TNFTPD(8) BSD System Manager's Manual TNFTPD(8)NAME
tnftpd — Internet File Transfer Protocol server
SYNOPSIS
tnftpd [-46DdHkKlnQqrsUuWwXzZ] [-a anondir] [-C user[@host]] [-c confdir]
[-e emailaddr] [-h hostname] [-L xferlogfile] [-P dataport]
[-V version]
DESCRIPTION
tnftpd is the Internet File Transfer Protocol server process. The server
uses the TCP protocol and listens at the port specified in the “ftp” ser‐
vice 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 connection. tnftpd
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
“/private/etc” to confdir. This changes the directory for the
following files: /private/etc/ftpchroot, /private/etc/ftpusers,
/private/etc/ftpwelcome, /private/etc/motd, and the file speci‐
fied by the ftpd.conf(5) limit directive.
-D Run as daemon. tnftpd will listen on the default FTP port for
incoming connections and fork a child for each connection. This
is lower overhead than starting tnftpd 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 hostname associated with the IP address that
tnftpd 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.
-k Allow use of the CCC command.
-K Require authenticated credentials.
-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 tnftpd 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
-z Require authorization.
-Z Require authentication.
The file /etc/nologin can be used to disable FTP access. If the file
exists, tnftpd displays it and exits. If the file
/private/etc/ftpwelcome exists, tnftpd prints it before issuing the
“ready” message. If the file /private/etc/motd exists (under the chroot
directory if applicable), tnftpd prints it after a successful login.
This may be changed with the ftpd.conf(5) directive motd.
The tnftpd server currently supports the following FTP requests. The
case of the requests is ignored.
Request Description
ABOR abort previous command
ACCT specify account (ignored)
ADAT supply authentication data
ALLO allocate storage (vacuously)
APPE append to a file
AUTH select authentication paradigm
CCC force cleartext commands
CDUP change to parent of current working directory
CWD change working directory
DELE delete a file
ENC send privacy protected command
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
MIC send integrity protected command
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
PBSZ set protection buffer size
PORT specify data connection port
PROT set data protection mode
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 tnftpd 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.
tnftpd interprets file names according to the “globbing” conventions used
by csh(1). This allows users to use the metacharacters “*?[]{}~”.
User authentication
tnftpd 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 per‐
formed. 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 direc‐
tory 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 cer‐
tain 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 anony‐
mous user is “-”, then the verbose messages displayed at login
and upon a CWD command are suppressed.
Display file escape sequences
When tnftpd displays various files back to the client (such as
/private/etc/ftpwelcome and /private/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 com‐
mands 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 peo‐
ple 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 permis‐
sions 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
mentioned above.
~ftp/tmp This directory is used to create temporary files
which contain the error messages generated by a con‐
version 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 direc‐
tory. 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
/private/etc/ftpchroot List of normal users whose root directory should
be changed via chroot(2).
/private/etc/ftpd.conf Configure file conversions and other settings.
/private/etc/ftpusers List of unwelcome/restricted users.
/private/etc/ftpwelcome Welcome notice before login.
/private/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 tnftpd
class ‘CLASS’.
/var/run/utmp List of logged-in users on the system.
/var/log/wtmp Login history database.
SEE ALSOftp(1), skey(1), who(1), getusershell(3), ftpchroot(5), ftpd.conf(5),
ftpusers(5), login.conf(5), syslogd(8)STANDARDS
tnftpd recognizes all commands in RFC 959, follows the guidelines in RFC
1123, recognizes all commands in RFC 2228 (although they are not sup‐
ported yet), and supports the extensions from RFC 2389, RFC 2428, and RFC
3659.
HISTORY
The tnftpd 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
tnftpd 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.
tnftpd 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 problems, as tnftpd can be fooled into connecting to any ser‐
vice 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 tnftpd uses a port that is one less than the port it is lis‐
tening on to communicate back to the client for the EPRT, LPRT, and PORT
commands, unless overridden with -P dataport. As the default port for
tnftpd (21) is a privileged port below IPPORT_RESERVED, tnftpd 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 tnftpd
providing a remote root compromise, tnftpd will permanently drop root
privileges if one of the following is true:
1. tnftpd is running on a port greater than IPPORT_RESERVED and
the user has logged in as a ‘guest’ or ‘chroot’ user.
2. tnftpd was invoked with -r.
Don't create ~ftp/tmp if you don't want anonymous users to upload files
there. That directory 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 can‐
not 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
