NAME¶

ftpd —

SYNOPSIS¶

ftpd	[ -AdDhlMnPSU ] [ -T maxtimeout ] [ -t timeout ] [ -u mask ] [ -z debug ] [ -z certsok ] [ -z certrequired ] [ -z secure ] [ -z verify=flags ] [ -z cert=certfile ] [ -z key=keyfile ] [ -z ciper=list ]

DESCRIPTION¶

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). Available options:

-4

Use IPv4 addressing only. The default is to offer service for both families, IPv6 and IPv4.

-6

Only provide IPv6 addressing capability.

-A

Permit only anonymous ftp connections or accounts listed in /etc/ftpchroot. Other connection attempts are refused. This option is no longer effective if PAM is enabled. Please refer to the README file for instructions to doing this with PAM.

-d

Debugging information is written to the syslog using LOG_FTP.

-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.

-h

The server will use data ports in the high port range for passive connections. This range is defined by the IPPORT_HIFIRSTAUTO and IPPORT_HILASTAUTO defines in <netinet/in.h>. In OpenBSD they are set to 49152 and 65535 respectively.

-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

Use numeric IP addresses in logs instead of doing hostname lookup.

-P

Permit illegal port numbers or addresses for PORT command initiated connects. By default ftpd(8) 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 transfers to the file /var/log/ftpd when this file exists.

-U

Each concurrent ftp(1) session is logged to the file /var/run/utmp, making them visible to commands such as who(1). This option at present is unsupporte and will always silently fail.

-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

Change the default umask from 027 to mask.

-z SSL-parameter

This option is only valid if ftpd has been built with SSL (Secure Socket Layer) support.

debug

Enable SSL related debugging.

ssl

Negotiate SSL at first, then use ftp protocol. In this mode ftpd only accepts connections from SSL enhanced ftp with option -z ssl. (Not yet implemented)

nossl, !ssl

switch off SSL negotiation

certsok

Look username up in /etc/ssl.users. The format of this file is lines of this form: user1,user2:/C=US/..... where user1 and user2 are usernames. If client certificate is valid, authenticate without password.

certrequired

client certificate is mandatory

secure

Don't switch back to unencrypted mode (no SSL) if SSL is not available.

verify=int

Set the SSL verify flags (SSL_VERIFY_* in ssl/ssl.h ).

cert=cert_file

Use the certificate(s) in cert_file.

key=key_file

Use the key(s) in key_file.

cipher=ciph_list

Set the preferred ciphers to ciph_list. (See ssl/ssl.h ).

The file /etc/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/motd exists, 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 (ignored)
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, either IPv4 or IPv6
EPSV	ask for a server port for fetching data
HELP	give help information
LIST	give list files in a directory (“ls -lgA”)
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
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
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.

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 five rules.

1. The login name must be in the password data base, /etc/passwd, 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.
2. The login name must not appear in the file /etc/ftpusers.
3. The user must have a standard shell returned by getusershell(3).
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).

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. In order that system security is not breached, it is recommended that the “ftp” subtree be constructed with care, following these rules:

FILES¶

/etc/ftpusers

List of unwelcome/restricted users.

/etc/ftpchroot

List of normal users who should be chroot'd.

/etc/ftpwelcome

Welcome notice.

/etc/motd

Welcome notice after login.

/etc/nologin

Displayed and access refused.

/var/run/utmp

List of users on the system.

/var/log/ftpd

Log file for anonymous transfers.

SEE ALSO¶

ftp(1), skey(1), who(1), getusershell(3), ftpusers(5), syslogd(8)

BUGS¶

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.