ftpd(1M)

Requires Optional ARPA Services Software

NAME

ftpd − DARPA Internet File Transfer Protocol server

SYNOPSIS

/etc/ftpd [−l] [−t timeout] [−T maxtimeout] [−u umask]

DESCRIPTION

ftpd is the DARPA Internet File Transfer Protocol server. It expects to be run by the Internet daemon; see inetd(1M) and inetd.conf(4). inetd runs ftpd when a service request is received at the port indicated in the ftp service specification in /etc/services; see services(4).

The −l option causes each FTP session to be logged in the syslog.

The −t option causes ftpd to timeout inactive sessions after timeout seconds. By default, ftpd will timeout an inactive session after 15 minutes.

A client can also request a different timeout period. The −T option sets to timeout the maximum timeout that client can request. By default, the maximum timeout is 2 hours.

By default, ftpd sets its umask to 027. To change this default umask, use the −u option.

ftpd currently supports the following commands (uppercase and lowercase are interpreted as equivalent):

Command 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

HELP Give help information

LIST Give list files in a directory (ls −l)

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

XCWD Change working directory

XMKD Make a directory

XPWD Print the current working directory

XRMD Remove a directory

The following non-standard or HP-UX specific commands are supported by the SITE command:

Command 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 are expected in the next updated FTP RFC.

The FTP server aborts 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 ftpd receives a STAT command during a data transfer, preceded by a Telnet IP and Synch, it returns the status of the transfer.

ftpd interprets file names according to the “globbing” conventions used by csh(1). This allows users to utilize the metacharacters *, ., [, ], {, }, ~, and ?.

ftpd authenticates users according to three rules:

• The user name must be in the password data base, /etc/passwd, and not have a null password. The client must provide the correct password for the user before any file operations can be performed.

• The user name must not appear in the file /etc/ftpusers (see ftpusers(4)).

• The user must have a standard shell returned by getusershell(3).

Optionally, a system administrator can permit public access or “anonymous FTP.” If this has been set up, users can access the anonymous FTP account with the user name anonymous or ftp and any non-null password (by convention, the client host’s name). ftpd does a chroot(2) to the home directory of the user ftp, thus limiting anonymous FTP users’ access to the system. 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 order to permit anonymous FTP, there must be an entry in the passwd(4) database for an account named ftp. The password field should be *, the group membership should be guest, and the login shell should be /bin/false. For example (assuming the guest group ID is 10):

ftp:*:500:10:anonymous ftp:/users/ftp:/bin/false

The anonymous ftp directory should be set up as follows:

~ftp The home directory of the ftp account should be owned by user ftp and mode 555 (not writable). Since ftpd does a chroot to this directory, it must have the following subdirectories and files:

~ftp/bin This directory must be owned by root and mode 555 (not writable). It should contain a copy of /bin/ls. This is needed to support directory listing by ftpd. The command should be mode 111 (executable only). If the FTP account is on the same file system as /bin, ~ftp/bin/ls can be hard link, but it may not be a symbolic link, because of the chroot. The command must be replaced when the system is updated.

~ftp/etc This directory must be owned by root and mode 555 (not writable). It should contain versions of the files passwd, group, and logingroup. See passwd(4) and group(4). These files must be owned by root and mode 444 (readable only). These are needed to map user and group ids in the LIST command, and to support (optional) sub-logins of anonymous FTP. Sub-logins can sometimes be used to allow access to particular files by only specific remote users (who know the sub-login password) without giving those remote users logins on the system. A sub-login user would access the system via anonymous ftp, and then use USER and PASS to change to the sub-login user.

~ftp/etc/passwd
This file should contain entries for the ftp user and any other users who own files under the anonymous ftp directory. Such entries should have * for passwords. ~ftp/etc/passwd should also contain entries for any desired anonymous FTP sub-logins. The sub-logins must have passwords, which must be encrypted as in passwd(4). Group IDs must be listed in the anonymous FTP group file, ~ftp/etc/group. The path names of home directories in ~ftp/etc/passwd must be with respect to the anonymous FTP home directory. A sub-login home directory should be owned by the sub-login user ID. The shell field is ignored, and can be empty.

For example, the anonymous FTP sub-login name subftp would have an entry in the FTP passwd file that resembles:

subftp:bAg6vI82aq5Yt:501:10:ftp sub-login:/subftp:

FTP sub-login IDs do not need to be present in the system /etc/passwd file. Assuming the anonymous FTP directory is /users/ftp, the sub-login home directory in the example would be created by user root as follows:

cd /users/ftp
mkdir subftp
chmod 700 subftp
chown 501 subftp
chgrp guest subftp

File ~ftp/etc/group should contain the group names associated with any group IDs in file ~ftp/etc/passwd and any group IDs of files in the anonymous FTP subdirectories. In the above example, ~ftp/etc/group would require an entry for guest, and the associated group ID would have to be the same as in the system’s /etc/group file.

~ftp/etc/logingroup
Permits anonymous ftp sub-logins to be members of multiple groups. Can be a hard link to FTP ~ftp/etc/group.

~ftp/pub (optional)
This directory is used by anonymous FTP users to deposit files on the system. It should be owned by user ftp and should be mode 777 (readable and writable by all).

~ftp/dist (optional)
Directories used to make files available to anonymous ftp users should be mode 555 (not writable), and any files to be distributed should be owned by root and mode 444 (readable only) so that they cannot be modified or removed by anonymous FTP users.

DIAGNOSTICS

ftpd replies to FTP commands to ensure synchronization of requests and actions during file transfers, and to indicate the status of ftpd. Every command produces at least one reply, although there may be more than one. A reply consists of a three-digit number, a space, some text, and an end of line. The number is useful for programs; the text is useful for users. The number must conform to this standard, but the text can vary.

The first digit of the message indicates whether the reply is good, bad, or incomplete. Five values exist for the first digit. The values and the interpretations of the values are:

1 The requested action is being initiated; expect another reply before proceeding with a new command.

2 The requested action is complete. The server is ready for a new request.

3 The command has been accepted, but the requested action requires more information.

4 The command was not accepted, the requested action failed, but the error condition is temporary and the action can be requested again.

5 The command was not accepted, the requested action failed, and the error condition would most likely occur again if the same command sequence is repeated.

The second digit indicates the functional area that the message addresses. The values of the second digit and the interpretations of these values are:

0 Syntax. A message with a 0 for the second digit indicates that a syntax error occurred.

1 Information. A message with a 1 as the second digit indicates that the message is in reply to a request for information.

2 Connections. A message with a 2 as the second digit indicates that the message is a reply to a request for control and data connection information.

3 Authentication and accounting. A message with a 3 as the second digit indicates that the message is a reply to a login or accounting procedure.

4 Not currently specified.

5 File system. A message with a 5 as the second digit indicates that the text following the number contains information concerning the status of the server file system.

The third digit provides a further clarification of the information supplied by the second digit. Following are several examples of messages. Note that ftpd’s replies match the number but not the text.

110 Restart marker reply. MARK yyyy=mmmm where yyyy is a user process data stream marker, and mmmm is ftpd’s equivalent marker

119 Terminal not available, will try mailbox

120 Service ready in nnn minutes

200 Command okay

211 System status, or system help reply

212 Directory status

230 User logged in, proceed

250 Requested file action okay, completed

331 User name okay, need password

350 Requested file action pending further information

425 Cannot open data connection

451 Requested action aborted: local error in processing

500 Syntax error, command unrecognized or command line too long

530 Not logged in

550 Requested action not taken; file unavailable, not found, no access

WARNINGS

The password is sent unencrypted through the socket connection.

Anonymous FTP is inherently dangerous to system security.

An error in the treatment of carriage returns in FTP clients and servers based on the 4.2BSD implementation (specifically, any ftp(1) or ftpd(1M) released prior to HP-UX 8.0) has been corrected. This correction may result in incorrect transfers of binary files when using the ascii transfer type. Avoid this problem by using the image (binary) transfer type.

AUTHOR

ftpd was developed by the University of California, Berkeley.

Museum

Related Articles