FTPD(8) MidnightBSD System Manager’s Manual FTPD(8)

NAME

ftpd — Internet File Transfer Protocol server

SYNOPSIS

ftpd [−46ADdEhMmOoRrSUvW] [−l [−l]] [−a address] [−P port] [−p file] [−T maxtimeout] [−t timeout] [−u umask]

DESCRIPTION

The ftpd utility is the Internet File Transfer Protocol server process. The server uses the TCP protocol and listens at the port specified with the −P option or in the ‘‘ftp’’ service specification; see services(5).

Available options:

−4

When −D is specified, accept connections via AF_INET socket.

−6

When −D is specified, accept connections via AF_INET6 socket.

−A

Allow only anonymous ftp access.

−a

When −D is specified, accept connections only on the specified address.

−D

With this option set, ftpd will detach and become a daemon, accepting connections on the FTP port and forking children processes to handle them. This is 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.

−E

Disable the EPSV command. This is useful for servers behind older firewalls.

−h

Disable printing host-specific information, such as the server software version or hostname, in server messages.

−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. By default, syslogd(8) logs these to /var/log/xferlog.

−M

Prevent anonymous users from creating directories.

−m

Permit anonymous users to overwrite or modify existing files if allowed by file system permissions. By default, anonymous users cannot modify existing files; in particular, files to upload will be created under a unique name.

−O

Put server in write-only mode for anonymous users only. RETR is disabled for anonymous users, preventing anonymous downloads. This has no effect if −o is also specified.

−o

Put server in write-only mode. RETR is disabled, preventing downloads.

−P

When −D is specified, accept connections at port, specified as a numeric value or service name, instead of at the default ‘‘ftp’’ port.

−p

When −D is specified, write the daemon’s process ID to file instead of the default pid file, /var/run/ftpd.pid.

−R

With this option set, ftpd will revert to historical behavior with regard to security checks on user operations and restrictions on PORT requests. Currently, ftpd will only honor PORT commands directed to unprivileged ports on the remote user’s host (which violates the FTP protocol specification but closes some security holes).

−r

Put server in read-only mode. All commands which may modify the local file system are disabled.

−S

With this option set, ftpd logs all anonymous file downloads to the file /var/log/ftpd when this file exists.

−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

This option instructs ftpd to use data ports in the range of IP_PORTRANGE_DEFAULT instead of in the range of IP_PORTRANGE_HIGH. Such a change may be useful for some specific firewall configurations; see ip(4) for more information.

Note that option is a virtual no-op in FreeBSD 5.0 and above; both port ranges are indentical by default.

−u

The default file creation mode mask is set to umask, which is expected to be an octal numeric value. Refer to umask(2) for details. This option may be overridden by login.conf(5).

−v

A synonym for −d.

−W

Do not log FTP sessions to /var/log/wtmp.

The file /var/run/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/ftpmotd exists, ftpd prints it after a successful login. Note the motd file used is the one relative to the login environment. This means the one in ~ftp/etc in the anonymous user’s case.

The ftp server currently supports the following ftp requests. The case of the requests is ignored. Requests marked [RW] are disabled if −r is specified.

Request Description
ABOR abort previous command
ACCT specify account (ignored)
ALLO allocate storage (vacuously)
APPE append to a file [RW]
CDUP change to parent of current working directory
CWD change working directory
DELE delete a file [RW]
EPRT specify data connection port, multiprotocol
EPSV prepare for server-to-server transfer, multiprotocol
HELP give help information
LIST give list files in a directory (‘‘ls -lgA’’)
LPRT specify data connection port, multiprotocol
LPSV prepare for server-to-server transfer, multiprotocol
MDTM show last modification time of file
MKD make a directory [RW]
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 [RW]
RNFR specify rename-from file name [RW]
RNTO specify rename-to file name [RW]
SITE non-standard commands (see next section)
SIZE return size of file
STAT return status of server
STOR store a file [RW]
STOU store a file with a unique name [RW]
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) [RW]
XPWD print the current working directory (deprecated)
XRMD remove a directory (deprecated) [RW]

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 [RW], e.g. ‘‘SITE CHMOD 755 filename’’
MD5 report the files MD5 checksum, e.g. ‘‘SITE MD5 filename’’
HELP give help information

Note: SITE requests are disabled in case of anonymous logins.

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. To avoid possible denial-of-service attacks, SIZE requests against files larger than 10240 bytes will be denied if the current transfer type is ASCII.

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.

The ftpd utility interprets file names according to the ‘‘globbing’’ conventions used by csh(1). This allows users to utilize the metacharacters ‘‘*?[]{}~’’.

The ftpd utility authenticates users according to six rules.

1.

The login name must be in the password data base 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 key(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 login name must not be a member of a group specified in the file /etc/ftpusers. Entries in this file interpreted as group names are prefixed by an "at" ‘@’ sign.

4.

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

5.

If the user name appears in the file /etc/ftpchroot, or the user is a member of a group with a group entry in this file, i.e., one prefixed with ‘@’, the session’s root will be changed to the directory specified in this file or to the user’s login directory by chroot(2) as for an ‘‘anonymous’’ or ‘‘ftp’’ account (see next item). See ftpchroot(5) for a detailed description of the format of this file. This facility may also be triggered by enabling the boolean "ftp-chroot" capability in login.conf(5). 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.

6.

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). When the −S option is set, all transfers are logged as well.

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. As a special case if the ‘‘ftp’’ user’s home directory pathname contains the /./ separator, ftpd uses its left-hand side as the name of the directory to do chroot(2) to, and its right-hand side to change the current directory to afterwards. A typical example for this case would be /usr/local/ftp/./pub. 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.

~ftp/etc

Make this directory owned by ‘‘root’’ and unwritable by anyone (mode 555). The files pwd.db (see passwd(5)) 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 passwd(5) is not used, and should not contain real passwords. The file ftpmotd, if present, will be printed after a successful login. These files should be mode 444.

~ftp/pub

This directory and the subdirectories beneath it should be owned by the users and groups responsible for placing files in them, and be writable only by them (mode 755 or 775). They should not be owned or writable by ‘‘ftp’’ or its group, otherwise guest users can fill the drive with unwanted files.

If the system has multiple IP addresses, ftpd supports the idea of virtual hosts, which provides the ability to define multiple anonymous ftp areas, each one allocated to a different internet address. The file /etc/ftphosts contains information pertaining to each of the virtual hosts. Each host is defined on its own line which contains a number of fields separated by whitespace:

hostname

Contains the hostname or IP address of the virtual host.

user

Contains a user record in the system password file. As with normal anonymous ftp, this user’s access uid, gid and group memberships determine file access to the anonymous ftp area. The anonymous ftp area (to which any user is chrooted on login) is determined by the home directory defined for the account. User id and group for any ftp account may be the same as for the standard ftp user.

statfile

File to which all file transfers are logged, which defaults to /var/log/ftpd.

welcome

This file is the welcome message displayed before the server ready prompt. It defaults to /etc/ftpwelcome.

motd

This file is displayed after the user logs in. It defaults to /etc/ftpmotd.

Lines beginning with a ’#’ are ignored and can be used to include comments.

Defining a virtual host for the primary IP address or hostname changes the default for ftp logins to that address. The ’user’, ’statfile’, ’welcome’ and ’motd’ fields may be left blank, or a single hyphen ’-’ used to indicate that the default value is to be used.

As with any anonymous login configuration, due care must be given to setup and maintenance to guard against security related problems.

The ftpd utility has internal support for handling remote requests to list files, and will not execute /bin/ls in either a chrooted or non-chrooted environment. The ~/bin/ls executable need not be placed into the chrooted tree, nor need the ~/bin directory exist.

FILES
/etc/ftpusers

List of unwelcome/restricted users.

/etc/ftpchroot

List of normal users who should be chroot’d.

/etc/ftphosts

Virtual hosting configuration file.

/etc/ftpwelcome

Welcome notice.

/etc/ftpmotd

Welcome notice after login.

/var/run/ftpd.pid

Default pid file for daemon mode.

/var/run/nologin

Displayed and access refused.

/var/log/ftpd

Log file for anonymous transfers.

/var/log/xferlog

Default place for session logs.

SEE ALSO

ftp(1), key(1), umask(2), getusershell(3), ftpchroot(5), login.conf(5), inetd(8), syslogd(8)

HISTORY

The ftpd utility appeared in 4.2BSD. IPv6 support was added in WIDE Hydrangea IPv6 stack kit.

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.

MidnightBSD 0.3 January 21, 2006 MidnightBSD 0.3