is the Internet File Transfer Protocol server process.
The server uses the
TCP
protocol 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.conf5
chroot
directive.
-C user
Check whether
user
would be granted access under
the restrictions given in
ftpusers(5)
and exit without attempting a connection.
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.conf5
limit
directive.
-D
Run as daemon.
will listen on the default FTP port for incoming connections
and fork a child for each connection.
This is lower overhead than starting
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
Sx Display file escape sequences )
-H
Equivalent to
Do -h
`hostname`
Dc .
-h hostname
Explicitly set the hostname to advertise as to
hostname
The default is the hostname associated with the IP address that
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.conf5
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.
-P dataport
Use
dataport
as the data port, overriding the default of using the port one less
that the port
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
Sx 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:
"grep 'xferlog: ' /var/log/xferlog | \"
" sed -e 's/^.*xferlog: //' Gt] wuxferlog"
The file
/etc/nologin
can be used to disable
FTP
access.
If the file exists,
displays it and exits.
If the file
/etc/ftpwelcome
exists,
prints it before issuing the
``ready''
message.
If the file
/etc/motd
exists (under the chroot directory if applicable),
prints it after a successful login.
This may be changed with the
ftpd.conf5
directive
motd
The
server currently supports the following
FTP
requests.
The case of the requests is ignored.
Request Ta Description
ABOR Ta abort previous command
ACCT Ta specify account (ignored)
ALLO Ta allocate storage (vacuously)
APPE Ta append to a file
CDUP Ta change to parent of current working directory
CWD Ta change working directory
DELE Ta delete a file
EPSV Ta prepare for server-to-server transfer
EPRT Ta specify data connection port
FEAT Ta list extra features that are not defined in RFC 959
HELP Ta give help information
LIST Ta give list files in a directory (``ls -lA
''
)
LPSV Ta prepare for server-to-server transfer
LPRT Ta specify data connection port
MLSD Ta list contents of directory in a machine-processable form
MLST Ta show a pathname in a machine-processable form
MKD Ta make a directory
MDTM Ta show last modification time of file
MODE Ta specify data transfer mode
NLST Ta give name list of files in directory
NOOP Ta do nothing
OPTS Ta define persistent options for a given command
PASS Ta specify password
PASV Ta prepare for server-to-server transfer
PORT Ta specify data connection port
PWD Ta print the current working directory
QUIT Ta terminate session
REST Ta restart incomplete transfer
RETR Ta retrieve a file
RMD Ta remove a directory
RNFR Ta specify rename-from file name
RNTO Ta specify rename-to file name
SITE Ta non-standard commands (see next section)
SIZE Ta return size of file
STAT Ta return status of server
STOR Ta store a file
STOU Ta store a file with a unique name
STRU Ta specify data transfer structure
SYST Ta show operating system type of server system
TYPE Ta specify data transfer type
USER Ta specify user name
XCUP Ta change to parent of current working directory (deprecated)
XCWD Ta change working directory (deprecated)
XMKD Ta make a directory (deprecated)
XPWD Ta print the current working directory (deprecated)
XRMD Ta remove a directory (deprecated)
The following non-standard or
UNIX
specific commands are supported by the SITE request.
Request Ta Description
CHMOD Ta change mode of a file, e.g. ``SITE CHMOD 755 filename''
HELP Ta give help information.
IDLE Ta set idle-timer, e.g. ``SITE IDLE 60''
RATEGET Ta set maximum get rate throttle in bytes/second, e.g. ``SITE RATEGET 5k''
RATEPUT Ta set maximum put rate throttle in bytes/second, e.g. ``SITE RATEPUT 5k''
UMASK Ta change umask, e.g. ``SITE UMASK 002''
The following
FTP
requests (as specified in
RFC 959
are recognized, but are not implemented:
ACCTSMNT
and
REINMDTM
and
SIZE
are not specified in
RFC 959
but will appear in the
next updated
FTP
RFC.
The
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.
interprets file names according to the
``globbing''
conventions used by
csh(1).
This allows users to use the metacharacters
``*?[]{}~
''
User authentication
authenticates users according to five rules.
The login name must be in the password data base,
/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
skey(1)
for more information on S/Key authentication.
S/Key is a Trademark of Bellcore.
The login name must be allowed based on the information in
ftpusers(5).
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
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.conf5
chroot
directive (if set),
or to the home directory of the user.
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.
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.conf5
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.conf5
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.conf5
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 suppressed.
Display file escape sequences
When
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.conf5
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 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.conf5
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
class
`CLASS'
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 2389RFC 2428
and
draft-ietf-ftpext-mlst-11
HISTORY
The
command appeared in
BSD 4.2
Various features such as the
ftpd.conf5
functionality,
RFC 2389
and
draft-ietf-ftpext-mlst-11
support was implemented in
Nx 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
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
Sx SECURITY CONSIDERATIONS
below for more details.
may have trouble handling connections from scoped IPv6 addresses, or
IPv4 mapped addresses
Po IPv4 connection on
AF_INET6
socket
Pc .
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
can be fooled into connecting to any service on any host.
With the
``checkportcmd''
feature of the
ftpd.conf5,
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
uses a port that is one less than the port it is listening on to
communicate back to the client for the
EPRTLPRT
and
PORT
commands, unless overridden with
-P dataport
As the default port for
(21) is a privileged port below
IPPORT_RESERVED
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
providing a remote root compromise,
will permanently drop root privileges if one of the following is true:
is running on a port greater than
IPPORT_RESERVED
and the user has logged in as a
`guest'
or
`chroot'
user.
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.conf5
directive
upload
then this directory cannot be abused by the user in this way, so it
should be safe to create.
