from
.Dq Pa /etc
to
.Ar directory .
.It Fl C
Check whether the specified user would be granted access under
the restrictions given in
.Pa /etc/ftpusers
and exit without attempting a connection.
.Nm
exits with an exit code of 0 if access would be granted, or 1 otherwise.
This can be useful for testing configurations.
.It Fl d
Debugging information is written to the syslog using LOG_FTP.
.It Fl l
Each successful and failed
.Xr 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.
.It Fl s
Require a secure authentication mechanism like Kerberos or S/Key to be used.
.El
.Pp
The file
.Pa /etc/nologin
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/motd
exists,
.Nm
prints it after a successful login.
.Pp
The ftp server currently supports the following ftp requests.
The case of the requests is ignored.
.Bl -column "Request" -offset indent
.It Request Ta "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"
.It CDUP Ta "change to parent of current working directory"
.It CWD Ta "change working directory"
.It DELE Ta "delete a file"
.It FEAT Ta "list extra features that are not defined in" Cm "RFC 959"
.It HELP Ta "give help information"
.It LIST Ta "give list files in a directory" Pq Dq Li "ls -lgA"
.It MKD Ta "make a directory"
.It MDTM Ta "show last modification time of file"
.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 "define persistent options for a given command"
.It PASS Ta "specify password"
.It PASV Ta "prepare for server-to-server transfer"
.It PORT Ta "specify data connection port"
.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"
.It RNFR Ta "specify rename-from file name"
.It RNTO Ta "specify rename-to file name"
.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"
.It STOU Ta "store a file with a unique name"
.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)"
.It XPWD Ta "print the current working directory (deprecated)"
.It XRMD Ta "remove a directory (deprecated)"
.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 CHMOD Ta "change mode of a file, e.g. ``SITE CHMOD 755 filename''"
.It HELP Ta "give help information."
.It IDLE Ta "set idle-timer, e.g. ``SITE IDLE 60''"
.It UMASK Ta "change umask, e.g. ``SITE UMASK 002''"
.El
.Pp
The following ftp requests (as specified in
.Cm RFC 959 )
are recognized, but are not implemented:
ACCT, SMNT, and REIN.
MDTM and SIZE are not specified in
.Cm RFC 959 ,
but will appear in the
next updated FTP RFC.
.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
.Cm 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
.Nm
interprets file names according to the
.Dq globbing
conventions used by
.Xr csh 1 .
This allows users to utilize the metacharacters
.Dq Li \&*?[]{}~ .
.Ss User authentication
.Nm
authenticates users according to five rules.
.Pp
.Bl -enum -offset indent
.It
The login name must be in the password data base,
.Pa /etc/pwd.db ,
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
.Xr skey 1
for more information on S/Key authentication.
S/Key is a Trademark of Bellcore.
.It
The login name must be allowed based on the information in
.Pa /etc/ftpusers
(see below).
.It
The user must have a standard shell returned by
.Xr getusershell 3 .
If the user's shell field in the password database is empty, the
shell is assumed to be
.Pa /bin/sh .
.It
If directed by the file
.Pa /etc/ftpchroot
(see below)
the session's root will be changed to the user's login directory by
.Xr chroot 2
as for an
.Dq anonymous
or
.Dq 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.
.It
If the user name is
.Dq anonymous
or
.Dq ftp ,
an
anonymous ftp account must be present in the password
file (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).
The server performs a
.Xr chroot 2
to the home directory of the
.Dq ftp
user.
If other restrictions are required (such as disabling of certain
commands and the setting of a specific umask), then appropriate
entries in
.Pa /etc/ftpd.conf
are required.
.El
.Ss /etc/ftpusers
The file
.Pa /etc/ftpusers
is used to determine which users may use ftp.
If the file does not exist, all users are denied access.
If it does exist, each line is a comment starting with
.Dq #
or a glob pattern that uses the same syntax as /bin/sh,
optionally followed by whitespace and
.Dq allow ,
.Dq yes ,
.Dq deny ,
or
.Dq no .
Each glob pattern is compared in turn against the username
until a match is found.
If the word following the matched glob pattern is
.Dq allow
or
.Dq yes
the user is granted access; if the word is
.Dq deny
or
.Dq no ,
or if the word is missing,
the user is denied access.
No further comparisons are attempted after the first successful match.
If no match is found, the user is granted access.
This syntax is backward-compatable with the old syntax.
.Pp
If a user requests a guest login, the ftp server checks to see that
both
.Dq anonymous
and
.Dq ftp
have access, so if you deny all users by default, you will need to add both
.Dq "anonymous allow"
and
.Dq "ftp allow"
to
.Pa /etc/ftpusers
in order to allow guest logins.
.Ss /etc/ftpchroot
The file
.Pa /etc/ftpchroot
is used to determine which users will have their session's root changed
to the user's home directory.
If the file does not exist, the root change is not performed.
If it does exist, each line is a comment starting with
.Dq #
or a glob pattern that uses the same syntax as /bin/sh,
optionally followed by whitespace and
.Dq yes
or
.Dq no .
Each glob pattern is compared in turn against the username
until a match is found.  If the word following the matched glob
pattern is
.Dq yes
or there is no following word, the root is changed.
If the word is 
.Dq no ,
or if no match is found, the root is not changed.
No further comparisons are attempted after the first successful match.
This syntax is backward-compatable with the old syntax.
.Ss /etc/ftpd.conf
The file
.Pa /etc/ftpd.conf
is used to configure various options.
Each line starting with a
.Dq #
is a comment (and ignored), and all other non-blank lines are treated
as configuration directives.
.Pp
Each configuration line may be one of:
.Bl -tag -width 4n
.It Sy checkportcmd Ar class Op Sy off
Check the
PORT
command for validity.
The
PORT
command will fail if the IP address specified does not match the ftp
command connection, or if the remote TCP port number is less than
.Dv IPPORT_RESERVED .
It is
.Em strongly
encouraged that this option be used, espcially for sites concerned
with potential security problems with ftp bounce attacks.
If class is
.Dq none
or
.Sy off
is given, disable this feature, otherwise enable it.
.It Xo Sy conversion Ar class
.Ar suffix Op Ar "type disable command"
.Xc
Define an automatic in-line file conversion.
If a file to retrieve ends in
.Ar suffix ,
and a real file (sans
.Ar suffix )
exists, then the output of
.Ar command
is returned instead of the contents of the file.
.Pp
.Bl -tag -width "disable" -offset indent
.It Ar suffix
The suffix to initiate the conversion.
.It Ar type
A list of valid filetypes for the conversion.
Valid types are:
.Sq f
(file), and
.Sq d
(directory).
.It Ar disable
The name of file that will prevent conversion if it exists.
A filename of
.Pa \&.
will prevent this disabling action.
.It Ar command
The command to run for the conversion.
The first word should be the full path name
of the command, as
.Xr execv 3
is used to execute the command.
The first instance of
.Sq %s
in
.Ar command
is replaced with the requested file (sans
.Ar suffix ) .
.El
.Pp
Conversion directives specified later in the file override earlier
conversions with the same suffix.
The order in which conversions is matched is the reverse of their
order in the file (i.e. a LIFO).
.It Sy display Ar class Op Ar file
If
.Ar file
isn't given or
.Ar class
is
.Dq none ,
disable this.
Otherwise, each time the user enters a new directory, check if
.Ar file
exists, and if so, display its contents to the user.
.It Sy maxtimeout Ar class Ar time
Set the maximum timeout period that a client may request,
defaulting to two hours.
This cannot be lesser than 30 seconds, or the value for
.Sy timeout .
Ignored if class is
.Dq none
or
.Ar time
isn't specified.
.It Sy modify Ar class Op Sy off
If class is
.Dq none
or
.Sy off
is given, disable the following commands:
CHMOD, DELE, MKD, RNFR, RMD, and UMASK.
Otherwise, enable them.
.It Sy notify Ar class Op Ar fileglob
If
.Ar fileglob
isn't given or
.Ar class
is
.Dq none ,
disable this.
Otherwise, each time the user enters a new directory,
notify the user of any files matching
.Ar fileglob .
.It Sy passive Ar class Op Sy off
If class is
.Dq none
or
.Sy off
is given, disallow passive (PASV) connections.  Otherwise, enable them.
.It Sy timeout Ar class Ar time
Set the inactivity timeout period.
(the default is fifteen minutes).
This cannot be lesser than 30 seconds, or greater than the value for
.Sy maxtimeout .
Ignored if class is
.Dq none
or
.Ar time
isn't specified.
.It Sy umask Ar class Ar umaskval
Set the umask to
.Ar umaskval .
Ignored if class is
.Dq none
or
.Ar umaskval
isn't specified.
.El
.Pp
In any configuration line,
.Ar class
is one of:
.Bl -tag -width "chroot" -compact -offset indent
.It Sy real
Normal user logins.
.It Sy chroot
Users that have been
.Xr chroot 2 ed.
.It Sy guest
.Dq anonymous
and
.Dq ftp
users.
.It Sy all
Matches any class.
.It Sy none
Matches no class.
.El
.Pp
The following defaults are used:
.Bd -literal -offset indent -compact
checkportcmd  none
display       none
maxtimeout    all    7200   # 2 hours
modify        all
modify        guest  off
notify        none
passive       all
timeout       all    900    # 15 minutes
umask         all    027
umask         guest  0707
.Ed
.Pp
Directives that appear later in the file override settings by previous
directives.
This allows
.Sq wildcard
entries to define defaults, and then have class-specific overrides.
.Pp
The
STAT
command will return the class settings for the current user as defined by
.Pa /etc/ftpd.conf .
.Ss Setting up a restricted ftp subtree
In order that system security is not breached, it is recommended
that the
subtrees for the
.Dq ftp
and
.Dq chroot
accounts be constructed with care, following these rules
(replace
.Dq ftp
in the following directory names
with the appropriate account name for
.Sq chroot
users):
.Bl -tag -width "~ftp/incoming" -offset indent
.It Pa ~ftp
Make the home directory owned by
.Dq root
and unwritable by anyone.
.It Pa ~ftp/bin
Make this directory owned by
.Dq root
and unwritable by anyone (mode 555).
The program
.Xr ls 1
must be present to support the
.Sq LIST
command.
This program should be mode 111.
.It Pa ~ftp/etc
Make this directory owned by
.Dq root
and unwritable by anyone (mode 555).
The files
.Pa pwd.db
(see
.Xr passwd 5 )
and
.Pa group
(see
.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 motd ,
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 ftp or its group.
.It Pa ~ftp/incoming
This directory is where anonymous users place files they upload.
The owners should be the user
.Dq 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.
.Pp
Anonymous users will be 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 mentioned
above.
.It Pa ~ftp/tmp
This directory is used to create temporary files which contain
the error messages generated by a conversion or
.Sq LIST
command.
The owner should be the user
.Dq ftp .
The permissions should be 300.
.Pp
If you don't enable conversion commands, or don't want anonymous users
uploading files (see
.Pa ~ftp/incoming
above), then don't create this directory.
However, error messages from conversion or
.Sq LIST
commands won't be returned to the user.
(This is the traditional behaviour.)
.El
.Sh FILES
.Bl -tag -width /etc/ftpwelcome -compact
.It Pa /etc/ftpchroot
List of normal users who should be chroot'd.
.It Pa /etc/ftpd.conf
Configure file conversions and other settings.
.It Pa /etc/ftpusers
List of unwelcome/restricted users.
.It Pa /etc/ftpwelcome
Welcome notice before login.
.It Pa /etc/motd
Welcome notice after login.
.It Pa /etc/nologin
If it exists, displayed and access is refused.
.El
.Sh SEE ALSO
.Xr ftp 1 ,
.Xr skey 1 ,
.Xr getusershell 3 ,
.Xr syslogd 8
.Sh STANDARDS
.Nm
recognizes all commands in 
.Cm RFC 959 , 
follows the guidelines in 
.Cm RFC 1123 ,
recognizes all commands in 
.Cm RFC 2228
(although they are not supported yet),
and supports the extensions from
.Cm RFC 2389.
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .
.Pp
The
.Pa /etc/ftpd.conf
functionality was implemented in
.Nx 1.3
by Luke Mewburn, based on work by Simon Burge.
.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.
.Sh SECURITY CONSIDERATIONS
.Cm RFC 959
provides no restrictions on the PORT command, and this can lead
to security problems, as
.Nm
can be fooled into connecting to any service on any host.
With the
.Dq checkportcmd
feature of the
.Pa /etc/ftpd.conf ,
PORT commands with different host addresses, or TCP ports lower than
.Dv IPPORT_RESERVED
will be rejected.
Use of this option is
.Em strongly
recommended.