FTPD(8) UNIX System V FTPD(8)
NAME
ftpd - DARPA Internet File Transfer Protocol server
SYNOPSIS
ftpd [-A | -a] [-C] [-c] [-d] [-l] [-v] [-T maxtimeout] [-t
timeout] [-p port] [-U ftpusers-file] [-u umask] [-r realm-
file] [-s srvtab]
[-w{ip|maxhostlen[,{striplocal|nostriplocal}]}]
DESCRIPTION
Ftpd is the DARPA 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:
-A Connections are only allowed for users who can
authenticate via the ftp AUTH mechanism. (Anonymous ftp
may also be allowed if it is configured.) Ftpd will ask
the user for a password if one is required.
-a Connections are only allowed for users who can
authenticate (via the ftp AUTH mechanism) and who are
authorized to connect to the named account without a
password. (Anonymous ftp may also be allowed if it is
configured.)
-C Non-anonymous users need local credentials (for
example, to authenticate to remote fileservers), and so
they should be prompted for a password unless they
forwarded credentials as part of authentication.
-c Allow the CCC (Clear Command Channel) command to be
used. This allows less secure connections, and should
probably only be used when debugging.
-d Debugging information is written to the syslog.
(Identical to -v)
-l Each ftp(1) session is logged in the syslog. If this
flag appears twice, additional information about
operations performed (such as files retrieved,
directories created, etc.) will be logged via syslog.
If it appears three times, some other statistics such
as the number of bytes transferred will be logged via
syslog as well.
-v Debugging information is written to the syslog.
(Identical to -d)
-T maxtimeout
A client may request a maximum timeout period allowed
set to timeout seconds with the -T option. The default
limit is 2 hours. This is different from the normal
inactivity timeout specified by the -t option (see
below).
-t timeout
The inactivity timeout period is set to timeout seconds
(the default is 15 minutes).
-p port
Run as a server and accept a connection on port.
Normally the ftp server is invoked by inetd(8).
-U ftpusers-file
Sets the full path and name of the ftpusers file to
use. The default value is normally /etc/ftpusers.
-u umask
Sets the umask for the ftpd process. The default value
is normally 027.
-r realm-file
Sets the name of the krb.conf file to use. The default
value is normally set by /etc/krb5.conf.
-s srvtab
Sets the name of the srvtab file to use for Kerberos V4
authentication. The default value is normally
/etc/srvtab.
-w {ip|maxhostlen[,{striplocal|nostriplocal}]}
Controls the form of the remote hostname passed to
login(1). Specifying ip results in the numeric IP
address always being passed to login(1). Specifying a
number, maxhostlen, sets the maximum length of the
hostname passed to login(1) before it will be passed as
a numeric IP address. If maxhostlen is 0, then the
system default, as determined by the utmp or utmpx
structures, is used. The nostriplocal and striplocal
options, which must be preceded by a comma, control
whether or not the local host domain is stripped from
the remote hostname. By default, the equivalent of
striplocal is in effect.
The ftp server currently supports the following ftp
requests; case is not distinguished.
Request Description
ABOR abort previous command
ACCT specify account (ignored)
ADAT send an authentication protocol message
ALLO allocate storage (vacuously)
APPE append to a file
AUTH specify an authentication protocol to be performed
CCC set the command channel protection mode to "Clear"
(no protection). Only available if the -c
command-line option was given.
CDUP change to parent of current working directory
CWD change working directory
DELE delete a file
ENC send a privacy and integrity protected command
(given in argument)
HELP give help information
LIST give list files in a directory (``ls -lgA'')
MIC send an integrity protected command (given in
argument)
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
PASS specify password
PASV prepare for server-to-server transfer
PBSZ specify a protection buffer size
PORT specify data connection port
PROT specify a protection level under which to protect
data transfers
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
UMASK change umask. E.g., SITE UMASK 002
IDLE set idle-timer. E.g., SITE IDLE 60
CHMOD change mode of a file. E.g., SITE CHMOD 755
filename
HELP give help information. E.g., SITE HELP
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 according to the following rules:
1. The user name must be in the password data base,
/etc/passwd.
2. An AUTH command must be accepted, the ensuing
authentication protocol (conducted via ADAT commands
and replies) must successfully complete, and the
authenticated user must permitted access. Otherwise, a
valid password which is not null must be provided by
the client.
3. The user name must not appear in the file
/etc/ftpusers.
4. The user must have a standard shell returned by
getusershell(3).
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
this is given as the client host's name).
In the last case, ftpd takes special measures to restrict
the client's access privileges. The server performs a
chroot(2) command 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; the following rules are recommended.
~ftp Make the home directory owned by ``ftp'' and unwritable
by anyone.
~ftp/bin
Make this directory owned by the super-user and
unwritable by anyone. The program ls(1) must be
present to support the list command. This program
should have mode 111.
~ftp/etc
Make this directory owned by the super-user and
unwritable by anyone. The files passwd(5) and group(5)
must be present for the ls command to be able to
produce owner names rather than numbers. The password
field in passwd is not used, and should not contain
real encrypted passwords. These files should be mode
444.
~ftp/pub
Make this directory mode 777 and owned by ``ftp''.
Users should then place files which are to be
accessible via the anonymous account in this directory.
If an ADAT command succeeds, the control channel must be
either integrity or privacy protected. In this case, the
MIC and ENC commands are the only commands allowed over the
control channel. The argument to the MIC command is a base
64 encoded string which, when decoded, is an ftp command
integrity protected with a cryptographic checksum. The
argument to the ENC command is a base 64 encoded string
which, when decoded, is an ftp command privacy and integrity
protected with encryption.
If an ADAT command succeeds, ftp replies will also be either
integrity or privacy protected.
If an ADAT command succeeds, the data channel can also be
integrity or privacy protected. The PROT command accepts S
for integrity and P for privacy protection. Unless an ADAT
command succeeds, the only protection level accepted by the
PROT command is C (clear).
SEE ALSO
ftp(1), getusershell(3), syslogd(8)
Lunt, S. J., FTP Security Extensions, Internet Draft,
November 1993.
BUGS
The anonymous account is inherently dangerous and should
avoided when possible.
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.
HISTORY
The ftpd command appeared in 4.2BSD.
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