FTPD(8)

NAME
ftpd - DARPA Internet File Transfer Protocol server

SYNOPSIS
ftpd [-A |-a] [-C] [-c] [-d] [-E] [-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)

-E  Don't allow passwords to be typed across unencrypted connections.

-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.

-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.