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FTPD(8) |
FreeBSD System Manager's Manual |
FTPD(8) |
ftpd —
Internet File Transfer Protocol server
ftpd |
[-468ABDdEhMmOoRrSUvW ]
[-l [-l ]]
[-a address]
[-P port]
[-p file]
[-T maxtimeout]
[-t timeout]
[-u umask] |
The ftpd utility is the Internet File Transfer Protocol
server process. The server uses the TCP protocol and listens at the port
specified with the -P option or in the
“ftp” service specification; see
services(5).
Available options:
-4
- When
-D is specified, accept connections via
AF_INET socket.
-6
- When
-D is specified, accept connections via
AF_INET6 socket.
-8
- Enable transparent UTF-8 mode. RFC 2640 compliant clients will be
told that the character encoding used by the server is UTF-8, which is the
only effect of the option.
This option does not enable any encoding conversion for server
file names; it implies instead that the names of files on the server are
encoded in UTF-8. As for files uploaded via FTP, it is the duty of the
RFC 2640 compliant client to convert their names from the
client's local encoding to UTF-8. FTP command names and own
ftpd messages are always encoded in ASCII, which
is a subset of UTF-8. Hence no need for server-side conversion at
all.
-A
- Allow only anonymous ftp access.
-a
- When
-D is specified, accept connections only on
the specified address.
-B
- With this option set,
ftpd sends authentication
success and failure messages to the
blacklistd(8)
daemon. If this option is not specified, no communcation with the
blacklistd(8)
daemon is attempted.
-D
- With this option set,
ftpd 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
ftpd from
inetd(8)
and is thus useful on busy servers to reduce load.
-d
- Debugging information is written to the syslog using
LOG_FTP .
-E
- Disable the EPSV command. This is useful for servers behind older
firewalls.
-h
- Disable printing host-specific information, such as the server software
version or hostname, in server messages.
-l
- Each successful and failed
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. By default,
syslogd(8)
logs these to /var/log/xferlog.
-M
- Prevent anonymous users from creating directories.
-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.
-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
-o is also specified.
-o
- Put server in write-only mode. RETR is disabled, preventing
downloads.
-P
- When
-D is specified, accept connections at
port, specified as a numeric value or service name,
instead of at the default “ftp” port.
-p
- When
-D is specified, write the daemon's process
ID to file instead of the default pid file,
/var/run/ftpd.pid.
-R
- With this option set,
ftpd will revert to
historical behavior with regard to security checks on user operations and
restrictions on PORT requests. Currently, ftpd
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).
-r
- Put server in read-only mode. All commands which may modify the local file
system are disabled.
-S
- With this option set,
ftpd logs all anonymous file
downloads to the file /var/log/ftpd when this file
exists.
-T
- A client may also request a different timeout period; the maximum period
allowed may be set to timeout seconds with the
-T option. The default limit is 2 hours.
-t
- The inactivity timeout period is set to timeout
seconds (the default is 15 minutes).
-U
- This option instructs ftpd to use data ports in the range of
IP_PORTRANGE_DEFAULT instead of in the range of
IP_PORTRANGE_HIGH . Such a change may be useful for
some specific firewall configurations; see
ip(4) for
more information.
Note that option is a virtual no-op in
FreeBSD 5.0 and above; both port ranges are
identical by default.
-u
- The default file creation mode mask is set to umask,
which is expected to be an octal numeric value. Refer to
umask(2)
for details. This option may be overridden by
login.conf(5).
-v
- A synonym for
-d .
-W
- Do not log FTP sessions to the user accounting database.
The file /var/run/nologin can be used to
disable ftp access. If the file exists, ftpd
displays it and exits. If the file /etc/ftpwelcome
exists, ftpd prints it before issuing the
“ready” message. If the file
/etc/ftpmotd exists, ftpd
prints it after a successful login. Note the motd file used is the one
relative to the login environment. This means the one in
~ftp/etc in the anonymous user's case.
The ftp server currently supports the following ftp requests. The
case of the requests is ignored. Requests marked [RW] are disabled if
-r is specified.
Request |
Description |
ABOR |
abort previous command |
ACCT |
specify account (ignored) |
ALLO |
allocate storage (vacuously) |
APPE |
append to a file [RW] |
CDUP |
change to parent of current working directory |
CWD |
change working directory |
DELE |
delete a file [RW] |
EPRT |
specify data connection port, multiprotocol |
EPSV |
prepare for server-to-server transfer, multiprotocol |
FEAT |
give information on extended features of server |
HELP |
give help information |
LIST |
give list files in a directory (“ls
-lgA ”) |
LPRT |
specify data connection port, multiprotocol |
LPSV |
prepare for server-to-server transfer, multiprotocol |
MDTM |
show last modification time of file |
MKD |
make a directory [RW] |
MODE |
specify data transfer mode |
NLST |
give name list of files in directory |
NOOP |
do nothing |
PASS |
specify password |
PASV |
prepare for server-to-server transfer |
PORT |
specify data connection port |
PWD |
print the current working directory |
QUIT |
terminate session |
REST |
restart incomplete transfer |
RETR |
retrieve a file |
RMD |
remove a directory [RW] |
RNFR |
specify rename-from file name [RW] |
RNTO |
specify rename-to file name [RW] |
SITE |
non-standard commands (see next section) |
SIZE |
return size of file |
STAT |
return status of server |
STOR |
store a file [RW] |
STOU |
store a file with a unique name [RW] |
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) [RW] |
XPWD |
print the current working directory (deprecated) |
XRMD |
remove a directory (deprecated) [RW] |
The following non-standard or UNIX
specific commands are supported by the SITE request.
Request |
Description |
UMASK |
change umask, e.g. ``SITE UMASK 002'' |
IDLE |
set idle-timer, e.g. ``SITE IDLE 60'' |
CHMOD |
change mode of a file [RW], e.g. ``SITE CHMOD 755 filename'' |
MD5 |
report the files MD5 checksum, e.g. ``SITE MD5 filename'' |
HELP |
give help information |
Note: SITE requests are disabled in case of anonymous logins.
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.
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.
The ftpd utility interprets file names
according to the “globbing” conventions used by
csh(1).
This allows users to utilize the metacharacters
“*?[]{}~ ”.
The ftpd utility authenticates users
according to six rules.
- The login name must be in the password data base 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 OPIE key, the
response from a successful USER command will include an OPIE challenge.
The client may choose to respond with a PASS command giving either a
standard password or an OPIE one-time password. The server will
automatically determine which type of password it has been given and
attempt to authenticate accordingly. See
opie(4)
for more information on OPIE authentication.
- The login name must not appear in the file
/etc/ftpusers.
- The login name must not be a member of a group specified in the file
/etc/ftpusers. Entries in this file interpreted as
group names are prefixed by an "at"
‘
@ ’ sign.
- The user must have a standard shell returned by
getusershell(3).
- If the user name appears in the file
/etc/ftpchroot, or the user is a member of a group
with a group entry in this file, i.e., one prefixed with
‘
@ ’, the session's root will be
changed to the directory specified in this file or to the user's login
directory by
chroot(2)
as for an “anonymous” or “ftp” account (see
next item). See
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
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.
- 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). When the
-S
option is set, all transfers are logged as well.
In the last case, ftpd takes special
measures to restrict the client's access privileges. The server performs a
chroot(2)
to the home directory of the “ftp” user. As a special case if
the “ftp” user's home directory pathname contains the
/./ separator, ftpd uses its
left-hand side as the name of the directory to do
chroot(2)
to, and its right-hand side to change the current directory to afterwards. A
typical example for this case would be
/usr/local/ftp/./pub. In order that system security
is not breached, it is recommended that the “ftp” subtree be
constructed with care, following these rules:
- ~ftp
- Make the home directory owned by “root” and unwritable by
anyone.
- ~ftp/etc
- Make this directory owned by “root” and unwritable by anyone
(mode 555). The files pwd.db (see
passwd(5))
and
group(5)
must be present for the
ls(1)
command to be able to produce owner names rather than numbers. The
password field in
passwd(5)
is not used, and should not contain real passwords. The file
ftpmotd, 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, otherwise guest users can
fill the drive with unwanted files.
If the system has multiple IP addresses,
ftpd 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
/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:
- hostname
- Contains the hostname or IP address of the virtual host.
- user
- Contains a user record in the system password file. As with normal
anonymous ftp, this user's access uid, gid and group memberships determine
file access to the anonymous ftp area. The anonymous ftp area (to which
any user is chrooted on login) is determined by the home directory defined
for the account. User id and group for any ftp account may be the same as
for the standard ftp user.
- statfile
- File to which all file transfers are logged, which defaults to
/var/log/ftpd.
- welcome
- This file is the welcome message displayed before the server ready prompt.
It defaults to /etc/ftpwelcome.
- motd
- This file is displayed after the user logs in. It defaults to
/etc/ftpmotd.
Lines beginning with a '#' are ignored and can be used to include
comments.
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.
As with any anonymous login configuration, due care must be given
to setup and maintenance to guard against security related problems.
The ftpd utility has internal support for
handling remote requests to list files, and will not execute
/bin/ls in either a chrooted or non-chrooted
environment. The ~/bin/ls executable need not be
placed into the chrooted tree, nor need the ~/bin
directory exist.
- /etc/ftpusers
- List of unwelcome/restricted users.
- /etc/ftpchroot
- List of normal users who should be chroot'd.
- /etc/ftphosts
- Virtual hosting configuration file.
- /etc/ftpwelcome
- Welcome notice.
- /etc/ftpmotd
- Welcome notice after login.
- /var/run/ftpd.pid
- Default pid file for daemon mode.
- /var/run/nologin
- Displayed and access refused.
- /var/log/ftpd
- Log file for anonymous transfers.
- /var/log/xferlog
- Default place for session logs.
The ftpd utility appeared in
4.2BSD. IPv6 support was added in WIDE Hydrangea IPv6
stack kit.
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.
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