ftpd - Internet File Transfer Protocol server
ftpd [-46ADdlMnPSU] [-T maxtimeout] [-t timeout] [-u mask]
ftpd 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).
The options are as follows:
-4 When -D is specified, forces ftpd to use IPv4 addresses only.
-6 When -D is specified, forces ftpd to use IPv6 addresses only.
-A Permit only anonymous ftp connections, accounts
listed in
/etc/ftpchroot or users in a login class with the
``ftp-chroot''
variable set (see below). Other connection attempts
are refused.
-D With this option set, ftpd will detach and become a
daemon, accepting
connections on the FTP port and forking
child processes
to handle them. This has 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.
-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.
-M Enables multihomed mode. Instead of simply using
~ftp for anonymous
transfers, a directory matching the fully qualified name of
the IP number the client connected to, and located
inside ~ftp,
is used instead.
-n Do not permit anonymous ftp logins. Normally they
are permitted.
-P Permit illegal port numbers or addresses for PORT
command initiated
connects. By default ftpd violates the RFC and
thus constrains
the PORT command to non-reserved ports and
requires it
use the same source address as the connection came
from. This
prevents the "FTP bounce attack" against services on
both the local
machine and other local machines.
-S With this option set, ftpd logs all anonymous downloads to the
file /var/log/ftpd when this file exists.
-T maxtimeout
A client may also request a different timeout period; the maximum
period allowed may be set to maxtimeout seconds with
the -T option.
The default limit is 2 hours.
-t timeout
The inactivity timeout period is set to timeout seconds (the default
is 15 minutes).
-U Each concurrent ftp(1) session is logged to the file
/var/run/utmp, making them visible to commands such
as who(1).
-u mask
Force the umask to mask, instead of the default
specified in
/etc/login.conf (usually 022). Also disallows
chmod.
The file /etc/nologin can be used to disable ftp access. If
the file exists,
ftpd displays it and exits. Note: this method will
disable all
non-root logins; see login(1) for further details. If the
file
/etc/ftpwelcome exists, ftpd prints it before issuing the
``ready'' message.
If the welcome file exists (/etc/motd by default),
ftpd prints it
after a successful login. If the file .message exists in a
directory,
ftpd prints it when that directory is entered.
The ftp server currently supports the following ftp requests. The case
of the requests is ignored.
Request Description
ABOR abort previous command
ACCT specify account (not implemented)
ALLO allocate storage (vacuously)
APPE append to a file
CDUP change to parent of current working directory
CWD change working directory
DELE delete a file
EPRT specify data connection port
EPSV prepare for server-to-server transfer
HELP give help information
LIST give list of files in a directory (ls -lgA)
LPRT specify data connection port
LPSV prepare for server-to-server transfer
MDTM show last modification time of file
MKD make a directory
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
REIN reinitialize (not implemented)
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
SMNT structure mount (not implemented)
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; not valid after login
XCUP change to parent of current working directory (deprec.)
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
UMASK change umask, e.g., SITE UMASK 002
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.
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.
ftpd interprets file names according to the ``globbing''
conventions used
by csh(1). This allows users to utilize the metacharacters
``*?[]{}~''.
ftpd authenticates users by using the service and type of
ftp, as defined
in the /etc/login.conf file (see login.conf(5)). An authentication style
may be specified by appending with a colon (`:') following
the authentication
style, i.e. ``joe:skey''. The allowed authentication
styles for
ftpd may be explicitly specified by the ``auth-ftp'' entry
in
/etc/login.conf.
ftpd authenticates users according to five rules.
1. The login name must be in the password database
and not have a
null password. In this case a password must be
provided by
the client before any file operations may be performed.
2. The login name must not appear in the file
/etc/ftpusers.
3. The user must have a standard shell as described
by shells(5).
4. If the user name appears in the file
/etc/ftpchroot, the session's
root will be changed to the user's login
directory by
chroot(2) as for an ``anonymous'' or ``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.
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).
Once a user is authenticated the user must be approved by
any approval
script defined (see login.conf(5)). If a valid approval
script (by either
:approve=...: or :approve-ftp=...: for the user's
class) is defined
then it is run and must exit with a 0 (success) status.
When ftpd is
running under the -D flag (and debugging is not turned on)
then the approval
script will be called with at least the following
variables specified
via the -v option (see login.conf(5)) to the approve
script:
Variable Description
FTPD_HOST The server's (virtual) hostname
For example (the line is broken to fit the page):
/usr/libexec/auth/approve_ftpd -v FTPD_HOST=ftp.mycompany.com username class service
When the user logs in to the anonymous ftp account, 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. 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 (mode 555).
~ftp/bin Make this directory owned by ``root'' and
unwritable by
anyone (mode 511). This directory is optional unless you
have commands you wish the anonymous ftp user to be able
to run (the ls(1) command exists as a builtin). Any
programs in this directory should be mode
111 (executable
only).
~ftp/etc Make this directory owned by ``root'' and
unwritable by
anyone (mode 511). The files pwd.db (see
pwd_mkdb(8))
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 pwd.db 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 Make this directory mode 555 and owned by
``root''. This
is traditionally where publicly accessible
files are
stored for download.
If logging to the /var/log/ftpd file is enabled, information
will be
written in the following format:
time The time and date of the download, in
ctime(3) format.
elapsed time The elapsed time, in seconds.
remote host The remote host (or IP number).
bytes The number of bytes transferred.
path The full path (relative to the ftp chroot space) of
the file transferred.
type The type of transfer; either `a' for
ASCII or `b'
for binary.
unused Unused field containing a `*', for
compatibility.
unused Unused field containing an `o', for
compatibility.
user type The type of user; either `a' for
anonymous or `r'
for a real user (should always be
anonymous).
name Either a system login name or the value given for
``email address'' if an anonymous user.
unused Unused field containing a `0', for
compatibility.
real name The system login name if the connection is not
anonymous, or a `*' if it is.
Although fields exist for logging information on real users,
this file is
only used for anonymous downloads. Unused fields exist only
for compatibility
with other ftpd implementations.
The ftpd daemon uses the following ftp specific parameters:
auth-ftp The list of authentication types available to
this class.
See login.conf(5).
ftp-chroot A boolean value. If set, users in this class
will be automatically
chrooted to the user's login directory.
ftp-dir A path to a directory. This value overrides the
login directory
for users in this class. A leading tilde
(`~') in ftp-
dir will be expanded to the user's home directory based on
the contents of the password database.
welcome The path of the file containing the welcome message. If this
variable is not set, /etc/motd is used.
For passive mode data connections, ftpd will listen to a
random high TCP
port. The interval of ports used are configurable using
sysctl(8) variables
net.inet.ip.porthifirst and net.inet.ip.porthilast.
/etc/ftpchroot list of normal users who should be chrooted
/etc/ftpusers list of unwelcome/restricted users
/etc/ftpwelcome welcome notice
/etc/login.conf authentication styles
/etc/motd printed after a successful login
/etc/nologin displayed and access refused
/var/log/ftpd log file for anonymous downloads
/var/run/ftpd.pid process ID if running in daemon mode
/var/run/utmp list of users on the system
ftp(1), login(1), skey(1), who(1), chroot(2), ctime(3),
group(5),
login.conf(5), motd(5), services(5), shells(5), ftpproxy(8), inetd(8),
pwd_mkdb(8), sysctl(8), syslogd(8)
The ftpd command appeared in 4.2BSD.
The server must run as the superuser to create sockets with
privileged
port numbers. It maintains an effective user ID of the
logged in user,
reverting to the superuser only when binding addresses to
sockets. The
possible security holes have been extensively scrutinized,
but are possibly
incomplete.
OpenBSD 3.6 June 18, 1996
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